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Morphological variability and diagnostics of two sculpins Icelus bicornis and I. spatula (Cottiformes: Cottidae) from the Arctic

The morphological variability of Icelus spatula Gilbert et Burke, 1912 and I. bicornis Reinhardt, 1840 was studied in order to clarify the diagnostic characters of these poorly studied fishes. Allometry, geographic variability and sexual dimorphism of species were evaluated by statistical methods based on 24 counts and 30 morphometric indices. Samples from 5 Arctic regions were studied: southwestern Greenland, Spitsbergen, Barents Sea, Laptev and East Siberian seas. An analysis of the variability of diagnostic characters showed that the following can be used to identify species with high certainty: 1) the shape of the urogenital papilla (males); 2) the presence/absence of spinules on the lower-posterior margin of scales of the lateral line below the pore of the canal and the degree of development of spinules on the dorsal margin of these scales; 3) the presence of scales at the base of the caudal fin; 4) presence/absence of bony granules on the skin between the lateral line and dorsal row of scales. Other characters (the number of scales in the lateral line and in rows on the body behind the base of the pectoral fin, the length of the nuchal spines) are more variable. No clinal changes in meristic characters were found over the studied areas of ranges of the two species. Greenland population of I. bicornis differs markedly from the samples from the Barents and Laptev seas, which suggests the possibility of the existence of groups of subspecies rank in these waters. An updated key for identification of juveniles, females and males of I. bicornis and I. spatula is provided.