Boreomysinae Holt et Tattersall, 1905

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 : 90-91

Boreomysinae Holt et Tattersall, 1905

Boreomysinae Holt & W. M. Tattersall, 1905: 130, 147;

1906: 45.— Zimmer, 1909: 45, 52, 130; 1933: 39.— Calman, 1909: 182.—Hansen, 1910: 4, 5, 9, 11, 24;

1925: 107, 110, 111; 1927: 23.—W. M. Tattersall,

1913: 869; 1939: 230; 1951: 3, 45.— Illig, 1930: 413,

557, 559.— Nouvel, 1943: 4, 6, 45, 64.—Banner, 1948: 361.—W. M. Tattersall & O. S. Tattersall, 1951: 26, 67, 126, 127.—O. S. Tattersall, 1955: 25, 66.—Birstein & Tchindonova, 1958: 279, 335.—Gordon, 1960: 304,

305, 307, 308, 311.— Ii, 1964: 15, 16.— Pillai, 1965:

1682, 1685, 1686.— Mauchline, 1980: 19, 39, fig. 5-2.— Murano & Krygier, 1985: 690.— Kathman et al., 1986: 29, 37.— Ledoyer, 1989: 67; 1990: 40; 1995: 603.—Ariani et al., 1993: 396, 401, 402.— Saltzman & Bowman, 1993: 325.— Müller, 1993: 22.—Brattegard & Meland, 1997: 77.—González et al., 2003: 1263.— Meland & Willassen, 2007: 1084, 1085, 1090, 1092, 1095–1097, 1099, 1100; Meland et al., 2015: 8, 12, 16, 18, 21.—Fukuoka, 2009: 406, 418.—Biju & Panampunnayil, 2011: 335.— San Vicente, Frutos & Sorbe, 2013: 769.— Wittmann, 2013: 392, 393, 399.— Sawamoto, 2014: 4.— Wittmann et al., 2014: 200, 202, 217, 229, 233, 235, 250, 253, 270, 272, 288, 296, 320, 321, 332, 343.— Wittmann & Ariani, 2019: 2, 5.— Wittmann, 2020: 15.— Kou et al. 2020: 3, 4, 7, 9, 12.

Boreomysidae .— Tchindonova, 1981: 26.—Staff of the Zoological Society of London, 1985: 398, 399.— Sirenko et al., 1996: 347.— Meland, 2002, webpage; 2003: 12, 13, 14.— Lowry & Stoddart, 2003: 428.— Petryashov, 1993a: 90; 2004a: 125; 2004b: 132; 2005b: 957, 963, 967, 970; 2009b: 122, 124; 2014a: 186.

Boreomysini (sic).—Birstein & Tchindonova, 1962: 62.

Type genus. Boreomysis G. O. Sars, 1869 ; by original monotypy.

Diagnosis. Pleomeres without pleural plates. Telson without spiniform setae in anterior part; with apical cleft. Appendix masculina present as bunch of setae on slight tubercle. Labrum without anterior spine; right lobe with inward-bent process. Antennal scale with smooth lateral margin, distally with non-articulated spine. Pereopod endopods rather similar, with pereopod 1 slightly stronger than others; carpus and propodus separated by oblique articulation; propodus internal articulation transverse. Oostegites, numbering seven, present on maxillipeds 2 and all six pereopods of females. Penes tubular. Female pleopods reduced to unsegmented plates. Male pleopods biramous; endopod 1 non-segmented; other endopods and all exopods multisegmented; endopods with movable preudobranchial lobe; exopod 3, and sometimes also exopod 2 with thick and short setae on distal segments. Uropodal exopod with incomplete proximal suture, its first segment with distolateral spiniform setae; endopod not subdivided. Statolith organic, rather small.

Comparison. Subfamily Boreomysinae differs from all the subfamilies of Mysidae by 1) the presence of the seven pairs of oostegites (maximum four in other subfamilies; seven pairs are also found only in the families Petalophthalmidae , Lepidomysidae [order Stygiomysida ] and order Lophogastrida ), 2) the incomplete proximal suture on the uropodal exopod (complete and distal in Siriellinae and Rhopalophthalminae , and absent in the rest of subfamilies), 3) the absence of the cercopods, but the presence of the polyspinal appendices in nauplioid (should be studied on a wider set of taxa). Differs from the most Mysidae subfamilies by 1) the rudimentary appendix masculina (similar only in some Heteromysinae ), 2) the presence of the inward-bent process on the right lobe of the labrum (similar only in some Erythropinae; this structure is also found in Lophogastridae and Gnathophausiidae of order Lophogastrida ), 3) the modification of the male pleopod exopod 3, rarely also exopod 2 (similar only in Gastrosaccinae), 4) the statolith being organic, non-crystalline (the same only in Ropalophthalminae; other subfamilies with crystalline); 5) the presence of the distolateral spiniform setae on the uropodal exopod, segment 1 (similar only in Siriellinae ).

