Malacostracans

Pronunciation

How to pronounce Malacostraca: /ˌmæləkəˈstreɪkə/

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Summary

Class Malacostraca is the largest class of the phylum Crustacea, encompassing around 40,000 species and exhibiting a wide diversity in body forms and ecological roles in marine, freshwater, and terrestrial environments.

Physical Characteristics

Malacostracans have a body divided into three main parts: a five-segmented head, an eight-segmented thorax, and an abdomen with six segments and a terminal telson. Each body segment typically has a pair of jointed appendages. They can vary in size from 1 cm to 36 cm in length, with structures such as a carapace that may cover the thorax and head.

Identification Tips

Look for the presence of three tagmata: head, thorax, and abdomen. Distinctive features include compound eyes on stalks (in most species), pleopods for swimming or brooding eggs, and a telson forming part of the tail fan.

Habitat

Malacostracans are predominantly marine and can be found in all marine environments. They also inhabit freshwater and terrestrial habitats, with significant representation in orders Amphipoda, Isopoda, and Decapoda.

Distribution

Worldwide distribution with approximately 40,000 species, including notable numbers in the decapods (15,000 species), isopods (10,000 species), and amphipods (9,500 species).

Diet

Diet varies widely; most species are scavengers but can include filter feeders, herbivores, and predators such as mantis shrimps and porcelain crabs.

Life Cycle

Typically exhibits gonochorism with distinct sexes. Larval development includes stages that may involve a naupliar larval form in some taxa, with variations across different groups.

Reproduction

Mating behavior involves multiple paternity in some species, and females typically brood their young. Male and female genital openings are situated on different thoracic segments.

Predators

Malacostracans are preyed upon by a variety of marine and terrestrial predators, including fish, birds, and some terrestrial mammals.

Ecosystem Role

Malacostracans serve as important components in aquatic ecosystems, functioning as scavengers and prey for a range of higher trophic levels.

Collecting Methods

• Seine nets
• Traps
• Hand collection
• Beachcombing

Preservation Methods

• Freezing
• Alcohol preservation
• Drying
• Taxidermy techniques

Evolution

Malacostraca is considered monophyletic, supported by both morphological and molecular traits. Their early evolution can be traced back to the Cambrian period, with diverse lineages adapting to multiple ecological niches.

Similar Taxa

• Entomostraca
• Branchiopoda
• Crustacea
• Remipedia

Misconceptions

The name Malacostraca suggests that they have soft shells, which is misleading: their shells are typically hard except immediately after moulting.

Tags

• Crustaceans
• Marine Biology
• Freshwater Biology
• Terrestrial Crustaceans
• Ecology