Hymenancora cristoboi Van, 2017, sp. nov.

Hymenancora cristoboi sp. nov.

Figures 102 a–i

Material examined. Holotype RMNH Por. 9920, 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. (Fig. 102 a) Thinly encrusting on a piece of a dead bryozoan, surface smooth but irregular. Lateral size about 1 x 1 cm, thicknes <1 mm. Color in alcohol pale orange. Consistency soft.

Skeleton. Hymedesmioid, with larger and smaller acanthostyles erect on the substratum, and scattered tornotes and abundant microscleres in the ectosomal and subectosomal regions.

Spicules. (Figs 102 b–i) Acanthostyles, tornotes, anchorate isochelae, sigmas.

Acanthostyles in a wide size range, divisible into larger partially spined (shaft smooth or sparingly spined) and smaller entirely spined categories, both provided with swollen profusedly spined heads; (1) large acanthostyles (Figs 102 b,b1) 174– 214 –237 x 12 – 14.2 –18 µm, and (2) small acanthostyles (Figs 102 c,c1), 83– 95 –106 x 7 – 8.8 –10 µm.

Tornotes (Figs 102 d), with mucronate apices, slightly dissimilar at opposite ends, either lightly spined (Fig. 102 d,d1) at one end, these forming a minority, or entirely smooth (Figs 102 d2,d3), forming the majority, size 156– 177 –201 x 3 – 3.6 –5 µm.

Anchorate isochelae tridentate with incipient fimbriae at opposite ends on the shaft; there are three size categories, the larger and middle-sized chelae (Figs 102 e–f) shaped similarly, the smallest (G= Fig. 102 g) more elongate; (1) largest chelae (Fig. 102 e), occasionally with four alae instead of three, caused by a split in the innermost ala, 36– 49.2 –54 µm, (2) middle-sized chelae (Fig. 102 f), 19– 22.2 –24 µm, and (3) small chelae (Fig. 102 g) almost overlapping in size with the middle-sized chelae but recognizable by shape, 12– 13.6 –18 µm.

Sigmas, symmetrical, with incurved apices, in a large size range, but divisible in at least two size categories (the smaller possibly further divisible), (1) larger (Fig. 102 h), 69– 81.3 –97 µm, and (2) smaller (Fig. 102 i), 18– 41.4 –54 µm.

Distribution and ecology. Guyana Shelf, sandy bottom at 130 m depth.

Etymology. Named after Dr Javier Cristobo (Instituto Español de Oceanografia, Gijon, Spain) to acknowledge his great efforts to unravel poecilosclerid taxonomy.

Remarks. To date no Hymenancora species have been reported from the Tropical Western Atlantic region. The genus is typically confined to colder and deeper waters. The present species appears close to the Chilean species H. tenuissima (Thiele, 1905) (as Hymedesmia). This differs from the present species in having only a single sigma category and only two chela categories the smaller of which has 5 alae, and all tornotes are heavily spined. Antarctic H. rufa (Kirkpatrick, 1907) (as Hymeraphia) is also similar but lacks sigmas entirely. The nearest record of Hymenancora is likely from Sao Paulo State at 500 m depth off SE Brazil (Hajdu & Lopes 2007, p. 355, as Myxilla (Ectyomyxilla) tenuissima), later reassigned to Hymenancora by Muricy et al. 2011, p. 164. It is possible that these records concern the present new species, but since no description of this material was presented by either Hajdu & Lopes or Muricy et al. it remains uncertain what the exact identity is. Lévi (1963) reported this same species from South Africa (as Ectyomyxilla tenuissima), but his description does not conform to Thiele’s, and this sponge is not likely to belong to Hymenancora.

I take this opportunity to discuss several homonyms involving the species name tenuissima.

Hymedesmia tenuissima Thiele, 1905 (p. 454) was transferred to Ectyomyxilla by Lévi (1963) (but see above), to Myxilla (Ectyomyxilla) by Hajdu & Lopes (2007) and subsequently to Hymenancora by Van Soest (2002c).

Myxilla tenuissima Dendy, 1905 (p. 169) was transferred to Hymedesmia by Topsent (1928) (p. 252) without comment. It is quite clear from Dendy’s description and figures of the spicules, that Topsent was right in considering Myxilla tenuissima to be a Hymedesmia. Topsent’s use of the combination Hymedesmia tenuissima (Dendy) created a secondary junior homonym of Thiele’s Hymedesmia tenuissima, but since the latter is now no longer considered congeneric with Hymedesmia, H. (H.) tenuissima (Dendy, 1905) remains valid.

The combination Myxilla tenuissima Row, 1911 (p. 345) is a junior primary homonym of Myxilla tenuissima Dendy, 1905. Even though Dendy’s species is now considered a Hymedesmia, this necessitates proposing a new name (ICZN art. 57.2). From its description, it is very likely that Row’s species is also a Hymedesmia, close to Dendy’s tenuissima, but its black color (vs. Dendy’s yellow) prevents synonymy of the two. In conclusion, I here propose Hymedesmia (Hymedesmia) rowi nom. nov. to replace Row’s Myxilla tenuissima.