Key to the Indo-West Pacific species of Aristeus

1 Body integument distinctly pubescent; lateral surface of merus of pereiopod III with subdistal movable spine....... A. virilis

-. Body integument naked; lateral surface of merus of pereiopod III without subdistal spine.............................2

2. Distance between lower end of cervical carina and branchiostegal carina nearly as long as distance between antennal and bran-

chiostegal spines; pleurobranchs of thoractic somites IV to VII greatly reduced to minute papillae without pinnules. A. alcocki -. Distance between lower end of cervical carina and branchiostegal carina about half distance between antennal and branchiostegal spines; pleurobranchs of thoractic somites IV to VII small but distinct, feather-like and with distinct branches.........3

3. Pereiopods I and II with chela more or less as long as carpus (<1.3 times in pereiopod I and <1.01 times in pereiopod II); pereiopod IV with carpus and propodus bearing less than 33 and 19 photophores, respectively; pereiopod V with carpus and dactylus bearing less than 34 and 17 photophores, respectively..................................................4

-. Pereiopods I and II with chela always longer than carpus (Ḻ 1.3 times in pereiopod I and Ḻ 1.04 times in pereiopod II); pereiopod IV with carpus and propodus bearing more than 32 and 19 photophores, respectively; pereiopod V with carpus and dactylus bearing more than 35 and 21 photophores, respectively.....................................................5

4. Pereiopod IV with carpus as long as or shorter than (Ĺ 1.00 times) merus; carpi of pereiopods I and IV with less than 10 photophores.................................................................................. A. mabahissae

-. Pereiopod IV with carpus longer than (Ḻ 1.05 times) merus; carpi of pereiopods I and IV with more than 10 photophores........................................................................................... A. semidentatus

5. Pereiopod II with fingers 1.5 times longer than palm; pereiopod III with fingers 1.35 times longer than palm; carpi of pereiopods II and III bearing 3 or more photophores, pereiopods IV and V with more than 55 photophores each on carpi and propodi.......................................................................................... A. antennatus

-. Pereiopod II with fingers less than 1.5 times as long as palm; pereiopod III with fingers less than 1.30 times as long as palm; carpi of pereiopods II and III without photophore, pereiopods IV and V with less than 40 photophores each on carpi and propodi.................................................................................. A. pallidicauda