A new species of Trischizostoma collected at depths of 1392–1420 m from western Mexico is described. It represents the first record of the genus in the NE Pacific. The new species is morphologically similar to T. circulare, T. tohokuense and T. richeri. These species all share a large rostrum, expanded eyes and an entire telson. Distinctive characters of the new species include a dorsally unnotched urosomite 1, a subconical coxa 2, a subtriangular propodus of gnathopod 1, a single seta and one protuberance on the palm of gnathopod 2, the presence of 10 spine-teeth in the outer plate of maxilla 1 and of a large, 1-articulate maxilla 1 palp, and the telson with 2 minute simple setae and 2 minute projections distally.

The deep-water mysid Ceratomysis spinosa Faxon, 1893, previously known from Panama, Japan, the Sea of Okhotsk, the Bering Sea and Alaska, USA is reported for the first time off the western coast of Mexico, in the eastern Pacific. The specimens, a male of 27.5 mm in total length (TL) and five females of 28.5–34.5 mm TL, were collected between depths of 1296 and 1580 m. The telson is illustrated, showing numerous setae on the lateral margins, and longer, robust setae in the distal third and on the posterior margin.