Specimens of Petalophthalmus armiger Willemoes-Suhm, 1875, were collected off western Mexico during a deep-water survey. Six males and 32 females were obtained from 18 sampling localities in western Mexico. The species is redescribed in detail, including illustrations of body and appendages, and SEM photographs of the mandibles. The new material indicates that P. armiger is widely distributed in the area and more common than previously thought in the eastern Pacific. Samples indicate that P. armiger inhabits water far offshore, where total depth exceeds 1000 m. Due to the lack of discrete samplings in the water column, however, the precise depth interval where P. armiger occurs cannot be defined.
The genus Metamysidopsis W. M. Tattersall is currently represented by two species in the eastern Pacific: M. elongata (Holmes, 1910) in California, U.S.A., and M. pacifica (Zimmer, 1918) in Peru and Panama. The distribution and some morphological details of both species are presented and discussed and a new species is described from the southern Gulf of California, western Mexico. Commonly used diagnostic characters for the species of Metamysidopsis are analysed based on data available in the literature. A diagnosis is provided for the three species occurring in the eastern Pacific and a key to the 10 currently known species of the genus is provided.
The rare pelagic mysid Amblyopsoides ohlinii (W.M. Tattersall, 1951) is reported for the first time off western Mexico and represents the first record in the Pacific Ocean south of Japan and the Kurile-Kamchatka Trench. So far, this species only has been recorded from seven localities in the North Atlantic and in the North Pacific. A complete description of the only specimen available (a male), including illustrations of all appendages and SEM images of the mandibles, is provided.
Mysidopsis gemina Price, Heard & Vargas, 2019, a species of mysid shrimp recorded for Pacific Costa Rica, was collected in western Mexico on October 19th, 2022, at the entrance of the Gulf of California. This is the first record north of Costa Rica and it represents a distribution range extension to the north of approximately 13 degrees of latitude. A comparison of the diagnostic morphological features of the Costa Rican and Mexican specimens is given.
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