FAUNA AND FLORA O F MANGROVE SWAMPS
175
fallen trees become converted to rotting logs and thus provide shelter
for several kinds of animals. The root systems with their ascending
and descending knees, and the buttresses which support the trunks
also provide shelter.
This portion of the maiigal supports a greater variety of ground
dwelling animals than any other portion. Crabs run everywhere. Most
of them are grapsids, species of Sarmatium, of Helice, of Ilyograpsus,
smaller species of Sesarma mainly of the subgenus Chiromaiztes : e.g.
S. eumolpe de Man, S. dussumieri HM-Edw., S. onychophora de Man,
and 8. indiarum Tweedie in Malaya ; and S. guttatum in eastern Africa.
Species of the subgenus Parasesarma such as S. melissa de Man are also
present in western Malaya. Two species of Metopograpsus, namely
M . frontalis Miers (= M . gracilipes de Man) and M . thukuhar, are
conspicuous. These two crabs seem not to overlap in distribution : the
former is south-east Asian and Australian, while the latter is found in
eastern Africa, Madagascar and several islands. M . messor Forsk. has
been reported from mangrove areas. This is the result of a confusion of
this species with M . thukuhar. M . messor occurs on stony shores as,
for example, among coral debris (Tweedie, 1049b ; Forest and Guinot,
1961 ; and personal observation).
I n moister places with a superficial layer of soft mud species of
Cleistostomcc, Tylodiplax, Ilyoplax and of other small ocypodid crabs
become common. Most of the species of these genera are rather local,
and only a very small minority of species are widespread.
Of all the crabs found in the bruguiera forests only Sarmntium
crassum Dana and Helice leachii Hess are widespread in the Indo-westPacific.
Juveniles of all species add to the confusion of identification.
The mud lobster Thalassina anomnla is abundant in forests of
Bruguiera gymnorhiza and of B. sexangula but not so conspicuous in
forests of B. cylindrica or of B. parv-flora. It is abundant, too, in the
thickets of Ceriops tagal in the vicinity of Darwin. By its activities
this animal may modify the substratum considerably. At Darwin the
soil level iii ceriops thickets was as much as 50 cm above the level of
adjacent bare areas. Throughout Malaysia, Indonesia and the wetter
parts of Australasia the heap of soil at the entrance of the burrow may
reach a height above the level of the water at medium high tides and
become colonized by the fern Acrostichum aureum, or more commonly
from Malaya to Australia by A . speciosum, and these ferns will shelter
the animals characteristic of the landward fringe.
Large sesarmas which burrow at the bases of the trees also burrow
into the mounds cast up by Thalassina, or even use as refuges the side
175
fallen trees become converted to rotting logs and thus provide shelter
for several kinds of animals. The root systems with their ascending
and descending knees, and the buttresses which support the trunks
also provide shelter.
This portion of the maiigal supports a greater variety of ground
dwelling animals than any other portion. Crabs run everywhere. Most
of them are grapsids, species of Sarmatium, of Helice, of Ilyograpsus,
smaller species of Sesarma mainly of the subgenus Chiromaiztes : e.g.
S. eumolpe de Man, S. dussumieri HM-Edw., S. onychophora de Man,
and 8. indiarum Tweedie in Malaya ; and S. guttatum in eastern Africa.
Species of the subgenus Parasesarma such as S. melissa de Man are also
present in western Malaya. Two species of Metopograpsus, namely
M . frontalis Miers (= M . gracilipes de Man) and M . thukuhar, are
conspicuous. These two crabs seem not to overlap in distribution : the
former is south-east Asian and Australian, while the latter is found in
eastern Africa, Madagascar and several islands. M . messor Forsk. has
been reported from mangrove areas. This is the result of a confusion of
this species with M . thukuhar. M . messor occurs on stony shores as,
for example, among coral debris (Tweedie, 1049b ; Forest and Guinot,
1961 ; and personal observation).
I n moister places with a superficial layer of soft mud species of
Cleistostomcc, Tylodiplax, Ilyoplax and of other small ocypodid crabs
become common. Most of the species of these genera are rather local,
and only a very small minority of species are widespread.
Of all the crabs found in the bruguiera forests only Sarmntium
crassum Dana and Helice leachii Hess are widespread in the Indo-westPacific.
Juveniles of all species add to the confusion of identification.
The mud lobster Thalassina anomnla is abundant in forests of
Bruguiera gymnorhiza and of B. sexangula but not so conspicuous in
forests of B. cylindrica or of B. parv-flora. It is abundant, too, in the
thickets of Ceriops tagal in the vicinity of Darwin. By its activities
this animal may modify the substratum considerably. At Darwin the
soil level iii ceriops thickets was as much as 50 cm above the level of
adjacent bare areas. Throughout Malaysia, Indonesia and the wetter
parts of Australasia the heap of soil at the entrance of the burrow may
reach a height above the level of the water at medium high tides and
become colonized by the fern Acrostichum aureum, or more commonly
from Malaya to Australia by A . speciosum, and these ferns will shelter
the animals characteristic of the landward fringe.
Large sesarmas which burrow at the bases of the trees also burrow
into the mounds cast up by Thalassina, or even use as refuges the side