Aplidium tuberosum, 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 : 1161-1163

Aplidium tuberosum sp. nov.

( Figures 11A–E )

Distribution

Type locality: Western Australia CSIRO SS10 / 05 (Albany, Stn 22, 118.2940E 35.3350S, 100 m, 22 November 2005, holotype WAM Z27512, QM G328112 : paratype QM G328129 ; further record: Jurien Bay, Stn 83, 113 m, 02.12.05 QM G328152 ) .

Description

The holotype has rounded lobes to vertical flattened plates branching from an irregular, basal, common trunk to form a firm, sandy, branching tree-like colony. The paratype is a single, laterally-flattened, paddle-shaped upright lobe, narrowing to the base, 14 cm high and about 10 cm maximum width. Sand is crowded throughout, especially in the central test core where it forms a skeletal support for the colony. Zooids are crowded, their thoraces at right angles to the outer surface and separated from one another by rigid, sand-filled partitions of test. They are arranged in small circles around small, shallow common cloacal cavities. Although presumably each of these common cloacal cavities has a central opening to the exterior, it was not detected amongst the crowded sand. The abdomina and posterior abdomina curve down into the central test and toward the base of the colony. The systems are crowded, although depressions in the surface test separate them from one another, and the colony breaks up readily.

Branchial tentacles extend down into the long siphon from a circle around the top. Thoraces are relatively short with a conspicuous six-lobed, terminal branchial aperture and a muscular antero-dorsal atrial lip from the body wall anterior to the atrial aperture which is on a small siphon. Stigmata are in about 12 rows with about 14 stigmata in each row, although these are obscured by contraction. The gut forms a narrow vertical loop. The small stomach with five parallel folds in its wall is half-way down the descending (proximal) limb of the gut loop. The long, narrow posterior abdomen contains a long series of irregular, thick, disc-shaped follicles. Sometimes one to three large cigar-shaped larvae 1.0 mm long are lined up in the atrial cavity. Epidermal vesicles are crowded in the larval test over the anterior two-thirds of the trunk. These are particularly conspicuous scattered around the wide, shallow, short-stalked antero-median adhesive organs. Epidermal ampullae were not detected. The tail reaches around the anterior end of the trunk.

Remarks

The length of these zooids is variable, although the number of rows of stigmata is always about 12, readily distinguishing the species from A. panis (which sometimes has similar colonies). The zooids of this species resemble some others in the genus with five stomach folds and a muscular atrial tongue separate from the opening. A. solidum ( Herdman, 1899) and Aplidium ritteri (Sluiter 1895) have similar colonies and five stomach folds, although both have small atrial tongues from the anterior rim of a small atrial opening. Larvae of both these species have a trunk only about half the size of the present species (1.0 mm) and the larva of A. ritteri is further distinguished from the present species in the presence of median ampullae. Other species with similar zooids reported in the present work have less sand internally and/or different systems and longer thoraces. The large larvae with crowded vesicles around the anterior part of the trunk resemble those of A. crateriferum although the latter species has a longer larval trunk.

Figures

Figure 11. Aplidium tuberosum sp. nov: (A, C, QM G328112; B, D, E, QM G328129) A, colony; B, surface of colony; C, zooid (C1, thorax and abdomen; C2 posterior abdomen); D, zooid (D1, thorax and abdomen; D2, posterior abdomen); E, larva. Scales: A, B, 2.0 cm; C, D, 0.5 mm; E, 0.1 mm.