212
WILLIAM MACNAE
Miss Jocelyn Crane has suggested to me (in conversation) that in
her opinion U . Zongidigitum is a form of U . bellator. If this is so, then
this species is tolerant of a very wide range of salinity for in the latter
form it occurs characteristically on flats with salt glistening on the
surface.
d. Breathing specializations
The crabs living in the mangal show various degrees of adaptation
towards a terrestrial life. These are mainly associated with respiratory
processes m d water economy, and these two are correlated with one
another. There is a tendency towards a vascularization of the walls of
the gill cavity. There is also a tendency towards an economical use
of water.
Land crabs of the genera Cardisoma, Geograpsus and Gecarcinides
and the hermits Coenobita and Birgus latro (see Harms, 1920, 1931)
show amongst them a considerable conquest of the land. Most of these
genera are not, however, normally related to the mangal, and apart
from the species ofCardisorna it is doubtful if any of them have become
terrestrial via the mangal.
There are two Indo-Pacific species of Cardisoma: C. carnifex is or
seems to be restricted to wooded, rather than forested, terrestrial
fringes of the mangrove areas, while C. hirtipes rarely, if ever, comes
down to sea-level. C. carnifex during most of the year does not stir far
from its burrow. C. hirtipes is reported to be able to go for several days
without visiting water ; it is apparently able to live and forage for some
time between its occasional visits to a well or pool of fresh or only
slightly brackish water.
The breathing technique used by Cardisoma is the same as that used
by several other crabs which live in the mangal and its landward
fringes, and also some of those characteristic of sandy beaches. Several
species of Ocypode, of Uca and presumably also several of the other
smaller ocypodid genera possess, like Cardisoma, gills which are reduced
in number and stiff so that they do not adhere to one another out of
water. The walls of the gill chamber are vascularized and so this acts
as a lung. This group of crabs pump air through the water that is
retained in the gill chamber and so require to make fairly frequent
visits to water to replace the water which is continually being used up
in breathing activities.
It has long been known that crabs of the genus Sesarrna have a
mechanism which is presumed to be connected with oxygenation of
water. A streaming of water over the carapace was first described by
Miiller (1863) for Aratus pisoni (H.M.-Edw.), an American sesarmine
WILLIAM MACNAE
Miss Jocelyn Crane has suggested to me (in conversation) that in
her opinion U . Zongidigitum is a form of U . bellator. If this is so, then
this species is tolerant of a very wide range of salinity for in the latter
form it occurs characteristically on flats with salt glistening on the
surface.
d. Breathing specializations
The crabs living in the mangal show various degrees of adaptation
towards a terrestrial life. These are mainly associated with respiratory
processes m d water economy, and these two are correlated with one
another. There is a tendency towards a vascularization of the walls of
the gill cavity. There is also a tendency towards an economical use
of water.
Land crabs of the genera Cardisoma, Geograpsus and Gecarcinides
and the hermits Coenobita and Birgus latro (see Harms, 1920, 1931)
show amongst them a considerable conquest of the land. Most of these
genera are not, however, normally related to the mangal, and apart
from the species ofCardisorna it is doubtful if any of them have become
terrestrial via the mangal.
There are two Indo-Pacific species of Cardisoma: C. carnifex is or
seems to be restricted to wooded, rather than forested, terrestrial
fringes of the mangrove areas, while C. hirtipes rarely, if ever, comes
down to sea-level. C. carnifex during most of the year does not stir far
from its burrow. C. hirtipes is reported to be able to go for several days
without visiting water ; it is apparently able to live and forage for some
time between its occasional visits to a well or pool of fresh or only
slightly brackish water.
The breathing technique used by Cardisoma is the same as that used
by several other crabs which live in the mangal and its landward
fringes, and also some of those characteristic of sandy beaches. Several
species of Ocypode, of Uca and presumably also several of the other
smaller ocypodid genera possess, like Cardisoma, gills which are reduced
in number and stiff so that they do not adhere to one another out of
water. The walls of the gill chamber are vascularized and so this acts
as a lung. This group of crabs pump air through the water that is
retained in the gill chamber and so require to make fairly frequent
visits to water to replace the water which is continually being used up
in breathing activities.
It has long been known that crabs of the genus Sesarrna have a
mechanism which is presumed to be connected with oxygenation of
water. A streaming of water over the carapace was first described by
Miiller (1863) for Aratus pisoni (H.M.-Edw.), an American sesarmine