Myrmekioderma rea ( De Laubenfels, 1934 )

Van, Rob W. M., 2017, Sponges of the Guyana Shelf, Zootaxa 1, pp. 1-225 : 56

Myrmekioderma rea ( De Laubenfels, 1934)

Figures 36 a–j

Anacanthaea rea De Laubenfels, 1934: 11 .

Epipolasis rea ; Van Soest & Stentoft 1988: 90, pl. X figs. 3–4, text-fig. 42.

Myrmekioderma rea ; Díaz et al. 1993: 303, figs. 39, 45; Castellanos et al. 2003: table 1, footnote d; Rützler et al. 2014: 72 .

Material examined. RMNH Por. 9788, 9789, Guyana, ‘Luymes’ Guyana Shelf Expedition, station 51, 7.6833°N 57.0333°W, depth 98 m, bottom calcareous sand, 30 August 1970 ; RMNH Por. 9820, Guyana, ‘Luymes’ Guyana Shelf Expedition, station 107, 7.7°N 57.5°W, depth 65 m, muddy sand bottom with shells, 5 September 1970 .

Description. The three specimens are dissimilar, Por. 9788 ( Fig. 36 a) is a broad knoll or club-shaped sponge of 8 x 3.5 x 3.5 cm. Color dark brown and surface uneven but optically smooth, overgrown with several other encrusting organisms. Por. 9789 ( Fig 36 f) and 9820 are finger-shaped fragments of maximum 6 cm high and 0.4–2 cm diameter, dark colored (probably discolored by verongid specimens in the same catch). Consistency firm.

Skeleton. The choanosomal skeleton consists of a dense confused mass of oxeas of all sizes, at the periphery of which there is a palisade of small oxeas arranged at right angles to the surface.

Spicules. ( Figs 36 b–e,g–j) Oxeas, trichodragmas.

Oxeas, in a wide range of shapes—fusiform, often curved, frequently with an abrupt curve in the middle, sharply pointed or mucronate, occasionally stylote modifications occur, the middle sized and smallest may be lightly or heavily spined—and in a wide size range, divisible in three overlapping categories, (1) largest ( Figs 36 b,b1 and Figs 36 g,g1), 664– 874 –978 x 19 – 31.3 –39 µm, (2) middle sized ( Figs 36 c and Fig. 36 h), 345– 451 –522 x 11 – 12.8 –16 µm, and (3) smallest ( Figs 36 d,d1 and Fig. 36 i, i1), 111– 276 –360 x 6 – 10.5 –14 µm.

Trichodragmas ( Fig. 36 e and Fig. 36 j), variably longer and shorter, 40–120 x 6–12 µm, individual raphides less than 1 µm in thickness.

Distribution and ecology. Guyana Shelf, Puerto Rico, Barbados, Colombia, Belize, 18–100 m depth ( Guyana Shelf 65–98 m).

Remarks. In assigning the present specimens—with hesitation—to Myrmekioderma rea we follow the redescription and discussion of the species by Díaz et al. (1993) (p. 303) and Rützler et al. (2014) (p. 72), and the refinement made by Zea in Castellanos et al. (2003) (footnote of their table 1). To demonstrate the reason for the hesitation I present the characteristic features of two of the specimens in Fig. 36 . The shapes, although different in both, are more conforming to M. rea s.l. than other Myrmekioderma species. The smaller oxeas were variably entirely smooth (RMNH Por. 9788) or heavily spined (RMNH Por. 9789 and 9820), the latter possessing both smaller and middle-sized spined oxeas. According to Díaz et al. (1993) this is not uncommon for Myrmekioderma species, as it was documented for Myrmekioderma gyroderma ( Alcolado, 1984) and the type species Myrmekioderma granulatum ( Esper, 1794) . Stylote modifications were found rather frequently in 9789 but were rare in 9788, not uncommonly reported for other Myrmekioderma species. The trichodragmas were distinctly divisible in a smaller and a larger size category in 9788, but showed a more continuous variation in 9789 and 9820; either condition has been reported for M. rea by various authors ( Díaz et al. 1993; Van Soest & Stentoft 1988). An independent support for the hypothesis that this wide variation is intraspecific is the fact that divergent samples 9788 and 9789 were obtained in the same trawl.

Two other species, Myrmekioderma gyroderma ( Alcolado, 1984) and Myrmekioderma laminatum Rützler et al. 2014 occur in the Greater Caribbean. The first occurs on shallow-water reefs and has distinct meandering surface grooves that remain visible in preserved condition, the second occurs in reef cavities, is encrusting and has overall thinner spicules.

Figures

FIGURE 36. Myrmekioderma rea (De Laubenfels, 1934), a, habitus of RMNH Por. 9788 (scale bar = 1 cm), b – e, SEM images of spicules, b, large oxea, b 1, detail of b, c, middle oxea, d, smallest oxea, d 1, enlarged image of d, e, detail of trichodragma f, habitus of RMNH Por. 9789 (scale bar = 1 cm), g, largest oxea, g 1, detail of g, h, middle oxea, i, smallest oxea, i 1, enlarged image of i, j, raphides of trichodragma.