Polyandrocarpa colemani Kott, 1992

Kott, Patricia, 2005, Novel Australian Polyzoinae (Styelidae, Tunicata), Journal of Natural History 39 (32), pp. 2997-3011 : 2999-3001

Polyandrocarpa colemani Kott, 1992

( Figures 1A , 5A ) Polyandrocarpa colemani Kott 1992, p 641 .

Distribution

New records: Queensland (Palm Beach reef, QM G308755 , G321000 ). Previously recorded (see Kott 1992): New South Wales (Arrawarra, Coffs Harbour, Cook I.). The species is known from 9–12 m in a restricted geographic area on the northern New South Wales coast and just north and south of the Queensland – New South Wales border .

Description

Colonies are invariably large (to 1 m maximum dimension), tough and leathery with an even surface, the zooids completely embedded in the surface layer of test and the independently opening round incurrent and excurrent apertures project only slightly from the surface. Kott (1992) noted that colonies are found along the top of ridges where they are exposed to maximum current flows. Newly recorded colonies are vertical lamellae, to 1 m high but only about 5–10 cm thick, with zooids opening all around the surface. They are fixed firmly to rocky substrates but although the test is particularly tough it is probable that the edge of the colony is presented to the prevailing current rather than their wider surfaces. The internal test in the centre of the colony has criss-crossing test vessels from the zooids.

Zooids are crowded and parallel to one another. They are narrow, to 1.5 cm long, and difficult to remove from the test. The body wall is particularly muscular with almost continuous circular bands externally around a layer of internal longitudinal muscles. The body wall lining the atrial cavity is crowded with vesicles. The branchial aperture is anterior on a short siphon and the atrial siphon is a similar length and projects from the mid-dorsal surface. In living colonies the zooids presumably lie at an angle to the surface. The dorsal tubercle has a transverse or curved slit. The endostyle in these zooids is almost the whole length of the branchial sac and the four branchial folds on each side also are straight and extend the full length of the branchial sac. Branchial folds have up to eight internal longitudinal vessels per fold and seldom more than one between. The gut forms a short, curved loop in the posterior third of the body. The oesophagus is moderately long and narrow and the long stomach, two-thirds of the length of the proximal limb of the gut loop, with 18 internal longitudinal folds, gradually increases in diameter to the distal end where it narrows abruptly to the intestine. The intestine curves into the pole of the loop and the descending limb curves postero-dorsally to form the secondary curve of the gut loop before turning anteriorly into the vertical rectum. A flat-topped endocarp is in the gut loop between the stomach and descending limb of the intestine. Short teardrop-shaped polycarps with five to eight pairs of male follicles beneath the ovarian sac are in one or sometimes two overlapping rows of up to six per row along each side of the body with their relatively long ducts directed toward the atrial aperture.

Remarks

Although there is some variation in the form of the colonies, they always are tough with a smooth surface and crowded zooids. Even in situ photographs do not show a great difference in the orientation of the apertures of this species, which must be especially dependent on prevailing external currents to separate the incurrent and expelled ciliary streams of water.

These colonies are unusually large for separately opening stolidobranch species in which there is no internal common cloacal cavity in which the positive water pressure maintains the turgidity of the colony. In the present case the strength of the test appears to constitute the main support for the large colonies. The species is also unusual in that the majority of Polyandrocarpa species do not have completely embedded zooids. Polyandrocarpa colligata Sluiter, 1913 from the Aru I. does have completely embedded zooids although it has an encrusting colony rather than the massive one of the present species, a vertical rather than a horizontal slit on the dorsal tubercle, small endocarps on the body wall rather than a single large flat-topped one in the gut loop, a smooth-rimmed anus and a shorter stomach than the present species (see below).

The very restricted geographic range is not often encountered in the Ascidiacea, especially in view of the large conspicuous colonies which are unlikely to be overlooked by scuba divers.

Certain Polycarpa spp. contain crowded vesicles as in the present species (see P. pedunculata: Kott, 1985 ). However, Polycarpa is distinguished from the present genus by its solitary habit.

Figures

Figure 1. (A) Polyandrocarpa colemani (QM G308755): left and right pallial wall showing gut and gonads. (B, C) Polyandrocarpa colligata (QM G308758): (B) colony surface; (C) gut loop. (D–H) Oculinaria australis (SAM E3267): (D) portion of colony; (E) inner pallial body wall on right showing gonads; (F) inner pallial body wall on left showing gut and gonads; (G, H) siphonal spines. In (G), the open base of the spine in the centre of the light micrograph is showing; in all the other spines, only the hollow centres of the pointed tips are in focus. Scale bars: 1.0 mm (A); 2.0 mm (B, D–F); 0.2 mm (C); 0.05 mm (G, H).

Figure 5. In situ images. (A) Polyandrocarpa colemani (QM G308755) (photograph: Merrick Ekins); (B) Oculinaria australis (SAM E3267) (photograph: K. Gowlett Holmes); (C) Stolonica vermiculata (QM G308756) (photograph: Neville Coleman); (D) Botryllocarpa elongata (SAM E3232) (photograph: K. Gowlett Holmes).