Art. XXIII.—Description of a Collection of Actinians from the Kermadec Islands.

Transactions and Proceedings of the Royal Society of New Zealand, Volume 46, 1913, Page 132

Art. XXIII.—Description of a Collection of Actinians from the Kermadec Islands. By F. G. A. Stuckey, M.A., Wellington. [Read before the Wellington Philosophical Society, 27th August, 1913.] The specimens were collected by Mr. W. R. B. Oliver in 1908. They include three New Zealand forms previously described, and four species which are new to science. The three forms already known are Actinia tenebrosa Farquhar, Phlyctenactis retifera Stuckey, and Paractis ferax Stuckey. The distribution of Actinia tenebrosa as given by me (1908) limited the species to Stewart Island and the neighbourhood of Cook Strait. Since then Professor Kirk has informed me that he saw it on Auckland Island; so that the distribution of the species may be set down as from the Kermadecs to Auckland Island. Mr. Oliver's discovery of Phlyctenactis extends the distribution of the genus as from Kermadec Islands to Stewart Island. In my original description of Paractis ferax, by a clerical error, I gave the number of mesenteries as 32 to 36 pairs. The species has 24 pairs, of which 6 pairs are perfect and fertile. Two pairs are directives. The mesenteries of the second and third cycles are feebly developed. The perfect mesenteries are as described and figured by me (Trans. N.Z. Inst., vol. 41, p. 388). The chief points in the diagnosis of the species are the muscular body-wall, the ectodermal invaginations and pits in the wall, and the regular hexamerous development of the mesenteries. Mr. Oliver's specimen is larger than any found by me, being 9 cm. in height. This species was found by Mr. Walton in Manukau Harbour, so that its known distribution is Kermadecs to Cook Strait. The following are the names of the species that are new to science: Zoanthus atroviridis n. sp., Isaurus fuscus n. sp., Epizoanthus oliveri n. sp., and Metridium canum n. sp. Zoanthus atroviridis n. sp. The collector describes this species as follows: “Dark green. A very slimy form occurring in large dense patches up to half a metre in diameter in rock-pools between tide-marks, Meyer Island. The individuals when expanded touched one another, thus entirely covering the rock-surface, and the colonies were mostly on the northern side of the rock-pools, where they would receive a minimum of sunshine.” Form. —There is a fairly thick encrusting coenenchyme, on which the polyps are arranged in groups rather than in lines or rows. The coenenchyme, as well as the body-wall, is covered with sandy particles. The polyps are of varying size, but all stand well up from the surface of the coenenchyme. Dimensions (of largest specimen, contracted).—Height, 30 mm.; diameter, 6 mm.; capitulum, 10 mm. in diameter. Body-wall.—In structure and in histological character the body-wall closely resembles that of Z. jukesii (Haddon and Shackleton, Trans. R. Dublin Soc., Dec., 1891). A remarkable character is the great thickness of the mesogloea. Sphincter Muscle.—There is a well-developed mesogloeal sphincter, very long, and tapering downwards.

Tentacles.—These are short, and in two series, about, 40 in each series. Mesenteries.—In the only specimen that I sectioned the mesenteries presented the usual brachycnemic arrangement. There were a pair of perfect and a pair of imperfect directives. In the sulco-lateral portion I found 14 pairs of mesenteries, and in the sulculo-lateral portion. 2 pairs. The mesenterial filaments are of the form typical of the family. Gonads.—None were found in the specimen sectioned. Isaurus fuscus n. sp. Of this species the collector says: “Pale brown., Noticed only in rock-pools between tide-marks, Fishing Rock, Sunday Island. There is only one specimen in the collection, and its colour in the preserved state is creamy-white. Form.—The base of the column is adherent, and follows the irregularities of the rock to which it is attached. The body is cylindrical, and transversely furrowed in contraction. The specimen had become flattened and misshapen. The oral disc and tentacles were strongly infolded. Dimensions.—Height, 22mm.; long diameter of column, 10 mm.; short diameter of column, 5 mm. Body-wall.—The body-wall is thick, and under the thin cuticle there is a subcuticular or peripheral layer of mesogloea, which is connected with the general mesogloea by strands which cross the ectoderm. The mesogloea is thick, and contains many lacunae and cell-islets. The endoderm is well developed. There are large endodermal and ectodermal bays. Tentacles.—These could not be seen in the contracted state. Mesenteries.—These present the usual brachycnemic condition, and were 44 in number. The brachycnemic couples were the twelfth and thirteenth from the perfect directives on one side, and the sixteenth and seventeen on the other side. The arrangement of the mesenteries with respect to the siphonoglyph is shown in the following diagram:— Sphincter Muscle.—There is a very strong mesogloeal sphincter. The cavities are closely lined with cells, and the mesogloea in the region of the sphincter has a fibrous appearance quite different from that of the other part of the body-wall. Epizoanthus oliveri n. sp. The collector's note on this species is: “Plentiful among a close-growing coralline alga in rock-pools between tide-marks, Fishing Rock, Sunday Island.” I have placed this species provisionally in the genus Epizoanthus, all recognizable features pointing to the correctness of this classification. The body-wall is so strongly encrusted with sand and ‘other hard bodies that it is impossible to make anything but fragmentary sections. Form.—There is an encrusting coenenchyme, on which, the polyps are closely set. Both coenenchyme and body-wall are encrusted with sand, &c.

Dimensions (of largest specimen, contracted).—Height, 17 mm.; diameter of column, 4 mm.; diameter of disc, 6 mm. Body-wall.—The wall is thin, the mesogloea occupying the greater part, and sending strands across the ectoderm. The ectoderm is almost obliterated by the great mass of sandy encrustation. The usual cell-islets and lacunae are present in the mesogloea, but I fourd no sign of an encircling sinus. Mesenteries.—The imperfect mesenteries are very short. I was unable from my sections to ascertain the exact number of mesenteries, owing to reasons already stated. Tentacles.—The tentacles were all infolded, and their number and arrangement could not be ascertained. Sphincter Muscle.—Traces of a mesogloeal sphincter were found. Metridium canum n. sp. The collector's description is: “Greyish. Abundant on the under-side of stones near low-water mark, Coral Bay, Sunday Island. This species…tolerates a muddy or sandy bottom.” Pedal Disc.—Adherent, rather wider than the column. Column.—Cylindrical. Longitudinally wrinkled in contraction. Cin-clides are present on the upper part of the column. Tentacles.—About 200 in number, crowded and arranged in four, or perhaps five, cycles. In some of the preserved specimens the tentacles have black tips. Body - wall. —The usual hexactinian features are observable. The mesogloea is comparatively thick, though variable in different portions of transverse sections. It appears fibrillar in structure, and contains numerous collections of cells. Sphincter:—A weak mesogloeal sphincter is present. Mesenteries.—There are four cycles, 45 pairs in all. Of these, only the primaries, 6 pairs in number, are perfect. Dimensions (of largest specimen, contracted).—Height, 9 mm.; diameter of column, 10 mm.; diameter of disc, 15 mm.