Arthropoda · arthropods

Portly spider crab

Libinia emarginata

Epialtidae · kelp & spider crabsIUCN: Not evaluated
Portly spider crab
Photo: R. P. Nodder · Public domain · Wikimedia Commons · resized

A slow, round spider crab of Northeast bays that often wears algae and debris as camouflage.

Fun factIts shell is covered in spines and knobs that collect mud and small animals, helping it hide.

Waters
Northeast US, Northwest Atlantic
Depth zone
Coastal shallows & estuaries, Continental shelf
Diet
Algae, carrion & small invertebrates
Size
Carapace up to 10 cm

Classification

Arthropoda › Malacostraca › Decapoda › Epialtidae

  1. Kingdom Animalia animals
    • Many-celled organisms that eat other living things for energy (heterotrophs)
    • Cells have no cell walls
    • Most can move at some stage of life
  2. Clade Bilateria bilateral animals
    • Body has a left and right side that mirror each other (bilateral symmetry)
    • Head end with concentrated nerves; three tissue layers
    • Includes about 99% of all living animal species
  3. Clade Protostomia protostomes
    • In the embryo, the first opening usually becomes the mouth
    • Main nerve cord runs along the belly (ventral)
    • Includes mollusks, worms, and arthropods
  4. Clade Ecdysozoa molting animals
    • Grow by shedding their outer layer (molting, ecdysis)
    • No cilia used for movement
    • Includes arthropods and nematode worms
  5. Phylum Arthropoda arthropods
    • Hard outer skeleton made of chitin (exoskeleton)
    • Jointed legs and a segmented body
    • The largest animal phylum by species count
  6. Subphylum Crustacea crustaceans
    • Two pairs of antennae
    • Branched (biramous) legs in many species
    • Most breathe with gills
  7. Class Malacostraca crabs, shrimp & kin
    • Body of a head, 8-segment thorax, and 6-segment abdomen
    • Includes crabs, shrimp, lobsters, krill, and isopods
  8. Order Decapoda ten-legged crustaceans
    • Ten walking legs, the first pair often with claws
    • Shell covers head and thorax together (carapace)
  9. Suborder Pleocyemata egg-brooding decapods
    • Females carry their eggs under the abdomen until they hatch
    • Includes true crabs, lobsters, and most shrimp
  10. Infraorder Brachyura true crabs
    • True crabs: abdomen tucked tightly under a broad carapace
    • Walk sideways on four pairs of legs
  11. Family Epialtidae kelp & spider crabs
    • Spider and kelp crabs that often decorate their shells for camouflage
  12. Genus Libinia
    • Species in the same genus are very close relatives and often look alike.
  13. Species Libinia emarginata Portly spider crab

Closest relatives in the guide