Ascidians of New Zealand.
Part IX. A New Species of Distaplia
[Read by title before Otago Branch on October 13, 1953; received by Editor, October 21, 1953.]
Genus Distaplia Della Valle, 1881.
(As emended by Brewin, 1953.)
Distaplia knoxi, n.sp (Text-fig. I, Figs. A, B, C, D, E, F.)
Colony with or without stalk (Figs. D. E. F.). Plane of attachment of head and stalk off the horizontal (Fig. D). Maximum measurements from eight colonies:—cushion-like forms, 1.9 cms. in diameter, 1.0 cms. above the substratum; stalked forms, head 2.3 cms. in diameter, 1.3 cms. in length, stalk, 2 cms. in diameter, 4 cms. in length. Zooids violet; test pale pink, firm, with numerous small test cells and pigment cells Round or oval systems of up to 11 zooids confined to the head region. Common cloacal apertures, one per system, round, 1 mm in diameter, 1.5 to 5 mms distant from one another.
Zooids up to 2 mms. in length, 1 mm. in width in the pharyngeal region, which has up to 40 fine longitudinal muscle bundles, 3 transverse. Rectaloesophageal region short, narrow. Abdominal region approximately as wide as the pharyngeal with two long, narrow, backwardly projecting diverticula (Fig. B), one the vascular process, and the other, which ends in a bulge containing the gonads, a reproductive diverticulum. Branchial aperture with six very short lobes, atrial surmounted by a wide, smooth-edged lappet.
Gut: Pharynx with 16 branchial tentacles of three orders of size, regularly arranged; dorsal lamina of three languets; on each side 4 rows of 13–14 stigmata up to six times as long as wide, longest in the posterior row; parastigmatic vessels absent. Oesophagus short. Stomach ovate, smaller towards the posterior end, its wall thrown into 14 shallow grooves (Fig. B). Intestine divided into a short narrow proximal portion and a wider distal portion Reservoir of intestinal gland round, comparatively large.
Reproductive System: Zooids hermaphrodite, with testis maturing before the ovary and continuing to produce sperms after the eggs are liberated. Reproductive diverticulum long, ending in a sac-like structure containing the testis composed of up to 9 lobes (7, usual number) and, posterior to the testis, the ovary with up to six eggs at different stages of development. Sperm duct long, straight, opening near anus. Oviduct thin-walled, forming in the pharyngeal region a large outpushing, the arms of which are of very different sizes (Fig. B). This outpushing plus the accompanying one of the mantle wall forms the brood pouch which is extensively developed before the eggs leave the ovary. The liberated eggs are approximately 0.45 mm. in diameter, heavily yolked and surrounded by two follicular layers, both of which are only one cell deep. In this species, as has been recorded in others of the sub-family (Brewin, 1953) there is suppres-
Text-Fig. 1.—Distaplia knoxi. A. Tadpole with one bud. × 32. B. Zooid with unfilled brood pouch, drawn from the right. × 32. C. Buds of another tadpole showing arrangement and degree of differentiation. × 105. D.E.F. Three colonies to show habit of growth. × 1.
sion of ova once the more advanced have been liberated. The brood pouches do not contain more than 3 embryos, usually only 1. The pouches are in the peripheral region of the head, the distal ends of the longer pouches being adjacent to the distal ends of the reproductive diverticula. Well developed tadpoles (Fig. A) were present in specimens collected in December, 1951 They measured up to 3.8 mms. in length, 0.7 mms. in diameter in the head region, and contained either a probud or 1 to 3 buds in a rudimentary stage of development (Fig C). There are 4 ampullae, two being associated with the ventral sucker.
Distribution: Cape Campbell (intertidal, on coastal rocks).
Type specimen in the Otago Museum.
Note: The position of the gonads in a backwardly-directed diverticulum of the abdominal region is characteristic of three species of Distaplia, D. stylifera (Kowalevsky), D. australensis Brewin and D. knoxi. D. knoxi differs from D. australensis in many ways, the more obvious being (1) the possession of small systems of zooids and numerous common cloacal canals and (2) the restriction of the brood pouches to the peripheral region of the head. It differs from D. stylifera principally in (1) the length of the reproductive diverticulum which is less than one half of the length of the zooid proper in D. stylifera and greater than the length of the zooid proper in D. knoxi; (2) the presence of a large round reservoir on the intestinal gland and (3) the greater number of eggs in the ovary and embryos in the brood pouch.
These include those given in previous papers of the series as well as:
Brewin, B. I., 1953. “Australian Ascidians of the Sub-Family Holozoinae and a Review of the Sub-Family.” Trans. Roy. Soc. N.Z., Vol. 81, pp. 53–64.
Kowalevsky, A., 1874. “Uber die Knospung der Ascidien.” Arch. mikr. Anat., Bd. 10.
Michaelsen, W., 1930. “Die Fauna Süd-West Australiens.” Ergeb. Hamb. S.W. Aust. Forsch. 1905, Bd. V.
Sluiter, C. Ph., 1909 “Die Tunicaten der Siboga Exped. 11 Abt., Die Merosomen Ascidien.” Siboga Exp., Bd. 56b.