Ascidians from the Chatham Islands and the Chatham Rise

Transactions and Proceedings of the Royal Society of New Zealand, Volume 84, 1956-57, Page 121

Ascidians from the Chatham Islands and the Chatham Rise By Beryl I. Brewin University of Otago [Received by the Editor, July 6, 1955.] Abstract Part I.–Ascidian fauna of the Chatham Islands and shelf. As a result of a survey made of the material collected by the “Chatham Islands 1954 Expedition” and that in the Otago Museum collections, the number of species recorded from the region is raised to 33, of which 17, including 7 new species (Synoicum sluiteri, Polyclinum sluiteri, Amaroucium siphonum, Amaroucium knoxi, Didemnum lithostrotum, Leptoclinides marmoreus, Pyura chathamensis), are recorded from the locality for the first time. The ascidian fauna is closely allied to that of New Zealand, 21 species being common to both, and the fact that the Chatham Islands are Convergence Islands is shown by the presence of ascidians recorded in New Zealand only from the northern end of the North Island (3 species) together with ones recorded only from the southern end of the South Island and/or Stewart Island (5 species). It is possible that Pyura chathamensis shows an evolution from the New Zealand fauna of a species endemic to the Chatham Islands. Part II.—Ascidian fauna of the Chatham Rise. The material collected from the western portion of the Chatham Rise by the “Chatham Islands 1954 Expedition” includes 9 recognisable species. Of these Polyclinum michaelseni, Amaroucium mernooensis, Leptoclinides auranticus and Amphicarpha michaelseni are new species and the other 5 are common to both New Zealand and the Chatham Rise. The New Zealand influence would appear to be markedly southern, three of the five species common to the two areas having been recorded only from the southern portion of the South Island of New Zealand and/or Stewart Island. Part I.–Ascidians from the Chatham Islands and Shelf Sixteen species of ascidians from the Chatham Islands, collected by the Schauinsland Expedition 1896–1897, were described by Sluiter in 1900. These species were re-surveyed by Michaelsen and incorporated in his papers on the ascidians from New Zealand, the Chatham and the Auckland Islands (1922, 1924). Another small record appeared in “The Marine Fauna of the Chatham Islands”, by M. W. Young (1930). Re-investigation of Young's material, which is housed in the Otago Museum, has shown that the list of ascidians given should be emended as follows:– Asterocarpa cerea (Sluiter) not Styela lactea Pyura pulla (Sluiter) not Pyura praeputialis Corella eumyota Traustedt not Corella japonica Pyura chathamensis, n.sp. not Boltenia tuberculata and should receive the following additions:– Pyura suteri Michaelsen Pyura cancellata Brewin The author is indebted to the Chatham Islands 1954 Expedition for a collection of twenty-two ascidians from ten stations on the Chatham Islands and the shelf surrounding them. Of the twenty-two, four—Corella eumyota, Asterocarpa cerea, Cnemidocarpa bicornuata and Pyura chathamensis—were represented in previous collections, seven proved to be new species and five only–all members of the family Synoicidae–were unidentifiable. (This was because of poor development of the gonads or excessive contraction of the pharyngeal region and it is possible that there may be among them representatives of the Synoicid species described from this locality by Sluiter, 1900.)

The list of species given below includes the sixteen ascidians described by Sluiter and reviewed by Michaelsen, the six in M. W. Young's material in the Otago Museum, and seventeen of those collected by the Chatham Islands 1954 Expedition. The total number of ascidian species recorded from the locality is increased to thirty-three. Of these, twenty-one are common to both New Zealand and the Chatham Islands. List of Species from the Chatham Islands and Shelf Synoicidae * Absent or unrecognisable in the material collected by the Chatham Islands 1954 Expedition. Synoicum fungosum (Herdman) Synoicum herdmani, n.sp. Polyclinum sluiteri, n.sp. *Aplidium foliaceum (Sluiter) * Amaroucium phortax f. typica (Michaelsen) * Amaroucium variable Herdman * Amaroucium constrictum Sluiter * Amaroucium circumvollutum Sluiter Amaroucium benhami Brewin Amaroucium scabellum Michaelsen Amaroucium siphonum, n.sp. Amaroucium knoxi, n.sp. Didemnidae * Didemnum studeri f. typica Hartmeyer * Didemnum lambitum (Sluiter) Didemnum candidum Savigny Didemnum mortenseni Michaelsen Didemnum lithostrotum, n.sp. Leptoclinides marmoreus, n.sp. Polycitoridae Cystodytes dellachiaiae (Della Valle) * Sycozoa sigillinoides Lesson Rhodosomatidae Corella eumyota Traustedt Botryllidae Botrylloides leachi Savigny Styelidae Alloeocarpa minuta Brewin * Amphicarpa schauinslandi Michaelsen Cnemidocarpa bicornuata (Sluiter) Asterocarpa cerea (Sluiter) Pyuridae * Pyura trita (Sluiter) Pyura chathamensis, n.sp. * Pyura pulla (Sluiter) * Pyura cancellata Brewin * Pyura suteri Michaelsen * Microcosmus hirsutus Sluiter Molgulidae * Molgula sluiteri (Michaelsen) Full descriptions are given only of genera and species not appearing in the author's papers on the ascidians from New Zealand waters, the range of variability of the other species being as follows:–

Didemnum candidum (15 fths., Hanson Bay; 25 fths., off Cape Young), Cystodytes dellachiaiae (15 fths., Hanson Bay), Corella eumyota (38 fths., S. of The Sisters), Botrylloides leachi (25 fths., off Cape Young) and Asterocarpa cerea (coastal rocks, Port Hutt) all fall within the range of variability given for specimens from the Otago Harbour (Brewin, 1946) as also do the following with the exceptions stated. Specimens of Cnemidocarpa bicornuata (38 fths., S of The Sisters) are of slightly larger size, up to 5.5 cm in length, and colonies of Amaroucium benhami (15 fths., off Hanson Bay; 33 fths., N. of The Sisters; 25 fths., off Cape Young) have fine shell fragments incorporated in the test and possess zooids somewhat slight in build. Alloeocarpa minuta Brewin, found on the test of specimens of Cnemidocarpa bicornuata and on shells of Astrofusus glans (70 fths., Petre Bay), differs from the Hauraki Gulf specimens (Brewin, 1951) only in the larger size of the individuals, up to 5 mm in diameter (2.5 mm, Hauraki Gulf) and in the greater number of branchial tentacles, 32 (16 to 24, Hauraki Gulf). (The gut of the specimens of Asterocarpa cerea was heavily infested with parasitic cysts and probably for this reason the gonads were poorly developed at a season when eggs are liberated in New Zealand waters.) Text-fig. I.–Synoicum herdmani A1-Anterior portion of zooid. A2–Portion of anterior region of post-abdomen. A3–Posterior end of post-abdomen. B–Colony. Description of Species Order Krikobranchia Seeliger. Genus Synoicum Phipps, 1774. Synoicum herdmani, n.sp. (Fig. 1, A1, A2, A3, B) Colonies (Text-fig. 1 B) in the form of small, sandy, flat-topped capitate lobes up to 1.5 cm in height above the substratum, and up to 1.3 cm in diameter in the head region. Stalk 1 cm long, 0.5 cm wide at the base and increasing gradually in width towards the head of the lobe Zooids orange opening on the head, in circular systems of 7 to 10 zooids Common cloacal apertures, small, circular, about 3 mm apart. Test yellow, transparent, heavily impregnated throughout with sand grains and shell fragments, with numerous small irregularly-shaped test cells and a few round granular cells. Zooids (Text-fig. 1A1, A2, A3) up to 1 cm in length, 0.8 mm in width in the pharyngeal region, which has 10 fine longitudinal muscle bundles, 13 transverse. Post-abdomen one-half zooid length. Branchial siphon terminating in six distinct lobes, atrial aperture with a single fleshy lappet, the lateral edges of which may be smooth or irregular in shape. Pharynx with 32 comparatively long tentacles of three orders of size. Dorsal lamina with 13 languets curving back at the level of the third stigmata from the mid-dorsal line; on each side 14 rows of 12 to 13 stigmata, 4 to 5 times as long as they are wide. Oesophagus,

