BIOLOGICAL STUDY OF CHESAPEAKE BAY WATERS 
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Hexapanopeus angustifrons (Benedict and Rathbun) is another common “mud 
crab ” in the offshore waters of Chesapeake Bay. It has been taken from regions 
where the depth ranges from 8 to 48 meters. The indications are that it is not a 
shore form, for the records of the United States National Museum do not include any 
specimens found on shore collecting trips. Rathbun (1905) speaks of its being found 
on oyster grounds in Connecticut, and the same is undoubtedly true in the Chesa- 
peake. It was brought up quite often from regions of shelly bottom during our 
cruises. Forty hauls of dredges, nets, and trawls brought to light over 100 specimens 
of this crab during the 1915, 1916, and 1920 cruises. They were taken at areas G, 
G ' , A, C, D, E, H, J , K, L, R, and S (close). None was caught farther up the 
bay than the region of area S, which is along the line between Governors Run and 
Janies Island. 
We have no records of any being taken in rivers or creeks, but it is possible that 
they may be found there, in the deeper waters especially, where there are oyster bars. 
Hexapanopeus has been found in the bay during all seasons of the year. The 
water in which specimens were caught varied in temperature from about 4° C. to 
about 25° C. The range of bottom salinities was from about 18.00 to almost 32.00 
per mille. These figures are based on 19 hauls and 50 specimens. 
Little is known concerning the breeding habits of this species, but the collection 
contains one ovigerous specimen caught at area E in July, 1920, and several juvenile 
forms taken during the cruises of October, December, 1915, and April, 1916. 
The Pinnotheridae, which includes those small forms which live commensally 
with various invertebrate animals, are well represented in Chesapeake Bay. Since 
it was not feasible to make any special effort to collect these interesting little crabs, 
the number of specimens is very small. Pinnotheres maculatus Say, the “mussel 
crab” (Rathbun, 1905) has been collected on two occasions, once off the mouth of the 
Potomac River and once at area D. The female is known to live in the gill cavity of 
the mussel, Mytilus edulis, and the male to lead a free-swimming existence. Also, 
the female is known to frequent Pecten tenuicostatus. 
Pinnotheres ostreum (Say), which has similar habits to those of P. maculatus except 
that it is a commensal in the oyster, probably is distributed over all those parts of 
the bay where oysters are found. However, none was collected on our cruises, and 
only a few specimens from Chesapeake Bay are in the United States National Museum. 
Most of these came from the southern part of the bay. 
Pinnixa cylindrica (Say), P. sayana Stimp., and P. chaetopterana Stimp., which 
are commensals of certain tubiculous annelids, were caught very seldom. P. cylindrica 
was captured once at area L, near the mouth of the Potomac River, in about 37 meters 
of water; P. sayana was found near the mouth of the Patuxent River — that is, at 
area R and at a locality near that area where the water was 48 and 7 meters deep, 
respectively; finally, P. chaetopterana was taken in 16 meters of water at area F, 
which is in the mouth of the bay. One haul of the “orange-peel bucket” in the latter 
case brought up 5 males and 6 females. 
Two species of the genus Sesarma, Sesarma cinereum (Bose) and S. reticulatum 
(Say), coming from Chesapeake Bay and vicinity, are in the collection of the United 
States National Museum. Neither of these has been collected on our cruises, which 
is not surprising, for they are shore or shallow-water forms. S. cinereum, called the 
“wood crab” and occurring “ under logs and drift and about wharves, wooden piles, 
etc.” (Rathbun, 1900, p. 583), has been collected from several localities in the bay: 
Near Thomas Point (between areas V and Z); Island Creek in the mouth of the 
