Esperia helios Fristedt 1887, p. 450 – 451; pl. 25, figs 25 – 29; Lambe 1895, p. 117; pl. II, fig. 4a – c

Mycale helios: Hentschel 1929, p. 931; Koltun 1959, p. 58 – 59

Description

( Figure 2 (a)) Sponge of more or less roundish form, up to 5.5 cm in diameter. The consistency is soft and compressible, but not strong in tension. The surface is slightly shaggy, sometimes with numerous elongated (up to 2 cm in height) and flattened projections. Colour ash grey. Two specimens examined.

Skeleton

( Figure 2 (b)) The main skeleton consists of longitudinal and branching multispicular fibres, connected by single spicules crossed at right angles. All spaces in between filled by densely packed sigmas and chelae. These form a structure of rosette shapes. Surface skeleton with protuberances of spicules arranged in plumose manner.

Spicules

( Figure 2 (c – e)) Styles straight or slightly curved at basal end, rather short-pointed, dimensions: 221.7 – 372 – 448.1 ( n = 30) × 11 – 13.8 – 15.8 ( n = 20) µm; palmate anisochelaes,

dimensions: 50.2 – 55.3 – 60 ( n = 15) µm; sigmas, both c- and s-shaped, dimensions: 26.3 – 31 – 36.2 ( n = 15) µm.

Distribution

North of New Siberian islands (st. A-20, A-33), East Siberian Sea, Chukchi Sea (Pitlekai), Beaufort Sea, Behring Strait and Behring Sea, Sea of Okhotsk (northern part), Sea of Japan (the Olga gulf). Depth range 22 – 62 m.

Remarks

Mycale helios, together with some other North Pacific species mentioned in this study (e.g. Polymastia rara), is a shallow-water form whose westernmost distribution limit within the Eurasian Arctic is apparently defined by the area of the New Siberian Islands. In contrast, the eastern border of the distribution range of some North Atlantic (e.g. Mycale ( Mycale) lingua (Bowerbank 1866), stylocordyla borealis (Lovén 1868)) and Arctic (e.g. Polymastia thielei Koltun 1964, Thenea valdiviae Lendenfeld 1907, Lycopodina cupressiformis ( Carter, 1874), Geodia hentscheli Cárdenas, Rapp, Schander, Tendal 2010) species is confined to the same area.

The question of the existence of a New Siberian barrier that prevents the spread of western and eastern Arctic faunas has been intensively discussed since the middle of the twentieth century. It has been suggested that these range disjunctions are related to the environmental differences between the eastern and western Arctic during the Pleistocene glacial period (for details, see Mironov and Dilman 2008).