short, narrow; stomach short, almost spherical, with a faint indication of internal folds; intestine narrow at first (with a characteristic short swelling in the narrow portion), widening consideably after the bend; anal aperture one-third way up pharynx, edge bi-lobed. Testis lobes up to 21 in number in posterior half or two-thirds of the post-abdomen. Ovary immediately anterior to the testis lobes (Fig. 1A2). No tadpoles in specimens collected 27.1 54. Distribution. Chatham Is., 15 fathoms, off Hanson Bay. Type Specimen. In the Canterbury Museum. Remarks. This species differs from S. fungosum (Herdman) previously recorded from the locality, in shape and size of the colony, width of the pharyngeal region, number of stigmatal rows, shape of post-abdomen and number of branchial tentacles. Of the species recorded from New Zealand waters it most closely resembles S. hypurgon (Michaelsen) from which it is separated by the size of the lobes, the width of the pharyngeal region, the number of stigmata per row, and the number of branchial tentacles. It is also unlike any species recorded from the Antarctic region or Australia. Genus Polyclinum Savigny, 1816 Polyclinum sluiteri n.sp. (Fig. 2, A1, A2, A3) Colony (Text-fig. 2 A2) a rounded mass 3.0 cm in the longest diameter and up to 1.7 cm in height above the substratum; attached to an empty shell of Austrofusus glans. Test translucent with numerous small test cells, fine sand grains imbedded in peripheral region. Zooids yellow in radiating systems around the common cloacal apertures which are elliptical, 1 mm in the longest diameter and 8 mm or more apart. Zooids (Text-fig. 2 A1) up to 6.5 mm in length, 1 mm in width in the pharyngeal region, which has 9 longitudinal muscle bundles, 14 fine transverse. Post-abdomen one-fourth or more of the body length. Branchial apertures with six extremely small lobes, atrial with a long lappet, the end of which may be tapering and simple or blunt and toothed. Pharynx with 32 tentacles of two orders of size regularly arranged. Dorsal lamina of 14 languets curving back opposite the fourth stigmata from the mid-dorsal line. On each side 15 rows of 18 to 19 stigmata, 5 to 6 times as long as wide, parastigmatic vessels absent. Papillae 14, i.e. slightly less in number than the stigmata. Oesophagus short, stomach smooth, globose, intestine twisted to form a small closed loop posterior to the stomach; rectum long, extending slightly more than half way up the thorax, where it ends in a two-lobed aperture. Post-abdomen pyriform, attachment to abdomen being by a long narrow stalk, gonads confined to the posterior swollen portion. Ovary situated among the testis lobes, which are seventeen or more in number. Tadpoles (Text-fig. 2 A3) up to 1.6 mm in length and 0.3 mm in width in the head region, present in the mantle cavity of specimens collected 31.1 54. Distribution. Chatham Is., 70 fathoms, off Petre Bay. Type Specimen. In the Canterbury Museum. Remarks. To quote Van Name 1945, p. 68, “The true Polyclinum are all very closely related to each other, their zooids apparently having nearly the same structure, so that we must depend chiefly on the gross characters of the colonies for distinguishing them”. No Polyclinum species have been recorded previously from the locality, and P. cerebrale Michaelsen is the only species recorded from New Zealand waters. P. michaelseni is separated from the latter by the lack of infolding of the surface of the colony, by the number of testis lobes and the position of the ovary. In pharyngeal arrangement it most closely resembles P. constellatum Savigny but is separated from that species by the position of the ovary and the angle of the post-abdomen. Genus Amaroucium Milne Edwards, 1841 Amaroucium scabellum Michaelsen (Fig. 2 B) Lit.: 1924, Amaroucium scabellum, Michaelsen, Vidensk. Medd. naturh. Foren, 77, pp. 374–383, Fig. 18. ? 1954. Amaroucium scabellum, Kott, B.A.N.Z. Antarc. Res. Exped., 1929–1931, Ser. B. 1, pt. 1, p. 176. (Apart from colour notes and observations on common cloacal canals the description of the colony is taken from Michaelsen's observations, a portion only of a colonial lobe being present in this collection.) Colony composed of flat-topped, irregularly top-shaped lobes connected by a basal membrane up to 100 mm in width. Lobes measuring at the free end up to 45 mm in the greatest diameter, at the attached end up to 30 mm in the greatest diameter and up to 25 mm in height above the basal membrane. Test firm, fawn in colour, heavily

