Taxonomy of Shellfish

9.1. Chief characters used in the identification of crab

Unit 9 - Taxonomy of Crabs

9.1. Chief characters used in the identification of crabs

Section (Infraorder) 2. Anomura
Normal abdomen; bent beneath the thorax or asymmetrical.
Few gills
Eg. Hermit crabs (Eupagurus), Coconut crabs (Birgus), Sand or Mole crabs (Hippa, Emerita Galathea).
Section (Infraorder) 3. Brachyura

• Abdomen greatly reduced, hard, permanently flexed under cephalothorax.
• Very large carapace.
• Rostrum and uropods absent.
• First legs unusually large and chelate.
• Few gills.

Eg. True crabs (Portunus, Carcinus, Uca)
Spider crabs (Macrocheira, Libinia)
This section consists of commercially important marine crabs. Hence it is dealt in detail.

Systematic position
Phylum : Arthropoda
Class : Crustacea
Sub-class : Malacostraca
Series : Eumalacostraca
Super-order: Eucarida
Order : Decapoda
Sub-order : Reptantia
Section (Infraorder): Brachyura

General morphology

Carapace is very large. Abdomen is greatly reduced and hard. It is greatly reduced and hard. It is permanently flexed under cephalothorax. Eyes are stalked. First pair of legs very large and chelate.

Chief characters used in the identification of crabs

Carapace shape, lateral and frontal spines, structure of 3rd maxilliped, structure and juxta - position of gonopods in males or the nature of gonopores in females coupled with the studies of the fourth arthrophragon are helpful in taxonomy of crabs.