Couplet (image if link)	Characters
1 previous	Abdomen projecting posteriorly. . . 2 Abdomen bent under thorax. . . 19
2 previous	General form shrimplike, laterally compressed. . . 3 General form not shrimplike, not laterally compressed. . . 14
3 previous	Pleura of second segment never overlapping those of first segment; first three pairs of legs chelate. . . 4 Pleura of second segment overlapping those of first segment; third pair of legs not chelate. . . 7
4 previous	Rostrum usually with ventral teeth. . . 5 Rostrum without ventral teeth. . . 6
5 previous	Petasma of male with distomesial projection long; distal fold expanded mesially to form large spined lobe; ventral costa with apex free. Thelycum of female with anteromesial corners of lateral plates extended to cover posterior process of median protuberance.. . . Penaeus brasiliensis Petasma of male with distomesial projection relatively short; distal fold not forming lobe; ventral costa with apex attached to adjacent membrane. Thelycum of female with anteromesial corners of lateral plates not extended, exposing posterior process of median protuberance.. . . Penaeus duorarum
6 previous	Telson with subterminal pair of fixed spines. . . Metapenaeopsis goodie Telson without subterminal pair of fixed spines. . . Trachypenaeus constrictus
7 previous	Carpus of second legs entire; first legs always with well-developed chelae. . . 8 Carpus of second legs usually subdivided into 2 or more joints; first pair of legs with chelae asymmetrical or sometimes obscure. . . 9
8 previous	Third maxillipeds leglike; body slender in most species. . . Periclimenaeus wilsoni Third maxillipeds broad, leaflike; body short and thick. . . Gnathophyllum modestum
9 previous	Eyestalks medium length to long, not covered by carapace; first legs not stronger than second. . . 10 Eyestalks short, usually covered by carapace; first legs stronger than second. . . 11
10 previous	Rostrum with 4 to 6 dorsal teeth, 1 of which on carapace well beyond post-orbital margin; 3 to 5 ventral teeth not restricted to rostrum tip. Dorsal antennular peduncle lacking accessory branch; stylocerite reaching just beyond middle of basal segment.. . . Lysmata wurdemanni Rostrum with 6 to 7 dorsal teeth, 2 or 3 of which on carapace well beyond post-orbital margin; 2 (sometimes 3, rarely 1) ventral teeth close to rostrum tip. Dorsal antennular peduncle with accessory branch; stylocerite usually distinctly overreaching distal margin of basal segment (sometimes just reaching).. . . Lysmata intermedia
11 previous	Epipods present on at least first two pairs of legs; dactyls of legs 3-5 simple. . . Alpheus formosus Legs without epipods; dactyls of legs 3-5 with two hooks at tip. . . 12
12 previous	Dactyls short, hooks strongly curved, ventral one usually bent at considerable angle to axis of dactyl. . . Synalpheus longicarpus Dactyls long, hooks continuing general direction of axis of dactyl. . . 13
13 previous	Frontal teeth more or less equilaterally traingular, at times with an inferior vertical prolongation to rostrum; basicerite strongly spinous above. . . Synalpheus minus Frontal teeth always longer than wide; rostrum armed with ventral prolongation that embraces ocellary beak; basicerite unarmed above. . . Synalpheus townsendi
14 previous	Abdomen straight, symmetrical, and calcified. . . 15 Abdomen coiled, asymmetrical, and membraneous. . . 16
15 previous	Carapace subcylindrical; antennal flagella long, strong, and spiny. . . Panulirus argus Carapace more or less flattened dorsoventrally, lateral margins sharp; antennae short, flagella replaced by plates with dentate or lobulate margins. . . Scyllarides aequinoctialis
16 previous	Third maxillipeds widely separated at base by sternum; chelipeds with right much larger than left, occasionally subequal . . . Pagurus carolinensis Third maxillipeds approximated at base; chelipeds subequal, or left much larger than right, rarely with right slightly larger than left. . . 17
17 previous	No paired appendages on abdominal segments; legs with longitudinal stripes. . . Clibanarius vittatus Paired appendages on first two abdominal segments of male and first abdominal segments of female; legs lacking longitudinal stripes. . . 18
18 previous	Anterior shield of carapace noticeably longer than broad. . . Paguristes tortugae Anterior shield of carapace not noticeably longer than broad. . . Paguristes sericeus
19 previous	Uropods present. . . 20 Uropods absent. . . 22
20 previous	Uropods rudimentary; last pair of legs held over carapace, adapted for grasping. . . Dromidia antillensis Uropods well developed for swimming; last pair of legs usually tucked under carapace. . . 21
