Polysyncraton snelliusi Oliveira & Rocha, 2019

Oliveira, Livia M., Hoeksema, Bert W. & Rocha, Rosana M., 2019, Polysyncraton (Ascidiacea, Didemnidae): a re-examination of some specimens and descriptions of three new species, European Journal of Taxonomy 519, pp. 1-25 : 17-19

Polysyncraton snelliusi Oliveira & Rocha sp. nov.

urn:lsid:zoobank.org:act:650A74FA-077A-46B4-B1EF-9BF5CC2B44E6

Fig. 11

Etymology

The name refers to the campaign vessel that collected the material.

Material examined

Holotype SURINAME • 1 colony; Guiana Shelf , stat. 97; 07°16.8′ N, 56°47.6′ W; 64 m depth; 13 Apr. 1966; HNLMS Snellius leg.; Onderzoek Continentaal Plat Suriname ( OCPS); RMNH.UROCH.1109.

Description

The colony is yellowish in preserved material, measuring 8 cm in diameter and 2 mm thick. It has an irregular shape, molding itself on top of a sponge. The colony surface has several common cloacal apertures with six to eight short lobes each ( Fig. 11b ). The cloacal cavity is wide and positioned at the thoracic level. The tunic is firm, brittle and with many papillae associated with one of the lobes of the oral siphons. The zooids form circular systems around the cloaca and also linear systems along the cloacal channels, which are marked by a depression on the colony surface. They have a brown colour, leaving white circular or irregular patches on the colony surface ( Fig. 11c ). Two types of stellate spicules are distributed in the tunic. The larger ones (40 to 60 µm in diameter) have six rays in transverse optical section, but many other shorter rays among the main ones. Also, the rays are either blunt or more pointed. The smaller spicules (23 to 50 µm in diameter, a few to 60 µm), have seven to eight conical rays with round tips in transverse optical section, without intermediate rays ( Fig. 11d ).

The zooids are 1.0 mm long. The oral siphon is short (0.2 mm), with six long triangular lobes. The atrial aperture is wide, exposing almost all the pharynx, without an atrial languet. The pharynx stigmata formula is 12, 12, 11, 9. The lateral thoracic organs are circular, not protruding and localised at the level of the 2 nd row of stigmata. The muscular process is lacking. The esophageal peduncle is short and straight. The testis is divided in four follicles surrounded by three coils of the sperm duct. The secondary gut loop does not overlay the stomach ( Fig. 11e ).

The larvae are elliptical, not gemmiparous, with the trunk 0.8 to 0.9 mm long. A tail with a diameter of 116 µm winds halfway around the trunk. The sucker of the central adhesive papilla is 95 µm in diameter and the peduncle is 235 µm long. There are 12 to 14 elongated, thin ectodermal ampullae on each side of the larva, 105 to 120 µm long ( Fig. 11f ). The sensorial vesicle (including ocellus and statocyte) is slightly posterior to the mid-dorsal region of the larval trunk. The ocellus is 54 µm long and 361 µm distant from the anterior region of the tail.

Remarks

Eight species of Polysyncraton have been reported from the Atlantic Ocean ( Rocha et al. 2012; Paiva et al. 2015) and none of them look like the one described herein. Polysyncraton snelliusi sp. nov. can be distinguished from P. cabofriense sp. nov. by the absence of papillae on the colony surface and the presence of gemmiparous larvae in the latter. Among other species with papillae on the colony surface, P. echinatum Kott, 2001 has a gelatinous tunic, stellate spicules without secondary rays and smaller larvae (trunk 0.6 mm long), with four subdividing ectodermal ampullae on each side; P. meandratum F. Monniot, 1993 has globular spicules with flat-tipped rays, a bifurcated atrial languet and larvae with eight pairs of ectodermal ampullae; P. pseudorugosum F. Monniot, 1993 has stellate spicules with sharp pointed rays and deeper common cloacal canals, seven testis follicles and smaller larvae with eight pairs of ectodermal ampullae.

Distribution

Type locality: Suriname ( Guyana Shelf).

Figures

Fig. 11. Polysyncraton snelliusi Oliveira & Rocha sp. nov. a. Preserved colony. b. Colony surface (arrow indicates the common cloacal aperture with lobes). c. Papillae on the colony surface. d. Spicules (large type). e. Abdomen with gonads, large arrow indicates the follicle (one follicle hidden) and the small arrow the sperm duct. f. Larva. Scale bars: e–f = 0.2 mm.