Polycarpa seges, Kott, 2009

Kott, Patricia, 2009, Taxonomic revision of Ascidiacea (Tunicata) from the upper continental slope off north-western Australia, Journal of Natural History 43 (31 - 32), pp. 1947-1986 : 1976-1978

Polycarpa seges sp. nov.

( Figure 3A–C )

Distribution

Type locality: western Australia CSIRO 05 / 07 ( Station 196-026, Ashmore, 12.43 S 123.60 E, 111 m, Sled tow, 18.5.07, holotype QM 328568) .

Description

The type specimen is laterally flattened, about 5 cm long and wide, with the conspicuously four-lobed apertures on short siphons at opposite ends of the upper surface about two-thirds of the body width apart. The test is slightly translucent but tough, flexible and wrinkled and furrowed on the surface. The body wall has a thin coat of fine parallel transverse muscle bands crossed by parallel longitudinal muscle bands forming a regular mesh. The lining of the siphons is conspicuously blistered (although this could be an artefact of collecting and/or fixing and preservation). A regular mesh of longitudinal and transverse muscle bands is in the body wall with outer longitudinal ones grouped into about 12 wide groups in the anterior part of the body, although they separate into a diffuse layer of evenly spaced fibres posteriorly. The transverse muscles are beneath the longitudinal bands and are evenly distributed along the whole length of the body. The 12 large and small alternating branchial tentacles are very pointed. The opening of the neural duct on the dorsal tubercle is a U-shaped slit. The branchial sac has four broad folds with six to eight short stigmata per mesh. Thick transverse vessels alternate with secondary transverse vessels and two thinner tertiary vessels alternate with the primary and secondary ones. Internal longitudinal branchial vessels are arranged according to the following formula: DL3 (8) 8 (12) 10 (19) 12 (20) 12 E. The dorsal lamina is a plain-edged membrane.

The gut is a short horizontal loop across the posterior end of the left side of the body. The oval stomach is about half the length of the proximal limb of the loop and is lined with about 20 fine parallel longitudinal folds. The margin of the anal opening at the base of the atrial siphon has about 12 small lobes. About 50 small polycarps are evenly distributed in the pallial body wall on each side of the body. On the left they are confined to the upper half of the body wall anterior to the gut loop. Each consists of oval to pear-shaped and slightly flattened testis follicles sometimes tightly applied around the sides of a central circular sac-like ovary but sometimes in the body wall slightly removed from the ovary. Fine vasa efferentia from the testis follicles join a short vas deferens on top of the ovary. The vas deferens opens with the short oviduct on the dorsal side of the polycarp.

Remarks

The numerous short gonads of this species resemble those of Polycarpa perstellata Monniot F. and C., 2003 from Fiji at 960 m (which has a short almost spherical stomach with relatively few rounded folds) and Bathyoncus arafurensis Monniot F. and C., 2003 from Indonesia down to about 500 m (which has a similar stomach to the present species but has other generic differences). Polycarpa arnoldi Michaelsen, 1914 from the Atlantic Ocean and the west Indian Ocean (Monniot C 2002) also has similar gonads but is distinguished by the endocarp in the gut loop and its short, wide stomach.

Figures

Figure 3. (Continued). (E) body opened along ventral midline showing gonads, endocarps and gut loop. (F) Molgula delicata (QM G328510), body seen from above showing muscles radiating from around the apertures and extending halfway down the body wall and the fine transverse muscle crossing the dorsal mid-line. Scales: A, 1.0 cm; B, D, 0.5 cm; C, 0.5 mm; E, 1.0 mm; F, 2.0 mm.