Larvae of Petrolisthes novaezelandiae Filhol, 1885 (Crustacea, Decapoda, Anomura)

Transactions of the Royal Society of New Zealand : Zoology, Volume 4, Issue 18, 25 July 1964, Page 229

Larvae of Petrolisthes novaezelandiae Filhol, 1885 (Crustacea, Decapoda, Anomura)

Robert G. Wear

By

Victoria University of Wellington

\Received by Editor, March 9, 1964.]

Abstract

The zoea and megalopa larvae of Petrolisthes novaezelandiae from Wellington Harbour, New Zealand, are described and a key to the zoea larval stages is given. The larvae differ from the generic larval type and can only be compared closely with those of the genus Porcellana. Consequential taxonomic implications are discussed.

Introduction

Porgellanid crabs, commonly known as " half -crabs " are widely known through Petrolisthes elongatus which is extremely abundant between the tide marks on nearly all rocky and stony beaches of New Zealand. However, adults of P. novaezelandiae are rarely found intertidally, but the species has been often recorded in depths between 2 fathoms and 40 fathoms in many New Zealand localities from the Bay of Islands south to the Otago Peninsula. The planktonic zoea larvae of the family Porcellanidae are characterised by an enormously long rostrum and posterior carapace spines. The larvae of three species are found in the Wellington Harbour plankton, with those of P. novaezelandiae being the most abundant.

LIST OF ABBREVIATIONS

Abd. = Abdomen. Abd. Seg. 6 = Abdominal Segment 6. An. = Anus. Arth. Br. = Arthrobranch. Basip. = Basipodite.

Carp. = Garpopodite. Cox. = Coxopodite. Opce. = Carapace. Dact. = Dactylopodite. Dist. End. = Distal Endite. End. 1-4 = Endites 1 to 4. Endop. = Endopodite Epip. = Epipodite. Ex. = Exite.

Exop. = Exopodite. Gill B. = Gill Buds. Inc. Pr. = Incisor Process. I.R. = Inner Ramus. Isch. = Ischiopodite. Lat. PI. = Lateral Plate.

Lat. Sp. = Lateral Spine. Med. PI. = Median Plate. Mer. = Meropodite.

Mol. S. = Molar Surface Mxpd. 3 = Maxilliped 3. O.R. = Outer Ramus. Ped. = Peduncle.

Per. 1-5 = Pereiopods 1 to 5. Pleur. Br. = Pleurobranch. Pip. = Palp.

Plpds. = Pleopods. Post. PI. = Posterior Plate. Post. Sp. = Posterior Spine. Pr. End. = Proximal Endite. Prop. = Propodite.

Prot. = Protopodite. Rost. = Rostrum.

Scaph. = Scaphognathite. Seg. 3-5 = Abdominal Segments 3 to 5. Tel. = Telson.

Materials and Methods

Thirty-five adults dredged from Wellington Harbour were kindly lent to the author by Dr Dell (Dominion Museum), and 32 adults dredged in 4 fathoms from the Bay of Islands were obtained through courtesy of the Marine Department, Wellington. Four adults and larvae of the United Kingdom species Porcellana longicornis were obtained from Dr Pike for comparative purposes.

Larvae were obtained from the Wellington Harbour plankton and living larvae were kept in the laboratory for rearing. These were identified to species after the second juvenile (post-megalopa) stage had been reared from the final zoea in the laboratory, and compared with the adult.

Two main zoea larval stages were recognised in the planktonic life history of Petrolisthes novaezelandiae. These have been termed zoeal stages 1 and 2 respectively. The first stage has two sub-stages which have been termed substages la and lb respectively. Within stage 2, sub-stages 2a, 2b and 2c have also been recognised. This is the conventional nomenclature used by Lebour (1943, 1950) in describing the zoea larval stages of the genera Petrolisthes and Porcellana. The larval stages were determined by rearing planktonic first stage larvae to a second stage in the laboratory, and the subsequently recognisable second stage larvae were obtained from the plankton and reared to a third zoea. Later stages were obtained in a similar manner. The laboratory reared zoeal stages were compared with those found in plankton samples and they corresponded in all essential details. There is a single megalopa larval stage which was not found in the plankton. This was reared from late stage larvae in the laboratory.

