7 Walking movement of crabs
The crab possesses 5 pair of legs, the first pair being large, stout and modified to chelate while other four are used for are for walking. The male crab folds it bigger chelate while walking. This makes it distinguishable from other crabs of backwater zone.
The crabs always move sideways, synchronizing each walking leg move one after the sideways.
Because of their 5 paired legs, they can move very fast and show high speed in movements for chasing, hunting as well as escaping predation and dangers.
The crabs are very sensitive to vibration since they possess small hairs over the legs, the hairs are not smooth and appears as spines.
SWIFT MOVEMENT BY THE CRABS
8 Borrows
Burrows are dwelling places for crabs and in order to build them they are using their short appendages to burrow the hole and long appendages to go out. The ghost crab Ocypode ceratophthalma (Pallas) creates burrows of variety shapes at different ages. Juveniles (mean carapace length 11 mm) produced shallow J-shaped burrows, which incline vertically into the substratum (mean depth 160 mm). Larger crabs (17–25 mm carapace length) have Y-shaped and spiral burrows (mean depth 361 mm). These Y-shaped burrows have a primary arm, which extends to the surface forming the opening, and a secondary arm which terminates in a blind spherical ending. The two arms join in a single shaft and end with a chamber at the base. The secondary arms and chambers are believed to be used for mating or as a refuge from predation. The spiral burrows have spiral single channel ending in a chamber. Older crabs (mean carapace length 32.6 mm) had simple, straight single tube burrows, which inclined into the substratum at mean of 73° and had a mean depth of 320 mm. During summer daytime periods, the burrows shelter the crabs from heat and desiccation stress. The sand surface temperature at the burrow opening was ~48 °C but temperatures inside the burrows can drop to 32 °C at a depth of 250 mm. Variation in the burrow architecture with crab age appears to be related to the crab’s behavior. Juvenile crabs have smaller gill areas and move out of the burrows regularly to renew their respiratory water and, as a result, they do not need a deep burrow. Larger crabs, in contrast, can tolerate prolonged periods without renewing their respiratory water and therefore create deeper and more complex burrows for mating and refuges. The burrow may slant down at a 45° angle, and has a “turn-about” chamber at the end. The tunnel home is constructed with wet grains of sand so that it will not collapse. In the winter Ghost Crabs hibernate in their burrows, “holding their breath” for six weeks by storing oxygen in specialized sacs near their gills.
ANATOMICAL FEATURES OF CRAB SHOWING APPENDAGES FOR BURROWING
9 Another rare observation included that their exoskeleton color changes behavior wise i.e. one shade during aggression, one during mating ,and one during foraging. This might be because of their hormonal secretions.
THIS MIGHT BE A TYPICAL OBSERVATION OF COLOR CHAGE OF CRABS
10 For communications between the two colonies of crabs, burrows are interconnected.
N.B: Since burrow interconnection cannot be specifically be identified because of experimental procedures and other problems, photography of this particular observation is not available.
AVIFAUNA STUDY AT ALANKARPUR
Diversity of avifauna is one of the most important ecological indicators to evaluate the quality of habitats. Now-a-days, avifaunal diversity has been decreasing due to the destruction of natural habitats and human disturbances. Random destruction of natural habitats by cutting nesting trees and foraging plants for commercial use of woods and lands are the main factor responsible for narrow down in avian foraging habitat and their nesting sites. Thus, many species of birds may be forced to inhabit in the urban areas and constrain them to breed there. Birds are essential animal group of an ecosystem and maintain a trophic level. Therefore, detail study on avifauna and their ecology is important to protect them.
Apart from studying and analyzing the nature and behavior of birds in forest region of talsari and effort to study the behavior of birds were done at a small village name alankarpur near Digha.
The main objective was to study the behavior of birds in anthropogenic conditions.
The time was usually from 6:30am to 8:30am when the surroundings are silent thus the time is favorable and plenty of birds will be available.
To study the avifaunal diversity we chose the Line Transect Method. This generally follows a way of bird watching in a linear fashion quite in the form of straight path extending from one point to another.