NEW YORK SHELL CLUB NOTES No. 243 June-July-Aug. 1978 Page 7 
THESE TOO ARE MOLLUSKS 
Morris K. Jacobson 
Parasitic forms are rare in the phylum Mollusca but some do exist. 
They range from the shell-bearing, completely recognizable ecto- 
parasites (= outside parasites) like Odostomia, Pyramidella, Bulimia 
and so on to completely degenerate endoparasites es inside para- 
sites) like Entoconcha, parasitic on a sea cucumber, which consists 
only of a wormlike tube with a siphon opening through the host's 
skin and a small proboscis. In between are forms like Gasterosiphon 
(also endoparasitic in a sea cucumber) which still has a recogniza- 
bly molluscan viscera. 
Most of the parasites are included in parasitic family groups: Ento- 
concha in Entoconchidae, Gasterosiphon in Stiliferidae, Eulimia in 
Bulimidae, Thyca in Capulidae and so on. But even in the "straight" 
family Lucinidae there are some members that are more or less para- 
sitic on echinoderms -- starfish, sea urchins, holothurians (= sea 
cucumbers). 
The accompanying pictures are figures of some of these mollusks: 
(a) Thyca entoconcha para- 
Sitic on a Starfish. 
(bv) Stilifer linckiae para- 
Sitic in Starfish. 
(c) Gasterosiphon deimatus 
(Stititertdse) para- 
sitic in holothurians. 
(d) Entoconcha mirabilis 
parasitic in holothu- 
rians. 
(e) Entoconcha mirabilis 
in its holothurian 
host, Synapta. 
(a) and (b) look something 
like mollusks; (c) is mol- 
luscan only in its inter- 
nal anatomy; (d) and (e) 
are two views of an entire- 
ly unmollusklike creature. 
It's important to remember 
that these forms are dis- 
tinctly molluscan as larvae, 
going through trochophore 
and veliger stages. It is 
only as they mature that 
they assume the degenerate 
parasitic shape. 

Fic. 14.10. PARASITISM IN GASTROPODS 
BIOLOGY OF MARINE ANIMALS, 
References and illustrations are from THE 597.) 
J. A. Colin Nicol, 1960, New York. (Fig. 14.10. P. 
