Diplosoma velatum Kott, 2001

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 : 1682-1683

Diplosoma velatum Kott, 2001

( Figure 13B, C )

Diplosoma velatum Kott, 2001: p. 345 –347, fig. 155, pl. 21 f, g.

Material examined

New Records: New Zealand, Crooked Arm Head (45° 25.121’S, 166° 56.00’E, 20 m, 2 February 2006, NIWA 49991 , one colony); Only Island, Long Sound (45° 57.774’S, 166° 52.2’E, 20 m, 28 January 2009, NIWA 49938 , two colonies); Nine Fathom Passage, Dusky Sound (45° 44.237’S, 166° 53.199’E, 20 m, 1 February 2009, NIWA 49956 ); Crayfish Heights, Thompson Sound (45° 13.182’S, 166° 58.655’E, 15 m, 31 January 2009, NIWA 49990 , two colonies) .

Previously recorded: South Australia (York Peninsula, Taipara Reef, Eyre Peninsula, Cathedral Rock and Kangaroo Island, Investigator Strait); Western Australia (Esperance, Oyster Harbour); Victoria (Western Port), see Kott 1962, 1975, 1976.

Description

Colonies are irregular, lobed fleshy sheets with large common cloacal apertures up to 10 mm diameter at the terminal ends of lobes ( Figure 13B ). Groups of zooids supported in test connectives can be seen inside the colony through the common cloacal apertures. The test is generally an opaque orange colour (YR 7/8) in colonies exposed to light. Colonies collected from low-light conditions at the head of Crooked Arm are cream ( Figure 13C ). The test is soft and slimy and colonies collapse when removed from water. Eight to ten zooids are embedded in groups in connectives with clear spaces of test between them. The zooids are 1.8 mm long with branchial apertures on short siphons and a large sessile atrial opening that exposes most of the branchial sac. There are approximately 10 stigmata per half row. The straight vas deferens divides two testis follicles, and a short retractor muscle projects from the posterior end of the thorax. Larvae develop below the zooids in the test connectives. They are large (1.0– 1.6 mm trunk length), with three long slender lateral ampullae on each side of three cup-shaped adhesive papillae on long stalks and have a blastozooid located halfway along the body. The larval test has numerous small clear granular inclusions 13 µm in diameter, also noted in larvae of the holotype from South Australia ( Kott 2001).

Remarks

Didemnum velatum is native to Southern and Western Australia. In Fiordland it has been recorded from Long Sound in the southern fiords and further north to Doubtful Sound, and the inner reaches of Crooked Arm ( Figure 1 ). This species may also be part of a Gondwana relict fauna. Given its relatively wide distribution throughout Fiordland, it is unlikely to be a recently introduced species, especially at the head of Crooked Arm, 14 km from the main entrance to Doubtful Sound.

Figures

Figure 1. Map of Fiordland on the south-west coast of the South Island, New Zealand showing location of sampling stations.

Figure 13. In situ images of: (A) Diplosoma listerianum (NIWA 49936); (B) Diplosoma velatum (NIWA 49990); (C) Diplosoma velatum (NIWA 49991).