Drawings and descriptions of the zoea larvae and of the megalopa larva are based on about 40 larvae of each stage. The coloured chromatophores are represented by the following code:

Measurements of the zoea larvae are given in " rostrum lengths", " carapace lengths", "posterior carapace spine lengths", and "total lengths". The rostrum length is measured from the base of the rostrum to its tip, the carapace length is measured from the base of the rostrum to the posterior middorsal margin of the carapace, and the posterior carapace spine length is measured from the posterior mid-dorsal margin of the carapace to the tips of the pair of posterior carapace spines. The total carapace length of the zoea larvae is measured from the tip of the rostrum to the tips of the posterior carapace spines. Measurements of the megalopa larva are given in " carapace length " and " carapace width ". The carapace length is measured from the tip of the rostrum to the posterior mid-dorsal margin of the carapace, and the carapace width is measured at right angles to the carapace length across the widest part of the carapace.

Nomenclature of the larval limbs and limb-segments is based on Borradaile (1926) and Hale (1927). The decapod larval terms “zoea” and “megalopa” are here employed in the sense suggested by D. I. Williamson (1957), and where possible the ambiguous term “ post-larva ” has been avoided. Non-larval stages following the megalopa have been termed “ juvenile stages ”.

The Zoea Larvae

The zoea larval stages of Petrolisthes novaezelandiae are found in the Wellington Harbour plankton throughout the year, but are most abundant in late spring and summer (November to January). Two zoea larval stages are essential in the life history. These are stages la and 2a. In moulting to stage 2a, stage la larvae may bypass stage lb. In moulting to stage 2c, stage 2a larvae may bypass stage 2b. Stage 2c may also be bypassed, as several stage 2b larvae moulted to the megalopa larva in the laboratory. It is therefore probable that the sequence of larval stages is either la >2a >2c > megalopa or la > lb > 2a > 2b > megalopa. This reduction in the number of zoeal stages is similar to the pattern shown for Porcellana longicornis and P. platycheles by Lebour (1943). Lebour notes that it is extremely doubtful if any larva moults through all possible five stages in reaching the megalopa stage.

A Key to the Zoea Larvae of Petrolisthes novaezelandiae

1 (4) Total carapace length less than 10.0 mm; eyes sessile and immovable; Ist antennae uniramous; endopodite of 2nd antennae shorter than exopodite; exopodite of Ist and 2nd maxillipeds with 4 natatory setae only; 3rd maxillipeds uniramous; pleopod buds absent; telson with 7+ 7 posterior setae; distal hooklets on 3rd posterior telson setae only

STAGE ONE

2 (3) Endopodite of 2nd antennae less than half the length of exopodite; no sign of 3rd maxillipeds or pereiopods

Stage la (Fig. 1)

3 (2) Endopodite of 2nd antennae greater than half the length of exopodite; 3rd maxillipeds and pereiopods present as small buds

Stage lb (Fig. 2)

4 (1) Total carapace length greater than 10.0 mm; eyes movable and borne on short stalks; Ist antennae biramous; endopodite of 2nd antennae longer than exopodite; exopodite of Ist and 2nd maxillipeds with about 12 natatory setae; 3rd maxillipeds biramous; pleopods present as small buds; telson with 8+ 8 posterior setae, with Bth (inner) pair arising from the central prominence; distal hooklets on 3rd and 4th telson setae

STAGE TWO

5 (8) Flagellum of 2nd antennae unsegmented; mandibles without palp; palps of Ist and 2nd maxillae unsegmented; pereiopods unsegmented; pleopod buds unsegmented.

6 (7) Peduncle of Ist antennae unsegmented; endopodite of 2nd antennae about twice the length of exopodite; pereiopods short and very slender; gill buds absent or very tiny

Stage 2a (Fig. 2)

7 (6) Peduncle of Ist antennae incompletely divided into 2 segments; endopodite of 2nd antennae greater than twice the length of exopodite; pereiopods strongly developed; all gill buds well formed

Stage 2b (Fig. 3)

8 (5) Flagellum of 2nd antennae visibly segmented beneath cuticle; mandibles with a slender, unjointed palp; palps of Ist and 2nd maxillae completely or incompletely segmented; pleopod buds massive and two-segmented

Stage 2c (Fig. 3)

Stage One Zoea

Stage la Stage la zoea larvae were obtained only from the plankton. It is unlikely that an earlier zoea larva exists in this species. Stage la is considered an essential larval stage to which all pre-zoea larvae moult, but is not as abundant in the plankton as expected for an essential larval stage.

Description. Cephalothorax: Total carapace length 7.3 mm to 7.9 mm. Rostrum 4.4 mm to 4.Bmm in length, tapered, roughly hexagonal in cross-section with an irregular row of small hair-like setae along each of its six angles. Carapace I.2mm to I.3mm in length, heart-shaped, smooth, and without setae. Posterior carapace spines I.7mm to I.Bmm in length, each with from three to six ventral setae close to its base. First three setae strongly developed, but more distal setae much reduced or occasionally absent. Eyes large, sessile, and without stalks. (Fig. 1, A.)

