358 CRUSTACEA 



H. pelagica Claus (Fig. 567). Shell 1.4 mm. long and 1.1 mm. 

 high; first antennae strongly curved: Atlantic and Pacific Oceans. 

 . 2. CoNCHCECiA Dana. Shell elon- 



gate with well-developed rostrum and 

 notch : 7 American species. 



C. magna Claus. Shell subquad- 

 rangular, higher behind than in front, 

 2.6 mm. long and half as high; dorsal 

 margin with a depression near the mid- 

 dle: widely distributed in the Atlantic 

 ^^fuSr^SinafSr and Pacific Oceans. 



Order 4. CIRRIPEDIA.* 



Body usually of large size and enclosed in a calcareous shell; animals 

 marine and sessile as adults, living either attached to rocks, timbers, or 

 seaweed, or as parasites on or in the bodies of crabs, mollusks, or other 

 marine animals. A cement gland in the penultimate joint of each anterior 

 antenna furnishes a secretion by means of which the barnacles are attached ; 

 the parasitic Rhizocephala fasten themselves to their hosts by means of 

 long root-like projections of the head. The body, like that of the 

 Ostracoda, is entirely enclosed in a carapace which arises on the back of 

 the head and thorax and falls in a right and left fold over the body, form- 

 ing the characteristic shell. The appendages are a pair of mandibles, two 

 pairs of maxillae, and six pairs of biramose and plumose thoracic append- 

 ages or legs. It is these legs which project from the shell and give the 

 animal its characteristic appearance. In some of the parasitic cirripeds the 

 number of pairs of thoracic legs is less than 6 and in the Rhizocephala 

 both they and the mouth parts are altogether wanting. The abdomen is 

 rudimentary. The digestive tract in the barnacles passes straight to the 

 anus at the hinder end of the abdomen; in the Rhizocephala no digestive 

 tract is present, the nutriment being absorbed through root-like projections 

 of the stalk which entwine the viscera of the crab on which the parasite 

 is living. 



With a few exceptions all cirripeds are hermaphroditic, a condition 

 which is undoubtedly correlated with their sessile habit of life. In a 

 few genera of barnacles {Ihla, Scalpellum) eomplementaiy males also 

 occur, which live in or near the genital openings of the hermaphroditic 

 individuals. Scalpellum ornatum, Ihla cummingi, and all the species of 

 the genera Cryptophialus and Alcippe, which burrow in the shell of 



* See "A Monograph of the Subclass Cirripedia," by Charles Darwin, 1851-1854. 

 "The Barnacles (Cirripedia) Contained in the Collections of the U. S. National 

 Museum," by H. A. Pilsbry, Bull. 60, U. S. Nat. Mus., 1907. 



