Molgula beringense, Sanamyan & Sanamyan, 2007

Sanamyan, Karen & Sanamyan, Nadya, 2007, Poorly known Ascidiacea collected in the vicinity of the Commander Islands and East Kamchatka, NW Pacific, Zootaxa 1579 (1), pp. 55-68 : 64-65

Molgula beringense sp.n.

( Figure 5 )

Material examined: RV Keldish, cruise 22, st. 2293, 92– 90m, 55°05.8'N, 165°53.5'E – 55°05.7'N, 165°54.2'E, 25 July 1990, five specimens. The specimens will be stored in Zoological Museum of Moscow University ( ZMMU). Holotype: ZMMU As-95.

Description. The specimens have a spherical or oval body, 8–14 mm in diameter, and are covered by thin and sparse hair-like test processes and sand grains, which are mostly attached to the body itself rather than to the hairs. A whole habitus suggests that they live unattached on a soft bottom or in sand. Apertures are close together on the upper surface of the body, siphons probably are long in life, short on contracted preserved specimens, and long on the body removed from the test. The body wall is thin and transparent. The musculature is mostly at and around the siphons and is composed of a continuous layer of circular siphonal muscles, thick, well-spaced muscle bands radiating from the siphons and ending abruptly more or less in a line not reaching middle of the body, and a wide bundle of thin parallel muscle fibers between the siphons ( Fig. 5 ). Two bands of short parallel transverse muscles detected only on some smaller specimens ( Fig 5B ) are along each side of the ventral mid line, interrupted only by the gut loop. About 12 short but much branched branchial tentacles, of which five (two lateral and one ventral) are the largest, are on a short velum. The undulating prebranchial band (characteristic for many Molgulidae ) is without dorsal indentation. The dorsal tubercle, with a small, transversely elongated slit, is close to the neural ganglion. The dorsal lamina has a smooth margin. The stigmata are long, making 0.5–1.5 coils. They form regular square rarely interrupted spirals arranged in seven longitudinal rows, the most ventral row with 12 spirals, the others with six, separated by five transverse vessels. Accessory spirals are not present. In two or three most ventral folds the spirals are almost flat, but they form more or less prominent infundibula in the folds on the dorsal half of the branchial sac. Apices of the infundibula are not subdivided. Thin intermediate transverse vessels cross each infundibulum but do not divide the stigmata. Seven well defined branchial folds have internal longitudinal vessels distributed according to a formula: (3)(6)(7)(8)(9)(10)(10)DL(9)(9)(10)(9)(9)(5)(5). Longitudinal vessels are not present between the folds. The primary gut loop is long, narrow and straight. The rectum, at a right angle to the descending limb of the gut loop, ends in a bilabiate anus with a smooth margin. Gonads are long, almost straight, bending slightly dorsally at their posterior (distal) ends. The left gonad is almost parallel to the primary gut loop, and the right one is parallel to the ventral line, just above and much longer than the small oval renal sac. Each gonad consists of a long central tubular ovary surrounded by rather large, mostly unbranched, regularly distributed testis follicles. Oviducts are of moderate length and open far from the atrial siphon. Vasa efferentia of individual male follicles join a vas deferens on the mesial surface of the ovary. The vas deferens has four to six openings on short papillae distributed evenly along its length.

Remarks. The structure of several species described from NE Pacific is not known in detail, but none of the existing descriptions exactly fits the present species.

The newly recorded specimens resemble the original description of M. apoploa (Huntsman, 1912) (correctly synonymized with M. pugetiensis Herdman, 1898 by Van Name, 1945) in the number of vasa deferentia projecting from the mesial surface of the ovary (up to six according to Huntsman, 1912a). The original description of M. pugetiensis is short and the detailed structure of gonads not known. They are described as "one ovate mass on each side" ( Herdman, 1898: 265) but the figure ( Herdman, 1898, Plate 14, Fig. 6 ) shows that the left gonad has a characteristic shape and its axis, at least at the distal (posterior) end of gonad, appears to be perpendicular to the gut loop rather than parallel to it. All specimens originally referred to M. apoploa and M. pugetiensis have only three or four internal longitudinal vessels on each fold of the branchial sac thus distinguishing them from the present species (which has up to ten).

Molgula hecateia (Huntsman, 1912) synonymized by Van Name (1945) with M. pugetiensis , might be a related species, however it is much larger, and although the detailed structure of the gonads is not recorded, the shape appears to be different, more oval, with the left gonad filling the whole secondary gut loop (Huntsman, 1912, Plate 17, Fig. 2 ) and the dorsal lamina forming "a number of large teeth or lobes" (Hutsman, 1912: 131). Although the significance of these features is not known it is unlikely that the present specimens are conspecific with M. hecateia .

Molgula pacifica (Huntsman, 1912) has, as the present species, seven branchial folds, each with up to 11 internal longitudinal vessels, but the gonads are wide, short and ovate (see Huntsman, 1912b, Plate17, Fig. 8). According to Huntsman (1912a) the structure of gonads is as in M. apoploa , but only two vasa deferentia are present. Further, unlike the present species, living unattached on soft bottom, M. pacifica is found attached to a rock on exposed shore and is not covered with attached sand.

Molgula cooperi and M. tzetlini recorded in the same region in the present work have very different gonads and the former has only six branchial folds.

Redikorzev (1941) described three species from NW Pacific, of which M. primitiva Redikorzev, 1941 has a dentate dorsal lamina, M. eobia Redikorzev, 1941 is conspecific with M. retortiformis Verrill, 1871 (K. San- amyan, type revision), and M. lapidifera Redikorzev, 1941 , from the Sea of Okhotsk, might be similar to the present species, but has extremely numerous male openings – 13 on the left gonad and 18 on the right. Nishikawa (1991: 157) compares M. lapidifera with M. siphonalis Sars, 1859 and M. xenophora: Tokioka, 1967 . However M. siphonalis is an unrelated species, with different gonads: a distinctly lobed ovary, no common sperm duct on the mesial surface of the ovary, and a distinct enlargement on the ascending limb of the intestine just before the pole of the gut loop (see Redikorzev, 1916, Fig. 16, Monniot, 1969b, Fig. 23). The constant presence of the latter feature is confirmed by examining the specimens of M. siphonalis from the White Sea. This feature and the structure of its gonads distinguish M. siphonalis from M. beringense sp.n.

Figures

FIGURE 2. Ciona gelatinosa (KBPIG 1127/1). A, body removed from the test; B, rectum and genital papilla; C, position of the specimen on the sea floor (from a photo).

FIGURE 5. Molgula beringense sp.n. A, holotype (ZMMU As-95) opened along ventral midline, branchial sac removed; B, juvenile specimen, body removed from the test.

FIGURE 6. Molgula tzetlini. A, specimen opened along ventral midline, branchial sac removed (KBPIG 1066/8); B, body removed from the test (KBPIG 725/6); C, right gonad and renal sac (KBPIG 700/3); D, gut loop and left gonad of juvenile specimen (KBPIG 723/5).