Aplidium crustum, Kott, 2008

Kott, Patricia, 2008, Ascidiacea (Tunicata) from deep waters of the continental shelf of Western Australia, Journal of Natural History 42 (15 - 16), pp. 1103-1217 : 1153-1155

Aplidium crustum sp. nov

( Figures 8A, B )

Distribution

Type locality: Western Australia CSIRO SS10 / 05 (Albany, Stn 22, 118.2940E 35.3350S, 100 m, 22 November 2005, holotype WAM Z27517 , QM G328107 ; paratype QM G328110 ; further specimen: Point D’ Entrecasteaux, Stn 18, 100 m, 21.11.05, QM G 328427 ) .

Description

Colonies are irregular slabs up to 11 cm in maximum extent, and up to 4.5 cm thick, growing over irregular substrates. Sand is crowded in the base and outer margins of the colonies, the marginal test slightly overlapping the quilted upper surface. Sand is less crowded on the upper surface and throughout the remainder of the colony. The quilted pattern is created by narrow depressions over circular common cloacal canals that surround rounded elevations of the surface. Branchial openings perforate the upper surface on these elevations. Large, sessile common cloacal apertures are at the junctions of some of the narrow canals, especially around the periphery of the upper surface inside the overlapping sandy marginal test.

Zooids are numerous and thread-like, criss-crossing one another through the moderately sandy internal test. Six-lobed branchial apertures are on short siphons and an atrial tongue of variable size arises from the anterior rim of the relatively small circular opening. The branchial sac is obscured by longitudinal muscle bands that extend from the thorax along each side of the zooids. Nevertheless, 15 rows of about 20 stigmata in each half row were detected. The relatively small, cylindrical stomach, halfway down the abdomen, has 20 particularly fine parallel longitudinal folds. Double series of male follicles are in the long posterior abdomen. Larvae were not found in either of the examined colonies.

Remarks

The present colonies are distinguished by their circular common cloacal canals with common cloacal apertures at their junctions, the relatively large number of folds in the stomach wall and the distribution of sand which is especially crowded in the base and outer margin of the colony. The species from the Indian Ocean and Western Pacific with similar colonies and common cloacal systems are Aplidium tabascum Kott, 1992a , the related A. cellis Monniot 1987 (with sand completely encrusting the test) and the possibly conspecific A. lobatum Savigny, 1816 (with a short posterior abdomen), Aplidium solidum (with similar cloacal systems and impregnated with sand) and A. lenticulum Kott, 1992a (distinguished by the origin of its atrial lip from the body wall in front of a short siphon rather than from the anterior rim of the opening). The colony also resembles some of A. scabellum ( Michaelsen, 1924) from New Zealand. However, all of these species have five folds of the stomach wall, distinguishing them from the present species with its 20 fine longitudinal folds (see Kott 1992a).

Figures

Figure 8. Aplidium crustum sp. nov. (QM G328107): A, colony surface; B, thorax and abdomen. Aplidium eudistomum sp. nov. (QM G328439): C, colony; D, section through colony showing zooids; E, zooid, showing organs of thorax and abdomen. Scales: A, 1.0 cm; B, E, 0.5mm; C, D, 5.0 mm.