Sponge fauna of the New Siberian Shoal: biodiversity and some features of formation Author Morozov, Grigori Author Sabirov, Rushan Author Zimina, Olga text Journal of Natural History 2019 2019-01-08 52 47 2961 2992 journal article 24132 10.1080/00222933.2018.1554166 bd9add32-702b-495c-9ed7-7ed98fb4c591 1464-5262 3654165 FA2EDE40-93E0-43B7-9ACF-ECCE12B0E671 Mycale ( Carmia ) helios ( Fristedt, 1887 ) ( Figure 2 (a – e)) 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. Figure 1. Map of sampling locations. Grey circles indicate stations (denoted by numbers) where sponges were present in trawls. Black dots show the stations where sponges were absent. Figure 2. Mycale helios : (a) habitus; (b) cross section; (c–e) scanning electron microscope (SEM) images of spicules; (c) style; (d) palmate anisochela; (e) sigma. 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 ).