80 THE LIFE OF THE MOLLUSCA 
taceans of different sorts (Ismatla and Splanchno- 
trophus) are to be found on Nudibranchs; another 
attaches itself to the float of JIanthina, which it 
matches in colour. Ostracotheres lives in the gills 
of the Giant Clam (Tridacna); while Pinnotheres 
takes up its abode within the shells of several 
different Bivalves, including the great Pearl Oyster, 
and one species has lately been found in Stvombus. 
A quaint little Mite (Piilodromus limacum) infests 
terrestrial Gastropods. It lives in the breathing 
chamber, and may be seen issuing therefrom and 
running with great rapidity over the body of its 
host, but what its connection with the mollusc may 
be is quite unknown. Another kind of Mite (A tax) 
is found on freshwater Mussels. 
Clear cases of commensalism on the part of 
molluscs with other animals are those of certain of 
the Pelecypods: Modtolaria marmorata lives in the 
integument of Ascidians; Montacuta, Lepton and 
Scioberetia dwell with Echinoderms. Jousseaumia 
is commensal in the chamber of a Sipunculid Worm 
(A spidosiphon), which is itself commensal in the coral 
genera Heterocyathus and Heteropsammia. Lefton. 
squamosum resides in the burrows of Annelids and 
Crustaceans ; Ephippodonta is commensal in the 
burrow of a Prawn; Vulsella lives in the substance 
of Sponges. The Gastropod Magilus, which takes 
up its abode in coral masses, and probably supports 
itself on the Infusoria and other small animals which 
