A new species of the genus Mysidetes Holt & Tattersall, 1906 (Peracarida, Mysida, Mysidae) from western Mexico

A new species of Mysida, belonging to the genus Mysidetes Holt & W.M. Tattersall, 1906, is described from the southeastern Gulf of California in western Mexico. Mysidetes sp. nov., the 18th species of the genus, is described from a single mature female. It is close to the Atlantic, large form of Mysidetes farrani (Holt & W.M. Tattersall, 1905) from which it differs by several morphological characteristics, particularly the shape and armature of the telson, the number and arrangement of internal setae within the telson cleft, the relative proportions of the antennal peduncle segments, and the number and distribution of spines on the uropods.

The telson in the new species has a shallower cleft, approximately 1/12 of the telson length, compared to a deeper cleft, 1/5 to 1/10 of telson length, in the large form of M. farrani. In Mysidetes sp. nov. the lateral telson margins bear fewer but more robust setae that extend less than half its length vs. more slender setae in 3/5 of telson length in the large form of M. farrani. Additionally, in M. farrani the combined length of the second and third antennal peduncle articles is about 3.5 times as long as their width vs. almost 5 times as long in M. sp. nov.

In M. farrani the uropodal endopod and exopod are approximately 1.5 times and twice as long as telson, respectively, vs. twice and 2.5 times as long as telson, respectively, in M. sp. nov. These morphological characteristic differences support the recognition of a new species of the genus Mysidetes.