True Crabs
Brachyura
Classification
- Phylum: Arthropoda
- Subphylum: Crustacea
- Class: Malacostraca
- Superorder: Eucarida
- Order: Decapoda
- Infraorder: Brachyura
Pronunciation
How to pronounce Brachyura: //brækˈjʊərə//
These audio files are automatically generated. While they are not always 100% accurate, they are a good starting point.
Images
Summary
The infraorder Brachyura encompasses a diverse group of decapod crustaceans known as true crabs, characterized by a reduced tail and possession of a hard exoskeleton. They occupy a variety of habitats and exhibit complex reproductive behaviors, diet flexibility, and cultural significance.
Physical Characteristics
Crabs are generally covered with a thick exoskeleton composed primarily of highly mineralized chitin. They have a short tail-like abdomen that is usually hidden under the thorax, a pair of chelae (claws), six walking legs, and two swimming legs. Size varies significantly among species, from a few millimeters in the pea crab to a leg span of up to 4 meters in the Japanese spider crab.
Identification Tips
Males often have larger claws than females, particularly noticeable in fiddler crabs. Males typically have a narrow and triangular abdomen, while females have a broader, rounded abdomen.
Habitat
Crabs inhabit all the world's oceans, freshwater environments, and land, particularly thriving in tropical regions.
Distribution
Crabs are found globally with about 850 species identified as freshwater crabs.
Diet
Crabs are omnivores, feeding primarily on algae, molluscs, worms, other crustaceans, fungi, bacteria, and detritus depending on availability and species.
Life Cycle
After hatching, crab larvae undergo several zoeal stages in the plankton before transitioning to the megalopa stage, then to juvenile crabs, which live on the ocean floor.
Reproduction
Crabs utilize chemical, visual, acoustic, or vibratory signals for mating, with most species exhibiting internal fertilization. Females carry fertilized eggs externally on their abdomen.
Predators
Larger marine animals such as fishes and sea birds prey upon crabs, while juvenile crabs are also vulnerable to various aquatic predators.
Ecosystem Role
Crabs play critical roles within their ecosystems as scavengers, predators, and prey, contributing to nutrient cycling and energy flow.
Economic Impact
Crabs constitute approximately 20% of all marine crustaceans caught and consumed worldwide, with annual captures reaching 1.5 million tonnes. Various species are of significant commercial value.
Cultural Significance
Crabs have influences in various cultural narratives and mythologies, including the constellation Cancer and stories from different cultures that depict crabs in various significances.
Collecting Methods
- Trapping
- Netting
- Hand-catching
Preservation Methods
- Freezing
- Canning
- Chilling
Evolution
Crabs first appeared during the Jurassic period, with their early fossils dating back to the Early Jurassic. They have undergone significant evolutionary changes, including the reduction of the abdomen and the robustness of the body.
Similar Taxa
- King crabs
- Porcelain crabs
- Anomura (hermit crabs and relatives)
Misconceptions
Some crabs like king crabs and porcelain crabs are often misidentified as true crabs but are not part of the infraorder Brachyura; both have evolved features similar to true crabs through carcinisation.
Tags
- Decapoda
- Crustaceans
- Marine Biology
- Fisheries
- Evolution