Crabs can be preserved wet in 6-10% formalin neutralized with Hexamine i.e., 100 gm per 1000ml formalin. To avoid limb-shedding the unique phenomena of autotomy alive crabs may be norcotized first with few menthol crystals or by adding few drops of chloroform and then preserved in spirit or formalinated spirit for a day or two, to make the autotomizing muscles as well their "breaking-planes' rigid. After this fixing,crabs can be preserved in 6-10% formalin for the laboratory studies.
The prepare a dry exhibit for long term exposure the carapace and the abdomial plate must be removed and glued back after scooping out the flesh. Strong formalin should be injected through the joints of legs and chelae. The carapace can be very easily removed with a simple technique. For theis crab could be held in left palm and let your left your left thumb and index fingers make a grip on the one side legs of the crab. Then the carapace can be pulled away by lifting the last anterolateral spine using the right thumb and simply open the abdominal plate on the ventral side and cut a portion with scissors to scoop out the flesh. Then the crab can be filled with Borax-an absorbant or dry sand and left for one or two hours under any light source. When the crab becomes free from moisture, the Borax or the sand can be brushed out. Strong formalin must be injected through the segmental joints of chela and leg by a syringe. The carapace and abdominal lates can be broken and then wired by a thin copper wire into position and glued with fevicol. Finally a coating with clear varnish "sheenlae " makes the crab shinning.
The colour retension in crabs is now experimented with 5% aqueous Solution of sodium arsenite to preserve red and related colours. Similarly neutralized formalin with glycerine is felt better for the preservation of grey or black coloured specimens. A mixture of 5 gm sodium arsenite and 5 cc formalin in 95 cc water helps to retain white iriedescent carapace colouration.
For the detailed
camera lucida taxonomical studies, the first pleopod or the third maxilliped
can be permanently mounted. Only the left pleopod or third maxilliped i.e.
right as viewed from ventral side of a crab can alone be removed. Afer
treating with caustic potash and staining in fast green,permanent balsam
mounts can be made. While mounting, it should be noted that if the gronopod
is viewed ventrally. Similarly the distal three segments of the third maxilliped
namely propodite, dactylopodite and carpopodite must be facing inwardly.
Temporary mounts can be made with glycerine and alcohol. Instead of camera
lucide, a squared micrometer eye piece is also used to make out line drawings.