impregnated with sand, and with numerous small test cells and pigment cells 6μ in diameter. Outer surface of the colony with a thick covering of sand grains except in the areas surrounting the branchial regions of the zooids and round the common cloacal canals, the tops of the lobes thus presenting the appearance of a network bounded by a firm edging (Michaelsen, Fig. 18). Common cloacal apertures circular, up to 1.25 mm in diameter, 5 to 9 mm apart. Zooids red, up to 11 mm long, 0.6 to 0.7 mm wide in the pharyngeal region, which has 19–20 fine longitudinal muscle bands, 19 transverse. Post-abdomen ½ to ⅔ of body length. Markedly characteristic of this species are two extremely wide muscle bands on either side of the mid-dorsal line in the pharyngeal region. These cross sharply over to the mid-ventral surface in the region of the oesophagus and continue down on the ventral side of the post abdomen (Text-fig. 2 B). Branchial aperture with six low lobes, atrial with one strong short lappet. Pharynx with 32 tentacles of 3 orders of size, regularly arranged. Dorsal lamina of 19 languets curving back for a very short distance opposite the sixth stigmata from the mid-dorsal line. On each side 20 rows of 20–22 stigmata, about 4 times as long as wide (zooids not fully extended), parastigmatic vessels absent Oesophagus short, narrow; stomach round with 6 longitudinal folds, intestine somewhat narrow in the region nearest the stomach, elsewhere wide, anal aperture with 2 or more lobes. (Gonads not discernible in present specimen.)? 14 testis lobes in the middle and postesior region of the post-abdomen, ovary anterior to the testis. Tadpoles, up to 1.1 mm in length. 0.44 mm m width, present in colonies collected in December, 1914. Distribution. Chatham Is., 15 fathoms, off Cape Pattison; 25 fathoms, off Cape Young. New Zealand, 30 fathoms, off Little Barrier Island; 35 fathoms, Colville Channel. 1. As the zooids of the colony in the present collection are very well expanded, the above account of zooid structure is fuller than that of Michaelsen (1924). 2. These specimens agree more closely with Michaelsen's than do those described from Macquarie Island and Kerguelen (Kott, 1954) in which the colonial lobes have long narrow stalks and surfaces bare of sand, the atrial lappet has three lobes and the pharynx but 10 to 15 rows of stigmata. Amaroucium siphonum, n.sp. (Fig. 2, C1, C2, C3) Colony (Text-fig. 2 C3) a large round mass 7 cm in the longest diameter, 3.5 cm in height above the substratum. Test colourless, transparent, with numerous small test cells, no bladder cells. Zooids orange red (Munsell ∝-YR 6/14) in circular systems of 5 to 9 around the common cloacal apertures, which are circular, 1 mm in diameter and 6 to 7 mm apart. Zooids (Text-fig 2 C1) up to 1.6 cm in length, 1 mm in width in the pharyngeal region which has 11 to 12 longitudinal muscle bands, 14 to 15 fine transverse. Post-abdomen approximately two-thirds of the body length, musculature not concentrated on any one side. Branchial aperture with six very small lobes, atrial at the end of a tube-like structure and surmounted by a wide, irregularly-edged lappet. Pharynx with 16 tentacles of three orders of size regularly arranged. Dorsal lamina of 14 short languets which curve backwards opposite the fifth stigmata from the mid-dorsal line. On each side 15 to 16 rows of 18 to 20 stigmata, 6 to 8 times as long as wide Parastigmatic vessels absent. Oesophagus long and narrow; stomach short, with 11 to 12 low longitudinal folds (Text-fig. 2 C2); intestine without any marked constrictions: anal aperture smooth-edged. Testis of approximately 25 lobes occupying the anterior three-fifths of the post-abdomen. Ovary in among the more anterior testis lobes. Tadpoles up to 1.6 mm in length and 0.4 mm in width in the head region present in the mantle cavity of specimen collected 28.1.54. Distribution. Chatham Is., 15 fathoms, off Cape Pattison. Type Specimen. In the Canterbury Museum. Remarks. This species is distinguished by the siphonal structure more characteristic of Sigllinaria, a genus from which these specimens are separated by the presence of common cloacal apertures. Amaroucium knoxi, n.sp. (Fig. 2, D1, D2) Colony a thin encrusting mass up to 2 mm in height above the substratum (Text-fig. 2 D1). Test colourless, transparent, with numerous small irregularly-shaped test cells, numerous circular granular cells and a few bladder cells. Zooids yellow, deepening to bright orange m the pharyngeal region, arranged in circular systems of 8 to 10 around the common cloacal apertures which are circular and up to 4 mm apart. Zooids (Text-fig. 2 D2) up to 4 mm in length, 0.6 mm in width in the pharyngeal region which has 14 longitudinal muscle bands, 13 transverse. Post-abdomen approximately three-quarters of body length, musculature not concentrated on any one side. Branchial aperture with

Text-fig. 2.—A–Polyclinum sluiteri. A1–Right side of zooid. A2–Colony. A3–Tadpole. B–Amaroucium scabellum. Left side of zooid. C–Amaroucium siphonum. C1–Right side of zooid. C2–T.S. stomach. C2–Portion of Colony. D–Amaroucium knoxi. D1–Portion of colony. D2–Left side of zooid. E–Didemnum mortenseni. E1–Left side of zooid. E2–Spicules.

six distinct lobes, atrial with three comparatively long lappets. Pharynx with 32 tentacles of three orders of size. Dorsal lamina of 13 languets which curve backwards opposite the second stigmata from the mid-dorsal line. On each side 14 rows of 10 stigmata, 2 to 3 times as long as wide. Parastigmatic vessels absent. Oesophagus short, narrow; stomach short, rounded, with 20 to 22 longitudinal folds; intestine narrow at first, widening considerably after the bend; anal aperture bi-lobed. Testis of approximately 35 lobes in the posterior two-thirds of the post-abdomen. Ovary immediately anterior to the testis lobes. No tadpoles present in specimens collected 27.1.54. Distribution. Chatham Is., coastal rocks, Kaingaroa. Type Specimen. In the Canterbury Museum. Remarks. A. constrictum and A variabile recorded from the Chatham Islands also possess tripartite atrial lappets. The present species is distinguished from both by the number of longitudinal folds in the stomach wall, and further from A constrictum by the number of rows of stigmata and from A. variabile by the number of stigmata per row. It is not identical with any species so far recorded from New Zealand, Australia or the Antarctic. Genus Didemnum Savigny, 1816. Didemnum mortenseni Michaelsen (Fig. 2, E1, E2) Syn. 1924. Didemnum mortenseni, Michaelsen, Vidensk. Medd. Naturh. Foren., 77, pp. 360–363, Fig. 1. ? 1954 Didemnum mortenseni, Kott, B A.N.Z. Antarc. Res. Exp., Ser B, 1, pt. 1, pp. 163–164. Colonies greyish white (one recorded as orange pink (R-YR 6/8), forming thin encrusting sheets up to 1.5 mm in height above the substratum. Zooids irregularly arranged around the common cloacal apertures which are circular, 5–7 mm apart and somewhat elevated above the surface of the colony Branchial apertures six-rayed, approximately 0.75 mm apart. Spiculation heavy right throughout the test, which is cartilagenous in nature and contains numerous small test cells. Due to the presence of common cloacal canals the test is spongy in the region level with the pharynx of the zooids. Spicules (Text-fig. 2 E2) 17μ to 60μ in diameter (up to 85μ Michaelsen), rounded with numerous radiating blunt projections. Zooids (Text-fig. 2 E1) up to 1.5 mm in length (1.75 mm, Michaelsen) and 0.4 mm in width in the pharyngeal region, which is twice as long as wide. Rectal-oesophageal region short. Branchial siphon comparatively long, terminating in 6 tapering lobes. Atrial aperture wide, exposing practically the whole dorsal side of the pharynx, no lappet Wide bladder-like “Sertenorgane” present one on either side of the pharyngeal region. These may or may not contain calcareous bodies similar to the spicules but of less regular shape. Pharynx with 16 small tentacles; dorsal lamina of 3 languets curving opposite the second stigmata from the mid-dorsal line; on each side 4 rows of 8 stigmata up to 5 times as long as wide. Oesophagus short, narrow; stomach short, rounded: intestine without marked construction; anal aperture level with the base of the pharynx, smooth-edged. Testis of 2 to 3 lobes. Sperm duct with 5 or occasionally 6 spiral coils. Ovary near testis with 1 or 2 yolky eggs, the largest of which measured 0.3 mm in diameter. Ovaries not always obvious in zooids with testis and probably seasonal developments of the testis occurs earlier than that of the ovary (Michaelsen, finding only male reproductive organs suggested that the colonies might be unisexual.) Distribution. Chatham Is., S. of The Sisters, 38 fathoms. Mernoo Bank, 41 fathoms. Elsewhere: Stewart Island, 25 fathoms (Michaelsen);? Tasmania, 128–676 metres (Kott). Remarks. In form and structure the Chatham Islands and Mernoo Bank specimens agree very closely with the type specimen from Stewart Island, New Zealand. Kott's specimens from Tasmania differ in having fewer coils to the vas deferens and more pointed spicules. Didemnum lithostrotum, n.sp. (Fig. 3, A1, A2, A3) Colonies thin encrusting sheets up to 15 cm in the longest diameter marked out in irregularly polygonal areas up to 10 mm in diameter (Text-fig. 3 A1). Common cloacal apertures circular, 0.3 to 0.5 mm in diameter, approximately 0.3 mm higher than the general surface of the colony (probably higher in living specimens), one per polygonal area, centrally situated (Text-fig. 3 A1). Height of colony above the substratum 0.9 mm at the periphery of each polygonal area, increasing to 1.6 mm nearer the common cloacal aperture. Up to 120 zooids 1 mm apart arranged more or less concentrically around each common cloacal aperture.

