Stelletta vervoorti Van, 2017, sp. nov.

Stelletta vervoorti sp. nov.

Figures 48 a–h

Stelletta spec. Van Soest & Stentoft 1988: 27, fig. 11.

Material examined. Holotype RMNH Por. 9942, Guyana, ‘Luymes’ Guyana Shelf Expedition, station 63, 7.5833°N 57.0667°W, depth 71 m, sandy bottom, 31 August 1970.

Additional material. ZMA Por. 0 3835, Barbados, 0.5 mile off Holetown, 13.25°N 59.6667° W, depth 100 m, coll. P. Wagenaar Hummelinck, #1442, 19 February 1964.

Description. Semiglobular (Fig. 48 a) with hispid surface, encrusted with shells and barnacles. Size 2.5 cm in diameter, 2 cm high. Color in alcohol light beige. One specimen from French Guyana photographed by CREOCEAN—if correctly recognized—has an on deck color of brown to redbrown.

Skeleton. Strictly radiate, with dichotriaenes dominant as a palisade at the surface, as well as present subcortically, where the cladomes carry small open spaces. Oxeas and other triaene types less common.

Spicules. (Figs 48 b–h) Oxeas in two categories, dichotriaenes, plagiotriaenes, anatriaenes, oxyasters.

Oxeas 1 (Figs 48 b,b1), thin, straight, distinguished from oxeas 2 by length-thickness relationship, tending to be somewhat asymmetrical, usually broken in the slides, (n=4), 2530–3420 x 12–16 µm.

Oxeas 2 (Figs. 48 c,c1), fusiform, but with sharply tapering ends, often curved, younger forms are thin and straight, 1070– 2213 –3390 x 14– 27 –40 µm.

Dichotriaenes (Figs 48 d,d1), with end of rhabdome thinly tapering, often wispy or curved, with cladome usually incurved; rhabdome 1890– 3217 –4620 x 22– 43 –61 µm, cladome diameter 228– 275 –324 µm, primary cladi 54– 84 –113 x 18– 26 –43 µm, secondary cladi 42– 81 –102 x 12– 25 –32 µm.

Plagiotriaenes, rhabdomes straight, with thinly tapering ends, rather variable in size, but not readily divisible in larger (Figs 48 e,e1) and smaller (Figs 48 f,f1) size classes; cladome with incurved or straight conical cladi; rhabdomes (n=5), 900–2436 x 10–48 µm; cladome diameter 72– 133 –186 µm, cladi 36– 89 –114 x 10 – 21.5 –31 µm.

Anatriaenes (Figs 48 g,g1), not common, thin, straight, with cladi curved away from the shaft, variable in length and cladome diameter; rhabdomes often broken (n=3), 1200–1556 x 10–27 µm; cladome diameter 66– 102 –180 µm; cladi 31– 66 –114 x 7– 15 –30 µm. We encountered some protriaenes in both the sections and the dissociated spicule slides, but these appear foreign as they were accompanied by some sigmaspires.

Oxyasters (Figs 48 h), with spines concentrated near the apices of the rays, diameter quite variable, but ray number variation limited, so the asters are not readily divisible in distinct types; diameter 6–11.8–15 µm, ray number 7–12.

Distribution and ecology. Guyana, Barbados, sandy bottom at 71– 100 m.

Etymology. Named after Prof. Dr Wim Vervoort, 1917–2010, former director of the Rijkmuseum van Natuurlijke Historie, and distinguished marine invertebrate taxonomist (Hydrozoa, Copepoda). Vervoort was the biologist on board of the Guyana Shelf Expeditions 1966–1970, responsible for the collection of the sponges in the present collection.

Remarks. The new species shares dichotriaenes with one other Central West Atlantic Stelletta species, viz. Stelletta ruetzleri Mothes & Silva, 2002 from the Brazilian SE coast, but that species lacks anatriaenes and has a thick crust of spheroxyasters at the surface. On paper, Ancorina individua Schmidt, 1870 from ‘Antillen’ and St. Croix could be conspecific with our material if Schmidt’s remark that it possesses ‘etwa 5 Ankervarietäten’ conforms to our diversity of triaenes. There are several ‘wet’ specimens (globular and of different sizes) from one of the two localities (St. Croix) in the Copenhagen Museum (confirmed by P. Cárdenas, pers.comm.), but no (re-)description of that syntype material has so far been made. A slide made from one of the St. Croix specimens was examined by me, and it revealed that there is indeed a large diversity of triaenes, dominated by various shapes of anatriaenes, but there are no dichotriaenes shaped like the above-described. Asters in the microscopic section are small and probably of a single type, but shape (oxyasters or tylasters) is uncertain due to the thickness of the slide. Additionally, the Natural History Museum (London), has a spicule slide from the Schmidt’s collection labeled ‘ Ancorina individua “121”, BMNH 1870.5.3.53 (re-examined by me). This conforms in its spicule composition to the Copenhagen type material. Due to the absence of dichotriaenes in Ancorina individua it is not likely to belong to the same species as the above described.

The boreal North Atlantic / Arctic species Stelletta rhaphidiophora Hentschel, 1929, as redescribed by Cárdenas & Rapp (2015), has similarly shaped dichotriaenes and plagiotriaenes, and oxyaster microscleres, but it lacks anatriaenes and the oxyasters have smooth rays, unlike our new species. Likewise, the North Atlantic widespread deep-sea species Stelletta tuberosa (Topsent, 1892a) as redescribed by Cárdenas & Rapp (2015), looks superficially like our new species, but the dichotriaenes have rhabdomes and cladi more than twice as thick, and oxyasters three times as large as those of our new species.

The Guyana material appears to belong to the same species as the specimen described previously as Stelletta spec. by Van Soest & Stentoft (1988). The spicule complement is closely similar: the protriaenes mentioned by Van Soest & Stentoft are in fact plagiotriaenes with short conical cladi such as found in several regional Stelletta ’s. A further difference would seem to be the small ‘chiasters’ of 3–6 µm diameter mentioned by these authors, but subsequent reexamination of the slides of the specimens demonstrated that these are oxyasters in a size range of 3–16 µm, quite similar to the present Guyana holotype.