Hymedesmia (Hymedesmia) bonairensis n. sp. (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) ...