Hamacantha (Vomerula) klausruetzleri Castello-Branco & Hajdu 2018, sp. nov.

Hamacantha (Vomerula) klausruetzleri sp. nov.

Fig. 3

Holotype. MNRJ 17983, Rio Grande Rise, SW Atlantic (PROERG, ERG 61‒L2, ‒ 33.5747S / ‒ 31.0970W), 1245‒ 1165 m depth, coll. R.V. ‘ Marion Dufresne’, 2011.07.15.

Diagnosis. This is the only species of Hamacantha (Vomerula) with two types of megascleres (styles and strongyles), two categories of diancistras, and two categories of sigmas.

Description. The single specimen is a thin transparent crust, 16 x 15 mm in area, and 1 mm thick (Fig. 3A). Surface smooth, with no visible oscula. Consistency very soft and fragile. Colour alive not recorded, and transparent to off white in ethanol.

Skeleton. Ectosomal skeleton comprising tangential tracts of styles and strongyles. Choanosomal skeleton cavernous with ascending tracts of megascleres ending in bouquets at the ectosome (Fig. 3B).

Spicules. Megascleres, styles and strongyles (Fig. 3C, D). Styles straight to slightly curved, smooth, and slightly fusiform with the end tapering gradually; 398‒452‒514 x 7 ‒10.2‒12 µm. Strongyles slightly curved, smooth: 291‒326.2‒349 x 10 ‒12.3‒14 µm. Microscleres two categories of diancistras and of sigmas. Diancistras I (Fig. 3E) stouter, nearly straight, without visible fimbriae, hooks each about 1/4 the total length, 175‒224.4‒262 µm. Diancistras II, cyrtancistra-like in shape, (Fig. 3F) stouter, without visible fimbriae, but terminal hooks well marked, 36‒44.2‒50 µm. Sigmas I C-shaped, with markedly curved ends, nearly orthogonal to the inner area (Fig. 3G in part and 3H), 74‒92.3‒115 µm. Sigmas II (Fig. 3I) C or S-shaped, 29‒38.5‒50 µm.

H. (V.) agassizi Topsent, 1920 340 – 416 x 8 – 10 127 – 140 Sigmas: 12 Gulf of Mexico sensu Van Soest (1984) 338 – 399 x 3 – 5 110 – 133 Sigmas: 11 – 21 Jamaica H. (V.) azorica Topsent, 1904 n.r. n.r. Raphides I: 120; Raphides II: 45 North Atlantic Ocean – Azores, Canary Islands, and Madeira / 200 – 1022 sensu Calcinai et al. (2013) 290 – 400 x 5 – 12 190 – 240 x 30 – 45 Raphides: 85 – 105 x 1.5 – 2.5; microxeas: 17.5 – 40 x 1.2 – 1.5 Strait of Sicily, Italy, Mediterranean / 539 H. (V.) bowerbanki Lundbeck, 1902 n.r. I: 160; II: 45 – 57; III: 21 – 28 Toxas: 80 – 157 North Atlantic Ocean – Greenland and Faroe Islands H. (V.) carteri Topsent, 1904 700 – 800 x 13 I: 110 – 150; II: 27 Sigmas: 20 North Atlantic Ocean – Azores, Canary Islands, and Madeira / 1165 – 1600

H. (V.) cassanoi Lehnert & Sigmas (occasionally Stone, 2016 460 – 675 x 8 – 14 145 – 212 x 14 – 22 centrotylote): 14 – 22 x 1 – Fairweather Ground, eastern Gulf of Alaska / 174 1.5 ......continued on the next page

H. (V.) megancistra Pulitzer – Finali, 1978 370 – 650 x 7 – 12; exotyles: 480 – 800 x 7 – 10 220 – 280 x 7 – 8.5 Raphides: 100 Tyrrhenian Sea, Golfo di Napoli, Mediterranean / 135

Distribution and ecology. Known only from its type locality, the Rio Grande Rise (SW Atlantic), at about 1200 m depth.

Etymology. The species is named in honour of Dr. Klaus Rüetzler, for his outstanding contribution to our knowledge of coral reef sponges and for his inspirational taxonomic studies on W Atlantic sponges.

Remarks. Hamacantha (V.) klausruetzleri sp. nov. is the only species in Hamacantha with two different types of megascleres, styles and strongyles, as well as two categories of diancistras and sigmas. From all congeners occurring in the Atlantic, the new species appears closest to H. (V.) carteri and H. (V.) esperioides for the similar possession of styles, two categories of diancistras, and sigmas. Nevertheless none of them has a second category of megascleres and of sigmas as observed in H. (V.) klausruetzleri sp. nov.