Monactis vestita ( Gravier, 1918 )

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 : 565-567

Monactis vestita ( Gravier, 1918)

( Figs. 2B , 6 B-C, Table 4)

Paractis vestita Gravier, 1918

Monactis vestita: Riemann-Zürneck 1986 ; Zamponi & Acuña 1992; White et al. 1999; Deserti et al. 2012

Material examined. MNRJ 9082 (one specimen), South Atlantic Ocean, Potiguar Basin, Rio Grande do Norte, Brazil, station Teste1000 (04° 9.3700’S, 036° 50.5998’W), April 30, 2011, 890– 900 m. MNRJ 9090 (two specimens), South Atlantic Ocean, Potiguar Basin, Rio Grande do Norte, Brazil, station MT 62 (04° 44.1888’S, 036° 24.9309’W), May 7, 2011, 425– 448 m. MOUFPE-CNI 869 (ten specimens), South Atlantic Ocean, Potiguar Basin, Rio Grande do Norte, Brazil, station Teste1000 (04° 9.3700’S, 036° 50.5998’W), April 30, 2011, 890– 900 m. MOUFPE-CNI 870 (eleven specimens), South Atlantic Ocean, Potiguar Basin, Rio Grande do Norte, Brazil, station MT 62 (04° 44.1888’S, 036° 24.9309’W), May 7, 2011, 425– 448 m. MOUFPE-CNI 871 (four specimens), South Atlantic Ocean, Potiguar Basin, Rio Grande do Norte, Brazil, station MT 84 (04° 25.8308’S, 036° 37.3678’W), May 6, 2011, 1964–2045 m. MOUFPE-CNI 872 (three specimens), South Atlantic Ocean, Potiguar Basin, Rio Grande do Norte, Brazil, station MT 72 (04° 40.1817’S, 036° 23.8647’W), May 7, 2011, 897– 908 m. MOUFPE-CNI 873 (two specimens), South Atlantic Ocean, Potiguar Basin, Rio Grande do Norte, Brazil, station MT 83 (04° 28.3642’S, 036° 24.7602’W), May 4, 2011, 1880–1950 m. LC 142 (eight specimens), South Atlantic Ocean, Potiguar Basin, Rio Grande do Norte, Brazil, station Teste1000 (04° 9.3700’S, 036° 50.5998’W), April 30, 2011, 890– 900 m. LC 143 (eleven specimens), South Atlantic Ocean, Potiguar Basin, Rio Grande do Norte, Brazil, station MT 62 (04° 44.1888’S, 036° 24.9309’W), May 7, 2011, 425– 448 m. LC 144 (eleven specimens), South Atlantic Ocean, Potiguar Basin, Rio Grande do Norte, Brazil, station MT 63 (04° 41.7490’S, 036° 31.1670’W), May 8, 2011, 375– 383 m. LC 145 (two specimens), South Atlantic Ocean, Potiguar Basin, Rio Grande do Norte, Brazil, station MT 72 (04° 40.1817’S, 036° 23.8647’W), May 7, 2011, 897– 908 m. LC 146 (four specimens), South Atlantic Ocean, Potiguar Basin, Rio Grande do Norte, Brazil, station MT 74 (04° 34.1484’S, 036° 41.6035’W), May 7, 2011, 902– 1073 m. LC 147 (one specimen), South Atlantic Ocean, Potiguar Basin, Rio Grande do Norte, Brazil, station MT 81 (04° 39.3740’S, 036° 4.6810’W), May 6, 2011, 1960–2003 m. LC 148 (two specimens), South Atlantic Ocean, Potiguar Basin, Rio Grande do Norte, Brazil, station MT 83 (04° 28.3642’S, 036° 24.7602’W), May 4, 2011, 1880–1950 m. LC 149 (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. LC 150 (two specimens), South Atlantic Ocean, Potiguar Basin, Rio Grande do Norte, Brazil, station MT 84 (04° 25.8308’S, 036° 37.3678’W), May 6, 2011, 1964– 2045 m. LC 151 (one specimen), South Atlantic Ocean, Potiguar Basin, Rio Grande do Norte, Brazil, station MT 85 (04° 21.3580’S, 036° 44.2730’W), May 4, 2011, 2025–2057 m.

Description. Column cylindrical and smooth, without any projections and not divided into regions. Body often very short and broad due to the distension of the pedal disc ( Fig. 6B ). Polyps ranging from 2 mm to 9 mm in height and exceeding 40 mm in diameter. Oral disc withdrawn, visible only in cross sections. Thirty-two tentacles, conical, not very long, tapering to a pointed tip and arranged in two regular cycles (16+16). Tentacles of the inner cycle lon- ger than those of the outer one. No cinclides. Two siphonoglyphs, each attached to a pair of directives. Mesenteries, gametogenic tissue and other inner structures perfectly visible through the thin, distended column. Mesenteries hexamerously arranged in four cycles (6 + 6 + 12 + 24) ( Fig. 6C ). Only the first cycle perfect and bearing acontia. Acontia small and rare, paler than the mesenterial filaments, lacking completely in some specimens. Specimens with only male or female gametogenic tissue. Sphincter strong, mesogleal, alveolar. Longitudinal muscle of the tentacles ectodermal. Retractor strong and diffuse. Individuals attached to octocoral branches, rocks, or mollusk shells.

Cnidom. Spirocysts, Basitrichs, Microbasic p -mastigophores ( Table 4).

Remarks. Some individuals have the column remarkably distended, especially those attached to big rocks, where the pedal disc sometimes extends beyond its borders, contracting the rest of the column considerably ( Fig. 6B ). White et al. (1999) indicated high variability of the polyp appearance corresponding to the type of substrata where it is found. In this study, the authors hypothesized that M. vestita is only associated with snails shells in the Pacific Ocean, since previous records in the Atlantic Ocean found it only attached to stones. However, the species have been collected by-catch in Uruguay associated with banks of bivalves ( Deserti et al. 2012), and we register for the first time M. vestita on Fissidentalium meridionale scaphopod shells, as well as on those of Drillia sp. (empty shells), supporting the high adaptability of this species to different benthic communities. Regarding the cnidom, we also found two types of spirocysts on tentacles (gracile and robust) similar to White et al. (1999), but unlike them we found three size classes of basitrichs in the tentacles, similar to Riemann-Zürneck (1986). We give the first comprehensive cnidom for specimens from Atlantic Ocean. M. vestita has a large bathymetric range from 200m (recorded in Argentina) to more than 5000m (in northeastern Atlantic Ocean).

Geographic distribution. Atlantic Ocean: northeastern Atlantic Ocean, Gulf of Mexico, Venezuela, Uruguay and Argentina ( Gravier 1918; Riemann-Zürneck 1986;, Zamponi & Acuña 1992; Deserti et al. 2012). Pacific Ocean: Oregon ( White et al. 1999). This study registers M. vestita for the first time in the Brazilian coast (Bacia Potiguar, RN).

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.