Euplectella sanctipauli Castello-Branco & Collins & Hajdu 2020, sp. nov.

Euplectella sanctipauli sp. nov. (Figs. 4 and 5) Type Material

Holotype. MNRJ 17630, São Paulo Ridge, Southwest Atlantic (‘Shinkai’ submersible Dive 1337—sample 5(1), Iata Piúna Expedition, 28 24 ′ 11.88 ″ S / 40 58 ′ 53.76 ″ W), 4,061 m depth, coll. E.P. Frazão, 29.IV.2013 LSID: urn:lsid:zoobank.org:act:8688B44F-7CAC-4A5B-8EBE-07400366CA9C

Only known Euplectella without sieve-plate. Principal skeleton composed by long, smooth stauractins, choanosomal hexactins and pentactins, dermalia/atrialia as hexactins with reduced sword-shaped distal ray with low proclined scales, or reduced as a tubercle (pentactins). Basalia as anchorate spicules with spined shaft and eight teeth on the head. Microscleres: fl oricomes, graphiocomes and hemioxyhexasters.

EXTERNAL MORPHOLOGY. The sponge consists of a delicate, thin-walled tube (Fig. 4) bearing a conspicuous surface reticulation, with dispersed oscula up to 4 mm in diameter, and basalia in a single tuft. Holotype (only specimen available), 137 mm long (including 34 mm long basalia/prostalia), 32 mm in maximum diameter.

SKELETON AND SPICULES (Figs. 4 and 5). Principalia mostly stauractins with rays 2.4–5.9 mm long, 12–17 µm in diameter (n = 4), and elongated or rounded ends.

Choanosomal spicules long, smooth hexactins (1.1–5.1 mm long rays (n = 10), elongated or rounded ends) and pentactins (3.8 – 7.6 mm long rays (n = 5), rounded ends). Dermalia and atrialia hexactins with a reduced and sword-shaped distal ray with low proclined scales (0.2–0.3 mm long), and tangential rays with elongated and rounded ends (0.3–0.4 mm long); pentactins with distal ray reduced as a tubercle, and smooth tangential rays (1.9–2.1 mm long; n = 2). Basalia composed of anchorate spicules with spiny shafts, and anchors with eight teeth. The largest spicule (broken) was 8.5 mm long. Microscleres are fl oricomes, graphiocomes and hemioxyhexasters. Floricomes with spined rays, and eight teeth on secondary rays, this last in number of 10–12 in each primary ray; diameter 110–130 µm, primary rosette 10–17 µm diameter. Graphiocomes observed with secondary rays always broken (68–85 µm long), primary rosette 10–14 µm diameter. Hemioxyhexasters (95–118 µm in diameter, n = 4) with two or three unbranched rays (45–50 µm in diameter); branched rays divide 7–10 µm from the origin and have secondary rays of length 10–20 µm (n = 4). (Fig. 5F).

DISTRIBUTION AND ECOLOGY. Known only from its type locality, São Paulo Ridge (Southwest Atlantic; 4,061 m depth). The single specimen was collected from soft sediment, apparently the sole megafauna in several meters of terrain, and seemingly devoid of any macro-epibionts.

ETYMOLOGY. The speci fi c epithet is used as a noun in apposition, derived from the species having been found at the São Paulo Ridge (deep SW Atlantic).

Euplectella comprises 18 species around the world (Reiswig & Kelly, 2018), classi fi ed by Tabachnick & Collins (2008) into four main groups recognizable on the basis of the architecture of their principal skeleton: (1) mainly stauractins, (2) mainly hexactins with a reduced proximal ray and some stauractins, (3) pentactins and some hexactins and (4) stauractins, hexactins, hexactins with reduced proximal ray, hexactins with two reduced rays, tauactins and diactins. Euplectella sanctipauli sp. nov. should be included in the fi rst group, in addition to E. aspergillum Owen (1841), E. curvistellata Ijima (1901), E. gibbsa Tabachnick & Collins (2008), E. marshalli Ijima (1895), E. oweni Herklots & Marshall (1868), E. paratetractina Tabachnick, Janussen & Menschenina (2008) and E. simplex Schulze (1896). The present species appears most similar to E. aspergillum, E. gibbsa and E. simplex, but differs from all of them by its possession of anchorate basalia with eight teeth, choanosomal hexactins and pentactins, and dermalia and atrialia including hexactins with a reduced and sword-shaped distal ray, as well as additional pentactins with distal ray reduced as a tubercle. In addition, E. aspergillum differs in having anchorate basalia with six teeth, and diactins; E. gibbsa differs in having anchorate basalia with four teeth, choanosomal tauactins and diactins; and E. simplex differs by its triactins and diactins. To date, this is the only Euplectella species without a sieve-plate, which clearly establishes E. sanctipauli sp. nov. as a new species.