NEW YORK SHELL CLUB Nop 
Page 6 September 1978 No. 244 5 
be of particular value if each crab could be placed 
tracy iaueuis in a viet along with a note indicating the length of 
the host mussel as well as the date and exact location of its col- 
lection. Such information would be extremely valuable in our con- 
tinuous studies of environmental pollution and deteriorating water 
quality in coastal zones and estuaries. 
I would be glad to furnish copies of papers on these crabs as well 
as more getalis as to how collections should be made, if individuals 
would write to me at the foregoing address. 
LIFE HISTORY OF SOME PINNOTHERIDAE 
The life history of these crabs is complicated. The mussel crab, 
Pinnotheres maculatus, was studied on the East Coast. In the early 
T960's Pearce (1977a.b) studied the ecology of several species of 
pea crab living on the West Coast. The East Coast mussel crab, and 
Fabia subquadrata, the West Coast mussel crab, were found to have 
very Similar life histories. Both AF pape ne pt abo ee 
by mother crabs located inside mussels such as Modiolus modiolus an 
isa iss edulis, which are common in certain portions of the seas off 
the Bast and West Coasts. When an egg hatches, a small crab larvae, 
called a zoea, escapes the host mussel and swims into the water col- 
umn. The tiny larvae are attracted to light and swim to the surface 
where they pass through several developmental stages, collectively 
called instars. The last instar is called a megalopa; this larval 
instar looks very much like the tiny adult crab. rs the megalopa 
Stage a drastic change occurs in the physiology and morphology of 
the crab larvae and the tiny crab leaves the water column and set- 
tles to the bottom where it finds its way into a host mussel or 
other bivalve species. 
After reaching the bottom, and finding an appropriate host, the tiny 
crab continues to develop through a number of true crab instars. 
These instars are quite small, less than a millimeter in diameter at 
the beginning and eventually reaching 2 to 3mm in carapace width. 
The tiny crabs have slender walking legs which allow them to move 
about inside the mussel. The exoskeleton, or shell, is quite soft, 
unlike free living crabs which have a well-calcified exoskeleton. 
The crabs feed on food taken in by the host mussel. As foodstuffs 
are collected on the gills of the host bivalve, the crab delicately 
cae eo materials which are entrained in mucous secreted by 
e valve. 
As previously mentioned, upon entering the host th crab 
passes through several moults, each of which eet ee nee 
which is slightly larger in size, Eventually, an instar is charac- 
gees ey, oe exoskeleton which is hardened much like that of free 
; vane crabs. Also, the walking legs, instead of being soft and 
ms indrical, are flattened and have long setae, or hairs, along 
; SRE) uate & margins. This particular instar (called the Stage 
tages ageat leaves its host bivalve, usually a mussel, and swims 
eo. ; water's surface; both males and females leave their host 
' sels. Sometimes hundreds of these small crabs can be seen swim- 
ming in the water of shallow estuaries and embayments. They can 
crabs. The females are fertilized when small packets of sperm are 