21 previous	Carapace and chelipeds covered with strong, transverse, ciliated rugae. . . Petrolisthes galathinus Carapace smooth with scattered tubercles, chelipeds roughly tuberculate, with hand fringed with long hair along lower margin. . . Megalobrachium soriatum
22 previous	Carapace noticeably longer than broad. . . 23 Carapace not noticeably longer than broad, usually noticeably broader than long. . . 29
23 previous	Eyes with orbits. . . 24 Eyes without orbits. . . 26
24 previous	Eyes with complete orbits; rostral horns widely divergent along most of their length. . . Macrocoeloma trispinosum Eyes with commencing orbits; rostral horns fused along most of their length. . . 25
25 previous	Carapace smooth. . . Pelia mutica Carapace with numerous spines on surface and margins. . . Libinia dubia
26 previous	Rostrum at least as long as carapace. . . 27 Rostrum shorter than carapace. . . 28
27 previous	Carapace nodulose; merus of walking legs with long distal spine; rostrum sparsely spined. . . Metoporhaphis calcarata Carapace smooth; merus of walking legs with distal spine no longer than other spines; rostrum multispinose. . . Stenorhynchus seticornis
28 previous	Walking legs diminishing in length from first to last; dactyl of first pair more curved than those of more posterior legs. . . Podochela sidneyi Walking legs subequal in length; dactyl of first pair less curved than those of more posterior legs. . . Inachoides forceps
29 previous	Last legs modified, distal articles flattened and often broadened to form swimming paddles. . . 30 Last legs essentially unmodified, used as preceding 3 pairs in walking. . . 33
30 previous	Posteriormost lateral carapace spine not noticeably larger than anterolateral carapace spines. . . 31 Posteriormost lateral carapace spine noticeably larger than anterolateral carapace spines. . . 32
31 previous	Carapace with 5 teeth on anterolateral margin. . . Ovalipes stephensoni Carapace with 9 teeth, alternating in size, on anterolateral margin. . . Cronius ruber
32 previous	Carapace wide, anterolateral margins forming arc of a circle with center near posterior margin. . . Portunus gibbesii Carapace narrow, anterolateral margins forming arc of a circle with center near middle of cardiac region. . . Portunus spinimanus
33 previous	Carapace widest nearer posterior margin. . . 34 Carapace widest nearer anterior margin. . . 36
34 previous	Chelipeds closely fitted internally to carapace; chelae with 6-7 dorsal teeth. . . Calappa flammea Chelipeds not closely fitted internally to carapace; chelae unarmed. . . 35
35 previous	Spine on or just above posterolateral margin close behind spine at lateral angle; rostral sinus U-shaped; attains large size. . . Mithrax hispidus Tubercle on or just above posterolateral margin close behind spine at lateral angle; rostral sinus V-shaped except in old adults; never attains large size. . . Mithrax pleuracanthus
36 previous	Small, usually commensal crabs with reduced eyes and orbits; carpus of third maxillipeds not articulating near anterointernal angle of merus. . . Parapinnixa bouvieri Free living crabs with eyes not strikingly reduced; carpus of third maxillipeds articulating at or near anterointernal angle of merus. . . 37
37 previous	Low anterior ridges on endostome (palate or roof of mouth) absent or not reaching to anterior margin of buccal frame. . . 38 Low anterior ridges on endostome (palate or roof of mouth) present and reaching to anterior margin of buccal frame. . . 39
38 previous	Transverse groove beneath extreme edge of frontal margin and row of granules or nodules paralleling it above (under magnification). . . Pseudomedaeus agassizii Front lacking such transverse groove, each half presenting a single edge (under magnification). . . Hexapanopeus paulensis
39 previous	Hairy covering over whole carapace forming thick coat concealing surface beneath (hair sometimes worn off). . . 40 Hairy covering of carapace not forming so thick a coat as to conceal surface beneath. . . 41
40 previous	Chelipeds spinose above; transverse row of long hairs across front. . . Pilumnus floridanus Chelipeds with beadlike tubercles above; notransverse row of long hairs across front . . . Pilumnus pannosus
41 previous	Two or more superhepatic spines. . . Pilumnus sayi No superhepatic spines. . . Pilumnus dasypodus

Any comments, suggestions, and questions are welcome:

Alan W. Harvey
Department of Biology
Georgia Southern University
Statesboro, GA 30460-8042
phone (912) 681-5784
e-mail aharvey@georgiasouthern.edu