COPEPODS OF THE WOODS HOLE REGION 491 



Female. — Head wider than long, squarely truncated anteriorly, 

 the truncated surface covered with tumid papillae of uniform size 

 and even distribution; a pair of short, stout, unbranched lateral 

 horns and often a third dorsal horn half as wide, all three standing 

 out nearly at right angles at the posterior end of the head. Neck 

 the same diameter throughout and varying greatly in length; the 

 trunk twice as wide as the neck and transversely ridged; the abdo- 

 men slightly less than half the length of the trunk, its plumes usually 

 profusely branched. Egg strings twice the body length or more. 

 First antennae 3-segmented; second antennae 2-segmented; man- 

 dibles, two pairs of maxillae, and the rudiments of maxillipeds pres- 

 ent in young females but disappearing in adults. Intervals between 

 the successive pairs of legs in the proportion of 10 : 30 : 35. Total 

 length, 160-200 mm. Egg strings, 300-350 mm. long. 



Remarks. — This species is common and may be distinguished by 

 the characters given in the key. The portion of the body outside of 

 the skin of the host affords lodging for algae, hydroids, and often 

 goose barnacles, and is sometimes completely covered with them. 



PENNELLA INSTRUCTA Wilson 



Figure 295, c 



Pennella instrticta Wilson, Proc. U. S. Nat. Mus., vol. 53, p. 122, pi. 18, 1917. 



Occurrence. — Found buried in the flesh of the common swordfish 

 captured off Marthas Vineyard and Nantucket. 



Distribution. — Not found elsewhere. 



Color. — Head and neck brownish yellow; trunk dark cinnamon- 

 brown, with interrupted transverse bands of yellow; plumose 

 appendages dark steel gray; egg strings brownish yellow. 



Female. — Head longer than wide, squarely truncated anteriorly, 

 the tumid papillae not covering the truncated surface, but arranged 

 in a pattern, leaving much of the surface bare; lateral margins of 

 head concave. Horns long, soft, and bluntly pointed, extending back- 

 ward parallel with the neck and close to it; never more than two 

 horns. Neck twice the length and half the width of the trunk, and 

 usually more or less bent and twisted. Trunk transversely ridged; 

 abdomen half as long as trunk ; plumules 24 in number on each side 

 and dichotomously branched. First antennae 4-segmented, heavily 

 armed with setae; second antennae 2-segmented; intervals between 

 the successive pairs of legs in the proportion of 1 : 5 : 6. Total length, 

 200-250 mm. 



Remarks. — This species is confined to the swordfish, into the flesh 

 of which it burrows until the copepod's head is brought into con- 

 tact with the fish's dorsal aorta. Around the head and neck of the 

 parasite is formed a tough cyst, which is often 2 inches or more in 

 diameter. 