Text-fig. 3.—A–Didemnum lithostrotum. A1–Surface of portion of colony. A2–Spicules. A3–Left side of zooid. B–Leptoclinides marmoreus. B1–Right side of zooid. B2–Colony. B2–Spicules. B4–View of posterior end of abdomen showing 5 testis lobes and ovum. C–Pyura chathamensis. C1–Juvenile specimen. C2–Spicules. C3–Spinules C4–Mature specimen. C5–Dissection showing body opened from the ventral surface, pharynx removed. C6 A, B, C–Edge of anus of three different specimens. C7, C8–Specimens collected by M. W. Young, 1925. C9 A, B–Dorsal tubercles; (1) of a juvenile and (2) of a mature specimen.

Test orange in colour (R-YR 6/8), cartilagenous with uniformly dense spiculation, and with numerous test and pigment cells. No bladder cells. Spicules (Text-fig. 3 A2) colourless, 10μ to 80μ in diameter with numerous radiating projections with rounded ends. Zooids (Text-fig 3 A3) deep orange in colour, up to 1.8 mm in length, 0.3 mm in width in the pharyngeal region (which is about three times as long as wide). Length of oesophagealrectal region equal to that of the wider, more posterior stomach-intestinal region Branchial siphon comparatively long terminating in six tapering lobes. Atrial aperture with a single short lappet. Pharynx with 16 tentacles of 3 orders of size regularly arranged, dorsal lamina of 3 languets turning back opposite the fourth stigmata from the mid-dorsal line: on each side 4 rows of 7–8 stigmata up to 4 times as long as wide Oesophagus comparatively long, stomach short rounded; intestine without marked constrictions; anal opening near the base of the pharynx, apertute smooth-edged. Testis of 2 lobes. Sperm duct with 6 spiral coils. Ovary near the testis, largest egg measuring 0.35 mm in diameter Tadpoles present in specimens collected 27.1 54, the largest measuring 0.4 mm in width in the head region, 1.5 mm in length. Distribution. Chatham Is., 15 fathoms, off Hanson Bay; 15 fathoms, off Cape Pattison. Mernoo Bank, 41 fathoms. New Zealand, coastal rocks, Stewart Is. (in author's collection of ascidians). Type Specimen. In the Canterbury Museum. Remarks. This species is clearly distinguished by the arrangement of zooids around the common cloacal apertures and the consequent pavement-like appearance of the colony. Genus Leptoclinides Bjerkan, 1905. D. B. Carlisle and A. I. Carlisle (1954) reduced the genus Leptoclinides Bjerkan to a sub-genus of the genus Didemnum Savigny and removed some species from the genus Leptoclinides into the genus Polysyncraton Nott. As the two latter genera are separated mainly by the degree of division of the testis it is highly probable that as new species are discovered this may be found to be an inadequate separation. Hence until more is known of all three genera, the author prefers, in the meantime, like Dr. Tokioka (1954) to retain the genus Leptoclinides. Leptoclinides marmoreus, n.sp. (Fig. 3, B1, B2, B3, B4) Colonies (Text-fig. 3 B2) in the form of thin encrusting mats, irregular in outline, up to 3 mm in height above the substratum. Appearance of colony marble-like, the basic colouring, pale yellow to dull warm yellow, being broken by dark grey streaks which follow to a certain extent the irregularly-elongated zooid systems. Branchial apertures small, approximately 1 mm apart Common cloacal apertures 6 mm or more apart, large, up to 2 mm in diameter and raised 1 mm above the general surface of the colony, oval in shape (probably circular in living specimens), each situated near the perimeter of a zooid system and usually near the outer edge of the colony. Spicules colourless, 10μ to 45μ in diameter, stellate with numerous radiating pointed projections (Text-fig. 3 B3). Test with numerous small test cells, pigment cells and spicules, and showing distinct layering. The upper region up to 0.2 mm in depth is without pigment or spicules (except for a few scattered in the surface layer), the layer immediately below (up to 0.1 mm) is pigmented and densely spiculated; and the ventral portion is unpigmented and lightly but very uniformly spiculated. Zooids (Text-fig. 3 B1) up to 1.6 mm length, 0.5 mm in width in the pharyngeal region Rectal-oesophageal region short with abdomen almost at right-angles to the pharynx. Branchial and atrial siphons both comparatively long. Pharynx with 12 to 16 tentacles of two orders of size, dorsal lamina of 3 short languets pointing back opposite the second stigmata from the mid-dorsal line; on each side 4 rows of 10 stigmata up to 6 times as long as wide. Oesophagus short, narrow; stomach short, round; intestine with characteristic narrowing near the stomach; anal aperture smooth-edged opening near the base of the pharynx. Testis (Text-fig 3 B4) of 5 lobes; vas deferens with 9 spiral coils. Ovary intestinal loop Eggs comparatively small in size and no tadpoles present in specimens collected 27.1 54. Distribution. Chatham Is., 30 fathoms, off Hanson Bay. Type Specimen. In the Canterbury Museum. Remarks. This species is separated from the three recorded from New Zealand waters–L. scidula, L. diemenensis, L. sluiteri–by the large size of the common cloacal apertures and their location near the periphery of the elongate zooid systems

