The morphological variability of four species of the euphausiid genus Thysanoessa Brandt, 1851 from Kamchatkan waters

The morphological variability of four species of the euphausiid genus Thysanoessa from Kamchatka waters was studied. The neglecta form and 18 variants of the abdomen structure were found in Th. inermis. Th. raschii and Th. inermis exhibited four variants of eye shape; Th. longipes had three variants. In Th. longipes and Th. raschii, a tooth on the lateral edge of the carapace can be positioned closer to the middle. The most variable morphological features in Th. raschii were the location of a tooth on the carapace; in Th. longipes, the length of the second pair of thoracic legs and the position of a tooth on the carapace; in Th. inspinata, the length of the second pair of legs; in Th. inermis, the eye shape and the structure of the abdomen. A new key for the identification of euphausiids of the genus Thysanoessa that inhabit the Russian Far Eastern seas is proposed.