Tetilla sibirica

Tetilla sibirica (Fristedt, 1887)

(Figure 12 (a – h))

Tethya sibirica Fristedt 1887, p. 436 – 437; pl. 24, figs 22 – 28; pl. 28, fig. 17; Hentschel 1929, p. 860 – 861, 916

Tetilla sibirica: Koltun 1966, p. 61 – 63, figs 32 – 33; pl. XVII, figs 1 – 3; pl. XVIII, fig. 1

Description

(Figure 12 (a – b)). Body elongated, more or less egg shaped, up to 6 cm in height and 5 cm in diameter; provided with long root-like processes, by which the sponge is anchored to the substrate. The surface is markedly hispid, often with alternating lengthwise ridges and grooves (only occasionally may specimens with quite even surfaces be found). A few oscula of roundish form often grouped at the summit. The consistency is rather firm. Colour from beige to dark brown. Ten specimens examined.

Skeleton

Skeleton of radially spiral structure. Cortex absent.

Spicules

(Figure 12 (c – h)). Large oxea, usually with unequal ends, dimensions: 1519.9 – 4125.85 – 6860 (n = 50) × 14.25 – 39.8 – 63.6 (n = 50) µm. Small oxea, slightly fusiform, with equal ends, dimensions: 516 – 1029 – 1471 (n = 50) × 19.6 – 34.55 – 44.7 (n = 50) µm. Anatriaenes, rhabdome length: 2241 – 3617.8 – 5838 (n = 50) × 7.6 – 12.6 – 18 (n = 50) µm; cladome length: 81.9 – 197.8 – 283.5 (n = 50) µm. Sagittal protriaenes, rhabdome length: 701 – 1241 – 2648.4 (n = 50) × 2.4 – 3.6 – 5.9 (n = 50) µm; length of paired cladomes: 23 – 39.6 – 97.3 (n = 50) µm; unpaired cladome length: 58.5 – 87.3 – 178.4 (n = 50) µm. Normal protriaenes, rhabdome length: 1417.6 – 2868 – 4424.8 (n = 20) × 5 – 9.2 – 13.3 (n = 20) µm; cladome length: 45 – 86.8 – 146.2 (n = 20) µm. Sigmas sinuous, spiny, dimensions: 14 – 20.5 – 27.3 (n = 50) µm.

Distribution

The east coast of Spitsbergen. The Kara (west of Yamal Peninsula; Taimur Island, Actinia Bay) and Laptev seas (st. L-9, L-11, L-12, L-19, O-8, O-12). The New Siberian Islands (st. A- 31, A-51, A-70, A-74), Chukchi Sea. Pacific coast of the Kuril Islands. Depth range: 7 – 54 m (Arctic seas), 127 – 414 (Pacific Ocean).

Remarks

Fristedt, in his monograph (Fristedt 1887), proposed Tetilla sibirica as a new species that differed from the previously described T. polyura Schmidt, 1870 on the basis of microsclere morphology. In accordance with Fristedt, the microscleres are represented in both cases by sigmas, but were spiny in T. polyura and smooth in T. sibirica.

Although all T. sibirica specimens examined in our study were characterised by the distinctly pronounced spination of sigmas, the accuracy of identification removed any doubts, firstly because craniella polyura has an additional category of spicules, represented by raphides, and secondly because the T. polyura sigmas exceeded 13 – 14 µm only in rare exceptions, and always had a globular swelling (tyle) on the shaft.

The macrosclere composition, morphology and dimensions of the examined specimens agree well with the original description of Tetilla sibirica. Despite the fact that Fristedt insisted on the absence of spines on the sigmas in T. sibirica, he might have overlooked them. Unfortunately, the presence (or absence) of spines was disregarded by both Hentschel (1929) and Koltun (1966). Re-examination of the type material is necessary.