Aplidium caelestis Monniot, 1987

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 : 1149-1150

Aplidium caelestis Monniot, 1987

Aplidium caelestis Monniot 1987, p. 517 ; Kott 1992a, p. 528 and synonymy.

Distribution

Previously recorded (see Kott 1992a): Western Australia (Rottnest Island, Shark Bay); South Australia (Great Australian Bight to Bass Strait); New South Wales ( Norfolk Island); Queensland (Capricorn Group to Lizard Island), New Caledonia, Marianas. New records: Western Australia CSIRO SS10/05 (Cape Mentelle, Stn 15, 97 m, 21.11.05, QM G328448; Bald I., Stn 35, 157 m, 24.11.05, QM G328063; Kalbarri, Stn 102, 96– 98 m, 05.12.05, QM G328465).

The new records confirm the wide geographic range of this species around the Australian continent.

Description

Some colonies (QM G328063 G328465) are irregular sheets with vertical, evenly spaced zooids more or less parallel to one another, lining the shallow thoracic common cloacal canals beneath shallow depressions in the surface. Other specimens (QM328448) are large dome-shaped to spherical colonies, slightly more fleshy on the upper surface where the zooids line the narrow, crowded, oval to elongate more or less parallel common cloacal canals that converge toward the top of the dome. Sand is present throughout the colonies, but is most crowded in the outer layers where it surrounds and is surrounded by the double rows of zooids and is in the thin layer of test over the common cloacal canals. The undersurface of the dome-shaped colonies is especially sandy and sometimes narrows to irregular root-like projections or stalks that may penetrate into the substrate.

The long, thread-like zooids are similar in all specimens. They are parallel to one another at the surface but criss-cross internally. Anteriorly they narrow to a prominent branchial siphon with the atrial tongue projecting from the body wall at the base of the branchial siphon, well separated from the small atrial siphon. The atrial tongue extend across the top of the common cloacal Five longitudinal folds are in the stomach wall. Gonads are in a long, thread-like posterior abdomen. A single immature larva being incubated in contracted zooids occupies almost half of the length of the atrial cavity.

Remarks

The large globular colonies described above are different from the encrusting ones usually reported for this species. However, although the colony shape is different, the systems, anterior tongue from the body wall anterior to the small atrial siphon, the long posterior abdomen and a single large larva in the atrium resemble previous reports of A. caelestis .

Systems are different from A. clivosum and A. crateriferum but zooids are similar. Aplidium lenticulum also has similar zooids but less sand, zooids are confined to the sides of the common cloacal canals and have more (16–20) rows of stigmata. Colonies of A. solidum are similar to the present species, although it has a more conspicuously quilted appearance, its common cloacal canals being circular, rather than elongate and more or less parallel to one another as they are in the present species. The zooids also are similar although in A. solidum the zooids are shorter, the anterior end not so conspicuously narrowed and the atrial lip rising from the margin of the anterior rim of the atrial siphon,