Malacostraca Characteristics

Systematic Position

Kingdom: Animalia
Sub-kingdom: Eumetazoa
Super-phylum: Ecdysosoa
Phylum: Arthropoda
Sub-phylum: Crustacea
Class 5 : Malacostraca

Carapace of Penaeus (red) Source: Wikipedia

Malacostraca Characteristics

Ø  Largest class of sub-phylum crustacea

Ø  Includes crabs, lobsters, shrimps etc.

Giant Tiger Prawn (Malacostraca, Wikipedia)

Ø  Fast movers

Ø  Usually marine, some are fresh water

Ø  Body with 20 segments (very rarely 21 segments)

Ø  Body is divided (tagma) into head, thorax and abdomen

Ø  Head with 5 segments, thorax with 8 segments and abdomen with 6 segments and a telson (total 20 segments)

Carapace of Crab (Source Wikipedia)

Ø  Bear abdominal appendages similar to Remipedia

Ø  Each body segments bear a pair of jointed appendages

Ø  Head with two pairs of antennae

Ø  First pair of antennae biramous

Ø  Second pair of antennae with exopods

Ø  Compound eyes present which is usually stalked

Ø  Mouth parts with mandibles, maxillules and maxillae

Ø  Three thoracic segments fused with the head to form cephalothorax

Ø  The appendages of cephalothorax forms the maxillipeds

Sally Lightfoot Crab (Malacostraca, Wikipedia)

Ø  Carapace usually present

Ø  Each thoracic segments biramous with endopods well developed

Ø  Endopods usually branched, which is being used for crawling or grasping

Ø  Each endopod with seven articulating segments

Ø  The endopod segments are coxa, basis, ischium, merus, carpus, propodus, and dactylus

Ø  In Decapods (an order of Malacostraca which includes crabs, prawns etc) the claw is formed by the articulation of the dactylus against an outgrowth of propodus

Ø  Pleopods present, used for swimming, burrowing and gas exchange

Ø  First and second abdominal pleopods modified into gonopods in males

Ø  Uropod present, uropod with telson makeup the tail fan

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