Cephalic Appendages: First antenna (antennule) (Fig. 1, B) unjointed with four long aesthaetes and three shorter aesthaetes at its tip. Second antenna (Fig. 1, G) consists of a short unjointed protopodite bearing a slender exopodite and a short endopodite. Endopodite usually bud-like, but if larger, is always less than half the length of exopodite. Endopodite with a small sub-terminal seta on outer margin. Exopodite reduced to a slender spine with two hair-like setae on its inner margin just below the tip.

Mandible (Fig. 1, D) without a palp. Molar surface thrown into a number of toothed ridges but incisor process small and ill-defined.

First maxilla (maxillule) (Fig. 1, E) comprises a flattened protopodite bearing a palp and two endites. Endites each fringed by an inner row and an outer row of four stout, coarsely plumose setae curved towards the mouth. Palp unjointed with three stout, coarsely plumose setae at its tip.

Second maxilla (Fig. 1, F) comprises a flattened protopodite bearing a broad scaphognathite, a palp (endopodite), and four endites. Inner pair of endites (coxopodite) separated from outer pair (basipodite) by a deep cleft. First (proximal) endite and fourth (distal) endite each with an inner row and an outer row of three stout, coarsely plumose curved setae. Second and third (inner) endites each with four such setae. Palp with three stout, coarsely plumose setae at its tip. Scaphognathite with a long, densely plumose seta at its proximal tip and four similar setae along outer distal margin. Outer proximal margin of scaphognathite with many fine hairs.

Thoracic Appendages: The first maxilliped (Fig. 1, G) consists of a short coxopodite and a long basipodite bearing a five-segmented endopodite and a two-segmented exopodite. Endopodite only slightly shorter than exopodite. Coxopodite has one sparsely plumose seta on inner margin. Ischiopodite, meropodite, carpopodite, and prcpodite of endopod each with three sparsely plumose setae on inner distal margins. Dactylopodite with three long, sparsely plumose setae at its tip and four similar subterminal setae. One very long, densely plumose seta on outer distal margin of propodite. Exopodite with four long, terminal natatory setae.

Second maxilliped (Fig. 1, H) similar to the first, but its endopodite is four-segmented and only half the length of the exopodite. Coxopodite is without setae. Basipodite with one sparsely plumose seta mid-way along inner margin and a similar seta on inner distal margin. First, second, and third segments of endopod each with two sparsely plumose setae along inner distal margins. One seta mid-way along inner margin of third segment. Fourth segment with three terminal setae and two subterminal setae. Outer distal margin of third segment has one long, densely plumose seta. Exopodite same as that of first maxilliped.

Buds of third maxillipeds and of pereiopods absent.

Abdomen: Abdomen comprises five segments and a telson. (Fig. 1, I.) Fifth abdominal segment longer and more slender than four proximal segments. Posterior dorsal margins of abdominal segments without spines or setae. Fourth and fifth segments with a pair of stout posterolateral spines and a pair of dorsal hairs.

Telson spatuliform with a posterior central prominence, but no anal spine. Seven posterior telson setae either side of posterior central prominence. First (outer) pair of setae short and smooth. Second pair much reduced and hair-like, a condition normal among Anomura and Thalassinidea. Third, fourth, fifth, sixth and seventh pairs very long and densely plumose. Third seta on each side with five or six curved booklets just below the tip on the inner margin. Fourth setae no more strongly developed than fifth, sixth or seventh pairs. Posterior dorsal margin of telson with six pairs of fine hairs arising close to bases of third, fourth, sixth, and seventh posterior telson setae respectively, and from central prominence.

Chromatophore Pattern ; The chromatophore pattern characterising all the zoea larval stages of Petrolisthes novaezelandiae is seen in the stage la zoea. The rostrum has alternating bands of orange and white chromatophores along its entire length. Posterior carapace spines each tipped with an orange chromatophore. Mid-gut green. Cephalic region with a paired orange chromatophore. An orange chromatophore is situated in the hind gut in each of the first, second, third and fourth abdominal segments, and around the anus in the telson.

Stage lb Stage lb zoea larvae were obtained from the plankton, and by moult from stage la in the laboratory. Stage lb is difficult to separate from stage la in some cases, and there is often considerable variation in both of these stages. Although stage lb is more common than stage la in the plankton, it is not an essential larval stage, as many stage la larvae moulted directly to stage 2a in the laboratory. Thus stage lb may be bypassed. The only completely satisfactory method of separating stage lb from stage la is by obtaining the former stage from the latter in the laboratory. However, in the plankton there is a complete gradation between these two sub-stages, and it is not certain if they are regularly separated by an ecdysis in natural conditions.

