Diagnosis of Family Caligidae from Boxshall & Halsey (2004):
"Body typically dorsoventrally flattened comprising caligiform cephalothorax, incorporating first to third pedigerous somites, a free pedigerous somite (bearing leg 4), a genital complex consisting of fused fifth pedigerous and genital somites (and possibly first abdominal somite in female), and a free abdomen of 1 to 3 somites. Cephalothorax sometimes folded bilaterally around median longitudinal axis, as in female Hermilius. Genital complex and abdomen elongate, or flattened with wing-like expansions, or provided with posterolateral processes in some genera. Abdomen suppressed in genera such as Anuretes. Genital apertures ventral, near posterior margin of genital complex. Caudal rami with 6 setae.
Rostrum absent; paired frontal plates usually present between antennules; lunules present or absent. Nauplius eye present. Antennule 2-segmented in both sexes; first segment with up to 27 setae, second with 14 setae. Segmental homologies indeterminate, probably I-XX and XXI-XXVIII. Male antennule non-geniculate, as in female. Antenna uniramous, comprising coxa, basis and laterally directed subchela formed by partial or complete fusion of endopod and distal claw; exopod absent: claw bifid (i.e. with accessory claw) in Hermilius. Postantennal process present, sometimes absent. Oral cone with opening formed by both labrum and labium. Mandible reduced to a stylet bearing teeth (usually 12) on one side near apex; palp absent. Maxillule bilobed, with basal portion incorporated into body wall; anterior lobe (palp) papillate, bearing 3 setae; posterior lobe (endite) an unarmed spinous process; one or both lobes occasionally absent. Maxilla brachiform, comprising syncoxa (lacertus) and basis (brachium) bearing calamus and canna distally. Maxilliped 2-segmented, comprising massive protopod (corpus) and distal subchela representing fused endopodal segments plus terminal claw. Sternal furca present or absent.
Swimming leg 1 with coxa and basis slightly offset; exopod 2-segmented; endopod 2-segmented, reduced to lobe, or absent. Inner seta on basis of leg 1 present. Leg 2 biramous, with protopod comprising coxa and basis; both rami typically 3-segmented, rarely 2-segmented, as in Arrama. Leg 3 with coxa and basis fused into flattened sympod; leg pair typically connected by expanded intercoxal sclerite and forming broad plate sealing rear margin of cephalothorax. Exopod 2 to 3-segmented, endopod 2 to 3-segmented, absent in Kabataella. First exopodal segment with large outer spine reflexed over ramus. Leg 3 reduced to simple lobe in Arrama. Fourth leg biramous only in Euryphorus, usually uniramous, comprising sympod formed by fused coxa and basis, and 1 to 3-segmented exopod; leg 4 sometimes reduced to single segment, or absent. Intercoxal sclerites present on legs 1 to 3. Spine and seta formula typically as follows:
coxa basis exopodal segments endopodal segments
leg 1 0-0 1-I I-1; III,I,3 0-0; 3 or reduced to lobe
leg 2 0-1 1-0 I-1; I-1; III,5 0-1; 0-2; 1,2,3
leg 3 0-1 1-0 I-1; I-1; III,4 0-1; 0-2; 4
leg 4 0-0 1-0 I-0; I-0; IV 0-1; 4 or absent
Leg 5 represented by papilla on margin of genital complex; armed with 3 setae and 1 on body surface representing outer seta of incorporated protopodal segment. Leg 6 represented by unarmed genital operculum in female; by papilla bearing up to 3 setae in male. Egg sacs uniseriate. Nauplii lecithotrophic, with balancers."