Polysyncraton millepore Vasseur, 1969

Kott, Patricia, 2005, New and little-known species of Didemnidae (Ascidiacea, Tunicata) from Australia (Part 3), Journal of Natural History 39 (26), pp. 2409-2479 : 2431-2432

Polysyncraton millepore Vasseur, 1969

( Figure 15A ) Polysyncraton millepore Vasseur 1969, p 917 ; Kott 2001, p 113 and synonymy; 2004a, p 741 and synonymy.

Distribution

Previously recorded (see Kott 2001, 2004a): Western Australia (Dongara); Queensland (Whitsunday I.); New Caledonia; West Indian Ocean ( Madagascar, Mozambique,

Tanzania, and northern Natal). New record: Western Australia (N of Port Hedland, WAM 122.93).

The newly recorded specimen was taken in a trawl at 38– 34 m.

Description

The newly recorded colony is a hard, brittle, biscuit-like plate with a rounded margin and spicules crowded throughout. The upper layer of test, forming the roof of the horizontal, thoracic common cloacal cavity, is brownish and contains thin, branched pigment cells. The margins of the stellate branchial apertures are outlined in white spicules. Sessile common cloacal apertures are randomly placed on the surface and are surrounded by dark pigment. The thoracic sheaths of the zooids as they cross the common cloacal cavity are white with spicules, as is the basal layer of test in which the abdomina are embedded. The majority of the spicules are stellate (to 0.66 mm diameter) with 11–13 pointed conical rays in optical transverse section. However, there are some with truncated, flat-tipped rays and also there are some globular spicules. Zooids are long and narrow, with a long tulip-shaped branchial siphon and a conspicuous spiculefilled siphonal lining. The atrial aperture has a characteristic slightly spoon-shaped, narrow atrial lip from the upper rim of the opening. Eight stigmata are in the anterior row of the narrow branchial sac. Six coils of the vas deferens surround a number of testis follicles.

Remarks

Despite its wide geographic range, this species is remarkably stable, with little apparent morphological variability. The colonies always are hard and biscuit-shaped, with darkly pigmented surface test and white basal test, the spicules include globular as well as stellate ones, and the characteristic spoon-shaped atrial lip is unique to this species. Although Kott (2001) reported only five coils of the vas deferens, six are shown in her figure ( Kott 2001, Figure 54C) and were detected in the newly recorded material.

Figures

Figure 15. Scanning electron micrographs of the calcareous spicules of: (A) Polysyncraton millepore (WAM 122.93); (B) Polysyncraton orbiculum (WAM 128.90); (C) Polysyncraton papyrus (SAM E3253); (D) Didemnum astrum (WAM 601.89); (E) Didemnum cilicium sp. nov. (SAM E3251, holotype); (F) Didemnum corium sp. nov. (SAM E3249, holotype); (G) Didemnum cygnuus (QM G308716); (H) Didemnum fragum (SAM E3266).