Synoicum macroglossum ( Hartmeyer, 1919 )

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 : 1139-1140

Synoicum macroglossum ( Hartmeyer, 1919)

( Figures 5F, G )

Macroclinum macroglossum Hartmeyer 1919, p. 126 .

Synoicum macroglossum Kott 1990a, p. 494 ; 2003, p. 1630.

Distribution

Previously recorded (see Kott 1992a, 2003): Western Australia (Cape Jaubert); Queensland (Mooloolaba, Mackay, Heron I., Swain Reefs). New records: Western Australia CSIRO SS10/05 (Bald I., Stn 39, 99 m, 24.11.05, QM G328104 five colonies).

The newly recorded colonies are from the most southerly location yet reported for this species and from the greatest depth. Previous records are from tropical locations albeit on the north-eastern and north-western parts of the continent. The new records suggest it could have a wider range.

Description

The newly recorded specimens are extensive slabs, to 0.75 cm thick and up to 13 cm in greatest extent. A thin surface layer of translucent test containing only sparse sand grains forms a layer over the surface. Beneath the surface, sand grains increase in density towards the base of the colony, that continues as a band of sandy test around the outer margin, framing the almost sand-free layer of test on the upper surface. Randomly spaced sessile common cloacal apertures are on the surface, although they are obscured by sparse sand and crowded zooids, the latter appearing to line canals converging to these common cloacal apertures.

Zooids are muscular, but small and narrow. They have a pronounced atrial lip from the body wall anterior to the small atrial siphon about one-third of the distance down the dorsal margin of the body. A small dorsal median papillum projects from the body wall behind the atrial siphon. Both siphons have a conspicuous sphincter muscle. The atrial lip often has a straight, toothed margin but it is variable, sometimes being long and pointed. The margin of the branchial aperture has six lobes and the atrial opening also has some small pointed processes around its entire rim. The branchial sac is long and narrow with about 20 rows of stigmata and only about 12 long and narrow stigmata in each half-row. The stigmata reduce in length towards the dorsal and ventral midlines. A short, narrow gut loop has a small, smooth-walled stomach about halfway down its proximal limb. Larvae have not been detected in any of the recorded specimens of this species.

Remarks

The species is unusual in the marked separation of the atrial lip from the siphon, the atrial lip in this genus usually projecting directly from the anterior rim of the opening. The separation of the lip from an excurrent siphon is more often seen in Polyclinum and Aplidium . However, this does not seem to indicate any particular phylogenetic affinity. The external appearance of the slab-like colonies is also distinctive with an upper almost naked layer of test framed by the sandy base and margins of the colony as in colonies of Aplidium crustum sp. nov. Kott (1992a) suggested that the present species was distinguished from the closely related S. papilliferum ( Michaelsen, 1930) , which has a similar atrial tongue and siphon, by its raised common cloacal apertures as well as its lack of an external layer of sand. However, only the latter distinction is confirmed in the newly recorded specimens.

Figures

Figure 5. Synoicum implicatum sp. nov. (QM G328098): A, colony; B, thorax and abdomen; C, antero-dorsal part of thorax. Synoicum laboutei (QM G328443): D colony; E, thorax and abdomen, both very much contracted. Synoicum macroglossum (QM G328104): F, thorax; G, abdomen and posterior abdomen. Synoicum obscurum (QM G328461): H, larva. Scales: A, D, 2.0 cm; B, 1.0 mm; C, E–G, 0.5 mm; H, 0.1 mm.