Pyura lignosa Michaelsen, 1908

Rocha, Rosana M. & Counts, Bailey Keegan, 2019, Pyura (Tunicata: Ascidiacea: Pyuridae) on the coasts of Panama, Zootaxa 4564 (2), pp. 491-513 : 497-498

Pyura lignosa Michaelsen, 1908

( Figures 5 , 6 )

Pyura (Halocynthia) lignosa Michaelsen, 1908: 256 , pl.1, fig. 9; pl. 2, figs 21, 22

Pyura lignosa: Monniot, 1994: 44 , fig. 1; Van Name, 1945: 336 (part)

Material Examined: DZUP PYU-144 , Isla Canales de Tierra , 7°44'39.7”N 81°34'45.2”W, leg. R. M. Rocha , 0 8.01.2009.

Description. This Pacific species is common in the region in shallow waters 2–5 m deep (low tide). It was found on rocky substrates in mainland, Isla Canales de Tierra and Isla Canales de Afuera, but only one sample was collected due to the difficulty of detaching the animal from the substrate. It is extremely camouflaged by encrustations on the dark tunic, which is thick and hard. The siphons are red with four small lobes, but they are situated in depressions in the tunic ( Figs 5A, B ), and when closed, it is impossible to spot the animal on the substrate. The size of our specimen with tunic was 7.5 x 6.5 x 7 cm, but larger and smaller animals were seen in the field.

The body wall is thick and opaque because the musculature forms a dense net of fibers in all directions ( Figs 5C, D ). Longitudinal muscles run from the siphons until the ventral margin. The atrial siphon is at half distance from the posterior region. The internal velum of the oral siphon has undulations covering the whole siphon, and there is a layer of tunic between the velum and the siphon musculature. The anterior third of the siphon lining is covered by spinules 50 µm long ( Figs 6C, G ).

There are 16 oral tentacles, flat and triangular. The first order ramifications appear along the posterior margin of the tentacle and are longer, while the second order ramifications are short and third order are minute ( Fig. 6F ). The dorsal tubercle is rounded, not protruding, with meandering aperture, while the peritubercle area forms a deep V ( Fig. 6D ). The dorsal lamina is divided in short triangular languets, 101 in total, many of which are not aligned (two or three were seen side by side). The languets are very delicate and break easily when touched.

The pharynx has six folds in each side and they are high but almost do not overlap. The folds on the left side are more curved than the ones on the right side ( Fig. 6A ). A total of 445 longitudinal vessels are distributed according the following formula (right to left):

E 4 (18) 11 (25) 12 (30) 15 (34) 8 (30) 10 DL 20 (27) 10 (33) 9 (35) 10 (32) 13 (28) 10 (16) 5 E

There is a large amount of short vessels linking the pharynx with the body wall or with other organs, meaning that the atrial cavity is small. Also we confirm the thick tissue and projections described by Monniot (1994) on the atrial side of the pharynx, along the dorsal region ( Fig. 6E ).

The alimentary canal forms a wide first loop occupying the whole left side, and a short and close secondary loop ( Fig. 6B ). There are a few large endocarps on the intestinal wall and also on the gonads. The green digestive gland forms one large portion. The anus contains a typhlosole, but the margin is smooth. The gonads are large and occupy most of the space of the atrial cavity in each side. They do not form well individualized lobes.

Remarks. Except by small differences in the number of tentacles and longitudinal vessels, this specimen agrees well with the description of P. lignosa by Monniot (1994). The individuals from Gulf of California and Nicaragua studied by Van Name (1945) and reported under the name P. lignosa do not seem to belong to this species and should be reviewed to have their identity correctly determined.

Figures

FIGURE 5. Pyura lignosa Michaelsen, 1908 A. Animal in the field showing open siphons with red margins (arrowheads). B. External view of preserved animal. C. Right side, tunic removed. D. Left side, tunic removed. Scale bar = 1 cm.

FIGURE 6. Pyura lignosa Michaelsen, 1908. A. Dissected animal showing the pharynx (stained). B. Dissected animal without the pharynx. C. Lining of the oral siphon. D. Stained anterior region showing oral tentacles and dorsal tubercle with meandering aperture (arrowhead). E. Detail of the atrial side of the dorsal region of the pharynx (stained). F. Detail of the oral tentacle (stained). G. Spinules in the oral siphon. Scale bar = 20 µm.