Polysyncraton galaxum Kott, 2004

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 : 2429-2430

Polysyncraton galaxum Kott, 2004

( Figures 4B–D , 14G , 18H )

Polysyncraton galaxum Kott 2004b, p 2478 .

Distribution

Previously recorded (see Kott 2004b): South Australia (Kangaroo I.); Tasmania (Tasman Peninsula). New records: South Australia (Kangaroo I., SAM E3250 ); Tasmania ( Port Davey , SAM E3261 ) .

Description

In preservative, the newly recorded colony from Tasmania is a flat, smooth encrusting sheet. Small inconspicuous common cloacal apertures are slits or four or five lobed openings with slightly protruding frilled lips. Branchial apertures are tightly closed and inconspicuous. However photographed in situ the surface of the colony is raised into evenly spaced, contiguous, uniform rounded lobes, each 5–7 mm diameter with a terminal common cloacal aperture. The specimen from South Australia is less contracted and in the in situ photograph its surface lobes are not so high. It has stellate branchial apertures lined with spicules. The preservative is stained yellow. In life, colonies are salmon-pink to a crushed strawberry colour. Each of the surface swellings contains a single common cloacal system, the zooids opening on the sides of the swellings or lobes around the central or terminal common cloacal aperture. The common cloacal cavity is shallow and horizontal at thorax level. Spicules are crowded tightly throughout the colony and the surface is raspy. They are stellate, to 0.07 mm diameter with seven to nine and occasionally five relatively short, robust, conical rays. In one of the specimens (SAM E3261) the spicules are to 0.07 mm diameter but in the other the largest spicules are only 0.05 mm diameter. Small stellate spicules to 0.02 mm diameter are present but are never as numerous as the larger ones.

Zooids have a narcissus-shaped branchial aperture, constricted at the base and with six pointed lobes around the opening. About eight stigmata are in the anterior row of the branchial sac. Zooids are in vegetative phase with oesophageal buds, and gonads were not detected. Short vascular stolons with terminal ampullae project from the ventral side of the double gut loop. A robust, tailed larva, the trunk 0.72 mm long, is in one colony (SAM E3250). It has 16 crowded lateral ampullae along each side of the three antero-median adhesive organs which have thick, swollen stalks. The tail is wound almost the whole way around the trunk. The cerebral vesicle contains a relatively large ocellus and otolith. A large, vertical, oval yolk mass is halfway along the trunk and a long horizontal external ampulla projects posteriorly from the base of the circle of lateral ampullae on the left side of the trunk.

Remarks

The in situ photographs of the newly recorded specimens and of the type specimens are very alike. Although the species was characterized partly by the numerous small spicules in some parts of the test, this is inconsistent and it is possible that the proportion of smaller spicules is affected by the part of the colony from which the sample came. Kott (2004b) observed the systems with zooids arranged around the common cloacal aperture, but did not specify their isolation from one another. Nevertheless, she did observe that they resembled the common cloacal systems in P. glaucum Kott, 2001 , which does have independent systems (albeit larger spicules to 0.09 mm diameter with 9–11 pointed rays in optical transverse section). Also similar to the present species are P. multiforme Kott, 2001 with spicules to 0.05 mm diameter and 17–19 pointed to blunt-tipped rays in optical transverse section, P. pavimentum Monniot, 1993 with large spicules to 0.1 mm diameter and 13–15 pointed to truncated rays in optical transverse section as well as some globular spicules, and the New Zealand species P. lithostrotum (Brewin, 1956) with almost globular spicules to 0.08 mm diameter, short, blunt spicule rays and different larvae. Polysyncraton pavimentum: Kott, 2002a , P. polysystema sp. nov. with large spicules to 0.08 mm diameter and 9–11 conical and truncated ray tips should be added to the list of similar species (see below, P. polysystema sp. nov.). The colony of the present species also differs from that of the related species listed above in that each independent system is contained in a lobe that projects from the surface of the colony rather than being a flat system level with the colony surface.

Figures

Figure 4. (A) Polysyncraton cuculliferum (QM G308715): larva. (B–D) Polysyncraton galaxum (SAM E3250): (B) thorax; (C) gut loop; (D) larva. Scale bars: 0.1 mm.

Figure 14. Scanning electron micrographs of the calcareous spicules of: (A) Leptoclinides decoratus (SAM E3257); (B) Leptoclinides dubius (WAM 1093.89); (C) Leptoclinides frustus sp. nov. (SAM E3255, holotype); (D) Leptoclinides kingi (WAM Z20557); (E) Leptoclinides minimus sp. nov. (WAM 30.84, holotype); (F) Leptoclinides pulvinus sp. nov. (QM G308742, holotype); (G) Polysyncraton galaxum (SAM E3250); (H) Polysyncraton glaucum (QM G308736).

Figure 18. In situ images of: (A) Leptoclinides decoratus (SAM E3257); (B) Leptoclinides frustus (SAM E3255, holotype); (C) Leptoclinides imperfectus (SAM E3243); (D) Leptoclinides lissus QM G308709); (E) Leptoclinides rigidus (QM G308708); (F) Leptoclinides seminudus (SAM E3264); (G) Polysyncraton cuculliferum (QM G308715); (H) Polysyncraton galaxum (SAM E3261).