There are few features which distinguish stage lb from stage la. These are described below.

Description. Cephalothorax: Total carapace length B.lmm to 9.2 mm, rostrum length 4.Bmm to 5.5 mm, carapace length I.smm to I.6mm and posterior carapace spine length I.Bmm to 2.lmm.

Cephalic Appendages: Outer ramus of first antenna (Fig. 2, A. O. R.) now incompletely separated from the peduncle. Endopodite of second antenna (Fig. 2, B. Endop.) shorter than exopodite, but always greater than half its length.

Thoracic Appendages: Third maxilliped and pereiopods present as small uniramous buds. (Fig. 2, G.)

Stage Two Zoea

Stage 2a

Stage 2a zoea larvae (Fig, 2, K) were obtained from the plankton, and by moult from stages la and lb in the laboratory. All stage 1 larvae moulted to stage 2a, and it is therefore an essential larval stage. These larvae are very common in the plankton and show remarkbly little variation. Stage 2a can be readily distinguished from stages la and lb by the characters below.

Description. Cephalothorax: Total carapace length 10.7 mm to 11.8 mm, rostrum length 7.omm to B.omm and carapace length I.7mm to 2.omm Posterior carapace spines 2.omm to 2.3 mm in length with ventral setae much reduced or occasionally absent. Eyes now movable and borne on short stalks.

Cephalic Appendages: First antenna (Fig. 2, D) now an unjointed peduncle bearing two short distal rami. The peduncle has four or five distal setae. Inner ramus short and without setae or aesthaetes. Outer ramus with four long aesthaetes and three shorter aesthaetes at its tip, and three more proximal groups of four aesthaetes. Endopodite of second antenna (Fig. 2, E. Endop.) now about twice the length of exopodite.

Mandible without palp as in stage one larvae.

First maxilla (Fig. 2, F) larger and more setose than in stage one. Endites each have an inner row and an outer row of five setae. Palp with an additional pair of setae just below tip on inner margin.

The three inner endites of second maxilla (Fig. 2, H. End. 1-3) each have six marginal setae. Distal endite with eight marginal setae. Palp with an additional two pairs of setae just below tip on inner margin. Scaphognathite with four long setae at proximal tip and nine setae spaced along outer and distal margins.

Thoracic Appendages: First maxilliped (Fig. 2, J) more setose than in stage one. Basipodite now with four pairs of setae along inner margin. Propodite of endopod now has four setae on inner distal margin. Ischiopodite, meropodite, carpopodite and propodite each with a long, densely plumose seta arising from outer distal margin. Twelve or 14 natatory setae on exopodite.

Second maxilliped (Fig. 2, G) now with two setae on inner margin of basipodite. Each of first, second and third segments of endopod with a long plumose seta on outer distal margin. Third segment with a similar seta mid-way along outer margin. Exopodite as in the first maxilliped of stage 2a.

Third maxilliped (Fig. 2, I) now biramous with unsegmented endopodite, and exopodite present as small bud arising from base of basipodite.

First pereiopod (Fig. 2, I) with rudimentary chela at tip. Succeeding four pairs of pereiopods present as small unjointed rods, the fifth being very small. No sign of epipodites or of gill buds.

Abdomen: Three pairs of pleopods now present as small ventral buds on second, third and fourth abdominal segments. (Fig. 2, K. Plpds.)

Telson (Fig. 2, L) now with eight pairs of posterior setae, with eighth (inner) pair arising from central prominence of telson, and slightly shorter than fourth, fifth, sixth and seventh pairs. Third and fourth pairs each with six or seven curved hooklets just below tips on inner margin.

Stage 2b Stage 2b zoea larvae (Fig. 3, A) were obtained from the plankton, and by moult from stage 2a in the laboratory. This stage may be bypassed, as a number of stage 2a larvae moulted to stage 2c. Stage 2b is common in the plankton and shows considerable variation, but can be distinguished from stage 2a by the characters below.

Description. Cephalothorax: Total carapace length 12.2 mm to 13.3 mm, rostrum length B.omm to B.Bmm, carapace length I.9mm to 2.lmm and posterior carapace spine length 2.3 mm to 2.4 mm.

Cephalic Appendages: First antenna (Fig. 3, B) with peduncle incompletely divided into two segments. Outer ramus with four groups of seven or more aesthaetes.

Endopodite of second antenna (Fig. 3, G. Endop.) now greater than twice the length of exopodite but less than three times its length.

Mandible (Fig. 3, D) with a well-defined incisor process separated from a ridged molar surface by a deep cleft.

