Tentorium Schmidt 1870

Genus Tentorium Schmidt, 1870

Diagnosis (emended from Boury­Esnault 2002):

Sponges are columnar or globular, protected by a dense cylindrical sheath of longitudinally placed principal spicules which form a solid imperforate layer. The cortical skeleton contains bundles of smaller spicules arranged in a palisade and is limited to the upper surface of the cylinder. Ostia are present on the upper surface. The oscula are at the tops of small papillae located on the upper surface. Spicules are subtylostyles and tylostyles.

Type species: Thecophora semisuberites Schmidt, 1870 (by original designation).

Tentorium papillatum (Kirkpatrick, 1908) (Figs. 10–11)

Synonymy

Suberites caminatus var. papillatus— Kirkpatrick 1908: 20 –21, pl. XV (16), pl. XVI (11–14).

Suberites papillatus— Burton 1929: 445; 1932: 336.

Suberites caminatus— Koltun 1964 (partly): 25, pl. IV (15–18).

Tentorium caminatus— Koltun 1976 (partly): 168.

Tentorium papillatum — Topsent 1917: 36, pl. IV(2); Boury­Esnault and van Beveren, 1982: 38 –39, pl. V(17–18), figs. 8c, d, e.

Material examined

SMF 10571 (7 specimens): PS67/074­7.

Description

External morphology. Sponges are mostly hemispherical or rarely more pillar­like, detached from substrata (figs. 10A, B). Their diameter may reach 16 mm. Surface is smooth or slightly granulated. From 1 to 4 exhalant papillae and numerous small protuberances are located on the upper surface whereas the lateral surface lacks these structures. The papillae measure 2.5–8 mm in height and 1.5–2.3 mm in diameter. They are cylindrical or slightly conical, getting thinner at the summit, where oscula of 0.5–2 mm in diameter are opened. Ostia are located exclusively at the tips of the small protuberances. The colour of the papillae, protuberances and the surface between them is more or less the same pale beige to whitish. Occasionally slight sediment dust makes the surface more greyish. The cortex is hardly detachable, nearly white in colour, rather dense and resilient in consistency. The choanosome is of similar colour, less dense but not very crumbly.

Skeleton. The choanosomal skeleton is constituted by the longitudinal tracts of principal spicules (fig. 10C). These tracts, initially measuring 150–220 µm in thickness, rise from the sponge base and branch into 2– 3 thinner tracts, which enter the cortex within the protuberances and diverge into bouquets. The cortical bouquets do not penetrate the surface which is therefore smooth. The cortex, measuring 420–440 µm in thickness, consists of a single palisade of small tylostyles (fig. 10D). This palisade is more or less regular over the whole surface. Within the protuberances it is intermingled with the principal bouquets and split by ostia. The palisade also continues to the lateral cortex, where the tylostyles do not change their polarity, staying perpendicular to the upper surface and tangentially to the lateral one. Skeleton of papillae is constituted by the ascending choanosomal tracts.

Spicules. Altogether 133 spicules from 2 specimens were measured. Two size categories are well marked (fig. 11A). The number of measured spicules of each category is given below, separately for each specimen (n1, n2).

Principal spicules are styles or subtylostyles with slightly subterminal, oval tyles which are only feebly developed (fig. 11B). They are usually straight, slender and slightly fusiform. Their dimensions are: length 814­ 1068 ­1743 µm, tyle diameter 8­12.9­18 µm, proximal diameter 5­12.2­19 µm, central maximal diameter 11­17.2­22 µm (n1=30, n2=20). Small tylostyles are usually straight, rather fusiform, with well­developed terminal spherical tyles (fig. 11C). They measure: length 145­348­671 µm, tyle diameter 6­12.9­18, proximal diameter 3­8.7­14 µm, central maximal diameter 5­15.0­26 µm (n=30, n2=53).

Type locality: Antarctic: Pacific sector: to the West of Balleny Islands, 462 m.

Distribution. Antarctic near­continent sectors (Koltun 1964; Sarà et al. 1992): N 5 including the Western Ross Sea and NN 8–9 including the Weddell Sea (present study as well). Depth: 90–1080 m (Koltun 1964); ca. 1050 m in the NE Weddell Sea (present study).

SW Atlantic: South Georgia (Koltun 1964; Sarà et al. 1992).

Southern Indian Ocean: Kerguelen, 177–315 m (Boury­Esnault & van Beveren 1982).

Remarks

The classification of Tentorium papillatum has been a matter of considerable debate. In 1886 Ridley and Dendy established a new species Suberites caminatus. A year latter they erected a new species, S. microstomus Ridley & Dendy, 1887, out of one syntype of S. caminatus. Kirkpatrick (1908) established new varieties for the species of Ridley and Dendy, S. caminatus var. papillatus differing from the typical morphs by the locality of ostia exclusively on the tops of small surface raisings and S. microstomus var. stellatus differing from the typical morphs by the stellate shape of the surface ostial areas and by the thicker and denser cortical tylostyles. Topsent (1917) raised the variety papillatus to species level and placed it in Tentorium, as T. papillatum. Burton (1929) agreed with validity of this species but kept it in Suberites, as S. papillatus. Koltun (1964) synonymized S. papillatus with S. caminatus and S. microstomus and gave the name of the senior synonym, S. caminatus. Llater he transferred caminatus to Tentorium without any comments (Koltun 1976). Boury­Esnault and van Beveren (1982) advocated the validity of S. microstomus and also followed Topsent (1917), maintaining papillatus in Tentorium.

Herein, we follow Topsent and Boury­Esnault & van Beveren considering papillatum a valid species of Tentorium; its regular radial skeleton and presence of papillae do not correspond with the accepted definition of Suberites (see van Soest 2002). Furthermore, the location of exhalant papillae and ostia exclusively on the upper surface, the single­layered cortex and only two tylostyle categories are typical of Tentorium. Nevertheless, T. papillatum considerably differs from the type species, T. semisuberites, and also from the recently described T. levantinum Ilan, Gugel, Galil & Janussen, 2003 in lacking a dense, solid, lateral sheath made of principal spicules placed longitudinally. Thus, the taxonomic position of T. papillatum remains uncertain.