Strongylacidon unguiferum, Van, Rob W. M., 2009

Van, Rob W. M., 2009, New sciophilous sponges from the Caribbean (Porifera: Demospongiae), Zootaxa 2107, pp. 1-40 : 21-23

Strongylacidon unguiferum n. sp.

( Figs 8 A–D)

Holotype. ZMA Por. 21067, Bonaire, Red Slave, 12.034°N - 68.259°W, under rubble, 4 m, 1987, coll. H.G.J. Pennartz #242.

Paratype. ZMA Por. 21068, same data as holotype, coll. G.J. Roebers # G02-12.

Additonal material (not belonging to the type series). ZMA Por. 12397 Belize, Dangriga, Pelican Cays, Cat Cay, lagoon, mangrove root, 16-11-1996, coll. K. Smith & C. Díaz #KS 96-11.

Description. Thinly encrusting, black-grey sponge, becoming greenish in alcohol, 1–2 mm in thickness, under coral rubble. Surface smooth. The type material is fragmented and beige colored. The holotype now consists of four coral fragments with patches of the sponge not exceeding 2 x 2 mm, and the paratype consists of two similar-sized fragments. The patches are tightly adhering to the coral surface overgrowing also dead bryozoans and Homotrema , but the surface may be peeled off easily.

Skeleton. Dendritic, rather scanty, consisting of bundles of 10–20 megascleres rising individually from the substrate and dividing dichotomously without anastomosing. At the periphery, the spicule bundles fan out to carry the surface membrane without forming a separate ectosomal skeleton. Organic surface membrane carries numerous scattered microscleres.

Spicules. Strongyles and isochelae.

Strongyles ( Figs 8 A–B) straight, cylindrical, isodiametrical, with evenly rounded symmetrical apices, 204- 218.7 -258 x 2 - 3.4 -4.5 µm.

Microscleres ( Figs 8 C–D) shallow-curved unguiferate isochelae, 15- 18.3 -22 µm in length, often slightly anisochelate by having different numbers of teeth at both ends of the same spicule: variously 3 or 5, occasionally 4, short conical sharp-ending teeth. Teeth are on average up to 1/8 of the length of the entire chela. Not uncommonly, the teeth are partly or entirely reduced ( Fig. 8 D) and such spicules simulate sigma shapes, but these are obviously the same spicule type, not constituting a separate category of microscleres.

Ecology. Encrusting undersides of coral rubble in shallow reef habitats, 4 m.

Etymology. The name refers to the unguiferate isochelae.

Remarks. The species may be also represented in the mangrove habitat and if such specimens are indeed the same species, it may be quite elaborate in shape and size, e.g. the specimens recorded above from Belize mangrove roots grew around a branch of Aplysina fulva over distances of 6 x 4 and 12 x 4 cm, with a thickness of 1–3 mm. This concerns the species named Strongylacidon aff. zanzibarense in Rützler et al. (2000), found commonly on mangrove roots in Belizean mangrove habitats in the Pelican Keys. Color, spicule sizes and skeletal characteristics match closely with the sub-rubble specimens, but size and habitat differences induced us to exclude these specimens from the type series.

Strongylacidon zanzibarense Lendenfeld (1897) from the beach of Kokotoni, Zanzibar, collected from the underside of stones, where the holotype apparently encrusted a crab, is quite similar in most characteristics: encrusting, 4–5 mm thickness, grey-brown in alcohol, strongyles and unguiferate chelae. However, the strongyles of that species although overlapping, are distinctly smaller (160–260 µm) and the chelae are only 6–9 µm. The shape of the chelae is apparently slightly anisochelate in being less curved at one end than at the other, but the number of teeth unlike that of S. unguiferum n. sp. is invariably 3 at both ends. The skeleton is supported by a symbiotic alga and the spicule bundles are ensheathed in spongin. With these small but clear differences it is unlikely that Zanzibar and Caribbean specimens belong to a single amphitropical species.

Western Atlantic Strongylacidon species include S. osburnense ( George & Wilson, 1919 as Phoriospongia ), S. poriticola van Soest (1984), S. viride van Soest (1984) and S. rubrum van Soest (1984), and possibly S. bermudae (de Laubenfels, 1950 as Fibulia ).

Strongylacidon osburnense is described as a thin white (in alcohol) sponge encrusting an alcyonarian coral, not unlike S. unguiferum n. sp. in thickness (1 mm). The strongyles are similar to that of S. unguiferum n. sp. but neatly separated in size (160–180 x 2–3 µm), the unguiferate chelae appear indistinguishable in size and shape from those of S. unguiferum n. sp., but there is an added genuine category of sigmas of 12–16 µm. Moreover, the skeleton of S. osburnense is not formed by spicule bundles, but by columns of sand grains ensheathed in spongin fibers. Together these characteristics make S. osburnense clearly distinct. The species is considered a junior synonym of Desmacidon griseum Schmidt (1870) by van Soest (2002a), so the species should be named Strongylacidon griseum .

Strongylacidon poriticola is a bright red encrustation on corals, with strongyles smaller and thinner (155–190 x 2 µm) and ‘anchorate’ chelae, which are after reexamination diagnosed as arcuate, with normal alae, not unguiferate. Strongylacidon viride (green-colored) and Strongylacidon rubrum (bright red) do not have chelae, only true sigmas (verified in type specimen slides), respectively 13–18 and 20–30 µm. Both have clearly smaller strongyles (not exceeding 204 µm).

Strongylacidon bermudae is an elaborate sponge with tubes of 12 cm height, quite unlike the thin encrustation described here (cf. Rützler, 1986; it has no microscleres, only bundles of strongyles, 180–200 x 2 µm). Assignment to Strongylacidon was made by van Soest (1984) on authority of Rützler (in litteris), but on paper it conforms to Batzella rather than to Strongylacidon . Its status needs to be reevaluated.

The known species assigned to Strongylacidon in the Central West Atlantic are keyed out below along with Batzella species.

Figures

FIGURE 8. Strongylacidon unguiferum n. sp., SEM images of spicules (Holotype ZMA Por. 21067). A – B. Strongyle and details of apices. C – D. Various shapes of unguiferate reduced chelae.