Boreomysis (Petryashovia), 2023

Daneliya, Mikhail E., 2023, Mysid Subfamily Boreomysinae (Crustacea: Mysida: Mysidae) in the Southeast Australian Deep-sea, Records of the Australian Museum (Rec. Aust. Mus.) 75 (2), pp. 87-124 : 105

Boreomysis (Petryashovia) subgen. nov.

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Etymology. The new subgenus name (defined as feminine) is dedicated to the crustacean biologist Victor Vladimirovich Petryashov (1956–2018). He studied taxonomy and biogeography of mysids and other groups of malacostracan crustaceans, and particularly contributed to the biogeographic division of the cold and moderate waters of the World Ocean, based on the distribution of mysids.

Type species. Boreomysis megalops G. O. Sars, 1872 , by present designation.

Diagnosis. Anterior margin of carapace without distinct rostral projection, angular, apically blunt or rounded, and with rather small, barely distinguishable ventrolateral projections. Eyes with normal rounded cornea. Pereopod propodus 1-segmented.

Comparison. The subgenus Petryashovia subgen. nov. is distinguished from the subgenus Boreomysis s. str. by the absence of the distinct rostral projection on the anterior margin of the carapace and the rather reduced ventrolateral projections; and by the 1-segmented propodus, which is 2-segmented in nearly all members of the subgenus Boreomysis s. str., except B. (B.) dubia . All species of Petryashovia subgen. nov. have somewhat normally developed eyes with rounded cornea and their maxilliped 2 carpopropodus never develops any distal modifications (found in many species of Boreomysis s. str.). Additionally, all species, except B. (P.) urospina sp. nov., possess an additional segment on the antennal peduncle, which makes it clearly 4-segmented (instead of 3-segmented in Boreomysis sensu stricto). This segment in reduced to a slight prominence between segments 2 and 4 in B. (P.) urospina sp. nov., with some barely visible segment borders, like in the species of Boreomysis sensu stricto, which I was able to inspect. This character was mentioned by O. S. Tattersall (1955) for B. insolita O. S. Tattersall, 1955 , and it is the same as in the type species B. megalops . A large 3rd segment in the 4-segmented antennal peduncle was also originally described by Pillai (1973) for B. kistnae Pillai, 1973 . The significance of this structure needs to be checked in other species of the subfamily.

Distribution and habitat. The subgenus is found in both hemispheres, in the North Atlantic, Indian Ocean and South Pacific, and can probably be considered as bipolar-tropical. However, it has not been yet recorded from the Antarctic.All species have been collected at somewhat shallower localities, from epi- to mesopelagic zones, and have not been found in the bathypelagial. By this, the subgenus Petryashovia subgen. nov. is also probably ecologically distinct from Boreomysis s. str., which is reflected in the rather normal structure of the eyes, and probably also in the reduction of the dorsal and ventromedial projections of the anterior margin of the carapace, more strongly developed in the bathypelagic species of Boreomysis s. str. A question arises than for the future research, is Petryashovia subgen. nov. a primitive group or the shallow water boreomysines evolved from the deep water?

Composition. The subgenus Boreomysis (Petryashovia) subgen. nov. includes Boreomysis (Petryashovia) megalops

G. O. Sars, 1872, Boreomysis (Petryashovia) kistnae Pillai, 1973 , Boreomysis (Petryashovia) insolita O. S. Tattersall, 1955 , and Boreomysis (Petryashovia) urospina sp. nov. The latter species is recorded from the Australian seas.