FAUNA AND FLORA OF MANGROVE SWAMPS
167
Species of Cerithidea, at low tide periods, cling to the more shady
side of the tsees (Fig. 49) and spread out over the soil while the tide is
in. They are commonest in the avicennia and bruguiera forests of the
landward fringe. Nerita birmanica Phil. clings to the lowermost levels
of the trunks and to the prop roots of Rhizophora. Thais ltissoti (Petit)
also occurs a t this level, being especially common where the barnacle
Chthainalzcs withersii Pilsbry is found on the trunks, twigs and pneumatophores. Occasionally Murex adustus also climbs off the surface of the
mud on to the bases of the trunks and on to the prop roots, etc.
Barnacles, chiefly forms or varieties of the tropicopolitan Balanus
amphitrite Darwin, of which the forma cirratus Darwin is the common
form at Singapore and in Malaya and f. denticulata the common form
in eastern Africa, are abundant on the prop roots of the rhizophora
trees. I n South East Asia Chthamalus withersii is also common and
lives a t a slightly higher level on the roots and trunks. Oysters, one or
other of the spiny forms of Crassostraea cucullata (Q. and G.), are also
abundant and compete for space with the barnacles. The tiny crab
Nannosesarma minuta (de Man) runs about among the barnacles and
oysters, as characteristic a form here as it is at a similar level on coral
islands off shore. The hermit crab Clibanarius longitarsus also climbs
into the trees, reaching heights well above that reached by normal
high tides.
B. “ Horizontal ” zonation through the mangal
The animals discussed in this section are those which live on or in
the substratum and rarely if ever climb the trees.
I n describing the zonation of these animals it is convenient to refer
them to the zones of trees and plants described above (see Figs. 17-19,
between pp. 104-105).
1. The landward fringe of the mangal
This is the equivalent of the supralittoral fringe of the Stephensons’
scheme for rocky shores.
On tropical and subtropical non-rocky shores from the level of high
water of ordinary spring tides upwards occur a number of crabs and
hermit crabs. These animals are mostly secretive in habit and are not
easily located, nor are their habits easy to study. These crabs rarely
occur in the mangal except in drier areas or on islands where the
pes-caprae association may abut on the mangal.
To this group belong such well-known forms as the robber hermit
crab Birgus latro L. which is only rarely and exceptionally encountered
in the mangal. Related forms of the genus Goenobita which carry shells
167
Species of Cerithidea, at low tide periods, cling to the more shady
side of the tsees (Fig. 49) and spread out over the soil while the tide is
in. They are commonest in the avicennia and bruguiera forests of the
landward fringe. Nerita birmanica Phil. clings to the lowermost levels
of the trunks and to the prop roots of Rhizophora. Thais ltissoti (Petit)
also occurs a t this level, being especially common where the barnacle
Chthainalzcs withersii Pilsbry is found on the trunks, twigs and pneumatophores. Occasionally Murex adustus also climbs off the surface of the
mud on to the bases of the trunks and on to the prop roots, etc.
Barnacles, chiefly forms or varieties of the tropicopolitan Balanus
amphitrite Darwin, of which the forma cirratus Darwin is the common
form at Singapore and in Malaya and f. denticulata the common form
in eastern Africa, are abundant on the prop roots of the rhizophora
trees. I n South East Asia Chthamalus withersii is also common and
lives a t a slightly higher level on the roots and trunks. Oysters, one or
other of the spiny forms of Crassostraea cucullata (Q. and G.), are also
abundant and compete for space with the barnacles. The tiny crab
Nannosesarma minuta (de Man) runs about among the barnacles and
oysters, as characteristic a form here as it is at a similar level on coral
islands off shore. The hermit crab Clibanarius longitarsus also climbs
into the trees, reaching heights well above that reached by normal
high tides.
B. “ Horizontal ” zonation through the mangal
The animals discussed in this section are those which live on or in
the substratum and rarely if ever climb the trees.
I n describing the zonation of these animals it is convenient to refer
them to the zones of trees and plants described above (see Figs. 17-19,
between pp. 104-105).
1. The landward fringe of the mangal
This is the equivalent of the supralittoral fringe of the Stephensons’
scheme for rocky shores.
On tropical and subtropical non-rocky shores from the level of high
water of ordinary spring tides upwards occur a number of crabs and
hermit crabs. These animals are mostly secretive in habit and are not
easily located, nor are their habits easy to study. These crabs rarely
occur in the mangal except in drier areas or on islands where the
pes-caprae association may abut on the mangal.
To this group belong such well-known forms as the robber hermit
crab Birgus latro L. which is only rarely and exceptionally encountered
in the mangal. Related forms of the genus Goenobita which carry shells