Suberites cebriones Morozov 2019

Suberites cebriones Morozov et al. 2019

(Fig. 3a–h)

Material analyzed. Laptev Sea, MMBI trawl survey 2014, st. A-66 (77.2316N, 137.065E), depth 33 m (1 specimen; KFU-LH-2/006); st. A-24 (76.2616N, 139.0433E), depth 15 m (1 specimen; KFU-LH-2/007); st. L-19 (75.1983N, 128.4633E), depth 45 m (1 specimen; KFU-LH-2/008).

Description. Sponge has the shape of a shallow cup, up to 3.5 by 4 cm, with walls about 1.5 cm thick and the depression around 1 cm deep (Fig. 3h). Body is attached by a weak, ill-developed stalk to the substrate, usually enveloping a polychaete tube or small pebbles. Surface smooth and even. Texture firm and almost incompressible, easily cut. Oscula in young specimens are inconspicuous. In adult specimens there is a sieve pore area at the bottom of depression. Colour beige.

Spicules. Megascleres fall into three distinct categories, viz. choanosomal subtylostyles and ectosomal tylostyles, with some specimens additionally containing stocky strongyles. The latter are never very abundant, usually 10–15 spicules per microscopic slide. Thus, a careful examination is required.

Large cylindrical subtylostyles (Fig. 3a–a 1) with only barely visible basal swelling, straight or slightly curved, rather short-pointed: 334–418±46–527 × 6.9–8.6±1.3–10.5 (n = 60) µm. Small tylostyles (Fig. 3b–b 1), slightly fusiform, short-pointed: 173–273±58–458 × 5–7±1.5–9.7 (n = 50) µm. Large, stocky strongyles (Fig. 3c), occasionally tylostrongyles: 79–166±48–300 × 10.6–13±2–18 (n = 30). Microscleres are exclusively microspined, ranging in shape from microstrongyles to microstyles and microxeas (Fig. 3d–f). Dimensions: microstrongyles, 11– 18.3±5.8–36.8 (n = 80) µm; microxeas, 30–41±8.4–57 (n = 140) µm; microstyles, 16–25.2±3.8–35 (n = 30) µm.

Skeleton. Choanosomal skeleton is a confused, almost halichondroid reticulation of large subtylostyles, cemented by a dense mass of microrhabds. In the ectosome there are well-defined bouquets of tylostyles, reinforced with a thick (up to ~ 100 µm) layer of microrhabds.

Remarks. Koltun (1966) recognized two morphotypes of S. domuncula var. ficus (= S. lutkenii) from the Barents and Laptev Seas (see Koltun 1966, Pl. XXXIV, figs. 1–3). Recently Morozov et al. (2019) recognized the same two morphotypes in the Laptev Sea, which they differentiated into separate species, viz. S. montalbidus (= S. lutkenii) and S. cebriones. Apart from differences in gross morphologies (fig-shaped vs. cup-shaped forms; corrugated vs. smooth surfaces) there are skeletal characters that are useful in species identification: as opposed to S. lutkenii, microrhabds in S. cebriones are distributed throughout both ectosome and choanosome in abundance. Additionally, microxeas in S. cebriones are much more stocky: a ratio of length to width in S. cebriones on average is 30% lower, compared to that of S. lutkenii (p value <0.001).

Suberites cebriones is an eastern-Arctic species, whose geographic range limits to the west are confined to the New Siberian Shoal area at the border between Laptev and East-Siberian Seas. It’s currently unknown how far eastwards along the Siberian coasts this species can be found, yet it apparently has a close relative, S. mineri (Laubenfels 1935), from the North Pacific.