374 LOWER FORMS OF MARINE LIFE 



in reality members of the crustacean order which, like the typical sea-squirts, are 

 free-swimming when young, but when adult either fix themselves head-downwards 

 to a rock or other convenient object and secrete a solid shell resembling in many 

 instances a miniature volcano, with the summit closed by movable bands, or 

 develop a flattened, triangular, many-valved shell supported on a long flexible 

 stalk. The former, or sessile, group is typified by the well-known acorn-barnacles 

 (Balanus) and the latter, or stalked, group by the ship-barnacles (Lepas) ; each of 

 these being respectively also the type of a family, namely, the Balanidce and the 

 Lepadidce. Before entering on their fixed stage the free-swimming larvse under- 

 go certain very remarkable structural stages. The adults of both groups display 

 clear evidence of their crustacean nature by the delicate plumes which sweep at 

 intervals, when the barnacles are active, from between the valves and draw in 

 currents of water; these being the modified legs of the larval form. It is from 

 these plume-like, or hair-like, appendages that the order derives its name of 

 Cirripedia, or hair-footed. The acorn-barnacles of European seas are quite small, 

 but in allied species from tropical seas the shells may be six or eight inches in height, 

 several frequently growing in clusters. The ordinary ship's barnacle, Lepas 

 anatifera, derives its second name from the old legend that bernicle geese were 

 hatched from this species. From their habit of attaching themselves to floating 

 timber, the shells of turtles, ships, and other moving objects, these barnacles have 

 acquired an almost world-wide distribution. 



Barnacles of one kind or another have occupied almost every available and 

 suitable situation. Certain species, chiefly belonging to the genera Coronula and 

 Tubicinella, take advantage of the bodies of whales as a basis of attachment, and 

 thereby probably secure a greater abundance and variety of food than their relatives 

 which live on rocks. It has been noticed in connection with the barnacle infesting 

 the southern black right-whale (Balcena australis) that were it not for some special 

 provision, the growth of the epidermis of the whale, coupled with the wearing away 

 of the outer layer, would soon cause the parasite to be shed, and, as a matter of 

 fact, this actually takes place with the dead shells. The living barnacle cannot, 

 however, be discarded in this manner, since it dissolves the part of the epidermis 

 with which its skin is in contact at the same rate at which fresh epidermal tissue 

 is formed below. Consequently the layer of epidermis between the barnacle and 

 the true skin never varies in thickness, and the parasite accordingly retains its 

 position, the shell disintegrating at the apex at the rate at which it grows at the 

 base. 



Perhaps the strangest situation for these organisms occurs in the species known 

 as Stomatolepas praegustator, which inhabits the mucous membrane of the throat 

 of the loggerhead turtle. Although sessile barnacles infest the external surface of 

 turtles and whales, while certain parasitic forms penetrate the integument of their 

 crustacean hosts, no other species is known to possess such a peculiar habitat. 

 StomatolejMS belongs to the subfamily Coronulince, and is nearly related to 

 Tubicinella and to Stephanolepas, a barnacle found imbedded in the horny plates 

 of the shell of the hawksbill turtle. A few years ago a specimen of the flat-tailed 

 sea-snake (Hydrtos platv/rus) was taken off Ceylon with a large bunch of barnacles 

 attached to the end of its tail so as to form a somewhat flower-like cluster. As 



