Dactylocalyx pumiceus Stutchbury, 1841

Dactylocalyx pumiceus Stutchbury, 1841

( Figs. 4–5 View FIGURE 4 View FIGURE 5 , Tab II)

Material examined. MNRJ 1499 and MNRJ 3253, Almirante Saldanha seamount (off Cape São Tomé, Rio de Janeiro State, 22.376 º S – 37.659 º W), Central II cruise, station 37 c, 552m depth, coll. R.V. “Astro Garoupa”, 6 /xi/ 1997.

Diagnosis. Dactylocalyx with thick walls composed of a dense network of irregularly branching and anastomosing tubules of small calibre (0.5–1.5mm lumen), completely penetrating the body wall; deep, round or oval holes, or longitudinally oriented grooves (2­ 11mm wide) which incompletely penetrate the body wall. Microscleres are spherical discohexasters and rare onychexasters.

Description. Specimens composed of fragments, the largest one has 67 x 34mm (length x width; Fig. 4 View FIGURE 4 A). Consistency rigid and fragile. Body wall penetrated on both outer and inner surfaces by deep circular pits or longitudinally­oriented meandering grooves (2­6.2 ­ 11mm wide); all framework surface completely porous, consisting of openings of small calibre tubes with lumen 0.5­1.2 ­ 1.5mm in diameter; tubules extending throughout body wall, branching and anastomosing.

Skeleton. Dictyonal framework with beams coarsely tuberculate, 40­48.9 ­ 60 m thick, mesh sides 200­274.6 ­ 375 m ( Fig. 4 View FIGURE 4 B).

Spicules (Table II). Free megascleres: large pentactins ( Fig. 5 View FIGURE 5 A) and hexactins ( Fig. 5 View FIGURE 5 B) with proximal rays always broken off; pentactins with tangential and proximal rays smooth or microspined, cylindrical or club­shaped, and straight or sinuous; hexactins with club­shaped tangential and distal rays, and acute proximal ray, smooth or microspined and straight or sinuous. Microscleres: abundant spherical discohexasters with short primary rays bearing 4–5 straight, microspined secondary rays ( Fig. 4 View FIGURE 4 C –D); rare onychexasters with microspined secondary rays ( Fig. 4 View FIGURE 4 E –F); no oxyhexasters.

Distribution. The distribution of the species is western Atlantic, from Brazil to the Caribbean, from depths of 91 to 1966m. The southwestern Atlantic bathymetric distribution of D. pumiceus was increased from 188m (Mothes de Moraes, 1977) to 552m deep.

Remarks. The genus Dactylocalyx contains only two valid species, D. pumiceus and D. subglobosus Gray, 1867 . Similarity in body form of the two species supports the argument that D. subglobosus might be a synonym of D. pumiceus , but the respective type specimens differ in microsclere contents—two classes of discohexasters in D. subglobosus versus one in D. pumiceus (Reiswig, 1991) .

Dactylocalyx pumiceus shows a remarkable discontinuity in its geographic distribution in the western Atlantic, with a large gap (over 5500km) between southeastern Brazilian specimens described here and its previously known southern Caribbean records. Part of this gap was corroborated by trawling (421–2137m deep) made by the R.V. "Thalassa" all along Bahia State (12–18 o S) in the scope of Programme REVIZEE, which failed to find D. pumiceus in the area, in spite of collecting other basiphytose hexactinellids (to be reported upon elsewhere).

TABLE II: Spicule dimensions of Dactylocalyx pumiceus Stutchbury, 1841 . Measures are expressed in m as: smaller­ mean­largerN. Ln = Length, Wd = width, Diam = diameter.