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WILLIAM MACNAE
depend on the fertility of the soil. There is, for example, always a very
obvious increase in the number of individuals of crabs in the vicinity
of the towns or villages established within the mangal. There are
differences, too, between accrescent and eroding shores. These latter
provide among the tumbled masses of mangrove peat many nooks and
crannies analogous to a rocky shore and hence give cover to several
species of xanthid crabs, a family characteristic of rocky shores and
shores with scattered coral dkbris.
a. Accrescent shores
As has already been mentioned, many shores occupied by mangroves
are continually having material deposited on them, and this material
becomes colonized by species of Avicennia or under special circumstances
by species of Sonneratia. Such shores have a characteristic fauna. Most
C
FIG. 56. Metaplax crenulatus. A, A female in characteristic pose (partly after a photograph by I. Polunin). The arrows indicate the direction of water flow while pumping
and reoxygcnating the water ; this process is almost constant while the crab is out
of water. B, Base of cheliped and pterygostome of 8. male, showing the " niusical
ridge " on the pterygostome, below the orbit and the " bow " on the merus of the
cheliped. C, Dorsal view showing direction o f water flow over the back, while the
crab is out of water. (ca. nat. size.)
WILLIAM MACNAE
depend on the fertility of the soil. There is, for example, always a very
obvious increase in the number of individuals of crabs in the vicinity
of the towns or villages established within the mangal. There are
differences, too, between accrescent and eroding shores. These latter
provide among the tumbled masses of mangrove peat many nooks and
crannies analogous to a rocky shore and hence give cover to several
species of xanthid crabs, a family characteristic of rocky shores and
shores with scattered coral dkbris.
a. Accrescent shores
As has already been mentioned, many shores occupied by mangroves
are continually having material deposited on them, and this material
becomes colonized by species of Avicennia or under special circumstances
by species of Sonneratia. Such shores have a characteristic fauna. Most
C
FIG. 56. Metaplax crenulatus. A, A female in characteristic pose (partly after a photograph by I. Polunin). The arrows indicate the direction of water flow while pumping
and reoxygcnating the water ; this process is almost constant while the crab is out
of water. B, Base of cheliped and pterygostome of 8. male, showing the " niusical
ridge " on the pterygostome, below the orbit and the " bow " on the merus of the
cheliped. C, Dorsal view showing direction o f water flow over the back, while the
crab is out of water. (ca. nat. size.)