Thoracic Appendages: Third maxilliped (Fig. 3, E) now well developed, with segments of its endopodite visible beneath the cuticle. Exopodite still a very short rod. Pereiopods (Fig. 3, E. Per. 1-5) more strongly developed than in stage 2a. There is still no sign of epipodites.

Gill buds are now present, and the gill formula which can be determined in stage 2b is as follows:

3rd maxillipeds per. 1 2 3 4 5

Arthrobranchs rudiment + 1 22 22 1

Pleurobranchs

Abdomen: Pleopods unjointed, rod-like, and twice the length of those in stage 2a.

Stage 2c Stage 2c zoea larvae (Fig. 3, F) were obtained from the plankton, and by moult from zoeal stages 2a and 2b in the laboratory. It is not an essential larval stage, as in the laboratory several stage 2b larvae moulted directly to the megalopa larva. Stage 2c is the final zoeal stage, but is comparatively rare in the plankton. Characters distinguishing stage 2c from stages 2a and 2b are described below.

Description. Cephalothorax: Total carapace length 13.7 mm to 14.8 mm, rostrum length 9.omm to 9.5 mm and carapace length 2.2 mm to 2.3 mm. Posterior carapace spines 2.5 mm to 3.omm in length with ventral setae reduced to little more than two or three small, indistinct protuberances at the base of each spine.

Cephalic Appendages: Second antenna (Fig. 3, G) with endopodite three times longer than its exopodite. Segments of flagellum (endopodite) visible beneath cuticle.

Mandible (Fig. 3, H) with a short unsegmented palp.

First maxilla (Fig. 3, I) with palp incompletely divided into two segments. Scaphognathite of second maxilla (Fig. 3, J. Scaph.) with five long plumose setae at its proximal tip and 12 similar setae spaced along outer margin. Palp incompletely three-segmented.

Thoracic Appendages: Third maxillipeds (Fig. 3, K) very strongly developed, with endopodite clearly segmented, but exopodite still unsegmented and without setae.

Peieiopods massively developed giving the thoracic region a "heavy" appearance. First four pairs incompletely segmented, but fifth pair unsegmented with a rudimentary chela at tip.

Abdomen ; Abdomen more massive than in stage 2b with pleopod buds large and twosegmented. Lateral spines on fourth and fifth segments much reduced.

Variations in the Zoea Larvae

Morphological variations in the zoea larvae of this species in the Wellington area are slight. There is little or no variation in the characters separating stage one larvae from stage two larvae. However, variation in the length of the rostrum, posterior carapace spines, and antennal endopodite, together with occasional irregularities in the setation of the thoracic appendages, may cause some difficulty in separating the sub-stages.

No larvae of this species have been examined from elsewhere in New Zealand to compare with those of the Wellington area.

The Megalopa Larva

Megalopa larvae (Fig. 4, A) were obtained by moult from zoea larval stages 2b and 2c in the laboratory, but were not found in the Wellington Harbour plankton.

Description. Cephalothorax: Carapace (Fig. 4, A) measures I.7mm to I.Bmm in length, and 1 4mm to I.smm wide. Front produced into two broad lateral lobes separated by a median depression. Depression anteriorly produced into a very small rostrum bearing about four anterior spines which are variable. Anterior margins of lateral lobes denticulate. Orbital notch very shallow. Post-ocular spines prominent. Strong pair of lateral carapace spines at level of second pereiopods, but sides of carapace otherwise finely denticulate or granular and fringed with fine hairs. Posterior margin smooth. Dorsal surface hairy, but without spines. Lateral ventral lobes (Fig. 4, F) setose with serrations and a strong spine anteriorly.

Eye-stalks with small anterior distal spine, short, and not protruding beyond margin of carapace.

Cephalic Appendages: First antenna (Fig. 4, D) consists of a three-segmented peduncle with distal segment bearing both inner and outer ramus. Basal segment swollen dorsally enclosing statocyst, with swelling produced anteriorly into six large spines and a number of short, stout spinules. Statocyst opening fringed with plumose setae. Second segment of peduncle without spines or setae, but third (distal) segment with two or three distal setae. Inner ramus of three segments, with a short hair arising from inner and outer margins of each of the first and second segments. Third segment with five fine hairs at tip. Outer ramus of ten segments. Eight basal segments short, compressed with many long aesthaetes arising from inner margins. Ninth segment long, slender, with two fine distal hairs. Terminal segment short with two fine hairs and a very long aesthaete at tip.