as well as by the number of coils of the vas deferens or the spicule size. It is unlike any of the species recorded from Australia and the Sub-antarctic. Order Ptychobranchia Seeliger. Genus Pyura Molina, 1782. Pyura chathamensis, n.sp. (Fig. 3, C1, C2, C3 C4, C5, C6A, B, C, C7, C8, C9A, B.) Body (Text-fig. 3 C4) somewhat laterally compressed, ovate, elongate in the anteroposterior direction, attached anteriorly by a long leathery stalk. Test of body thrown into longitudinal ridges separated on each side by three deep grooves. Tubercles usually confined to summits and sides of ridges, present on the distal half of most juvenile and some adult specimens, but on the distal third only of most adults, size and shape of tubercles varying according to age, those of juvenile specimens being narrow, pointed up to 1.8 mm long, 1.0 mm wide at the base (Text-fig. 3 C1), those of adult specimens being rounded 2 to 3 mm long, 3 to 5 mm wide at the base Anterior end of branchial aperture formed by the body proper, rest surmounted by three lobes of thick test, the median one being the thickest and most extensive. Atrial aperture flanked by two very thick short lobes and occasionally by up to four small ones as well. The lobes around the branchial and atrial apertures may have developed from tubercles, though in some tiny specimens they themselves carry tubercles. Test leathery; colour–confined to outer portion–deepening with age to a dull dark purple except on the tubercles and the lobes surrounding the apertures where a dull orange colouring is usually found, pearly white internally; containing numerous small test cells, blood vessels, and in the outer layer pigment cells and calcareous spicules up to 0.4 mm in length (Text-fig. 3 C2). Siphonal spinules elongate, pointed, up to 0.035 mm long, 0.018 mm wide (Text-fig. 3 C2). Incrustation light on the body proper but heavy on some of the stalks, usually due to sertularians Measurements based on the study of fifteen specimens are: Length, 1.0 cm to 5.0 cm, breadth, 0.5 cm to 3.0 cm; depth, 0.4 cm to 2.3 cm; stalk, 0.5 cm to 32.0 cm long, 0.4 cm to 0.5 cm wide near the point of attachment, 0.4 cm to 1.2 cm wide at junction with body; distance between apertures, 0.5 cm to 3.1 cm; thickness of test, 1 mm to 3 mm. Mantle tough, semi-transparent, with strong circular muscle bundles around siphons and strong longitudinal muscle bands radiating out from the siphonal region. Pharynx with 32 feathery tentacles of 4 orders of size regularly arranged, 4 orders of branching; opening of dorsal tubercle varying according to age, the simple horseshoe with inrolled ends seen in juvenile forms becoming thrown into more and more convolutions according to the age of the individual (Text-fig. 3 C9A, B); neural gland a small round cushion below and slightly to the right of the nerve cord; dorsal lamina composed of 19 to 36 curved languets the number being somewhat closely related to the size of the specimen; on each side 6 longitudinal folds; longitudinal vessels 61 to 104 on right, 65 to 107 on left, samples of arrangement being:– Length of Specimen Arrangment of Vessels on Right Total 1.0 cm E 3(5)1(9)1(11)1(10)1(10)1(7)1 DL 61 2.5 cm E 5(8)2(12)2(12)2(12)2(13)2(13)1 DL 86 4.5 cm E 5(10)2(12)3(13)3(15)2(14)2(14)2 DL 97 4.5 cm E 5(12)2(14)2(15)2(16)2(14)3(13)2 DL 102 Transverse vessels irregularly arranged. Stigmata straight, 8 to 12 in the meshes between the folds, 6 to 8 times as long as wide, parastigmata present. Gut loop (Text-fig. 3 C.5) occupying practically the whole length and more than one-half of the width of the left side of body. Oesophagus narrow; little difference in width between stomach and intestine, the latter bearing “problematical organs” on the second half of the loop; usually five pairs of liver lobes (occasionally 4), of which the pair second from the intestine is usually the smallest. Anal aperture wide, hooded, edge (Text-fig. 3 C6A, B, C) usually smooth but varying degrees of scalloping shown in 20 per cent. of the specimens. Atrial velum frilled, up to 1.5 mm wide, edge scalloped. One hermaphrodite lobed gonad present on each side of the body (Text-fig. 3 C5) Lobes somewhat rectangular, arranged in a single row, 9 to 13 on right, 10 to 13 on the left, decreasing in size towards gonoduct, openings close to the atrial aperture. Gonads not distended in specimens collected 30.1.54. Distribution. Chatham Is., Waitangi, on wharf piles. Type Specimen. In the Canterbury Museum. Remarks. Two stalked Pyuras have been recorded from New Zealand waters (P. pachydermatina Herdman from the South Island and Stewart Island and P. spinossissima Michaelsen from the North Island). The differences between the two have been listed (Brewin, 1952). The specimens in the collection of the Chatham Island 1954 Expedition are distinguished from both the two above by deeper pig-

mentation with stronger orange colouration, smaller size of the body, restriction of tubercles to the distal half of the body and the number of stigmata per mesh between the folds 8 to 12 (7 to 9, P. pachydermatina, 12 to 16, P. spinossissima). However, they show distinct resemblance to P. spinossissima in the number of lobes surrounding the apertures and in the number of longitudinal vessels between the folds 1 to 3 (1 to 4, P. spinossissima, 6 to 7, P. pachydermatina). Furthermore, external resemblance to the juvenile form of P. spinossissima (Brewin 1952, Plate I, Fig. 1) is also quite marked in some small specimens (Text-fig. 3 C7, C8) in the Otago Museum. The latter were collected by M. W. Young “attached to a pipi shell, north coast, Chatham Island, 29 7.1925”, and it is interesting that these 1925 specimens bear a closer resemblance to the juvenile forms of P. spinossissima than do the 1954 specimens. There can be no doubt that P. chathamensis, P. spinossissima and P. pachydermatina are closely related, and it is highly probable that they represent direct or indirect radiations from one original species. Evidence is in favour of P. chathamensis being an offshoot from P. spinossissima and possibly the exposure of the Chatham Islands has been a deciding factor in determining the size and form of stalked pyurid capable of survival in the locality. As experiments showing the development of the three species under a wide range of environmental conditions are not practicable, it seems preferable to consider all three as separate species. (As in P. pachydermatina and P. spinossissima a great amount of internal as well as external change occurs as growth proceeds, not only in external appearance but also in the shape of the opening of the dorsal tubercle and in the number of longitudinal vessels.) Part II.–Ascidians from the Chatham Rise. The Chatham Rise is an irregular expanse of shallow sea linking New Zealand and the Chatham Islands. It reaches depths less than 100 fathoms in the region shelving the Islands and in two banks on its westerly end–64 Fathom Bank and the Mernoo Bank. The collection of ascidians which forms the basis of the present account is the first to be made from this region and for it the author is indebted to the Chatham Islands 1954 Expedition, who established five stations along the western portion of the Rise. Of the twelve ascidians represented, five occur also in New Zealand waters, four are new species, and three cannot be identified with certainty. The latter belong to three separate families, Synoicidae, Didemnidae and Botryllidae. List of Species from the Chatham Rise Synoicidae *Species from depths greater than 100 fathoms. Polyclinum michaelseni, n. sp. † Species from the Mernoo Bank. Amaroucium mernooensis, n.sp. Didemnidae † Didemnum mortenseni Michaelsen † Didemnum lithostrotum, n.sp. † Leptoclinides auranticus, n.sp. Botryllidae * Botryllid sp. Styelidae † Cnemidocarpa bicornuata (Sluiter) † Cnemidocarpa stewartensis Michaelsen † Cnemidocarpa nisiotis (Sluiter) † Amphicarpa michaelseni, n.sp.

