Vol. XVIII February, igio. No. j 



BIOLOGICAL BULLETIN 



A NEW GENUS OF PARASITIC GASTROPODS. 



HAROLD HEATH. 



A number of gastropods are known, living parasitically upon 

 the body of certain echinoderms, which retain the shell and 

 typical internal organization so that their systematic position is 

 readily established. On the other hand several endoparasitic 

 species exist which have become so highly modified that they 

 stand in much the same relation to the free-living forms as Sac- 

 cidina to the typical cirripedes. Owing to the lack of any de- 

 tailed information relating to their ontogenetic development the 

 relationship of such forms is highly problematical. And further- 

 more it is difficult to accurately follow the stages of the phylo- 

 genetic metamorphosis which the body has undergone, and 

 accordingly to establish the homologies of some of the principal 

 organs. Schiemenz ' in a very suggestive paper has attempted 

 to construct a hypothetical animal connecting the least modified 

 species like Sty lifer on one hand with the highly degenerate 

 types represented by Entoconcha. In several respects the animal 

 here described resembles the hypothetical form and in a measure 

 enables us to follow some of the changes which the more degen- 

 erate species have undergone. 



My attention was attracted to this gastropod by my friend 

 and colleague Dr. W. K. Fisher who discovered it in a species 

 of starfish {Brisinga evermanni Fisher) taken by the U. S. F. C. 

 Str. "Albatross" in the neighborhood of the Hawaiian Islands 

 (sta. 3467) at a depth of 310 fathoms. It occupied the coelomic 

 cavity close to the base of one of the arms, producing a marked 

 distention (Fig. 2, PI. I.) of the body wall. The animal was un- 



^ P. Schiemenz, " Parasitische Schnecken-Kritische Referat," ^/t?/. CentralbL, 

 Bd. 9. 



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