THE BURROWING BARNACLES (CIRRIPEDIA: ACROTHORACICA ) 27 



to begin moving depends to some degree on the salinity of the water. 

 Deviations slightly above or below normal salinity appear to hasten 

 the action. 



The sperm move in a typical thrashing manner. The nearly uni- 

 form diameter of the sperm makes it difficult to determine a head 

 end. The movement is distributed along the length of the sperm. 



Embryology and Mating Behavior 



The embryology of members of the order Acrothoracica has been 

 the subject of several papers, especially Trypetesa lampas by Kiihnert 

 (1934), Berndtia purpurea by Utinomi (1961), and Cryptophialus 

 melampygos by Batham and Tomlinson (1965). 



The major embryonic sequence of egg, nauplius, metanauplius, 

 cyprid, and young barnacle is found in the Acrothoracica as it is in 

 the entire subclass. A striking feature of the Acrothoracica, however, 

 is that most species retain their larva to the cyprid stage within the 

 mantle cavity of the female, before they are released into the sea. In 

 some species, notably Cryptophialus melampygos, the larvae have no 

 swimming appendages, and hence must crawl and be splashed from 

 place to place. These species have extremely dense infestations (over 

 3,350 individuals in a 5-inch Haliotis iris). 



Motile animals have a capacity for a complex courtship behavior, 

 which informs the partner of mating readiness. The immobile bar- 

 nacles not only cannot develop such a complex courtship, they are 

 further handicapped by being more or less permanently within a hard 

 capsule. The automatic response of closing the opercula on any in- 

 truding object would seem to discourage random search behavior by a 

 neighbor's penis. The Thoracica have remained very fertile, however, 

 with the aid of a chemical messenger. Collier, Ray, and Wilson (1956) 

 have shown that as little as 14 ;ugms/l of ascorbic acid (vitamin C) 

 will cause one species of Balanus to initiate mating behavior. Barnes 

 (1962) showed that the seminal plasma of B. balanus contains 21 

 jLigms of vitamin C per ml. of semen deposit. Thus, the first mature 

 balanoid initiates a chain reaction. 



The Acrothoracica have a great advantage in having a motile male, 

 yet he must synchronize with the female if fertilization is to be effec- 

 tive, and he is cemented down, so apparently does not move around 

 to give or receive behavioral clues. It is my opinion that the partial 

 burial of the male within a pocket of the female's mantle tissue in the 

 immediate area of the ovary is a means for the synchronization of 

 sexual development, perhaps on the part of the maturation of the 

 male under some chemical mediation of the female. 



