Ascidia protecta Van Name, 1945

Nishikawa, Teruaki & Namikawa, Hiroshi, 2021, A Detailed Description of the Long-Overlooked Tunicate Ascidia protecta (Ascidiacea), Based on the Type and Non-Type Specimens from the Gulf of California, Species Diversity 26 (1), pp. 1-5 : 2-3

Ascidia protecta Van Name, 1945 ( Figs. 1–2 ; Table 1 )

Ascidia sydneiensis protecta Van Name, 1945: 190–191 .

Description. Body 26.0– 61.7 mm long, with oval outline, flattened laterally, and attached to substratum usually by entire right (usually more or less depressed) side (entire left side in paralectotype). Both siphons conspicuous, 6-lobed, completely surrounded by a longitudinally elongate, conspicuously ridged oval ring ( Fig. 2A, F ) (a low ridge only on right side in AMNH Ch. 1739), with minute conical or round papillae, up to 0.5 mm tall ( Fig. 2A ) (type specimens), or elongate conical projections extending onto ridge and siphon vicinity, up to 3 mm long (NSMT-Pc 4481) ( Fig. 2F ). Tunic cartilaginous; thick (up to 7 mm), rather tough, translucent pale yellowish (49.0– 61.7mm specimens), thin but tough, translucent white (26.0–34.0 mm specimens). Surface sometimes covered with hydrozoan colonies.

Mantle body often damaged on right side at time of collection ( Fig. 2C, H ). Branchial siphon terminal, base of more or less elongated atrial siphon at anterior two-fifths of mantle proper (3 larger specimens), near midpoint of mantle (2 smaller specimens); both siphons 6-lobed. Siphonal musculature very well developed; mantle musculature developed only along entire dorsal edge, comprising short, thick, dense, yellowish or fleshy pink transverse fibers ( Fig. 2B, C, G, H ); muscles absent around neural complex. Epidermis and connective tissue of mantle wall narrowly thickened around siphonal area ( Fig. 2B ), probably underlying oval tunic ridge. Tentacles simple, mostly elongated of variable size, distribution crowded, numbering ca. 100 (smaller specimens) to ca. 180 (largest specimen); prebranchial zone narrow, smoothsurfaced. Ciliated groove basically C-shaped with both horns rolled inwards ( Fig. 2D ), but often somewhat complicated ( Fig. 2E ); a narrow longitudinal groove behind dorsal tubercle 1.5 to 3.5 times as long as tubercle, a neural complex along groove. Edge of dorsal lamina markedly serrated by tips of ribs projecting beyond laminal edge, each rib derived from adjoining transverse vessel. Number of inner longitudinal vessels 36 (L) and>40 (R, uncertain due to damage) in lectotype, 44 (L) and 44 (R) in paralectotype, 24 (L) and 35 (R) in NSMT-Pc 4481, 45 (L) and 50 (R) in NSMT-Pc 4482; up to 140 transverse vessels; secondary papillae distinct, but lacking intermediate papillae. Up to 12 stigmata per mesh in larger specimens, 3–4 stigmata in smaller specimens. Stomach usually oval ( Fig. 2B ), rarely cylindrical ( Fig. 2G ), located at postero-dorsal corner of mantle body; internal plication obscure. Intestine almost isodiametric (except in lectotype—bottom part of second loop weakly swollen; Fig. 2B ). Visceral mass occupying posterior 75% (lectotype) to 90% of mantle body proper, usually anteriorly well beyond anterior base of atrial siphon ( Fig. 2G ) (except lectotypevisceral mass extending to midlevel of atrial siphon; Fig. 2B ). A tunic vessel issuing from mantle near stomach in lectotype ( Fig. 2B ) and paralectotype. Bottom (=distal) half of first intestinal loop bent dorsad at 90 degrees or deeper, its axis almost parallel to that of second loop (long axis) of stomach ( Fig. 2B, G ). Second loop very deep, narrow and closed, its axis passing through middle to end of proximal (pre-bent) half of ascending branch of first loop. Rectum short, with bi-lobed anus. Gonad more or less mature in bottom half of first loop, even in smallest specimen (NSMT-Pc 4482, 34.0 mm long).

Remarks. The examined specimens from the Gulf of California can all be regarded as conspecific on the basis of similarities in the tunic depression around the siphonal area with distinct siphons, the mantle musculature (excepting siphonal musculature) situated only along the entire dorsal edge and comprising dense short thick transverse fibers, and a massive visceral mass with a markedly curved first intestinal loop and deep narrow second loop (see also Table 1 ).

Figures

Fig. 1. Map showing localities of Ascidia protecta Van Name, 1945, including unconfirmed “Angel de la Guardia Island”.

Fig. 2. Ascidia protecta Van Name, 1945 from the Gulf of California. A–D, lectotype (AMNH No. 1711, 49.0mm); E, paralectotype (AMNH No. 1711, 61.7mm); F, NSMT-Pc 4481; G–H, NSMT-Pc 4482. A, tunic, right side, arrow indicates cut made during original examination; B, G, left side of mantle body, LMT and RMT indicate left and right mantle thickening, respectively (probably underlying siphonal area tunic ridge) (both omitted for G); C, H, right side of mantle body (RMT of H omitted); D, E, ciliated groove; F, tunic, left side, hydrozoan colonies over surface omitted. Scales for A–C indicate 10mm; for D–E, 1mm; F–H, 5mm.