FAUNA AND FLORA O F MANGROVE SWAMPS
207
niques. Members of this genus feed on edible trifles, either plant or
animal, which are stranded on the mud on which they live. Their
maxillipeds are relatively unmodified except in so far as they have,
along the edges of the distal segments, a number of setae which would
retain the food while it was being washed by the stream of water being
pumped through the buccal cavity.
Only one species of Macrophthalmus, namely M . depressus, is
characteristically found in the mangal. This species unlike many of its
congeners is not a burrower ; it occurs in the sandy bottoms of drainage
channels and becomes rarer as these become deeper and develop into
gullies or creeks. It lies in the sand with only the eyestalks showing
and appears to filter detritus and nanoplankton from the water by
way of the maxillipeds which act as a fishing net. But this is not its
sole method of feeding for several may be found around a piece of
carrion which is picked to pieces in the normal way of crabs. Specimens
were once surprisingly found by Macnae and Kalk (1962a) when
digging in the sand of the “avicennia parkland” at Inhaca. So it
would appear that when the tide is full they spread out from the
channels.
Crabs of the genus Sesarma seem not to be restricted to any particular grade of particle size of the substratum. The species common in
eastern Africa range from fine mud to coarse sand. Recent observations
seem to suggest that these crabs may be to some extent dependent on
the substratum for at least a part of their food. Day (1967) has reported
that S. catenata a t Knysna feeds at night by “ spooning up the surface
silt, sucking out the detritus, and discarding the silt as pseudofaecal
pellets ”.
In April 1967 at Inhaca and again in July at Quissanga in northern
Moqambique it was noticed that pools within certain groves of Avicennia
marina had a sandy bottom which was covered by a flocculent layer of
diatoms. This felt of diatoms was broken by strips from which the
cover had been removed. The only animals in these pools were S.
ortmanni and S . eulimene ; a t Inhaca it was suspected and at Quisssnga
confirmed that both these crabs feed by delicately scooping up the
surface film using the spoon-tipped chelae. As the crabs progressed they
left tracks some 20 mm wide from which the brown scum had been
removed. Under these circumstances no pseudofaecal pellets were
made. Pseudofaecal pellets are common in areas occupied by these
sesarmas on fine muddy substrata.
8. rneinerti has been seen to devour human faeces and drag such
material to the burrows. I n what appeared to be the village fishermen’s
latrine at Morrumbene in central Mopambique (lat. 24”s.) I found the
207
niques. Members of this genus feed on edible trifles, either plant or
animal, which are stranded on the mud on which they live. Their
maxillipeds are relatively unmodified except in so far as they have,
along the edges of the distal segments, a number of setae which would
retain the food while it was being washed by the stream of water being
pumped through the buccal cavity.
Only one species of Macrophthalmus, namely M . depressus, is
characteristically found in the mangal. This species unlike many of its
congeners is not a burrower ; it occurs in the sandy bottoms of drainage
channels and becomes rarer as these become deeper and develop into
gullies or creeks. It lies in the sand with only the eyestalks showing
and appears to filter detritus and nanoplankton from the water by
way of the maxillipeds which act as a fishing net. But this is not its
sole method of feeding for several may be found around a piece of
carrion which is picked to pieces in the normal way of crabs. Specimens
were once surprisingly found by Macnae and Kalk (1962a) when
digging in the sand of the “avicennia parkland” at Inhaca. So it
would appear that when the tide is full they spread out from the
channels.
Crabs of the genus Sesarma seem not to be restricted to any particular grade of particle size of the substratum. The species common in
eastern Africa range from fine mud to coarse sand. Recent observations
seem to suggest that these crabs may be to some extent dependent on
the substratum for at least a part of their food. Day (1967) has reported
that S. catenata a t Knysna feeds at night by “ spooning up the surface
silt, sucking out the detritus, and discarding the silt as pseudofaecal
pellets ”.
In April 1967 at Inhaca and again in July at Quissanga in northern
Moqambique it was noticed that pools within certain groves of Avicennia
marina had a sandy bottom which was covered by a flocculent layer of
diatoms. This felt of diatoms was broken by strips from which the
cover had been removed. The only animals in these pools were S.
ortmanni and S . eulimene ; a t Inhaca it was suspected and at Quisssnga
confirmed that both these crabs feed by delicately scooping up the
surface film using the spoon-tipped chelae. As the crabs progressed they
left tracks some 20 mm wide from which the brown scum had been
removed. Under these circumstances no pseudofaecal pellets were
made. Pseudofaecal pellets are common in areas occupied by these
sesarmas on fine muddy substrata.
8. rneinerti has been seen to devour human faeces and drag such
material to the burrows. I n what appeared to be the village fishermen’s
latrine at Morrumbene in central Mopambique (lat. 24”s.) I found the