Polyandrocarpa arianae, Monniot, Françoise, 2016

Monniot, Françoise, 2016, A new species of Polyandrocarpa (Ascidiacea, Styelidae) in the Mediterranean Sea, Zootaxa 4132 (1), pp. 87-96 : 87-91

Polyandrocarpa arianae n. sp.

Figures 1 , 2 .

Etymology: name of my grand-daughter Ariane.

Stations: Corsica, off Porto Vecchio, 5/ 1995, 90m coll. C. Monniot Type (MNHN S1 POL.A 50).

IFREMER “Medits” T 77, 42° 48.13N- 4° 42.68E, 20/06/2013, 584m- “Medits” T 72, 43° 05.41N –4° 09.53E, 6/ 2014, 95m.- “Medits” T 80, 43° 04.45N –4° 00.97E, 24/06/ 2014, 98m (MNHN S1 POL.A 53–55).

The colonies are composed of clumps of upright elongated zooids ( Fig 1 A) linked at their base to a common sheet of tunic and also with some stolons arising from the body sides. The body size is variable in the same colony but does not exceed 18mm in height. The siphons are slightly protruding, the oral is apical and the atrial a little lower ( Fig 1 A,D,G). They have 4 lobes and open in a cross. The tunic is thin but resistant and impregnated with sand and mud on the body sides, but it becomes thicker basally. Extracted from the tunic the body wall is extremely thin and transparent ( Fig.1 B,D,G). On the body the network of crossed muscular fibres is weak as a felting, and the siphon sphincters are not strong. The number of oral tentacles is variable reaching 30-35 on a line, in three orders of size, at the base of a large thin velum. The prepharyngeal band forms a wide V. The dorsal tubercle is a protruding button opening anteriorly in a C at the top of an elongated neural ganglion.

The branchial sac is wide with 4 low but complete folds on each side ( Fig.2 B,D). The dorsal lamina is long and low with a smooth edge, not displaced toward the left. The folds are distant from each other with generally 4 well isolated longitudinal vessels in the spaces ( Fig 2 B,D). They all reach the basal curved line of the endostyle. For example two formulae are:

RE 4 (10) 4 (11) 4 (11) 4 (8) 1 DL (11) 3 (11) 4 (12) 4 (10) 3 EL

RE 4 (9) 5 (11) 4 (10) 4 (8) 1 DL (11) 4 (10) 4 (10) 4 (11) 3 EL

There is always 1 entire longitudinal vessel between the dorsal lamina and the first fold on the right ( Fig.2 B,D). Parastigmatic vessels are present everywhere on elongated stigmata.

The digestive tract occupies the posterior part of the left body side ( Fig. 2 E). It begins with a narrow oesophagus, followed by a round stomach with internal folds (about 8 plications on the mesial side). The primary gut loop is very short and closed ( Fig. 2 E). The rectum is long and narrow ending in a gaping anus fringed with round lobes. There is no gastric caecum. The gut is only linked to the body wall and the branchial sac by bridles. There are no endocarps either inside the gut loop or on the body wall. The gonads are not in a line but irregularly distributed on both sides at some distance from the ventral line ( Figs 1 B, 2E). Ten to 12 sausage-like polycarps are on the right side and 9 to 10 on the left side in the largest zooids. They are only linked to the body wall and the branchial tissue by thin bridles. The central ovary lies on a double row of lobed male vesicles ( Fig 2 A). Each testis vesicle is lobed ( Fig. 2 E) and has a thin duct which encircles the side of the ovarian tube which connects to a longitudinal common sperm duct ending against the female papilla ( Fig.2 A).

A ring of numerous thread-like tentacles arises from the base of a large velum at the atrial opening ( Fig.2 C). The atrial velum is inflated in numerous round bubbles ( Fig.2 C) (not found on the oral velum) and they do not seem to be due to contraction.

Remarks. P. arianae n. sp. somewhat resembles P. zorritensis ( Van Name,1931) in its colony shape and size, it lives in the same geographic area (though P. zorritensis is introduced in the Mediterranean (Brunetti 1978-79) but deeper but differs from it in several important internal characters which are described below. A comparison will be made also with P. rollandi Tokioka, 1961 from the Pacific Ocean which also differs by few characters.

Figures

FIGURE 1. Polyandrocarpa arianae n. sp. A, part of a colony; B, individual without tunic; C, D, left and right sides of a specimen removed from tunic. Scale bars: A = 1 cm; C, D = 4 mm.

FIGURE 2. Polyandrocarpa arianae n. sp. A, several polycarps; B, branchial tissue of a specimen from “ Medits ”; C, internal side of the atrial siphon; D, branchial sac and E, body wall of a specimen from Corsica. Scale bars: A = 0.5 mm; B = 1 cm; C = 1 mm; D, E = 5 mm.