Isosecuriflustra pinniformis Vieira, Gordon, Souza & Haddad, 2010, n. sp.

Isosecuriflustra pinniformis n. sp.

(Figures 8–11, Table 4)

Material examined. Holotype. MZUSP 0 277, Brazil, project REVIZEE South SCORE, RV ‘Prof. Wladimir Besnard’, station 6661. Paratype. MZUSP 0 278, Brazil, project REVIZEE South SCORE, RV ‘Prof. Wladimir Besnard’, station 6674.

Diagnosis. Colony unilaminar, with overall shape resembling a feather; zooids rectangular to hexagonal with entirely membranous frontal surface and a D-shaped operculum; spines, avicularia and kenozooids absent; ovicells immersed in succeeding zooid and closed by operculum of the maternal autozooid, with reddish embryos.

Etymology. The epithet pinniformis alludes to the characteristic feather shape of colonies.

Description. Colony erect and flexible, lightly calcified, unilaminar, unbranched, feather-shaped, with slender proximal stem; larger colony (holotype) about 25 mm high and 4.5 mm wide; colonies attached by chitinized rhizoids in basal part of colony. Zooids more or less rectangular to hexagonal, tapering somewhat medially. Frontal surface entirely membranous; cryptocyst and gymnocyst absent; operculum D-shaped, with yellowish distal edge. No spines, avicularia or kenozooids. Ovicell hyperstomial, immersed in succeeding autozooid, closed by operculum of maternal autozooid, with reddish embryos.

n min–max mean SD Autozooid length 20 0.778–0.976 0.879 0.051 Autozooid width 20 0.222–0.358 0.287 0.038 Ovicell length 20 0.346–0.445 0.401 0.026 Ovicell width 20 0.358–0.457 0.415 0.022 Remarks. Alloeoflustra Hayward & Winston, 1994 was established for Flustra angusta Kluge, 1914 from Antarctic waters, and included two other Antarctic species, Flustra tenuis Kluge, 1914 and Flustra thysanica Moyano, 1972. The genus was characterized by the absence of spines or frontal calcification and an ovicell that is closed by the operculum of the maternal autozooid, but Hayward (1995) noted that these characters conform to Isosecuriflustra Liu & Hu, 1991 (type species Flustra tenuis Kluge, 1914), which became a senior subjective synonym. Isosecuriflustra pinniformis n. sp. resembles other species of the genus in having unilaminar colonies, no spines or frontal calcification, and the ovicell closed by the operculum, but the Brazilian species has no avicularia. The endemic Antarctic species Isosecuriflustra tenuis (Kluge, 1914) also has unilaminar colonies, but they are dichotomously branching to a few centimeters high, have slender avicularia at the bifurcation of zooid rows and along branch margins, and smaller ovicells (see Hayward 1995). Two other species with triangular avicularian mandibles were redescribed by Hayward (1995) ― Isosecuriflustra angusta (Kluge, 1914), characterized by very slender bilaminar, highly branched colonies (see Rosso 1994, fig. 2d; Hayward 1995, fig. 59C, D), and Isosecuriflustra thysanica (Moyano, 1972), with a broader bilaminar colony up to 5 cm high (see Hayward 1995, fig. 61B).

Rosso (1994) noted differences between specimens of I. tenuis collected at Terra Nova Bay and material collected by other authors (e.g. Androsova 1972a, b; López Gappa 1982). The Terra Nova Bay colonies have a pale yellow colour and grow up to 4 mm wide, while other Antarctic specimens grow as larger colonies with wider and stronger branches, pink or red in colour. Moyano (1996) introduced the name Isosecuriflustra rubefacta for a pink and broad-fronded phenotype of I. tenuis while agreeing with previous authors that the two did not otherwise differ in zooid dimensions and morphology.

Distribution. Brazil: off São Paulo state, 122–147 m (present study).