Didemnum molle ( Herdman, 1886 )

Kott, Patricia, 2007, New and little-known species of Didemnidae (Ascidiacea, Tunicata) from Australia (part 4), Journal of Natural History 41 (17 - 20), pp. 1163-1211 : 1186

Didemnum molle ( Herdman, 1886)

Diplosomoides molle Herdman 1886, p 310 .

Didemnum molle: Kott 2001, p 208 and synonymy.

Distribution

Previously recorded (see Kott 2001): the species is known to have a wide geographic range in tropical coralline habitats from the West Indian Ocean to the West Pacific ( Fiji) and from Okinawa ( Ryukyu Is , Japan) to the southern Great Barrier Reef and Houtman’s Abrolhos , Cockburn Sound and Esperance (southwestern Australia). New records: Queensland ( Great Barrier Reef : 14.685 ° S, 145.365 ° E, 17 m, with larvae QM G308878 ; 14.685 ° S, 145.535 ° E, 27 m, QM G308865 ) .

Remarks

The newly recorded colonies are the characteristic soft, flask-shaped form, their shape in life maintained by the positive pressure gradient between the incurrent stream of water through the branchial aperture of each zooid and the excurrent stream through the rounded terminal common cloacal aperture. Colonies are known to subdivide across the common cloacal aperture which maintains its terminal position in the replicates. The occurrence of this species in inter-reefal areas is presumably dependent on the availability of stable hard substrata in order for the filtering activity (which maintains the shape of the colony) to be sustained without interruption. The central common cloacal cavity is filled with green symbiotic Prochloron that adhere to the lining of the common cloacal cavity and are released in the streams of mucus that are secreted when the colony is disturbed. Usually the species is taken from relatively shallow depths and colonies are known to move up coral debris toward the light, presumably to ensure requirements for photosynthesis in the symbionts of this (probably at least partially) autotrophic species. A depth of 27 m for one of the newly recorded colonies is greater than that usually recorded for the species. One of the newly recorded specimen lots (QM G308878) collected in October contains developing larvae of the usual form.