Protopodite of second antenna (Fig. 4, E. Prot.) is of two segments (coxopodite and basipodite). Basal segment short, partially concealed in the orbital cavity, and does not protrude beyond superior margin of carapace. Endopodite (Fig. 4, A; E) long, slender, consisting of about 25 segments. Basal segment with two small spines on inner margin. Remainder each with four short setae on distal margins. Antennal scale (Fig. 4, E) rudimentary and without teeth or setae.

Mandible (Fig. 5, A) strongly calcified, with prominently ridged molar surface separated from toothed incisor process by a narrow cleft. Palp of three segments, but two basal segments usually incompletely separated. Terminal segment with a number of short setae.

First maxilla (Fig. 5, B) is similar to that of the zoea larvae. Proximal and distal endites each fringed with many short setae curved towards the mouth. Palp of two segments, with one or two setae on terminal segment only. Exite thin, flattened, and without setae.

Second maxilla (Fig. 5, C) flattened and plate-like as in the zoea larvae. First (proximal) endite is fringed with about 18 coarsely plumose setae arranged in two rows. Second and third (inner) endites each with between six and ten such setae.

Fourth (distal) endite with between 12 and 14 marginal setae. Palp three-segmented but with only three or four setae. Scaphognathite with 40 or more marginal setae.

Thoracic Appendages: First maxilliped (Fig. 5, D) consists of flattened setose coxopodite and basipodite, rudimentary endopodite without setae, and strongly developed twosegmented exopodite with four or five plumose setae on margins of distal segment.

Second maxilliped (Fig. 5, E) not flattened, and more closely approaches the structure of a generalised crustacean thoracic limb. Coxopodite and basipodite clearly separated, each with a number of long plumose setae along inner margins. Endopodite curved inwards and five-segmented. Ischiopodite and meropodite with plumose setae along inner margins. Carpopodite and propodite with plumose setae distally, and dactylopodite with a terminal tuft of stout, plumose setae. Exopodite strongly developed and three-segmented. Basal segment with three outer and six inner marginal setae, second segment without setae, and distal segment with six long natatory setae at tip.

Protopodite of third maxilliped (Fig. 5, F) consists of setose coxopodite and basipodite. Gills comprise two arthrobranchs, the more anterior being rudimentary and the more posterior well formed. Epipodite small and setose. Endopodite very large and laterally expanded. Ischiopodite with ventral surface medially expanded into a broad plate fringed with plumose setae, and upper margin above plate with seven pairs of long, plumose setae. Meropodite with ventral surface similarly expanded. Anterior margins serrated but without spines. Inner margin above ventral plate with seven pairs of very long, bipinnate setae. Carpopodite with ventral surface not greatly expanded. Inner margin with ten very long, bipinnate setae and six shorter setae distally. Outer margin with six small, anteriorlyinclined spines including distal corner. Propodite with about 12 long, bipinnate setae along inner border and 12 short setae above these and along distal margin. Dactylopodite with 12 very long marginal bipinnate setae. Exopodite (Fig. 5, F. Exop.) three-segmented but much reduced. Basal segment arises from base of basipodite as in the zoea larvae, and with five or six marginal setae. Terminal segments without setae.

First pereiopod (cheliped) (Fig. 4, A) short, flattened, and laterally expanded as in the majority of the Porcellanidae. Left and right chelae equal or slightly sub-equal, having the seven segments of the typical decapod walking leg. Coxopodite and basipodite short and concealed beneath carapace. Coxopodite with small epipodite and well-formed gills with lamellae visible. Basipodite without exopodite. Ischiopodite short, setose, without spines. Meropodite short, broad, setose, with inner (anterior) border denticulate, terminating in a spine. Carpopodite twice the length of meropodite. Anterior margin with two very large spines and a number of small spinules, posterior margin with four spines including posterior distal corner. Propodite + dactylopodite (hand) twice as long as broad. Fixed and movable fingers broad, flattened, and as long as palm, with their tips curved inwards to meet. Inner margin of propodite (palm) and dactylopodite (movable finger) setose, and outer margin of propodite with many short spinules and setae. Propodite with dorsal row of spines extending from its base to base of dactylopodite.

The second, third and fourth pereiopods are similar. (Fig. 4, A. Per. 2—4.) The following description is based on the second pereiopod. Coxopodite and basipodite short, setose, without spines, and hidden beneath carapace. Gills comprise two arthrobranchs and one pleurobranch with lamellae visible. Epipodite small. Ischiopodite short, setose, without spines. Meropodite three times the length of carpopodite, twice the length of propodite, and three times the length of dactylopodite, all being slender, only slightly flattened, freely setose, and without prominent spines. Dactylopodite bulbous with tip extended into an inwardly-curved point.

