Sponges of the Guyana Shelf Author Van, Rob W. M. text Zootaxa 2017 1 1 225 journal article 37320 10.5281/zenodo.272951 e2c88f4c-3ac2-45f9-95e4-99b75561a081 1175-5326 272951 6D68A019-6F63-4AA4-A8B3-92D351F1F69B Clathria (Thalysias) complanata sp. nov. Figures 94 a–f Material examined. Holotype RMNH Por. 9972, Suriname , ‘ Snellius O.C.P.S. ’ Guyana Shelf Expedition, station F38, 7.23°N 56.4067°W , depth 81 m , 5 May 1966 . Description. Ramose sponge, with irregularly dividing and occasionally anastomosing flattened knotty branches. Surface smooth, no apparent oscules. Color in alcohol light brown. Size 12 cm high, branches, 5–8 mm in widest dimension, individual branches up to 8 cm long. Consistency wiry, tough. FIGURE 94. Clathria (Thalysias) complanata sp. nov. , a, habitus of holotype RMNH Por. 9972 (scale bar = 1 cm), b–f, SEM images of spicules, b, style, b1, details of b, c, large subtylostyle, c1, details of c, d, small subtylostyle, d1, details of d, e, palmate isochela, f, toxa. Skeleton. The surface skeleton consists of closely adjacent brushes of subtylostyles with densely crowded microscleres in the surface membrane. The brushes have a basal column of larger subtylostyles carrying a bouquet of smaller subtylostyles. The choanosomal skeleton of the branches consist of an irregular reticulation of knotty amber-colored spongin fibers, with sparse coring of megascleres, and without apparent echinating spicules. Main fibers, 150–200 µm in diameter, ascending in the center of the branches, secondary fibers, 40–60 µm in diameter, branch off irregularly and divide again at right angles. This system of fibers cored with megascleres is separated from the ectosomal skeleton by subdermal spaces of about 300 µm. Spicules. ( Figs 94 b–f) Styles, subtylostyles, isochelae and toxas. Styles ( Figs 94 b,b1), fusiform, straight or slightly curved, with smooth shaft, and almost exclusively smooth heads, although some were observed with faint spination; large size variability but no clear size categories, 176– 448 –602 x 8 – 13.4 –19 µm. Subtylostyles, straight, with microspined, subterminally constricted heads, divisible into (1) longer ( Figs 94 c,c1) and usually thicker, 301– 380 –498 x 3 – 6.7 –10 µm, and (2) shorter ( Figs 94 d,d1) and usually thinner, 141– 205 –258 x 3 – 4.4 –8 µm. Isochelae ( Fig. 94 e), with prominent alae and thick, sometimes slightly swollen shaft, 15– 20.4 –25 µm. Toxas ( Fig. 94 f), with open curve and slightly upturned, smooth apices, 33– 46.4 –61 µm. Distribution and ecology. Guyana Shelf, soft bottom, 81 m depth. Etymology . Complanatus (L.) = flattened, referring to the smoothly flattened condition of the branches. Remarks. The species is uniquely characterized by having smooth flattened branches and lacking echinating (acantho-)styles. No matching descriptions were encountered in the literature on Western Atlantic Clathria s.l. Keys on Caribbean species of Clathria s.l. ( Van Soest 1984 ) and of Clathria (Thalysias) (Zea et al. 2014) did not key out the present species, nor is it recognizable among the Gulf of Mexico species (re-)described by Gómez (2014) . NE Brazilian species described ( Boury-Esnault 1973 ; Vierra de Barros et al. 2013 ; Santos & Pinheiro 2014 ; Sandes & Pinheiro 2015 ) and reviewed (Sandes & Pinheiro 2015 ) also failed to provide a matching species.