Mysidium Dana, 1852

Wittmann, Karl J. & Wirtz, Peter, 2019, Revision of the amphiamerican genus Mysidium Dana, 1852 (Crustacea: Mysida: Mysidae), with descriptions of two new species and the establishment of two new subgenera, European Journal of Taxonomy 495, pp. 1-48 : 38-39

Key to the subgenera and species of Mysidium Dana, 1852

Anisomysini with well-developed eyes. Antennal scale lanceolate, without spines, but setose all around, with small terminal segment. Thoracopods essentially normal, endopods with 2- or three-segmented carpopropodus. All pleopods of females and pleopods 1–3, 5 of males reduced, uniramous, unsegmented. Fourth male pleopod longest, biramous with setose, unsegmented endopod and with 3- or 4-segmented exopod; subterminal and terminal segments of exopod each ending in large modified seta. Uropods with setose margins, without spines. Telson longer than broad, with entire or incised terminal margin; with spines and laminae only on distal half. Genus Mysidium Dana, 1852 (endemic in tropical to subtropical, mainly euhaline, also metahaline coastal waters of the East Pacific at 21–26° N and the West Atlantic from 32° N to 24° S, including Gulf of California, Gulf of Mexico and Caribbean) ........................................................................ 1

1. Telson linguiform to subrectangular, terminally not emarginated or at most with a rounded, shallow indentation; male pleopod 4 with four-segmented exopod .............................................................. 4

– Telson with distinct apical cleft separating two broadly rounded, apical lobes .............................. 2

2. Antennal scale not extending beyond antennular trunk .......... Mysidium iliffei Băcescu, 1991 (from entrance of a sea cave in Jamaica, 18° N; poorly known, therefore not assigned to any subgenus)

– Antennal scale extending well beyond antennular trunk; male pleopod 4 with three-segmented exopod: Orientomysidium Wittmann subgen. nov........................................................................... 3

3. Sympod of male pleopod 4 with strong endite at 2/5 sympod length from basis; both sexes with blunt laminae on terminal margins of telson and its cleft ............................................................................ .......................................................................... Mysidium (Orientomysidium) columbiae (Zimmer, 1915) comb. nov. ( Bahamas, Caribbean, southern Gulf of Mexico, coast of Brazil, 24° N to 8° S)

– Endite of sympod of male pleopod 4 reduced to indistinct projection; both sexes with acute laminae on terminal margins of telson and its cleft .......................................................................................... Mysidium (Orientomysidium) antillarum Wittmann sp. nov. ( Curaçao and Bonaire, 12–13° N)

4. Thoracic endopod 3 with two-segmented carpopropodus; subterminal segment of exopod of male pleopod 4 with bifid, modified seta ....................................... Occimysidium Wittmann subgen. nov. ( Mysidium (Occimysidium) pumae Ortiz, Hendrickx & Winfield, 2017 , Gulf of California, 23° N)

– Thoracic endopod 3 with three-segmented carpopropodus; subterminal segment of exopod of male pleopod 4 with unbranched, modified seta: subgen. Mysidium Dana, 1852 ..................................... 5

5. Telson terminally with a shallow, rounded indentation ................................. Mysidium (Mysidium) gracile ( Dana, 1852) ( Bermuda, Caribbean, Gulf of Mexico, coast of Brazil, 32° N to 24° S)

– Telson terminally not emarginated .................................................................................................. 6

6. Telson spatulate, its terminal portion triangular with rounded tip ...................................................... .......................................... Mysidium (Mysidium) triangulare Wittmann sp. nov. ( Curaçao, 12° N)

– Telson with traverse or with convex, continuously rounded terminal margin ................................. 7

7. Median segment of mandibular palp without setae on outer margin; basal segment of carpopropodus of thoracic endopod 3 measures 0.6 times total length of carpopropodus .......................................... Mysidium (Mysidium) rickettsi Harrison & Bowman, 1987 (Pacific coast of Mexico, 21–26° N)

– Median segment of mandibular palp with setae on both margins; basal segment of carpopropodus of thoracic endopod 3 is half total length of carpopropodus ................................................................ 8

8. Pleopod 1 rod-like in both sexes; unevenly rounded hump on outer face of distal segment of maxillula ............................................................................................................................................. Mysidium (Mysidium) rubroculatum Băcescu & Ortiz, 1984 (Gulf of Mexico, Cuba, 22–23° N)

– Pleopod 1 bilobate in both sexes; about evenly rounded hump on outer face of distal segment of maxillula .......................................................................................................................................... 9

9. Cornea diameter <2.5 times as long as terminal segment of antennular trunk................................... ........................................................................................................ Mysidium (Mysidium) integrum W.M. Tattersall, 1951 ( Bermuda, Bahamas, Caribbean, Gulf of Mexico, coast of Brazil, 32° N to 23° S)

– Cornea diameter> 2.5 times as long as terminal segment of antennular trunk ................. Mysidium (Mysidium) cubanense Băcescu & Ortiz, 1984 (Gulf of Mexico, Cuba, Bonaire, Curaçao, 12–23° N)