Full descriptions are given only of genera and species not appearing in the author's papers on ascidians from New Zealand waters or in the first part of the present paper, the range of variability of the other species being as follows:– Specimens of Cnemidocarpa bicornuata (41 fathoms, Mernoo Bank) fall within the range of variability given for specimens from the Otago Harbour as also do those of Cnenidocarpa stewartensis (41 fathoms, Mernoo Bank) with the exception that one specimen had a higher count of gonads–9 on the right side. Specimens of Cnemidocarpa nisiotis fall within the range of variability given for specimens from the vicinity of Christchurch and the colonies of Didemnum mortenseni and Didemnum lithostrotum (both from 41 fathoms, Mernoo Bank) exhibit no differences from the ones described from the Chatham Islands. Description of Species Order Krikobranchia Seeliger. Genus Polyclinum Savigny. 1816. Polyclinum michaelseni, n.sp. (Fig. 4, B1, B2) Colonies (Text-fig. 4 B2) almost spherical masses, the largest 6.5 mm in diameter and up to 6.0 mm in height above the substratum. Fine sand grains imbedded in the peripheral region of the test and forming a dense incrustation, broken only by the small branchial apertures and the single common cloacal aperture which is central, circular, 1.5 mm in diameter. Test translucent, with numerous small round cells (colour in life not noted). Zooids (Text-fig. 4 B1) up to 5.0 mm in length, and 1.2 mm in width in the pharyngeal region which has a weak musculature of fine fibres not concentrated into bundles. Post-abdomen one-fifth of the zooid length. Branchial aperture with six lobes so small that the aperture appears smooth-edged to the naked eye. Atrial lappet wide with free end tapering or blunt. Pharynx with 32 comparatively long tentacles of three orders of size regularly arranged. Dorsal lamina of 14 comparatively long languets curving back opposite the third stigmata from the mid-dorsal line. On each side 16 rows of 17 stigmata, three times as long as wide, parastigmatic vessels absent. Papillae 14–i.e., slightly less numerically than the stigmata. Oesophagus short; stomach smooth, globose; intestine twisted to form a small closed loop; rectum long, extending two-thirds of the way up the pharynx where it ends in a bilobed aperture. Post-abdomen pyriform, stalk length equal to that of the posterior swollen region containing the gonads. Ovary anterior to the testis blocks which number up to twenty. One or two tadpoles (measuring up to 0.8 mm in length, 0.2 mm in width in the head region) present in mantle cavity of specimen collected 10.2.54. Distribution. Chatham Rise, 44° ° 4′S., 178° 04′ W., 260 fathoms. Type Specimen. In the Canterbury Museum. Remarks. This species is characterized by the presence of a single common cloacal aperture. Genus Amaroucium Milne Edwards, 1841. Amaroucium (Aplidium) mernooensis, n.sp. (Fig. 4, A1, A2). Colonies (Text-fig. 4 A2) composed of small orange-red flat-topped lobes up to 2 mm in the longest diameter and 2 mm in height above the substratum. Test clear orange with numerous small test cells but no bladder cells, surface layer (except that covering the tops of the lobes) heavily mcrusted with fragments of shell and with sand grams. Zooids orange red, arranged around the common cloacal apertures which are circular and up to 1 mm in diameter, there being either one central or two common cloacal apertures per lobe. Zooids (Text-fig. 4 A1) up to 8 mm in length and up to 0.5 mm in width in the pharyngeal region, which has 12 longitudinal muscle bands, 4 fine transverse. Post-abdomen one-half of the body length, musculature showing a tendency to concentration on the ventral side. Branchial aperture 8-lobed, atrial with a long lappet divided in three lobes near the distal end. Pharynx with 16 branchial tentacles of three orders of size, regularly arranged, dorsal lamina of 4 languets curving backwards opposite the third stigmata from the mid-dorsal line; on each side 5 rows of 11 to 12 stigmata, 8 to 10 times as long as wide. No parastigmatic vessels Oesophagus long narrow; stomach short round with 5 longitudinal folds; intestine without marked constriction; anal aperture bi-lobed. Eleven or more testis lobes in the posterior half of the post-abdomen. Ovary in among anterior testis blocks. Tadpoles, up to 9 mm long, 0.25 mm wide in the head region, present in the mantle cavity of specimens collected 23.1.54.

Text-fig. 4.—A–Amaroucium mernooensis. A1–Right side of zooid. A2–Two colonies. B–Polyclinum michaelseni. B1–Left side of zooid. B2–Colony. C–Leptoclinides auranticus. C1–Right side of zooid. C2–Diagrammatic transverse section of colony. C3–Spicules. C4- Posterior end of abnormal zooid in which the testis is divided into two portions, each with its own spirally-coiled vas deferens. These unite near the intestinal loop. D–Botryllid sp. Left side of bud, showing small lateral bud with ovaries. E–Amphicarpa michaelseni. E1–Portion of colony. E2–Tadpole. E3–Dissection showing body opened from the ventral sunface, pharynx removed.

