Herdmania momus ( Savigny, 1816 )

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 : 1207-1209

Herdmania momus ( Savigny, 1816)

Cynthie momus: Savigny 1816, p. 43 .

Herdmania momus: Kott 2002b, p. 366 and synonymy.

Distribution

Previously recorded (see Kott 2002): Queensland ( Southeastern Queensland to Noosa, Great Barrier Reef to Lizard I.) Western Pacific (Coral Sea Plateau, Indonesia, Philippines, New Caledonia, Fiji),? West Indian Ocean, Red Sea. New records: Western Australia CSIRO SS10 /05 (Point D’ Entrecasteaux, Stn 17, 378 m, QM G328433 ; Albany, Stn 25, 398 m, 23.11.05, QM G328157 , 10 juvenile specimens; Bald I., Stn 34, 408 m, 24.11.05, QM G328153 , 100 juvenile specimens); Mediterranean ( Nishikawa 2002) .

The new records are the first from the southern coast of the continent and the most southerly and probably the deepest known records of this species. They are always juveniles, sexually mature species not being present. Also they are unusual in apparently being numerous on the open sea floor and rooted in soft sediments rather than being fixed to hard coralline habitats in shallower waters and as well as being relatively common over an extensive expanse of the sea floor around Albany and Bald I., they are also common over a considerable depth range.

Description

The newly recorded colonies are small (to about 2.5 cm diameter), soft, and globular to gooseberry-shaped with a fur of root-like processes along the ventral part of the body and almost sessile apertures at opposite ends of the upper surface. Each aperture is surrounded by four large slightly protuberant triangular lobes of relatively thick test, but otherwise the test is thin, flaccid and translucent with a very fine coat of sand attached to the outer surface. Internally the body wall contains moderately crowded echinated spines characteristic of the genus. Some internal damage to many of these specimens appears to have been caused by the spicules becoming tangled in the body wall, branchial sac and the test possibly when specimens were agitated during collection. These reach only about halfway down the body wall. Some circular muscle bands also are present around each siphon. The dorsal tubercle has a C-shaped opening with the open interval turned slightly to the right and both horns turned in to varying extents. The branchial sac has up to nine broad branchial folds on the right side of the body and eight on the left. As reported in Kott (2002b, Figure 4E, K ), the gut forms an open loop around the posterior half of the left side of the body. The anus is bilabiate but each lip is broken up into irregular, relatively shallow rounded anal lobes. A single clump of compact liver lobules is in the pyloric region at the proximal end of the gut. On the left, the gonad is enclosed in the gut loop and the right gonad is in a symmetrical position on the right side of the body. Gonads are more or less straight club-shaped organs in all these specimens. They consist of convoluted ovarian tube with clumps of branched testis follicles along each side so that the testis follicles appear to take a convoluted course along the surface of the ovary. Each clump of testis follicles has vasa efferentia joining short vas deferens that open separately along the surface of the convoluted ovary. The oviductal opening, at the distal end of the ovary, is covered by a large hood from the internal body wall as shown in Kott (2002b, Figure 4F–H ). Many of the specimens are sexually mature, with mature eggs in the ovary, apparently mature testis follicles and the characteristic hood (formed from the body wall) that covers the opening of the ovarian tube.

Remarks

Despite their small size relative to the size of mature specimens formerly reported for this species, some of these specimens are sexually mature, and there is a possibility that they are a temperate species distinct from this well-documented tropical species. However, apart from their size, their habitat and their geographic location, a morphological character distinguishing these small specimens from H. momus was not detected. The spirals of the slit on the dorsal tubercle are not so well developed and the convolutions of the ovarian tube and continuity of the band of clumps of testis follicles are not as conspicuous as they are in the larger tropical specimens. However these are some of the few probable age/size-associated characters in the specimens. The general form of the gut loop, liver lobes, gonads, gonoducal openings and body muscles are as previously described for this species.

A species of similar body form and consistency, H. mentula Kott, 2002b , has been recorded from the north-western Australian coast. Like H. fimbriae Kott, 2002b , a similar species from the southern and north-eastern coasts, H. mentula is distinguished from the present species by its vas deferens that extends the whole length of the ovary to a single opening near the oviducal opening that often is associated with an elaborate fringe. Also, although H. fimbriae has a lobed anus like the present species, H. mentula has a simple four-lobed anus. Herdmania grandis also has a lobed anus like the present species, but usually is readily distinguished from all other species by its large size, more numerous and longer muscles in the body wall and the absence of gonoducal membranes associated with either the male or female openings.

Family MOLGULIDAE Lacaze Duthiers, 1877

Figures

Figure 4. Sigillina grandissima (QM G328124): A, larva. Synoicum chrysanthemum (B2,3, C, QM G328097; B1, D, (QM G328060)): B1–3, colonies; C, thorax, abdomen and posterior abdomen (showing male follicles); D, larva. Scales: A, C, 0.5 mm; B, 2 cm; D, 0.2 mm.