Heteromysini Norman, 1892

Daneliya, Mikhail E., 2021, On the Mysid Crustacean Genus Heteromysis (Mysidae: Heteromysinae) of the Tasman Sea, with Notes on the Tribe Heteromysini, Records of the Australian Museum (Rec. Aust. Mus.) 73 (1), pp. 1-50 : 5-6

Heteromysini Norman, 1892

Heteromysinae Norman, 1892: 148 , 158.

Heteromysini .— Wittmann, 2008: 353; 2020: 242.— Wittmann et al., 2014: 320, 340, 346.— Wittmann & Chevaldonné, 2016: 2.— Wittmann & Wirtz, 2017: 132−133, 147.— Wittmann & Griffiths, 2017: 17, 42.— Wittmann & Ariani, 2019: 5.—Wittmann & Abed- Navandi, 2019: 82; 2021: 136.— Meland et al., 2015: 7.— Ortiz & Lalana, 2017: 67.— Price et al., 2018: 2.

Diagnosis. Male process of antennula rather small, rudimentary. Pereopod 1 endopod differentiated from pereopod 2 endopod, more or less prehensile, with 2-segmented carpopropodus (3-segmented only in Platyops stenoura comb. nov., see below). All pleopods reduced to simple plates in both sexes.

Comparison. Only two rather important features separate Heteromysini from Harmelinellini Wittmann, Ariani et Lagardère, 2014 : a rudimentary nature of the male process on the antennula and of all pleopods in both sexes. In Harmelinellini , the male process is rather well-developed, and the male pleopod 3 is uniquely long and 2-segmented. From the members of the tribe Mysidetini Holt et Tattersall, 1906 , it can be distinguished by the differentiation between the pereopods 1 and 2 endopods (rather similar in Mysidetini ), among which the endopod 1 carpopropodus is 2-segmented (in all species except Platyops stenoura comb. nov. (see below), where it is 3-segmented) and stronger than endopod 2 carpopropodus, and endopod 2 carpopropodus is 3-segmented or multisegmented. In Mysidetini , both endopods are rather similar, with carpopropodus typically 3-segmented or multisegmented (similar, but 2-segment only in Corellamysis ).

Remarks. Heteromysini received separate tribal status within the subfamily Heteromysinae in the work of Wittmann (2008), with the reference to the study of Meland & Wilassen (2007), where, in fact, the former tribe Heteromysini within the subfamily Mysinae was upgraded to the subfamily level. Only in the subsequent monographic study Wittmann et al. (2014) distinguished the tribe Heteromysini from the other two tribes, Harmelinellini and Mysidetini within the subfamily Heteromysinae , and provided a diagnosis of the tribe. The nominotypical tribe Heteromysini was retained for the heteromysine genera with a very small or reduced appendix masculina, a prehensile endopod of the pereopod 1 with a 2-segmented or fused carpopropodus, normal endopods of the pereopods 2–6, two or three pairs of oostegites, large or small, mostly tubular penes, mostly with distinct terminal lobes, males of certain species with some pleopods bearing modified setae, the telson with the cleft (despite the absence of the cleft in certain Heteromysoides ) and smooth margins or distally with spiniform setae (despite the presence of spiniform setae along the entire margin in certain Heteromysis species ). The tribe contained five genera: Heteromysis , Heteromysoides , Ischiomysis , Platymysis Brattegard, 1980 and Retromysis . The only feature that was thought to distinguish Heteromysini from Mysidetini was a prehensile pereopod 1 endopod. The first issue here was the genus Heteromysoides , which contained species both with a prehensile and a non-prehensile pereopod 1 endopod. The second issue, which came simultaneously with the work of Wittmann et al. (2014), was the genus Corellamysis San Vicente et Monniot, 2014. A clear member of the subfamily Heteromysinae , Corellamysis has a unique structure of the pereopods. All the endopods are prehensile, and the first three pairs rather similar, but differentiated from other endopods ( San Vicente & Monniot, 2014). The genus could either be separated in its own tribe or incorporated into an existing one. Curiously, in a recent study, Shimomura & Fujita (2017) completely avoided the use of family-group heteromysine taxa.

There is a rather clear discrimination of Heteromysini from Harmelinellini , as discussed above in the Comparison. However, in comparing Heteromysini and Mysidetini a clear difference is seen only between marginal genera (subgenera) from these tribes, respectively, like Heteromysis (Gnathomysis) , with an extremely developed gnathopodlike pereopod 1 carpopropodus, and Mysidetes Holt et Tattersall, 1906 , with a normal, multisegmented one. Within Heteromysis , certain species have a rather weekly prehensile pereopod 1 carpopropodus, while it is clearly differentiated from other pereopods, though not so strongly, in Deltamysis from Mysidetini .

Heteromysini and Mysidetini can be distinguished by the 2-segmented pereopod 1 carpopropodus vs. 3-segmented or multisegmented. As a result, I also transfer here Bermudamysis Băcescu et Iliffe, 1986 . The only exclusion is Platyops stenoura comb. nov. (see below), with the 3-segmented carpopropodus of the pereopod 1, when the other three members of the genus Platyops , which incorporates certain former species of Heteromysoides , have the 2-segmented carpopropodus, and even prehensile, as in P. dennisi . Thus, formally Platyops would belong to Heteromysini , but the genus, indeed, is a connection between the two tribes. Still another character that can be used to distinguish Heteromysini from Mysidetini is the differentiation between the pereopod 1 and 2 endopods, which are nearly identical in Mysidetini . The importance of this character was first realized by S. I. Smith (1874), subsequently forgotten, and I recover it here.

Composition. The tribe contains six genera: Heteromysis , Bermudamysis , Ischiomysis , Platymysis , Platyops and Retromysis , among which only members of Heteromysis are found in the Tasman Sea.