COPEPODS OF THE WOODS HOLE REGION 393 



Suborder MONSTRILLOIDA 



Posterior antennae and mouth parts entirely lacking in the adults 

 of both sexes ; only the merest trace of an alimentary canal, incapable 

 of functioning. The fully developed copepod is thus unable to feed 

 and must subsist upon nourishment accumulated during its juvenile 

 parasitic existence; the sexually mature stage is devoted wholly to 

 reproduction. The group is divided into two families, which differ 

 radically in their characters. 



Family Monstrillidae. — Fifth thoracic segment forming a movable 

 articulation with the fourth, but firmly attached to the sixth (geni- 

 tal), segment; body elongate, urosome considerably narrower than 

 the metasome, both cylindrical. Eggs not carried in ovisacs or brood 

 pouches, but glued to a pair of slender filaments issuing from the 

 ventral surface of the genital segment. In the male these filaments 

 are replaced by a single clavate appendage, within which the sper- 

 matophores are carried before extrusion. First antennae extending 

 straight forward in line with the body axis and parallel with each 

 other. Parasitic during the larval stages, free swimming and pelagic 

 in the adult stage. 



Family Thespesiopsyllidae. — Fourth thoracic segment forming a 

 movable articulation with the third, but firmly attached to the fifth 

 segment; anterior body much wider than the posterior and some- 

 what flattened. Eggs carried in two ovisacs attached to the sides of 

 the genital segment. First antennae extending outward at right 

 angles to the body axis; the first three pairs of legs biramose, rami 

 3-segmented; fourth and fifth pairs uniramose, 3-segmented. Free 

 swimming and pelagic in the adult stage, the larval stages as yet 

 unknown. 



Family MONSTRILLIDAE 



Genus MONSTRILLA Dana, 1848 



Head fused with the first segment and in the female half the entire 

 body length or more, shorter in the male ; free segments and urosome 

 tapered regularly, with rounded lateral margins. Urosome 3-seg- 

 mented in female, 4-segmented in male; caudal rami lamellar, each 

 with five or six setae. First antennae elongate and obscurely seg- 

 mented; basipods of legs very large and flattened; rami short, exo- 

 pod longer than endopod, with only two outer spines ; fifth legs 

 lamellar in female and 1-segmented, with three or four marginal 

 setae, in the male reduced to a mere knob tipped with two setae or 

 lacking. 