Fifth pereiopod (Fig. 4, A. Per. 5) much reduced, closely folded against sides of carapace and not used in walking. This is the normal condition in the Galatheidea. Gills comprise one arthrobranch and one pleurobranch with very small epipodite. Segments freely setose but without spines. Tip of dactylopodite with incompletely-formed chela.

Abdomen: Abdomen comprises six segments and a telson. The sixth abdominal segment which is fused with the telson in the zoeal stages is now separate. Segments short, setose, laterally expanded, and dorsoventrally compressed. First and sixth segments smaller. Pleopods functional, biramous, flattened, arising from ventral side of each of second, third,

and fourth segments. Pleopods of second segment (Fig. 4, B) and of third segment with rudimentary endopodite without setae and exopodite with 14 marginal setae. Pleopods of fourth segment (Fig. 4, G) smaller with exopodite having 12 marginal setae. Sixth abdominal segment with paired uropods (Fig. 5, G), consisting of short protopodite bearing broad flattened endopodite and similar exopodite of equal length. Protopodite with lateral distal spine. Endopodite with about 15 marginal plumose setae and exopodite with about 20 such setae.

Telson (Fig. 5, G) divided into unpaired median plate and paired lateral and posterior plates, but separation of plates incomplete in some megalopa larvae. (Fig. 5, H.) Triangular median plate with two fine dorsal hairs, triangular lateral plates each with one dorsal hair. Posterior plates each with free margins lined with about 12 plumose setae which vary in length.

Chromatophore Pattern: A pair of large red chromatophores occur slightly median to the post-ocular carapace spines. Carpopodite and propodite of cheliped with scattered small red chromatophores. A red chromatophore is situated medially in each of the first, second, third, and fourth abdominal segments, and in the telson.

Variations in the Megalopa Larva

Bennett (1932) records that variation among adults of Petrolisthes novaezelandiae is quite marked. This is also true of the megalopa larvae. Significant variations occur mainly in the spinulation of the depressed rostrum, the number of denticles on the sides of the carapace, and in the spinulation of the distal joints of the chelipeds.

Discussion

The zoea larvae of Petrolisthes novaezelandiae have all the distinguishing characters common to the zoea larvae of the genera Petrolisthes and Porcellana. These are listed by Gurney (1942). These larvae, however, show a remarkable similarity to described larvae of the genus Porcellana, and they have some characters not found in described larvae of the genus Petrolisthes.

The usual characters used in the separation of decapod larvae into genera do not seem to apply when separating Porcellana from Petrolisthes. The application of these characters, for example the number of pleopods, the spinulation of the abdominal segments, and the nature of the rostrum, carapace, and carapace spines, suggests that the genera Petrolisthes and Porcellana are homogeneous.

Characters separating the larvae of these two genera have been discussed by Gurney (1942) and by Lebour (1943, 1950). The key given by Lebour (1943) is based on the form of the telson, and may be summarised as follows:

(1) In known larvae of the genus Porcellana, the seventh posterior telson seta (fifth long seta) is situated outside the central prominence in stage one larvae. In stage two an eighth telson seta (sixth long seta) arises from the central prominence of the telson.

(2) In known larvae of the genus Petrolisthes, the fifth long telson seta is found on the central prominence in stage one. In stage two there is no sixth long seta, but a central tooth which is also on the central prominence.

However, when considering the zoea larvae of Petrolisthes novaezelandiae the use of telson characters seems to be unreliable. On the form of the telson P. novaezelandiae must be placed in the genus Porcellana. The differences between the

zoea larvae of Petrolisthes novaezelandiae and Porcellana longicornis are summarised below.

(1) The zoea larvae of Petrolisthes novaezelandiae are slightly larger than those of Porcellana longicornis.

(2) In Petrolisthes novaezelandiae zoeae the exopodite of the third maxilliped has no setae in stage two, and is less strongly developed throughout larval life than that of Porcellana longicornis.

(3) The small dorsal hairs on the fourth and fifth abdominal segments of Petrolisthes novaezelandiae are not found in Porcellana longicornis.

(4) The telson of Petrolisthes novaezelandiae has six pairs of posterior dorsal hairs, and there are distal hooklets on the first and second long posterior setae in stage two. In Porcellana longicornis dorsal telson hairs are not found, and there are distal hooklets only on the first long posterior telson setae in stage two.

(5) Distal booklets are found on both the inner and outer margins of the posterior setae in Porcellana longicornis, but only on the inner margin of the setae

in Petrolisthes novaezelandiae.

