Page 2 October 1978 No. 245 NEW YORK SHELL CLUB NOTES 
WHO LIKES MOLLUSKS? 
Morris K. Jacobson 
Not only shell collectors, shore dinner diners, and interior decora- 
tors. Below some other molluscophiles less well known. 
Serpulids (worms which build long calcareous tubes), barnacles, and 
Banen ahs species use molluscan shells, alive and dead, to be 
sedentary on. Hermit crabs (Paguridae) are well-known mollusco- 
philes -- or rather "philes" of their empty shells. But did we 
know that here an instinct is displayed to form associations with 
certain other organisms, all perched on the erstwhile domicile ofa 
defunct prosobranch, an association often mutually beneficial? 
There are, for example, sponges, hydroids, zooanthids (a kind of 
anemone which forms a hard container for itself), actinarians (sea 
anemones) and bryozoans (moss animals). All such creatures are ap- 
parently delighted not only with the solid molluscan base to rest 
upon, but also with their pleasant company. It should be noted 
that the actinarians and the sponges are sometimes deliberately 
placed on the shell by Pagurus to serve as protection (actinarian 
stinging cells, nematocysts, scare off some foes) and as camouflage 
(the sponges). The hydroid colonies (H dractinia) help the hermit 
crab even more: they extend the mats they form beyond the mouth of 
the shell they rest upon, and thus is enlarged the living space 
available for the crab inhabitant. 
In one case a real chummy odd couple occurs. Nereis, the "blood 
worm" well known as bait to fishermen, lives in whelk shells (Busy- 
con, Buccinum etc.) already inhabited by a hermit crab. The worm 
usually lies withdrawn in the upper whorls of the shell. But what 
happens if the crab is about to dine? One observer reports: "While 
I was feeding one of my soldiers (=hermit crabs) I saw protrude 
from between the body of the crab and the whelk shell the head of 
--. Nereis which rapidly glided around the crab's right cheek and, 
(seizing) the morsel of food ... forcibly dragged it from the crab's 
very mouth, I beheld with amazement ... that though the crab re- 
covered his hold, he manifested not the least signs of anger... 
Sometimes (the crab) gave a sudden start (while fighting for its 
food) ... which frightened the worm and made it let go and retreat." 
Sounds like an episode from the TV show of the same name. 
Then there are the pea crabs (Pinnotheridae) who live inside the 
mantles of such bivalves as Mytilus, Venus and others. MThese are 
more than mere tenants, as once believed. It has been discovered 
that they steal some of the food which the mollusks have imprisoned 
in mucus bands to provide for themselves -- the crabs merely steal 
the food-laden bands for themselves. Often they also weaken or in- 
jure the gills of the bivalves and thus the pinnotherids approach 
the stage of being parasites (See: "Parasitic Crabs and Mollusks," 
by Jack B. Pearce, NYSC NOTES No. 244, September 1978). Less 
well-known tenants of mollusks are the shrimp Pontonia which lives 
in the mantle cavity of the bivalve Pinna and the small fish Apo- 
gonichthys found regularly inside live stromb shells. 
Another molluscophile is not even an animal is i j 
: . is le-celled 
algae called, because of its yellow color, Gdosegiehe (ar aenthes is 
the Greek for "yellow"). Zooanthellae are Found in the mantle tis- 
sues of Tridacna, where they grow and reproduce in a kind of green- 