Distribution. Chatham Rise, Mernoo bank, 41 fathoms. Type Specimen. In the Canterbury Museum. Remarks. This species is unlike any previously recorded from Chatham Islands. It is separated from A. thomsoni (recorded from New Zealand) mainly by the flat-topped form of the colony, the presence of only 1 or 2 zooid systems per lobe and the restriction of gonads to the posterior half of the post-abdomen. Genus Leptoclinides Bjerkan, 1905. Leptoclinides auranticus, n.sp. (Fig. 4, C1, C2, C3, C4). Colonies in the form of thin encrusting mats, irregular in outline, 1 mm to 2.2 mm in height above the substratum Colouring orange (R-YR 6/10) fading to white at the edges. Branchial apertures very small, six-rayed, 0.5 mm to 1.2 mm apart Common cloacal apertures scattered over the surface of the colony, small, circular and less than 1 mm in diameter in preserved specimens. Spicules colourless, 10μ to 60μ in diameter, stellate with numerous radiating pointed projections (Text-fig. 4 C3). Test with numerous small test cells, bladder cells, pigment cells and spicules, and showing distinct layering (Text-fig. 4 C2). The upper region up to 0.5 mm in depth is colourless, spiculeless (except for the few scattered in the surface layer) and contains numerous bladder cells; the layer immediately below (up to 0.4 mm) is pigmented and densely spiculated, and the more ventral portion is lightly but very uniformly spiculated. Zooids (Text-fig. 4 C1) up to 1.0 mm in length, 0.3 mm in width in the pharyngeal region. Rectal-oesophageal region short with abdomen lying almost at right angles to the pharynx. Branchial siphon comparatively long, surmounted by six very short lobes. Atrial aperture at the end of a backwardly-directed siphon, which opens into a wide cloacal canal. Pharynx with 16 tentacles of two or three orders of size regularly arranged; dorsal lamina of 3 short languets curving backwards opposite the second stigmata from the mid-dorsal line; on each side 4 rows of 11–12 stigmata up to four times as long as wide. Oesophagus short, narrow, stomach short, round; intestine with characteristic narrowing near the stomach: anal aperture smooth-edged, opening level with the anterior end of the posterior row of stigmata. Tests of 5 to 6 lobes; vas deferens with 7 spiral coils. (Text-fig. 4 C4 depicts an abnormal zooid showing division of both the testis and the proximal end of the vas deferens.) Ovary in intestinal loop. Eggs small in size and no tadpoles present in specimens collected 23.1 54. Distribution. Chatham Rise, Mernoo Bank, 41 fathoms (on test of Cnemidocarpa nisiotis and on shell fragments). Type Specimen. In the Canterbury Museum. Remarks. This species is distinctly separated from the three species of Leptoclinides recorded from New Zealand. In colony form it agrees most closely with L. sluiteri Brewin, but is separated from it by the greater number of stigmata per row, the larger size of the spicules and the fewer coils in the vas deferens. It differs from L. sparsus Mich. in possessing more stigmata per row and in the absence of star-shaped pigment cells; from L. diemenensis it is separated by the much smaller size of the zooids and the far thinner colony; nor is it identical with any of the species previously recorded from the Southern hemisphere. Order Ptychobranchia Seeliger Family Botryllidae Verrill, 1871. Among the material collected from the Chatham Rise Station 59 (43° 38′ S., 177° 19′ W., depth 290 fathoms) is a Botryllid which resembles Botrylloides leachi in appearance and mode of growth. The zooids are up to 5 mm in length, 1 mm in width and have up to 18 rows of stigmata arranged on the following lines:–D.L. 8/4/4/6 E. or D. L.8/5/5/6 E. Young and extremely small buds alone show gonadial development (Text-fig. 4 D) and in them ovaries only are discernible. The phenomenon of gonads appearing in the newly-formed bud has been recorded previously for a Botryllid with only 4 rows of stigmata–Botryllus primigenus Oka. Family Styelidae Sluiter, 1895 Genus Amphicarpa Michaelsen, 1922. Amphicarpa michaelseni, n.sp. (Fig. 4, E1, E2, E3). Individuals sack-like, up to 7 mm in width and in depth and 12 mm in height above the substratum, connected by basal stolonic outgrowths of up to 1.5 mm in diameter (Text-

fig. 4 E1). Test clear, cartilagenous, 0.2 to 0.4 mm in thickness and with surface heavily incrusted with fine sand grains. Apertures vermilion, up to 1 mm in height and (in the larger specimens) approximately 5 mm apart. Mantle wall yellow, musculature weak. Pharynx with 40 to 60 long filiform branchial tentacles of two orders of size regularly arranged. Opening of dorsal tubercle a long slit. Neural gland a small round cushion-like structure. Dorsal lamma a plain narrow membrane. Pharyngeal folds two in number on each side. Longitudinal vessels arranged on the following plan:– E 6 (7) 6 (8) - D.L. - (8) 5 (7) 6 E. E 6 (7) 6 (8) 1 D.L. - (9) 4 (8) 6 E. Four to eight stigmata between the longitudinal vessels. Stigmata up to ten times as long as wide and crossed by parastigmatic vessels. Oesophagus short; stomach, short, round, with 15 to 16 longitudinal folds and a short caecum (Text-fig. 4 E3); intestine wide, strongly curved with problematical organs on the ventral region adjacent to the stomach; anal aperture smooth-edged. Atrial velum with a single row of fine filiform tentacles about 0.1 mm in length Endocarps few (4–7 on each side) scattered over the mantle wall. Gonads unisexual arranged in rows parallel to the endostyle (Text-fig. 4 E3). In one specimen 19 testes and 5 ovaries on the right, 29 testes on the left, and even greater number, recorded for larger specimens, in which as many as 20 embryos are present in the mantle cavity. Tadpoles up to 2.8 mm long, 0.5 mm in width in the head region and with characteristic brown markings (Text-fig 4 E2) present in specimens collected 23 1.54. Distribution. Chatham Rise, Mernoo Bank, 41 fathoms. Type Specimen. In the Canterbury Museum. Remarks. This species differs from A. schauinslandi Mich. previously recorded from Chatham Island in the possession of two longitudinal folds on each side of the pharynx (not 4), in the greater number of branchial tentacles, 40–60 (ca. 16, A. schauinslandi) and in the distribution of male polycarps, the greater number being on the left side of the body (on the right, A. schauinslandi). Discussion Finlay, in 1928, concluded that “the Recent Molluscan fauna of the Chatham Islands is not a remnant or an evolution of the Tertiary fauna found there, but a re-population from the mainland, in Post-Pliocene times, but yet long enough ago for characteristic regional species and sub-species to have evolved”, and Knox (1954) from a study of the intertidal ecology also reached the conclusion that the intertidal region of the Chatham Islands has been populated from New Zealand. The ascidian fauna of the Chathams certainly shows a close alliance with that of New Zealand. Of the 33 species here listed, 21 have been recorded from New Zealand; 12 (including the 7 new species here described) have been found only in the Chatham region. The Chatham Islands are Convergence Islands lying not only in the sweep of cool sub-antarctic water which flows up past the east coast of the South Island of New Zealand (Deacon, 1937) but also in the current of warm subtropical water which flows down past the east coast of the North Island of New Zealand (Fleming, 1952) and it is not surprising that previous workers–Powell (1933), mollusca; Moore (1949) algae; Knox (1954) intertidal species–have shown that the intertidal fauna and flora of these islands include an odd mixture of species characteristic of the northern and southern parts of New Zealand. The ascidian species common to New Zealand and the Chatham Islands can be placed in five divisions according to their distribution in New Zealand, and from a study of them it can be seen that the ascidian fauna also contains a mixture of species characteristic of the northern and southern parts of New Zealand (see divisions B and E respectively in the summary below). Distribution in New Zealand of Ascidians Common to New Zealand and the Chatham Islands (A) Species recorded from the entire eastern coastline. Nine–Amaroucium phortax f. typica, Didemnum candidum, Cystodytes dellachiaiae, Corella eumyota, Botrylloides leachi, Cnemidocarpa bicornuata, Asterocarpa cerea, Pyura trita, Pyura cancellata.

