Asbestopluma (Asbestopluma) gracilior Schmidt 1870

Asbestopluma (Asbestopluma) gracilior (Schmidt, 1870)

Figures 81 a–f

Cometella gracilior Schmidt, 1870: 49.

Asbestopluma gracilior; Rützler et al. 2009: 299.

Material examined. RMNH Por. 9734, Guyana, ‘Luymes’ Guyana Shelf Expedition, station 101, 8.0167°N 57.4°W, depth 500 m, Agassiz trawl, muddy bottom, 4 September 1970.

Examined for comparison. BMNH Schmidt slide, 1870.5.3.97, labeled ‘ Cometella gracilior Schmidt n.g.n.sp., 66 (on backside of slide an unpublished genus name), Florida’.

Description. Stalked, thin-branched tree-like sponge (Fig. 81 a). Upper part a bilateral symmetrically branched ‘body’, with side branches curved upwards, ending in a thin ‘peak’, the lower half is a stalk that is thickest at the bottom. There is a color difference between the cream ‘body’ and the pale brown stalk. Total length 4.5 cm, stalk 2.5 cm, ‘body’ 2 cm. The ‘body’ is 3 mm in widest expansion, the stalk 1–1.5 mm.

Skeleton. The stalk and the ‘body’ axis are supported by a thick bundle of long styles, the skeleton of the side branches consists of long and shorter styles. The surface of the body axis and side branches is covered by acanthotylostrongyles/styles, echinating the axial bundles and forming a tangential ectosomal layer. Microscleres are densely covering the outsides of the ‘body’ parts.

Spicules. (Figs 81 b–f) Styles, acantho(tylo-)strongyles, sigmancistras, anisochelae.

Styles in two distinct shapes and sizes, (1) long, fusiform styles (Figs 81 b,b1), from the main axis, 777– 988 – 1140 x 22 – 24.3 –26 µm, and (2) shorter subtylostyles (Figs 81 c,c1), faintly polytylote, from the side branches, 576– 671 –729 x 12 – 14.4 –16.5 µm.

Strongyles (Fig. 81 d) or tylostrongyles, acanthose, thin, curved, 61– 99 –132 x 1.5– 1.9 –2.5 µm.

Sigmancistras (Fig. 81 e), largely resembling sigmas, but with slightly asymmetrical endings one of which is indistinctly bladed, 23– 25.4 –31 µm.

Palmate anisochelae (Figs 81 f), with characteristic Asbestopluma -shape, with upturned spur on the median lower ala, and the upper side alae leaving a slight stretch of the shaft clear, 9– 11.3 –13 µm.

Distribution and ecology. Guyana Shelf, Gulf of Mexico, 500–630 m depth.

Remarks. There is a problem with the original description and depiction of Schmidt’s (1870) Cometella gracilior: he pictures (pl. V fig. 9) a small sponge consisting of a long stalk and a small oval, seemingly smooth body (resembling Rhizaxinella clava Schmidt, 1870, see below, or perhaps Stylocordyla sp.), and with it there is a drawing of a thick style with a peculiar cut-off end. His description (p. 49) is somewhat more elaborate, as he mentions papilla-like outgrowths of the body (not visible in the drawing). The description lacks the mention of microscleres. The slide of Schmidt in the Natural History Museum (London) labeled ‘ Cometella gracilior n.g.n.sp.’ does not show a content conforming to Schmidt’s description and it is quite likely that the slide was not made from the specimen in Schmidt’s drawing (his pl. V fig. 9). As Hajdu & Vacelet (2002) (p. 637, at the bottom of the right hand column) stated, the contents of this slide are styles, subtylostrongyles, sigmancistras and anisochelae, as well as a few sections that make it clear that these conform closely to our Guyana specimen. In fact, the Guyana specimen resembles to a large extent the shape, structure and spiculation of the type of the genus Asbestopluma, A. (A.) pennatula (Schmidt, 1875). A major difference is the presence of two size categories of anisochelae in A. (A.) pennatula, but otherwise the two species are similar. Since Hajdu & Vacelet (2002) assigned the status of lectotype to BMNH slide 1870.5.3.97, I am confident that the present Guyana specimen indeed belongs to A. (A.) gracilior, despite the discrepancy with Schmidt’s drawing, and to a lesser extent his unrecognizable description. However, there is an alleged type specimen in the BMNH collection, which was obtained in an exchange with the Museum of Comparative Zoology (cf. Desqueyroux-Faúndez & Stone 1992). This specimen has been recently found in the BMNH collection (Ms Emma Sherlock in litteris), labeled ‘Alligator Reef, BMNH 1939.2. 10.45 (sp) MCZ Exchange (MCZ 8130)’. It has the shape of Schmidt’s pl. IV fig. 9, and in all probability is not an Asbestopluma, but possibly Rhizaxinella clava or Stylocordyla. Thus, it appears we have here a confusing case of either a mislabeled specimen or a mislabeled slide because the two do not match (the specimen likely to represent a Rhizaxinella or Stylocordyla, the slide an Asbestopluma). Since there is only a single specimen and a single slide, lectotype designation of BMNH 1870.5.3.97 might be contested. It is beyond the present study to settle this matter.