Boreomysinae is most similar to the subfamilies Siriellinae and Rhopalophthalminae . From both subfamilies it differs by the larger number of the oostegites (seven against three), and the telson having the deep cleft (only slight concavity in some Siriellinae ). Out of these two subfamilies, Boreomysinae is more similar to Siriellinae , from which it is additionally distinguished by the absence of any spine on the labrum (present in Siriellinae ), the absence of the paradactylary setae brush on the pereopodal endopods (present in Siriellinae ), the organic vs. mineral statolith. It also differs from Rhopalophthalminae by the strong development of all pereopods (endopod of pereopod 6 reduced, with sexual dimorphism in Rhopalophthalminae ), the presence of the penes (absent in Rhopalophthalminae ), the complete absence of the pleural plates of the pleomeres (present on the male pleomere 1 in Rhopalophthalminae ), the non-segmented vs. 2-segmented uropodal endopod, the presence of the lateral spiniform setae on the uropodal exopod (absent in Rhopalophthalminae ).

Habitat and Biology. Predominantly oceanic deep-water mysids. Being exclusively marine subfamily, it cannot though be considered purely oceanic, as certain members also inhabit seas, including inland (e.g., the Marmara Sea in the Mediterranean basin). The family cannot also be considered purely deep water as well. Certain species of the subgenus Petryashovia subgen. nov. have been found exclusively in the epi- and upper mesopelagic waters. Mostly stenobathic, but some species occasionally penetrate subsurface waters. Epi-mesopelagic, bathypelagic, or benthic bathyal. Micronektonic. Macroplanktonic. Feed on phyto- and zooplankton during vertical migrations ( Mauchline, 1980).

Remarks. Considering both morphological and molecular evidence, Boreomysinae is clearly not related to Leptomysinae , which it was originally compared with. Currently it is not possible to unequivocally resolve the phylogenetic position of boreomysines. The question about their taxonomic rank, subfamily or family, also cannot be resolved by phylogenetic methods. The paraphyly of Mysidae , if boreomysids were considered a family, should not be an obstacle. The key criterion is the degree of morphological differentiation, and it is rather minor in boreomysids in comparison with other mysid subfamilies. At the current stage of our research, we know only one unique character in boreomysids (within Mysidae ) concerning the presence or absence of organs. It is the number of oostegites in the females. Considering that its state is primitive, this character does not increase the uniqueness of the group. The second character, the degree of the articulation development in the uropodal exopods, is an intermediate stage of the exopod oligomerization in mysids, making boreomysids an intermediate group. Finally, the third character, the presence of the polyspinal appendices in nauplioids, has not been studied in various groups, and its significance is still to be estimated. Hansen (1921) described the so called “dorsal organ” in three boreomysinae species, which he did not find in two inspected species of Mysinae . Taxonomic significance of this structure needs to be confirmed on a wider set of mysid taxa. Most of the species in the newly described Petryashovia subgen. nov. possess a clear additional segment on the antennal peduncle, which makes it 4-segmented. A reduced form of this segment is found in other members of the subfamily, particularly in theAustralian species of Boreomysis and Neobirsteiniamysis , studied here. The structure of the antennal peduncle must be studied in other members of the family, as well as across the order. If all above mentioned features prove to be diagnostic for boreomysines, a full family status can be reconsidered. At the current stage of our knowledge the subfamily rank for Boreomysinae is more evident.

The pereopod propodus is not divided in Neobirsteiniamysis and Boreomysis (Petryashovia) subgen. nov., but consists of two subsegments in nearly all species of Boreomysis sensu stricto. Therefore, this character is not used in the subfamily diagnosis. In the newly discovered B. (P.) urospina sp. nov., which has only one segment in the propodus, the musculus flexor dactyli starts from about the distal third of the carpus ( Fig. 9M ), unlike species with the 2-segmented propodus, where the muscle is entirely within the propodus. Consequently, the taxonomic significance of this character for the subfamily is also reconsidered. Quite a number of the boreomysine species possess rather acute rostrum and partially reduced eyes. Hence, I exclude these characters from the earlier diagnosis as well. The suture of the uropodal exopod is not always at the base of the ramus. To be precise, it is set at the proximal half of the ramus, and, as it is discovered in B. (P.) urospina sp. nov., can also be almost at the half of the ramus. The latest definition of the subfamily ( Wittmann et al., 2014) did not contain some earlier characters, like the presence of the telson cleft, the structure of the appendix masculina, labrum, pereopod carpus and propodus, the presence of the spiniform setae on the proximal segment of the uropodal exopod. A revised diagnosis is proposed here, incorporating relevant, previously used characters.

Composition. Includes two genera: Boreomysis and Neobirsteiniamysis . Both of them can be found in the Australian waters.

Figures

Figure 9. Boreomysis (Petryashovia) urospina sp. nov., holotype, male, 33 mm, AM P.106628. (A) labrum, ventral; (B) mandibular palp, posterior; (C) right mandible, ventral; (D) left mandible, ventral; (E) maxilla 1, posterior; (F) maxilla 2, anterior; (G) maxilliped 1, anterior; (H) dactylar claw of maxilliped 1; (I) medial seta of maxilliped 1 basal endite; (J) maxilliped 2, anterior; (K) medial serrated seta of maxilliped 2 dactylus; (L) medial seta of maxilliped 2 carpopropodus; (M) pereopod 1 endopod, posterior; (N) pereopod 1 carpus, anterior; (O) medial setae of pereopod 1 merus; (P) medial seta of pereopod 1 carpus; (Q) paradactylary seta of pereopod 1; (R) penis, lateral. Scales (mm): A–G, J, M, N, R = 1.0; H, I, K, L, Q = 0.25; O, P = 0.5.