Hamacantha (Hamacantha) boomerang, Hajdu, Eduardo & Castello-Branco, Cristiana, 2014

Hajdu, Eduardo & Castello-Branco, Cristiana, 2014, Hamacantha (Hamacantha) boomerang sp. nov. from deep-sea coral mounds at Campos Basin, SW Atlantic, and redescription of H. (H.) schmidtii (Carter, 1882) (Hamacanthidae, Poecilosclerida, Demospongiae), Zootaxa 3753 (4), pp. 384-390 : 385

Hamacantha (Hamacantha) boomerang sp. nov.

Figs. 1 B–H

Holotype. MNRJ 14339, Campos Basin, Brazil (ECOPROF 6, -22,382820 – -40,122579, off Farol de São Tomé), 607 m depth, coll. CENPES/PETROBRAS, 2008.09.25.

Diagnosis. This is the only species of Hamacantha (Hamacantha) with oxeas as megascleres, three categories of diancistras, and one of toxas.

Description. The single specimen is a moderately thick crust, 21 x 10 mm in area, and 2-3 mm thick ( Fig. 1 C). Surface smooth to the eye and slightly velvety to the touch, no oscula were seen. Consistency very soft, fragile. Colour alive not recorded, off white in ethanol.

Skeleton. Ectosomal skeleton comprising a loose tangential reticulation of oxeas. The transparent ectosomal layer allows the cavernous choanosome to be seen in situ, which is traversed by abundant longitudinal tracts of megascleres whose endings support the ectosome.

Spicules. Megascleres oxeas ( Fig. 1 D), slightly fusiform, straight or slightly curved, tapering gradually, rarely styloid, 271- 462.3 -630 µm long and 7- 12.1 -18 µm thick. Diancistras occur in three clear-cut categories. Larger ones ( Fig. 1 E) stouter, nearly straight, fimbriae and notches well marked, hooks each about 1/3 of the total length, 125- 141.4 -155 µm long. Intermediate ones ( Fig. 1 F) slender, contorted, slightly bent, fimbriae nearly closing the space between terminations and main shaft, notches inconspicuous, 45- 57.9 -69 µm long. Smaller ones ( Fig. 1 G, I) slender, contorted, markedly bent (boomerang-like), fimbriae nearly closing the space between hooks and main shaft, slightly more developed on the main shaft, forming wing-shaped structures slightly incised away from shaft, notches inconspicuous, 20- 23.3 -29 µm long. Toxas accolada shape, no recurved arms ( Fig. 1 H), 58– 68.6 –82 µm long.

Distribution and ecology. The species is known only from its type locality, the continental slope at Campos Basin (SE Brazil). The specimen is growing on a fragment of a dead coral, Solenosmilia variabilis Duncan, 1873 , together with an apparent new species of Stelletta .

Etymology. The specific epithet, boomerang , is used here as a noun in apposition, and conveys geometric information on the shape of the smaller category of diancistras. These are markedly bent in their central portion, as is the case of typical V-shaped Australian indigenous boomerangs.

Remarks. See below.

Figures

FIGURE 1. Collecting locality, external morphology and spicules of Hamacantha (Hamacantha) boomerang sp. nov. (holotype, MNRJ 14339). A, portion of the South American continent showing location of Campos Basin. B, collecting locality at Campos Basin. C, external morphology of the holotype (arrows) encrusting a fragment of a dead coral, Solenosmilia variabilis. D, oxeas. E, large diancistras. F, intermediate diancistras. G, smaller diancistras. H, accolada toxas. I, smaller diancistras in greater detail. Scales: B, 100 km; C, 1 cm; D, 100 µm; E – H, 20 µm; I, 5 µm.