Synoicum occidentalis Millar, 1982

Page, M. J., Willis, T. J. & Handley, S. J., 2014, The colonial ascidian fauna of Fiordland, New Zealand, with a description of two new species, Journal of Natural History (J. Nat. Hist.) 48 (27 - 28), pp. 1653-1688 : 1663-1666

Synoicum occidentalis Millar, 1982

( Figures 6 , 7A )

Synoicum occidentalis Millar,1982: p. 17 , 19–20, Fig. 6 a–e .

Material examined

New records: Thompson Sound, Crayfish Heights (45° 18.182’S, 166° 58.656’E, 15 m, reef wall, coll. M. Page, 30 January 2006, NIWA 49997 , two colonies); Breaksea Sound, First Cove (45° 34.74’S, 166° 44.43’E, 15 m, 1 February 2009, NIWA 49972 , one colony); Whangarei Harbour (35° 18.8915’S, 174° 28.398’E, 6 m, 2 November 2005, 2 WRE054 -AN, one colony); Breaksea Sound, Sunday Cove (45° 35.601’S, 166° 44.42’E, 5 m, 22 December 2011, NIWA 68123 , two colonies) .

Previously recorded: New Zealand, west coast of the South Island near Jackson’ s Head ( Millar 1982).

Description

The colony is composed of groups of roughly circular cushions, each with 5–8 common cloacal apertures. The cushions arise from a common basal mat up to 10 cm in diameter and appear to grow as buds from the parent colony, spreading across the substratum. The zooids form rows along anastomosing canals that extend radially from numerous, slightly raised common cloacal apertures. The test is a pale yellow colour (Y8/10) transparent and free of sediment ( Figure 7A ).

The zooids are robust, measuring up to 9 mm long, the thorax being one-third of the total zooid length ( Figure 6A ). The branchial siphon has six sharply pointed lobes, with seven large and 10 small oral tentacles at its base. A wide spatulate languet surmounts the atrial aperture, occasionally with serrations at its distal end. The size and shape of the languet can vary markedly between zooids and is dependent on the degree of contraction of fine muscles. The dorsal anterior end of the thorax is expanded around the atrial aperture to form an atrial cavity. Approximately 11 longitudinal muscles on each side and 15 transverse muscles form a muscular network around the atrial aperture and the anterior half of the thorax ( Figure 6B ). The muscles converge into two distinct bands on the posterior thorax. The right-hand side band crosses above the stomach to the left side of the abdomen where it runs parallel to the left-hand band ( Figure 6C ). The bands separate on the post-abdomen; the one from the right side crosses back over and runs the length of the post-abdomen, the one on the left continues down the left side of the post-abdomen.

The branchial sac has 18–20 rows of small stigmata with 14 stigmata per half row. The abdomen is half the length of the thorax and it has a short oesophagus with a large globular smooth walled stomach. Usual divisions of the intestine lie in a short gut loop. A wide rectum extends up the atrial cavity opening in a bilabiate anus adjacent to the fourth row of stigmata. In contracted zooids, the post-abdomen is drawn up the left side of the abdomen level with the inside pole of the gut loop. The post-abdomen is full of maturing testis follicles for its entire length. No ovary was observed in the zooids. Larvae were not present in colonies from Fiordland. However, larvae found in colonies from Whangarei Harbour (2 WRE054 AN) are the same as the holotype described by Millar (1982). They have a trunk length 0.8 mm long with four pairs of lateral ampullae and at least three smaller adjacent

ampullae, each side of three long narrow adhesive papillae and masses of anteriordorsal and posterior-ventral vesicles.

Remarks

The colonies examined from Fiordland agree closely with the holotype from the south west coast of the South Island described by Millar (1982). Synoicum occidentalis appears to be widely distributed throughout New Zealand, also being recorded from Kaikoura ( Stocker 1985) and Whangarei, in the North Island (2WRE054AN).

Figures

Figure 6. Synoicum occidentalis.(NIWA 49997): (A) thorax and abdomen; (B) thorax showing transverse and longitudinal muscles; (C) abdomen showing longitudinal muscle bands; scale bar:(A–C) 1 mm.

Figure 7. In situ images of: (A) Synoicum occidentalis (NIWA 49972); (B) Synoicum stewartense (NIWA 49984). (C) Aplidium benhami (NIWA 49993,); (D) Aplidium coronum sp. nov. (NIWA 60890); (E) Aplidium coronum sp. nov. (NIWA 49995, holotype); (F) Aplidium phortax (NIWA 9947).