COMMENSALISM OF LOXOSOMA 



489 



forms the vestibule and alimentary canal of a new calyx. Hence 

 the phenomenon which may so commonly be noticed in Pedicellina 

 of a " young head on old shoulders." The loss of the calyces may 

 have some relation to the formation of the " brown bodies " in the 

 Ectoprocta. 



Another Entoproct, Loxosoma (Fig. 245) is remarkable for 

 being the only Polyzoon which is not colonial. The buds, which 

 are formed in two lateral series, break off as soon as they are 

 mature, and at once begin to lead an independent existence. 

 Loxosoma is further remarkable for being almost invariably 

 found commensally with other animals, where it may occur in 

 enormous numbers. L. phascolosomatum, common in the Channel 

 Islands, is only found on the tip of the tail of Phascolosoma 

 (see p. 428), which inhabits the mud of Zostera-beds. Other 

 species are found on the external surface of 

 certain sponges (Tethya, Euspongia, Caco- 

 spongia) ; or on the outside of a compound 

 Ascidian, Leptoclinum, which may itself be 

 carried about as a detachable covering on 

 the back of a crab (Dromia). Another 

 species is found 011 the ventral surface of 

 the Polychaet Aphrodite, and of its ally 

 Hermione. 



L. annelidicola, an interesting species 

 recently investigated by Prouho, 1 was origi- 

 nally described in 1863 as a Trematode, 

 und3r the name of Cyclatella. It escaped 

 further notice until it was again found in 

 the neighbourhood of Eoscoff, in Brittany, on 

 certain Polychaets belonging to the family 

 Maldanidae (see p. 332). The calyx has a 

 very flattened form, and is borne on a short 

 stalk, which terminates in a large attaching 

 disc, formerly mistaken for the sucker of 

 features in which this species differs from other members of the 

 genus are shown by M. Prouho to be correlated with its mode of 

 life. The animal has the habit of lying flat on its back, the 

 disc at the end of its stalk being firmly attached to the skin of 

 the worm, and its short stalk being bent round into a curve so 



1 Arch. Zool. Exp. 2 ser. ix. 1891, p. 91. 



Fig. 244. Side view of 

 Loxosoma annelidicola 

 Van Ben. and Hesse, 

 x 50. (From Prouho.) 



a Trematode. The 