In the opinion of this author these differences warrant only specific status. Specific characters described for the larvae of Porcellana longicornis and P. platycheles by Lebour (1943) and for P. inequalis by Gurney (1938) and P. bluteli by Bourdillion-Casanova (1956) show more significant variation between the species than is shown between P. longicornis and Petrolisthes novaezelandiae. Hence on larval evidence P. novaezelandiae should be placed in the genus Porcellana.

The taxonomic character separating adults of the genus Petrolisthes from those of the genus Porcellana is, according to Thomson (1898), in the nature of the peduncle (protopodite) of the second antenna. In the genus Petrolisthes the basal joint of the antennal peduncle is short, partially concealed in the orbital cavity, and does not protrude beyond the superior margin of the carapace. In adults of the genus Porcellana the basal joint of the antennal peduncle is long, and forms an acute and somewhat flattened projection external to the orbit, and is joined to the superior margin of the carapace. By this character, Petrolisthes novaezelandiae should be placed in the genus Petrolisthes.

However, on comparing adults of this species with those of Porcellana longicornis, the author found no further differences which could justify the present generic separation.

Summary

(1) In Petrolisthes novaezelandiae there are two main zoeal stages which include the sub-stages la, lb, 2a, 2b, and 2c, of which la and 2a are essential in the planktonic life history. Larvae are present throughout the year and are the commonest porcellanid species in the Wellington plankton. They are most abundant in the late spring and summer peak of the spawning period. The megalopa larva, not found in the plankton, was reared in the laboratory.

(2) From the key of Lebour (1943) which is based on previously described porcellanid larvae, the larvae of P. novaezelandiae should be placed in the genus Porcellana. The reliability of the telson as a character separating larvae of the genus Porcellana from those of the genus Petrolisthes is therefore in doubt.

1 3) Characters separating the zoea larvae of Petrolisthes novaezealandiae and Porcellana longicornis are of lesser significance than the characters used to distinguish species within the genus Porcellana, and probably therefore warrant only specific status.

(4) According to the literature the primary character separating adults of Petrolisthes from those of Porcellana is in the nature of the peduncle of the second antenna (Thomson, 1898) and on this character the nominal species Petrolisthes novaezelandiae Filhol, 1885 was correctly placed in the genus Petrolisthes. No further differences which could warrant generic distinction between adults of P. novaezelandiae and those of Porcellana longicornis have been found.

Acknowledgments

I thank the Marine Department (Wellington) and Dr R. K. Dell (Dominion Museum) for the loan of reference specimens, and Dr R. B. Pike for helpful guidance and discussions. I am indebted to the Zoology Department technicians, academic staff, and students who were together responsible for plankton collections from Wellington Harbour. I am grateful to Professor L. R. Richardson for placing the Zoology Department's plankton collection at my disposal.

Literature Cited

Bennett, E. W., 1932. Porcellanids and Porcellanopagurus from New Zealand. Rec. Cant. Mus. N.Z., 3 (7) pp. 469-481. 1 pi.

Borradaile, L. A., 1926. Notes upon Crustacean Limbs. Ann. Mag. nat. Hist., ser. 9, 17, pp. 193-213, pis. 1-10.

Bourdillion-Casanova, L., 1956. Note sur la Presence de Porcellana bluteli (Risso) alvarez dans le Golfe de Marseille et sur le Developpement Larvaire de cette espece. Rapp. Comm. int. Mer Medit., 13, pp. 225-232. Figs. 1-10.

Filhol, H., 1885. Passage de Venus sur le Soleil. Mission de I’lle Campbell. Zoologie. 3 (2) pp. 408-409, pi. 48, figs. 4, 5.

Gurney, R., 1938. Notes on some Decapod Crustacea from the Red Sea, VII-VIII. Proc. tool. Soc. Land., ser. B, 108, pp. 73-84, pis. 1-6. 1-306, figs. 1-122.

Hale, H. M., 1927. The Crustaceans of South Australia. (1). Government Printer, Adelaide, Australia, 1927, pp. 1-201, figs. 1-202.

Lebour, M. V., 1943. The larvae of the genus Porcellana (Crustacea, Decapoda) and Related Forms. /. Mar. biol. Ass. U.K., 25, no. 4, pp. 721—737, figs. I—l2. Soc. Lond., 120 (2) pp. 369-379, figs. 1-7.

Thomson, G. M., 1898. A Revision of the Crustacea Anomura of New Zealand. Trans. N.Z. Inst., 31, pp. 169-197, pis. 20, 21.

Williamson, D. 1., 1957. Crustacea, Decapoda, Larvae. I—General. Fich. Ident. Zoopl., no. 67, 1957, pp. 1-7, figs. 1-32.

Robert G. Wear,

Zoology Department,

Victoria University,

P.O. Box 196, Wellington.