Sponges of the Guyana Shelf Author Van, Rob W. M. text Zootaxa 2017 1 1 225 journal article 10.5281/zenodo.272951 e2c88f4c-3ac2-45f9-95e4-99b75561a081 1175-5326 272951 6D68A019-6F63-4AA4-A8B3-92D351F1F69B Hamacantha (Vomerula) agassizi Topsent, 1920 Figures 78 a–d Hamacantha agassizi Topsent, 1920 : 11 , fig. 2a; Van Soest 1984 : 143 , fig. 56. FIGURE 78. Hamacantha (Ƒomerula) agassizi Topsent , 1920 , a, habitus of RMNH Por. 9849 (scale bar = 1 cm), b–d, SEM images of spicules, b, style, b1, details of b, c, diancistras, d, sigma, d1, detail of d. Material examined. RMNH Por. 9849, Suriname , ‘ Luymes O.C.P.S. II’ Guyana Shelf Expedition, station M97, 7.3083°N 54.1667°W , depth 130 m , bottom coarse sand, 16 April 1969 . Description. Thickly to massively encrusting soft sponge ( Fig. 78 a), growing together with other encrusting sponges, hydroids and serpulids. Size of fragmented specimen approximately 14 x 10 x 1 cm . Color in alcohol orange-brown. Surface irregularly lobulate, with detachable surface membrane spanning large subdermal spaces. Skeleton. At the surface there is a tangential reticulation of intercrossing thin megasclere tracts, 25–40 µm (3–7 spicules) in diameter, with many microscleres interspersed. The surface skeleton is carried by plumose spicule bundles, at their base wide (230–350 µm) and with many spicules included, subdividing and thinning out (100–150 µm) towards the surface. Spicules. ( Figs 78 b–d) Styles, diancistras, sigmas. Styles ( Figs 78 b,b1), straight or curved lightly, smooth, slightly fusiform, 361– 405 –438 x 6 – 7.3 –9 µm. Diancistras ( Figs 78 c), in adult condition with fimbriae (razor-surfaces) only extensive at the apices and just below the notches (keyhole-like openings), middle part of shaft rounded; in presumed immature spicules they are elongate sigma-like without clear keyholes; size of mature spicules 119– 125 –147 µm (width approximately 40 µm), size of immature spicules 108– 124 –134 µm. Sigmas ( Figs 78 d,d1), rounded, with one of the apices bird-beak shaped, 11– 12.4 –16 µm. Distribution and ecology. Guyana Shelf, Gulf of Mexico , Jamaica , 130–151 m depth. Erroneously reported from the Azores by Van Soest (1984) (p. 144). Remarks. The specimen agrees closely in shape and spiculation with previous descriptions by Topsent (1920) and Van Soest (1984) . A second Hamacantha ( Vomerula ) species occurring in the Central West Atlantic, H. (V.) tenda ( Schmidt, 1880 ) differs in possessing toxas and lacking sigmas [(cf. Topsent 1920 (p. 9), and Hajdu 2002 (p. 667)]. The sizes of the megascleres and diancistras of that species are distinctly larger than those of H. (V.) agassizi .