(B) Species recorded only from the northern portion of the North Island. Three–Amaroucium scabellum, Amaroucium circumvollutum, Alloeocarpa minuta. (C) Species recorded from the southern portion of the North Island, the South Island and Stewart Island. Three–Sycozoa sigillinoides, Pyura pulla, Pyura suteri. (D) Species recorded only from the northern portion of the South Island. One–Aplidium foliaceum. (E) Species recorded only from the southern portion of the South Island and/or Stewart Island. Five–Amaroucium benhami, Didemnum studeri f. typica, Didemnum mortenseni, Didemnum lithostrotum, Molgula sluiteri. (It must be noted that all conclusions as to the distribution of species must carry the proviso “as far as is at present known, our knowledge of the ascidian fauna of New Zealand, like that of the Chatham Islands, being still incomplete, and our knowledge of the ascidian fauna of Antarctica being due to the sporadic collections made by visiting research vessels). Of the 21 species common to New Zealand and the Chatham Islands, 7 only have a wider distribution–3, (Didemnum candidum, Cystodytes dellachiaiae, Botrylloides leachi) are practically world-wide; 3, (Sycozoa sigillinoides, Corella eumyota and most probably Asterocarpa cerea (Brewin, 1945) are circum-south-polar; and 1 (Didemnum studeri f. typica) has been recorded also from South America. Amaroucium variabile, a species recorded from the Chatham Islands but not as yet from New Zealand waters, has been found at Kerguelen and may also prove to be circum-south-polar. Of the 3 species said to be common to the Chatham Islands and the Australian or Malayan region (Synoicum fungosum, Didemnum mortenseni, Cnemidocarpa bicornuata) the Australian accounts are far from convincing. Hence at present no claim can be sustained for an Australo-Malayan influence on the Chatham Island ascidian fauna. Knox (1954) has drawn attention to the complete absence from the Chatham fauna of many of the species of mollusca and arthropoda found commonly on New Zealand shores. In a group such as the ascidians, in which the majority of species inhabit the sub-littoral fringe and the sub-littoral zone, tidal and weather conditions play such a large part in field collection that several visits to any given locality are necessary before a complete faunal list can be prepared. Hence at present any comment on absences from the Chatham Islands ascidian fauna would indeed be premature. This also holds for remarks concerning endemic species. Finlay (1928) reached the conclusion that molluscan repopulation of the Chatham Islands took place long enough ago for characteristic species and subspecies to have evolved. In the ascidians only in the stalked Pyuras is there any evidence of a Chatham Island species having evolved. P. chathamensis is obviously related to the two New Zealand stalked Pyuras and more closely to the northern P. spinossissima. Its distinguishing characters are, moreover, more apparent in specimens collected in 1954 than in ones collected in 1925. In this connection note should be made of the fact that throughout the whole Pyura pachydermatina group, i.e., the stalked Pyuras of the Australian-New Zealand region, a great amount of radiation has occurred with development of many closely-related forms. Kott (1952) recognises among the Australian forms 3 varieties of P. pachydermatina, 2 varieties of P. australis and P. spinifera. The recorded ascidian fauna of the Chatham Rise is merely the known fauna of that portion of the Rise nearest New Zealand. As would be expected, it shows a close alliance with the ascidian fauna of New Zealand, five species being common to both. The latter can be placed in two divisions according to their distribution in New Zealand. (A) Species recorded from along the entire eastern coastline. Two–Cnemidocaipa bicornuata, Cnemidocarpa nisiotis.

(B) Species recorded only from the southern portion of the South Island and/or Stewart Island. Three–Didemnum mortenseni, Didemnum lithostrotum, Cnemidocarpa stewartensis. The ascidian fauna of the Chatham Rise, unlike that of the Chatham Islands, has no species that are found in New Zealand only in the northern regions. There is, however, a marked southern influence. Four new species are described from the Chatham Rise, but in the present state of our knowledge it would be unwise to consider them endemic. Due to the topography of the Rise, the present collection includes material from the comparatively shallow Mernoo Bank (7 species, 5 of which occur in New Zealand waters) as well as material from depths greater than 100 fathoms (4 species). Of the latter Polyclinum michaelsem is described, but the other three (a Botryllid, a Didemnid and a species of Amaroucium) are unidentifiable owing to contraction of muscles or underdevelopment of gonads. Explanation of Lettering at.–atrial siphon. av.–atrial velum. b.–bud. bc.–bladder cell layer. br–branchial siphon. ccl.–common cloacal aperture. enc.–endocarp. end.–endostyle. l.m–longitudinal muscle. l.s.–lightly spiculated layer. po.–“problematical organs” ps.–pigmented and spiculated layer. s.d.–sperm duct. sl.–stolon. so.–seitenorgane. st.–stomach. ♂–testis. ♀–ovary. Literature Cited Brewin, B. I., 1946. Ascidians in the Vicinity of the Portobello Marine Biological Station, Otago Harbour, Trans. Roy. Soc. N.Z., 76, pt. 2, pp. 87–131. —— 1951. Ascidians of New Zealand Pt. VI. Trans. Roy. Soc. N.Z., 79, pt. I, pp. 104–113. —— 1952. Ascidians of New Zealand Pt. VIII. Trans. Roy. Soc. N.Z., 80, pt. 2, pp. 187–195. Carlisle, D. B. and A. I., 1954. Notes on the Didemnidae I. Jour. Mar. Biol. Ass. U.K., 33, pp. 21–25. Deacon, G. E. R., 1937. The Hydrology of the Southern Ocean. “Discovery Reports” 15, pp. 1–155. Finlay, H. J., 1928. The Recent Mollusca of the Chatham Islands. Trans. N. Z. Inst, 59, pp. 232–286. Fleming, C. A., 1952. “The Antarctic To-day,” A. H.& A. W. Reed, Wellington. Herdman, W. A., 1882. Report on the Tumcata collected during the Voyage of H.M. S. Challenger during the years 1873–76. Pt. I. Ascidiae Simplices. Rep. Voy. Challenger Zool., 6, pp. 1–135. —— 1886. Ascidiae Compositae. Rep. Voy. Challenger Zool., 14, pp. 1–432. Knox, G. A., 1954. The Intertidal Flora and Fauna of the Chatham Islands. Nature, 174, pp. 871–874. Kott, P. & Thompson, H., 1954. Tunicata. B.A.N. Z. Antarctic Research Expedition 1929–1931. Reports, Ser. B, 1, pt. 4, pp. 123–185. Michaelsen, W., 1922. Ascidiae Ptychobranchiae und Diktyobranchiae von Neuseeland und den Chatham-Inseln. Vidensk. Medd. naturh. Foren., 73, pp. 359–498. —— 1924. Ascidiae Krikobranchiae von Neuseeland, den Chatham und den Auckland Inseln. Vidensk. Medd. naturh. Foren, 77, pp. 363–434. Moore, L. B., 1949. The Marine Algal Provinces of New Zealand. Trans. Roy. Soc. N.Z., 77, pp. 187–189. Powell, A. W. B., 1933. The Marine Mollusca of the Chatham Islands. Rec. Auck. Inst. and Mus, I, pp. 181–208. Sluiter, C. Ph., 1900. Tunicaten aus den Stillen Ocean. Zool. Jahrb. Syst., 13, pp. 1–35. Tokioka, T., 1954. Contributions to Japanese Ascidian Fauna X. Notes on some Ascidians collected in Osaka Bay (2) Publ. Seto Mar. Biol. Lab., IV, No. 1, pp. 75–98. Young, M. W., 1930. Marine Fauna of the Chatham Islands. Trans. N. Z. Inst., 60, pp. 136–166. Miss Beryl I. Brewin Zoology Dept. University of Otago Dunedin.