types of crabs - Parker Core Knowledge

Understanding the Context

What is a Crab? Basic Biology and Classification

Crabs belong to the order Decapoda, which means “ten legs”—a defining trait of all true crabs. They typically feature:

• Hard calcium-carbonate exoskeleton
  
• Large, bulging eyes on stalks
  
• Strong, jointed claws used for feeding and defense
  
• Segmented body divided into cephalothorax and abdomen

Most crabs are marine, but some species live in brackish water, freshwater, or even on land. They range from micro-scaled crabs no bigger than a human fingernail to gargantuan species that stretch over 12 feet across.

Key Insights

Major Types of Crabs by Habitat and Species

To better understand crab diversity, it helps to categorize them by environment and appearance. Below is a guide to the most interesting types:

1. Marine Crabs: Ocean Dwellers

Final Thoughts

Marine crabs thrive in saltwater habitats and include diverse families such as Grapsidae, Ocypodidae, and Petrolistiaeidae (mud crabs and fiddler crabs).

• Fiddler Crabs (Genus Uca)
  Known for their dramatically asymmetrical claws—one claw can be up to two-thirds the crab’s body size—fiddler crabs are famous for territorial displays and burrowing in sandy shores.

• Blue Crab (Callinectes sapidus)
  A prized delicacy in seafood cuisine, blue crabs are prized for their sweet, firm meat and spread across the Atlantic and Gulf coasts.

• Japanese Spider Crab (Macrocheirakanaga)
  The largest crab species by leg span (up to 3.8 meters / 12.5 ft), this deep-sea creature has spindly legs meant for slow movement rather than speed.

2. Brackish and Estuarine Crabs