Diplastrella spirastrelloides, Van, Rob W. M., 2017

Van, Rob W. M., 2017, Sponges of the Guyana Shelf, Zootaxa 1, pp. 1-225 : 170

Diplastrella spirastrelloides sp. nov.

Figures 106 a–f

Material examined. Holotype RMNH Por. 9843, Guyana, ‘ Snellius O.C.P.S. ’ Guyana Shelf Expedition, station H57, 7.595°N 56.8767°W, depth 94 m, bottom coarse sand shells, 11 May 1966 .

Description. ( Fig. 106 a) Three fragments presumed to have originally been a single piece, thinly encrusting on sandy rubble. Thickness about 2 mm, lateral size several cm2. Surface microhispid. Color in alcohol dirty white to pale beige. Consistency soft.

Skeleton. Small groups of tylostyles erect on the substratum rising beyond a thick mass of microscleres.

Spicules. ( Figs 106 b–f) Tylostyles, diplasters.

Tylostyles, slightly fusiform, with prominent rounded tyles, in a large size range, divisible in two-three overlapping categories, (1) largest ( Figs 106 b,b1), with prominent tyles, faintly curved especially in the upper half, 528–952 x 15.5–24 µm, (2) middle-sized ( Figs 106 c,c1), 324–486 x 12 –14.5 µm, and (3) small ( Figs 106 d,d1), 267–374 x 5–12 µm, the latter tend to have slightly irregular tyles. Overall, tylostyles measure 268– 542 –952 x 5 – 15.4 –24 µm.

Diplasters with conical rays, in two shapes/size ranges, (1) large spheraster-like, slightly extended spicules ( Fig. 106 e), 31– 41.6 –48 µm, and (2) small condensed, irregular, spiraster-like spicules ( Figs 106 f), 11– 18.3 –26 µm

Distribution and ecology. Guyana Shelf, on sandy-shelly bottom at 94 m depth.

Etymology. The name refers to the smaller diplasters resembling compressed spirasters.

Remarks. The new species is very similar in spiculation to the type species of Diplastrella , Mediterranean D. bistellatus ( Schmidt, 1862) (originally Tethya bistellata ) as redescribed by Rützler (2002b) (p. 221–222). Differences are the smaller tylostyles, only up to 630 µm, and the less compact smaller spiraster-like microscleres in D. bistellatus . A second species of Diplastrella in the Central West Atlantic is D. megastellata Hechtel, 1965 . This differs strongly in having large (up to 79 µm) irregular, anthaster-like microscleres in addition to small diplasters. See for a detailed view of the spicules Rützler et al. 2014 (p. 36 fig. 14).

A further dubious species, Diplastrella ministrella , was erected by Gammill (1997), but his description is unrecognizable, contains no information on the spicules and the in situ illustration of the specimen is of low magnification lacking any details that would make it possible to recognize it. No material was apparently kept. It is possible that Gammill’s species is the same as D. spirastrelloides sp. nov., but there is no way to verify this and it seems inescapable to declare the name a nomen nudum in the sense of art.13 of the ICZN. I contemplated using the name ministrella for the present species (which would remove the unavailability of the name), because the present diplasters are indeed small compared to those of D. megastellata . However, the habitat (Bahamian reefs at shallow depth) is clearly different from soft substratum at 94 m depth off Guyana, rendering the conspecificity unlikely. Apart from the above discussed, the genus Diplastrella has four additional species, two in the Mediterranean, one in East Africa, and one in the South Pacific ( Van Soest et al. 2016). This distribution pattern appears incomplete and more species are expected to be found.

Figures

FIGURE 106. Diplastrella spirastrelloides sp. nov., a, habitus of holotype RMNH Por. 9843 (scale bar = 1 cm), b – f, SEM images of the spicules, b, large tylostyle, b 1, details of b, c, middle-sized tylostyle, c 1, details of c, d, small tylostyle, d 1, detail of d, e, large diplaster, f, small diplasters.