Poliopogon amadou Thomson (1877)

(Figs. 2 and 3)

Examined Material

MNRJ 17629, São Paulo Ridge, Southwest Atlantic (‘Shinkai’ submersible Dive 1335— sample 6(3), Iata Piúna Expedition, 28 29 ′ 53.88 ″ S/41 39 ′ 11.88 ″ W), 3,060 m depth, coll. A. Augustin, 26.IV.2013.

DESCRIPTION. Lophophytous sponge, semi-funnel to fan-shaped body, following Schulze (1887) “leaf rolled up in a semi-funnel, with a concave gastral, and a convex external surface”. Specimen 173 mm long (including 12 mm long basalia), and 67 mm in diameter (adjacent to basalia), compressible and rough (fi g. 2). Basalia composed of broad tufts of anchoring spicules. Brown color in situ and after preservation in ethanol.

SKELETON AND SPICULES. Quadrangular framework composed of regular and pinular pentactins, where the latter have their pinular ray piercing the sponge inwards. Basalia with two-toothed smooth anchorates, 371–543 µm wide anchors; smooth monaxons with clavate distal ends (100–229 µm diameter), and sceptres with three-toothed distal ends (1,201–2,946 × 4–10 µm). Dermalia and atrialia consisting of smooth pentactins with conical ends forming quadrangular meshes (sagittal rays, 552–2,619 × 19–29 µm; tangential rays, 368–621 × 19–29 µm); pinular pentactins with pinular rays perpendicular to the plane of the quadrangular meshes (dermal—pinular ray 310–533 × 7–10 µm; tangential rays 77–126 µm; atrial – pinular ray 252–407 × 7–10 µm, tangential rays 58–97 µm). Uncinates in two size categories: macrouncinates (795–3,589 × 4–10 µm), and mesouncinates (76–192 × 1–2 µm). Microscleres include amphidiscs in three size categories: macramphidiscs with smooth shafts (116–261 µm long, umbel 38–72 × 43–77 µm height × width), mesamphidiscs (36–68 µm long, umbel 12–19 × 9–19 µm height × width), and micramphidiscs (21–36 µm long, umbel 7–14 × 7–12 µm length × width). The latter two with spined shafts. Microhexactines (diameter 81–127 µm, ray width 3–5 µm), micropentactines (diameter 74–146 µm, ray width 2–5 µm), rarely microstauractines of similar dimensions, all with spined rays (fi g. 3). Rare hexadiscs.

DISTRIBUTION AND ECOLOGY. Former records from the Azores (Thomson, 1873), and the Canary Islands (Thomson, 1877, Schulze, 1887), 2,789–4,022 m deep (Tabachnick & Menshenina, 2002). This is the fi rst fi nding of the species in the South Atlantic, where it is thus far only known from the São Paulo Ridge (SW Atlantic) (present paper), at 3,060 m depth. The single specimen collected was growing on basaltic rock with other sponges likely of the same species, albeit in very low densities. No epibiontic macro- or megafauna could be seen from the images obtained (Fig. 2).

The single specimen collected by the Iata Piuna expedition matches the original description of Thomson (1877) and redescription by Tabachnick & Menshenina (2002). The latter authors mentioned that whereas macramphidiscs are clearly separable from the smaller amphidiscs, separation of second and third categories as mesamphidiscs and micramphidiscs is not always straightforward. It is not clear to us whether Tabachnick & Menshenina (2002) were referring to every specimen as a rule, the holotype included.

Regardless, in our material the three categories were clearly separable, if not entirely on the basis of dimensions, but surely when the micromorphology of these microscleres was taken into account. The rare hexadiscs seen in our specimen had previously been reported from a single specimen from the Great Meteor Bank (29 58 ′ 51.560 4 ″ N/28 29 ′ 12.645 6 ″ W, 2,480–2,550 m depth; Tabachnick & Menshenina, 2002).