100
MABINE MOLLUSCS AS HOSTS FOR SYMBIOSES
but in addition will catch newly formed mucus-food masses with its
walking legs, then reach beneath its abdomen with its chelipeds, comb
the legs, and pass the food on to the mouth. It is while engaged in this
type of commensalistic feeding that the crabs injure their hosts
mechanically. Since the " metabolic dependency " concept of parasitism is believed to be the most objective and appears to be a far more
useful one, further physiological studies on Pinnotheres must be forthcoming before we can definitely establish these crabs as parasites.
The only evidence available at tliis time that suggests metabolic
dependency of pinnotherid crabs on their hosts is the apparent hostspecificity of certain species (Pearce, 1962). Exceptions, however, exist.
For example, Pinnotheres pugettensis, which most frequently occurs in
the large tunicate Haloc~nthia igaboja, has been found by Pearce to
occur in both H . aurantium and Ascidia paratropa. Also, while adults
of the mussel crab, Fabia subquadrata, are typically found in horse
mussels, Modiolus modiolus, in the waters of Puget Sound, the immature
crabs, according to Pearce, are frequently found in a number of smaller
bivalve species. The latter situation, however, may well reflect a change
in host during development rather than non-host specificity. Again,
while adult pinnixid crabs, Pinnixa faba and P. littoralis, almost
invariably occur only in the horse or giant calm, Schizothaerus capax,
juveniles of these species are ubiquitous in 5t wide range of bivalves and
larger limpets. It should be pointed out that even in the instances of
Pabia subquadrata, Pinnixa faba and P. littoralis, the fact that the
adults are host-specific indirectly suggests rather specific metabolic
dependency. Pearce (1962) has reported that differences, especially in
the integument, as seen with the light microscope and in electron
micrographs, between P. faba and P. littoralis and free-living brachyurans exist and has suggested that these differences " are the result
of adaptation to a protective, symbiotic environment ".
Various other invertebrates have been reported from within the
mantle cavities of marine molluscs. For example, in Southern California,
a shrimp of the genus Betaeus is found in abalones. According to Hart
(1964), this hooded shrimp is B. harfordi and its natural range extends
from Maddalena Bay, Mexico, to Fort Bragg, California. It is most
commonly found as a commensal in the pink abalone, Haliotis corrugata,
but is also found within the red abalone, H . rufescens, the black
abalone, H . cracheridii, and the green abalone, H . kamtschatkana. In
addition, it has been found in H . walbalensis, fI. sorenseni and H .
assirnilis.
It is also known that the so-called boring clam, Diplothyra smithii,
occurs on and in the shell of Crassostrea virginica. Galtsoff (1964) has
MABINE MOLLUSCS AS HOSTS FOR SYMBIOSES
but in addition will catch newly formed mucus-food masses with its
walking legs, then reach beneath its abdomen with its chelipeds, comb
the legs, and pass the food on to the mouth. It is while engaged in this
type of commensalistic feeding that the crabs injure their hosts
mechanically. Since the " metabolic dependency " concept of parasitism is believed to be the most objective and appears to be a far more
useful one, further physiological studies on Pinnotheres must be forthcoming before we can definitely establish these crabs as parasites.
The only evidence available at tliis time that suggests metabolic
dependency of pinnotherid crabs on their hosts is the apparent hostspecificity of certain species (Pearce, 1962). Exceptions, however, exist.
For example, Pinnotheres pugettensis, which most frequently occurs in
the large tunicate Haloc~nthia igaboja, has been found by Pearce to
occur in both H . aurantium and Ascidia paratropa. Also, while adults
of the mussel crab, Fabia subquadrata, are typically found in horse
mussels, Modiolus modiolus, in the waters of Puget Sound, the immature
crabs, according to Pearce, are frequently found in a number of smaller
bivalve species. The latter situation, however, may well reflect a change
in host during development rather than non-host specificity. Again,
while adult pinnixid crabs, Pinnixa faba and P. littoralis, almost
invariably occur only in the horse or giant calm, Schizothaerus capax,
juveniles of these species are ubiquitous in 5t wide range of bivalves and
larger limpets. It should be pointed out that even in the instances of
Pabia subquadrata, Pinnixa faba and P. littoralis, the fact that the
adults are host-specific indirectly suggests rather specific metabolic
dependency. Pearce (1962) has reported that differences, especially in
the integument, as seen with the light microscope and in electron
micrographs, between P. faba and P. littoralis and free-living brachyurans exist and has suggested that these differences " are the result
of adaptation to a protective, symbiotic environment ".
Various other invertebrates have been reported from within the
mantle cavities of marine molluscs. For example, in Southern California,
a shrimp of the genus Betaeus is found in abalones. According to Hart
(1964), this hooded shrimp is B. harfordi and its natural range extends
from Maddalena Bay, Mexico, to Fort Bragg, California. It is most
commonly found as a commensal in the pink abalone, Haliotis corrugata,
but is also found within the red abalone, H . rufescens, the black
abalone, H . cracheridii, and the green abalone, H . kamtschatkana. In
addition, it has been found in H . walbalensis, fI. sorenseni and H .
assirnilis.
It is also known that the so-called boring clam, Diplothyra smithii,
occurs on and in the shell of Crassostrea virginica. Galtsoff (1964) has