Tetranemertes ocelata, Cherneva & Ellison & Zattara & Norenburg & Schwartz & Junoy & Maslakova, 2023

Cherneva, Irina, Ellison, Christina I., Zattara, Eduardo E., Norenburg, Jon L., Schwartz, Megan L., Junoy, Juan & Maslakova, Svetlana A., 2023, Seven new species of Tetranemertes Chernyshev, 1992 (Monostilifera, Hoplonemertea, Nemertea) from the Caribbean Sea, western Pacific, and Arabian Sea, and revision of the genus, ZooKeys 1181, pp. 167-200 : 167

Tetranemertes ocelata sp. nov.

Fig. 8

Diagnosis.

Tetranemertes ocelata sp. nov. differs from most other species of the genus by uniformly pinkish orange body color without distinct markings. It most resembles T. pastafariensis sp. nov., from which it differs by having much larger ocelli, and more intense color (pinkish orange as opposed to pale yellow). It differs from T. paulayi sp. nov. by having larger eyes, paler body color, and colorless blood. DNA sequences also clearly differentiate this species from all other sequenced species of the genus (Table 5 ).

Material examined.

Type material in the form of histological sections is deposited with the Smithsonian Institution's National Museum of Natural History : holotype 685_061202_2 (USNM1156296), paratype 685_061202_4 (USNM 1156298). See Table 1 for additional specimens, accession numbers, and Table 2 for collecting information .

Description.

External appearance of live specimens. Body long and thin, thread-like, tangles easily, up to 12 cm long at rest, but can stretch up to 50 cm. Body width varies from 0.1 mm posteriorly to 0.7 mm in the head region. Head dorso-ventrally flattened; the rest of the body cylindrical in cross-section. Most of the time the worm remains loosely and irregularly tangled and coiled. The head contracts linearly when disturbed. Background color from very pale yellow to salmon color or deep pinkish orange (Fig. 8A ). The epidermis appears pale and translucent to transparent, the deepest color associated with the gut. Small specks of darker orange or pale brown pigment scattered throughout the epidermis, others associated with the central nervous system.

Head slightly wider than adjacent body, triangular or spear-shaped, reminiscent of the shape of a snake’s head. Anterior tip of head bluntly rounded. Head demarcated from the body by a single shallow ventro-lateral cephalic furrow, formed by a pair of cerebral organ furrows meeting mid-ventrally, and creating an anteriorly directed “V” (Fig. 8D ). Posterior cephalic furrow is lacking. Mouth and rhynchopore are combined into a single anterior ventral rhynchostomopore. The head is widest at the level of the cephalic furrow.

Ocelli are proportionally much larger than in other species of the genus, resemble those of cratenemertids and reptant polystiliferans, reddish brown in color, arranged in four rows (two on each side of head, almost directly on top of each other). Eyes of the more lateral/ventral rows are larger than the eyes in the medial/dorsal rows (Fig. 8C, D ).

Cerebral ganglia large, translucent, with specks of pinkish pigment, and very wide commissures. Cerebral organs anterior to the cerebral ganglia, visible on squeeze preparations of the head (Fig. 8C ).

Rhynchocoel and proboscis. Length of rhynchocoel unknown. Proboscis very short (a few mm long), restricted to the anterior-most part of body. Basis of central stylet long and cylindrical, variably rounded or slightly bilobed posteriorly. Shaft of central stylet straight, sculpted with weakly spiraling groves. Two accessory stylet pouches, each with two accessory stylets (Fig. 8B ).

Reproduction. Reproductive specimens collected at Carrie Bow Cay, Belize in June 2002.

Habitat.

Subtidal coral and shell rubble (with significant quantity of orange sponge) at the depth of 20-71 m depth.

Geographic distribution.

Caribbean Sea (Belize) and the Gulf of Mexico.

Etymology.

Specific epithet refers to the size of the ocelli, which are larger than in the other described species of this genus.

Figures

Figure 8. Tetranemertes ocelata sp. nov. A external appearance in life B proboscis armature showing bilobed basis and sculpted stylets C head compressed under coverslip to show number and arrangement of eyes, cerebral organs and cerebral ganglia D head in ventro-lateral view showing eyes and the cephalic furrow (arrowhead). Abbreviations: cg - cerebral ganglion, co - cerebral organ. Scale bars: 1 mm (A); 50 μm (B); 0.2 mm (C, D).