CLASSIFICATION OF CRUSTACEA. 305 
Cuass. I. CRUSTACHA. 
Arthropoda breathing by gills situated on the legs, or respiring through 
the body-walls. Body in the higher forms divided into two regions, a 
cephalo-thorax and abdomen. Two pairs of antenne ; mandibles usu- 
ally witha palpus. Heart nearly square, or in the lower forms tubular. 
Often a distinct metamorphosis. Sexes distinct, except in a few cases 
(certain barnacles, etc.). 
Order 1. Branchiopoda. Thoracic feet leaf-like ; one to three pairs of 
maxille ; number of body-segments varying from a few to 
sixty ; cephalo-thorax often well developed, and forming a 
bivalved shell, Young usually a Nauplius. Suborder 1. 
Ostracoda (Cypris). Suborder 2. Cladocera (Daphnia). Sub- 
order 8. Phyllopoda (Limnadia, Apus, Branchipus, and Ar- 
temia.) 
Order 2. Entomostraca.—A cephalo-thorax developed ; mandibles and 
three pairs of maxille ; five pairs of thoracic feet, no ab- 
dominal feet ; without any gills. The parasitic forms more 
or less modified in shape, with sucking mouth-parts ; all 
the young of the nauplius form, Suborder 1. Copepoda 
(Cyclops). Suborder 2. Siphonostoma (Lernea, Caligus, and 
Argulus). 
Order 8, Cirripedia.—Sessile often retrograded ; antennz not devel- 
oped, living parasitically, the appendages of the head some. 
times forming root-like organs. Young hatched in the nau- 
plius state. Suborder 1.—Rhizocephala (Sacculina, Pelto- 
gaster). Suborder 2.—Genuine Cirripedia (Balanus, Lepas.) 
Order 4, Edriopthaima.—No cephalothorax, thoracic segments dis- 
tinct ; respiration often carried on by the abdominal feet, 
Suborder 1. Jsopoda (Idotea, Asellus). Suborder 2. Am- 
phipoda (Gammarus). 
Order 5. Phyllocarida.—Body compressed ; rostrum distinct from the 
carapace ; thoracic feet leaf-like ; no metamorphosis. (Ne- 
balia.) 
Order 6. Thoracostraca.—Cephalothorax well marked, abdomen often 
bent beneath the cephalothorax; breathing by gills attached. 
to the maxillipedes and legs. Heart often nearly pentagonal. 
Usually a well-marked metamorphosis; young called a 
Zoéa. Suborder 1. Cumacea (Cuma). Suborder 2. Syncarida 
(Acanthotelson). Suborder 3. Stomapoda (Squilla). Sub- 
order 4. Schizopoda (Mysis). Suborder 5. Decapoda (Cran- 
gon, Astacus, Homarus, Cancer). , 
