(Figs 13 A–H)
Holotype. ZMA Por. 21065, Bonaire, Jachthaven, 12.162 °N - 68.286 °W, under rubble, 3.5 m, 30 -06- 1987, coll. R. Pennaerts & G.J. Roebers, # J.07.07- 103.
Paratype. ZMA Por. 21066, same data as the holotype, coll. G.J. Roebers # 73.
Additonal material (not belonging to the type series). Bonaire, Punt Vierkant, 12.116 °N - 68.295 °W, under rubble, 5 m, 1987, coll. G.J. Roebers, #G.02- 5.
Description. Thinly encrusting under coral rubble. Surface bumpy, provided with small areolae. Color an intense rich yellow (like egg yolk) or paler yellow; in alcohol it is greyish white. Consistency soft.
Skeleton. Acanthostyles erect on the surface, tornotes loosely arranged in the ectosome. Densely scattered sigmas in all parts of the sponge.
Spicules. Tornotes, acanthostyles in two size categories, isochelae in two size categories, sigmas in two size categories.
Tornotes (Figs 13 A–B) thin, slim, with slightly unequal endings, one mucronate, the other oxeote, 179- 192.6 - 213 x 1.5- 2.1 - 2.5 µm.
Large acanthostyles (Fig. 13 C), with blunt spines at the head, 144- 176.1 - 207 x 4 - 5.3 - 6.5 µm; small acanthostyles (Fig. 13 D), 48- 63.1 - 75 x 3 - 3.6 - 4.5 µm.
Large sigmas (Fig. 13 E), shaped normally, 35- 38.7 - 42 µm; small sigmas (Fig. 13 F), thin, shaped normally, 11- 12.8 - 14 µm.
Large arcuate isochelae (Fig. 13 G), with the shaft grooved on the outside, 17- 20.6 - 24 µm; small isochelae (Fig. 13 H), with reduced side alae attached to the shaft over their entire length, 9- 9.8 - 11 µm.
Ecology. Under stones at shallow depth, 3.5– 5 m.
Etymology. Named after the island of Bonaire, Netherlands Antilles.
Remarks. Among the species of Hymedesmia (Hymedesmia) known from Central West Atlantic waters, the new form stands out by the possession of sigmas, in two size categories. Elsewhere in the North Atlantic Ocean, approx. 15 species of Hymedesmia are known to possess sigmas, but only one species, H. ebria Alander (1937) from deep water fjord habitat (180–210 m) in northern Norway has a similar spicule complement of sharp-ending tornotes, two size classes of acanthostyles, more than one size class of chelae and two size classes of sigmas. However, the chelae of H.ebria occur in three sizes, the largest of which is clearly much larger (55–75 µm) than the largest chela in our new species. Further differences are the larger size of both sigma categories in Alander’s material (20–30 and 55–75 µm), and the larger size of both acanthostyle categories (350–425 and 125–145 µm).
Caribbean Hymedesmia (Hymedesmia) species comprise H. nummota de Laubenfels (1936) from deep water off Florida, H. jamaicensis van Soest (1984) from deep water off Jamaica, H. palmatichelifera van Soest (1984) from the Curaçao reefs, H. agariciicola van Soest (1984) from the Curaçao reefs, H. curacaoensis van Soest (1984) from the Curaçao reefs, and H. caribica Lehnert & van Soest (1986) from Jamaican deep reefs. Hymedesmia agariciicola has orange color and spicule sizes similar to that of the new species and the small chela category is similarly palmate-like, but it lacks sigmas, and the tornotes are thinner, shorter and equiended. There can be no question that the new species is conspecific with H. agariciicola as the sigmas are the dominant microsclere in the former. None of the other Caribbean species show close relationship with the new species in spicule complement and chela morphology.
To help identify species in this difficult group a key to the Central West Atlantic Hymedesmia (Hymedesmia) is presented below updating the table given in van Soest (1984: table 3, p. 84).