Eudistoma circumvallatum ( Sluiter, 1900 )

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 : 1673-1675

Eudistoma circumvallatum ( Sluiter, 1900)

( Figure 11A )

Distoma circumvallatum Sluiter, 1900: p. 8 –9, pl. 1 fig. 4, pl. 2 fig. 6.

Polycitor (Eudistoma) circumvallatum Brewin, 1946: p. 102 –03, fig. 8; 1951: p. 104; 1952b: p. 187; 1958a: 440; 1960: p. 119.

Material examined

New records: Breaksea Sound, First Cove (45° 44.237’S, 166° 53.199’E, 16 m, 1 February 2009, NIWA 49966 , two colonies); Tiwai Point, wharf pilings (46° 35.525’S, 168° 21.137’E, 9 m, 20 August 2007, MJP37-01 , three colonies); Portobello, Otago Peninsula (45° 49.720’S, 170° 38.418’E, 1 m, 6 June 2006, MJP36-01 , two colonies) .

Previously recorded; New Zealand, Portobello Peninsula, Hauraki Gulf, Cape Kidnappers, Stewart Island ( Brewin 1946, 1951, 1952b, 1958a, 1960); Cook Strait ( Sluiter 1900).

Description

The small round colony heads of Eudistoma circumvallatum are whitish and transparent, the yellow-cream zooids clearly visible beneath the test ( Figure 11A ). The largest colonies are 15 mm high and 7 mm in diameter, attached to the substratum by a short stalk. There are no systems and the tightly packed zooids open separately to the surface of the colony. The test is soft and gelatinous without incorporated sediment. The zooids have a short thorax (1.0– 1.2 mm long), which is often contracted by nine longitudinal and 12–20 transverse muscle bands. The atrial and branchial apertures have six distinct lobes, the atrial aperture being on a short posteriorly-directed siphon. The branchial sac has three rows of 9–12 stigmata per side. The abdomen has a long oesophageal neck (7–9 mm long), typical of the genus. The distal end of the abdomen containing the gut loop is wider than the thorax. There is a small globular, smooth stomach situated towards the posterior end of the descending limb of the gut loop. The stomach, the duodenal region and small posterior stomach are pigmented bright yellow, often giving colonies a subtle yellow colouration.

Remarks

There are presently two species of the genus Eudistoma in New Zealand. A recent introduction from Australia, Eudistoma elongatum ( Herdman 1886) , has become established in Northland ( Handley 2005). This species is genetically and morphologically distinct from Eudistoma circumvallatum ( Smith et al. 2007) and can be distinguished by colony morphology, the musculature of the thorax, the number of stigmata and the size and pigmentation of the stomach and long cylindrical drooping colonies up to 180 mm long.

Figures

Figure 11. In situ images of: (A) Eudistoma circumvallatum (NIWA 49966); (B) Pseudodistoma cereum (NIWA 49992); (C) Pseudodistoma novaezelandiae (MNP7398) from the Kermadec Islands; (D) Trididemnum shawi sp. nov. (NIWA 10872, holotype); (E) Didemnum jucundum (NIWA 10873); (F) Didemnum lithostrotum (NIWA 49980).