Nodastrella nodastrella Topsent

Nodastrella nodastrella (Topsent)

Synonymy: Rossella nodastrella (Topsent 1915: 1, Figs. 1–5; Topsent 1928: 76, Pl. III Fig. 22, Pl. IV Fig. 3).

Material examined: The holotype (MOM-INV-21666 (04 1353)) described by Topsent (1915) from the Azores, collected by S.A.S. le Prince de Monaco, off San Miguel, St. 3140, on August 18, 1911, depth 1378 m. One specimen (HBOI 7-VIII-09 -1-002, USNM 1150046, SMF 11754) from deep-water Lophelia coral reefs off Cape Canaveral, Florida, lat. 28°47.621 N, long. 79°37.430 W, depth 759 m, collected August 07, 2009 using manned submersible Johnson-Sea-Link II.

Description: The holotype is a small (probably juvenile) specimen, 3.5 cm high and 2 cm max. width with a deep central osculum. The specimen from Florida, USNM 1150046, is 24.5 cm high, the body is vase-shaped with the osculum (ca. 15 cm wide) having outward-flaring margins (Fig. 1). Whereas the dermal surface of the holotype shows a few diactine prostalia, the USNM specimen is smooth. The USNM specimen is white to greyish and is attached to a scleractinian coral (Lophelia pertusa L.); the holotype is also basiphytous and attached to the skeleton of another hexactinellid sponge, Hertwigia falcifera Schmidt (Topsent 1915).

Skeleton (Figs. 1–2, Table 1): Dermal skeleton is a web of microspined stauractins (occasionally with rudimentary tubercle of fifth ray), some tauactins with or without rudimentary fourth ray, some diactins with or without rudimentary third and fourth rays, and very rarely isolated pentactins; the web covers the paratangential rays of large, smooth (except for slightly rugose ray tips), orthotropal hypodermal pentactins. Atrial skeleton is a web of hexactins and pentactins, combined with some stauractins and rare tauactins. Choanosomalia are chiefly diactins varying in size from few mm to several cm, with rounded to pointed microspined or smooth tips, sometimes with one end swollen. The smaller diactins are commonly centrotylote; in the holotype some smaller diactins protrude as prostalia beyond the dermal surface. Further choanosomal megascleres are microspined hexactins and pentactins of variable sizes. Microscleres are calycocomes most abundant near the dermal surface, spherical discasters most abundant near the atrial surface, and oxyhexasters. We did not observe any microdiscohexasters, but they are documented in the original description, as rare stellate microdiscohexasters with 11–13 secondary rays (Topsent 1915: Fig. 5 m; the spicule shown in his Fig. 5 a is more likely a small calycocome). Calycocomes have very short primary rays bearing calyces with 7–8 microspiny secondary rays, discasters have ~10–20 microspiny secondary rays and inflated centre hiding the axial cross and entire primary rays. Oxyhexasters are of two types: 1) pappocome-like oxyhexasters, which are always holoxyhexasters, with distinct primary rays ending in conspicuous discs bearing 5–7 straight, microspiny secondary rays, and 2) (only found in the holotype; see Remarks) normal oxy- and few hemioxyhexasters with 1–3 secondary rays and very short primary rays.

Remarks: Despite the fact that Topsent (1915) did not notice, or at least did not mention, the presence of two distinct types of oxyhexasters, the pappocome-like oxyhexasters are the most prominent diagnostic character of N. nodastrella. They are holoxyhexasters with a convex, plate-like terminal of each primary ray, on which the secondary rays are attached. The 5–7 straight secondary rays radiate outwards and give the hexaster a spherical appearance, best seen in LM, as the secondary rays tend to break off during preparation and were hardly ever found in situ in SEM. We refrain here from calling these spicules pappocomes because the number of secondary rays is much smaller than in "true" pappocomes (see Tabachnick 2002a; see also Tabachnick and Reiswig 2002 for a discussion of the term). In the holotype, these oxyhexasters are combined with normal (hemi)oxyhexasters, and there seem to be transitional forms between both spicule types, whereas in the Florida specimen only the pappocome-like oxyhexasters were observed. However, because the morphological gap between the two specimens from each side of the Atlantic may be closed or confirmed by further findings we refrain from the erection of subspecies based on the scarce material presently available.