Phelliactis Simon 1892

Phelliactis sp.

(Fig. 2D, 6A,E-F, Table 6)

Material examined: MNRJ 9094. (one specimen), South Atlantic Ocean, Potiguar Basin, Rio Grande do Norte, Brazil, station MT 83-2 (04° 27.0256’S, 036° 25.6086’W), May 21, 2011, 1896–1931 m.

Description. Tall, cylindrical, cream-colored body, somewhat asymmetrical, 13.5 cm high by 6.5 cm width on its longest axis. A big manganese nodule was retained almost completely inside the body, forming a distinct cavity at the base with half the height of the sea anemone (Fig. 6A). The pedal disc was very damaged and mesenteries and associated structures at the aboral side printed on the rock when it was removed for further observation. Column divisible into a smooth, light pink scapulus, withdrawn due to contraction of the oral disc, and a thick, tuberculated scapus. Between 150 and 160 flat to conical tubercles, some with pointed tips, forming longitudinal and transverse rows (Fig. 6E). Oral disc large, bilobed. Approximately 140 short, thin, threadlike tentacles distributed in two marginal cycles. Deep actinopharynx, about two-thirds the length of the body. Two large siphonoglyphs, each attached to a pair of directive mesenteries. Five cycles of mesenteries at the mid-column. Mesenteries are less numerous at the oral side, where four cycles are observed near the oral disc. First and second cycles perfect, including directives, other cycles imperfect. Retractor muscles weak and diffuse (Fig. 6F). Longitudinal muscle of tentacles ectodermal. Radial muscles of the oral disc meso-ectodermal, stronger over the exocoels than over the endocoels. Mesogleal marginal sphincter, alveolar, weak, stratified in the upper portion of the column, where it forms a broader band but abruptly tapering downwards showing scattered and elongated alveoli in longitudinal rows. Acontia rare and small. No gametogenic tissue observed.

Cnidom. Spirocysts, Basitrichs, Microbasic p -mastigophores (Table 6).

Remarks. Seven species of Phelliactis are registered in the South Atlantic Ocean (data from Ocean Biogeographic Information System- https://obis.org/), but only three of them are known from Brazil: Ph. capricornis, Ph. pelophila, and Ph. robusta (present study). The correct identification of species for this genus requires caution and a minute analysis (Doumenc 1975), which was not possible with the material at hand. Nonetheless, we find it to be distinct from the other Phelliactis species found in the studied area. For example, Ph. robusta, possesses strictly six pairs of perfect mesenteries and also differs from Phelliactis sp. in coloration and thickness of the column.