Phelliactis robusta Carlgren, 1928

De Melo, Yago A., Targino, Alessandra K. G. & Gomes, Paula B., 2020, New records of family Hormathiidae (Cnidaria: Actiniaria) from Brazilian coast with description of Paraphelliactis labiata n. sp., Zootaxa 4766 (4), pp. 557-574 : 567-568

Phelliactis robusta Carlgren, 1928

( Fig. 2C , 6D , Table 5)

Phelliactis robusta Carlgren 1928 ; 1942; Riemann-Zürneck 1973; Doumenc, 1975; Fautin et al. 2005.

Material examined. MNRJ 9093 (one specimen), South Atlantic Ocean, Potiguar Basin, Rio Grande do Norte, Brazil, station MT 82-2 (04° 33.1742’S, 036° 15.0847’W), May 20, 2011, 2030–2074 m. MOUFPE-CNI 867 (one specimen), South Atlantic Ocean, Potiguar Basin, Rio Grande do Norte, Brazil, station MT 82-2 (04° 33.1742’S, 036° 15.0847’W), May 20, 2011, 2030–2074 m. LC 152 (three specimens), South Atlantic Ocean, Potiguar Basin, Rio Grande do Norte, Brazil, station MT 82-2 (04° 33.1742’S, 036° 15.0847’W), May 20, 2011, 2030–2074 m.

Description. Large sea anemones, with specimens reaching 111.6 mm high and 33.7 to 59.4 mm wide. Pedal disc well developed, wrapping rocks or glass sponge threads ( Fig. 6D ). Column very thick, divided into scapus and scapulus. Scapus provided with very thick, polyhedric, sometimes flat tubercles, that form well-marked furrows where the thin cuticle can be seen. Scapulus strongly tuberculated, with tubercles irregularly arranged and decreasing in size towards the oral disc. No cinclides. Oral disc large, bilobed and asymmetrical. Tentacles large and threadlike, with mesogleal thickenings at the base, measuring approximately 11 mm in length. Tentacles nearly 130 in number, arranged in five marginal cycles. Two siphonoglyphs, each attached to a pair of directive mesenteries. Mesenteries hexamerously arranged in five cycles (6+6+12+24+48), more numerous at the base, where they are approximately 150 in number. First cycle perfect and sterile, other cycles imperfect. Gametogenic tissue from the second to fourth cycle of mesenteries. Marginal sphincter mesogleal, alveolar, positioned near the endodermal side. Retractor muscles weak and diffuse. Longitudinal musculature of tentacles ectodermal. Parietobasilar muscles poorly developed. Acontia present.

Cnidom. Spirocysts, Basitrichs, Microbasic p -mastigophores ( Table 5).

Remarks. The specimens in this study were collected at depths greater than 2000 meters, which is consistent with the bathymetry known for the species, which may reach over 2400 m depth ( Molodtsova et al. 2008). The largest individual was attached to a rock and a smaller one was attached to branches of a hexactinellid sponge ( Fig. 6D ). Several foraminifera species, as well as Diacria sp. shells and sponge spicules, were found inside the gastric cavity of these specimens.

Riemann-Zürneck (1973) was the first author to present the cnidom of the column for the species, reporting the absence of microbasic p -mastigophores, often found in other Phelliactis species. We also did not find such cnidae in the column of our specimens and the description of our samples perfectly matches those of Riemann-Zürneck (1973) and Doumenc (1975) for specimens from the North Atlantic.

Geographic distribution. Phelliactis robusta is in the Eastern North Atlantic Ocean from depths as great as 2100m ( Van Praet et al. 1990). We register the species for the first time in the South Atlantic Ocean (Potiguar Basin, RN, Brazil).

Figures

FIGURE 2. A) Paraphelliactis labiata n. sp., holotype. B) Monactis vestita on Drillia sp. empty shell. C) Phelliactis robusta. D) Phelliactis sp. Abbreviations: Mn, manganese nodule. Scale bars: A, 30 mm; B, 10 mm; C, 20 mm.

FIGURE 6. External view and histology of the sea anemones in this paper. A, E–F) A, E–F) Phelliactis sp. A) Detail of the distended base holding a manganese nodule. B–C) Monactis vestita. B) Individual with base greatly distended, evidencing the arrangement of mesenteries. C) Cross section through the midcolumn, showing the four cycles of mesenteries (represented in roman letters). D) Individual of Phelliactis robusta attached to hexactinellid sponge fibers. E) Detail of the tubercles at distal column, near the oral disc. F) Cross section at the midcolumn showing a pair of mesenteries from the second cycle and the diffuse musculature of the retractor (arrows). Abbreviations: Re, retractor muscle. Scale bars: A and D, 10 mm; B, 5 mm; C, 0.5 mm; and E, 2 mm; F, 200 μm.