Contributions to Zoology, 85 (3) – 2016Rob W. M. van Soest: Sponge-collecting from a drifting ice floe: the Porifera obtained in the Kara Sea by the Dutch Polar Expedition 1882-83

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Family Polymastiidae

Radiella hemisphaerica (Sars, 1872) (Fig. 7a-d)


Fig. 7. Radiella hemisphaerica (Sars, 1872), ZMA Por. 01844, a habitus (scale bar 1 cm); b-d SEM images of spicules; b longest tylostyle, b1 details of apices and middle of longest tylostyle; c intermediate subtylostyle, c1 details of apices and middle of intermediate subtylostyle; d ectosomal tylostyle.

Trichostemma hemisphaericum Sars, 1872: 63, pl. 6 figs 1-15.

Polymastia hemisphaerica; Vosmaer, 1885: 12, pl. 1 figs 20-21, pl. 2 figs 17-20, pl. 3 figs 1-5, pl. 5 figs 8-11, 16; Koltun, 1966: 78, text-fig. 51, pl. 29 figs 1-5.

Material. ZMA Por. 01844, Russia, Kara Sea, Varna Expedition, stat. 70, 71.3333°N 63.6333°E, depth 77.5 m, coll. J.M. Ruijs, field nr. 40, 20 February 1883; label text ‘Polymastia mammillaris Müller, det. E. Arnesen’; ZMA Por. 01850, Kara Sea, Varna Expedition, locality not noted on the available labels, depth between 75 and 170 m, coll. J.M. Ruijs, 1882-1883; label text ‘Bruchstück Polymastia spec.’ + illegible small label, possibly original.

Description. Discoidal, circularly-flattened, dark brown sponges (Fig. 7a), with a transparent fringe at the peripheral edge, at the upper surface covered by light brown papillae, with a single central larger oscular papilla. Ten individuals (ZMA Por. 01844) and a small fragment on a mussel (01850). Largest individual 5 cm in diameter, 1 cm in thickness, papillae number approximately 100; smallest complete individual 1 cm in diameter, with four papillae including the oscular papilla. Fringe of the larger specimens approximately 3-4 mm wide.

Skeleton. The upper surface skeleton consists of a palisade of smaller spicules, which are proper tylostyles, arranged at right angles to the surface; choanosomal skeleton consists of a subectosomal confused layer of intermediate sized spicules, and below that and also forming the lower surface are the longest spicules parallel with the undersurface and fanning out into the fringe. All these longer spicules are ‘subtylostyles’, i.e. they are stylote with a faint subterminal constriction.

Spicules. (Fig. 7b-d) Fusiform tylostyles and subtylostyles.

Longest subtylostyles (Fig. 6b, b1), possibly divisible in the choanosomal ones 1146-2100 × 16-19 µm and those forming the fringes, 2400-3600+ × 15-26 µm (upper size probably considerably longer but no unbroken spicules were observed in the preparations).

Intermediate subtylostyles (Fig. 7c, c1) 468-1520 × 11-13 µm.

Ectosomal tylostyles (Fig. 7d) 162-306 × 8-18 µm.

Remarks. The specimens conform closely to Sars’ (1872) description and figures, and at least to Vosmaer’s (1885) and Koltun’s (1966) P. hemisphaerica. Other records may need further verification.