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.
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).
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)
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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.