Gammaropsis, Lilljeborg, 1855

Paz-Ríos, Carlos E. & Pech, Daniel, 2019, Gammaropsis elvirae sp. nov., a widely distributed amphipod (Amphipoda: Photidae) in the Yucatan Shelf, with ecological comments and a key for the genus in tropical America, Zootaxa 4555 (3), pp. 359-371 : 368

Key to species (males) of Gammaropsis in tropical America

1. Lateral cephalic lobes round............................................................................. 2

- Lateral cephalic lobes acute or subacute................................................................... 4

2. Coxae 1–4 longer than broad. Gnathopod 2 propodus subequal than carpus. Pereopods 5–7 basis broadly expanded. Epimeral plates toothed. Uropod 3 peduncle subequal in length than both rami................................... G. shuterlandi

- Coxae 1–4 slightly broader than long. Gnathopod 2 propodus longer than carpus. Pereopods 5–7 basis slightly expanded. Epimeral plates rounded. Uropod 3 peduncle shorter in length than both rami......................................... 3

3. Gnathopod 2 propodus enlarged, with small convoluted processes on posterior margin. Gnathopod 2 dactylus short, less than one half in length of propodus. Gnathopod 1 carpus shorter than propodus. Inner plate of maxilla 1 with acute apex. Telson emarginated............................................................................ G. elvirae sp. nov.

- Gnathopod 2 propodus greatly enlarged, smooth on posterior margin. Gnathopod 2 dactylus long, beyond than one half in length of propodus. Gnathopod 1 carpus subequal than propodus. Inner plate of maxilla 1 with round apex. Telson entire.................................................................................................. G. dubia

4. Lateral cephalic lobes subacute. Uropods 1–2 spiniform, lacking apical robust and slender setae. Inter-ramal process on peduncle of uropod 2 present......................................................................... G. sophiae

- Lateral cephalic lobes acute. Uropods 1–2 normal, with apical robust and slender setae. Inter-ramal process on peduncle of uropod 2 absent....................................................................................... 5

5. Gnathopod 2 palm with two medial tooth........................................................... G. martesia

- Gnathopod 2 palm with or without a medial tooth............................................................ 6

6. Gnathopod 2 palm with a medial tooth. Coxa 7 unexpanded or greatly expanded.................................... 7

- Gnathopod 2 palm without a medial tooth. Coxa 7 unexpanded or slightly expanded................................. 9

7. Lateral cephalic lobes acute and distally toothed. Coxa 7 greatly expanded. Pereopods 3–5 merus lineal. Epimeral plates toothed. Urosome dorsally cusped. Telson emarginate......................................................... 8

- Lateral cephalic lobes acute, but not distally toothed. Coxa 7 unexpanded. Pereopods 3–5 merus expanded. Epimeral plates not toothed. Urosome not dorsally cusped. Telson entire................................................... G. spinosa

8. Gnathopod 2 propodus subequal than carpus in length. Gnathopod 2 palm nearly transverse, defined by a tooth. Uropod 3 rami subequal................................................................................... G. thompsoni

- Gnathopod 2 propodus longer than carpus in length. Gnathopod 2 palm oblique, not defined by a tooth. Uropod 3 inner ramus slightly longer than outer ramus................................................................... G. tonichi

9. Maxilla 1 inner plate setose. Gnathopod 1 basis produced into a posterodistal lobe, strongly setose. Gnathopod 2 palm not defined by a tooth. Coxa 7 slightly expanded...................................................... G. shoemaker

- Maxilla 1 inner plate naked. Gnathopod 1 basis lineal, unproduced and not strongly setose. Gnathopod 2 palm defined by a tooth. Coxa 7 unexpanded...................................................................... G. arawakia