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Invertebrates · 9 species guides

Crustaceans: Crabs, Lobsters, Krill & Shrimp

Crustaceans are arthropods that typically have hard exoskeletons, jointed limbs and two pairs of antennae, including crabs, lobsters, hermit crabs, krill, mantis shrimp and horseshoe crabs’ ecological neighbours; most are aquatic and many support commercial fisheries.

Two pairs of antennae
Most crustaceans have two antennal pairs; insects have one; arachnids have none.
Exoskeleton and moult
A hard cuticle is shed in moults so the animal can grow — soft-shell crabs are recently moulted.
Crab versus lobster
Crabs typically have a short abdomen tucked under; lobsters have a long muscular abdomen used for swimming.
Krill schools
Krill are small swimming crustaceans that form vast aggregations — whale food at planetary scale.

Crustaceans moult to grow. Two pairs of antennae and biramous limbs are classic marks, though body plans vary from crab discs to krill swarms. Krill underpin Southern Ocean food webs. Coconut crabs climb trees. Mantis shrimp punch with extraordinary speed. Horseshoe crabs are chelicerates, not crustaceans — a confusion pair worth stating clearly.

Crustacean fisheries remove huge biomass; krill fishing sits at the base of polar food webs. Warming and acidification shift ranges and moulting success, so stock collapses can arrive faster than management cycles. Hermit crabs use borrowed shells; true crabs tuck a short abdomen underneath. This page gathers those marks before the linked guides document status. WARN crustacean guides linked here cover crabs, lobsters, hermit crabs, krill, mantis shrimp and horseshoe crabs, with an explicit note that horseshoe crabs are chelicerates. Consumers and fishers both benefit from knowing which landings sit at the base of polar food webs.

Key facts

  • Crustaceans usually have two pairs of antennae and a moulted exoskeleton.
  • Krill support penguins, seals and baleen whales in the Southern Ocean.
  • Mantis shrimp are stomatopods famous for extremely fast strikes.
  • Coconut crabs are the largest land arthropods and climb for fruit.
  • Horseshoe crabs are not true crabs — they are chelicerates.
  • Overfishing and warming seas restructure crustacean fisheries worldwide.

How to recognise them

The features that separate this group in the field, in the order they are usually most useful.

Two pairs of antennae
Most crustaceans have two antennal pairs; insects have one; arachnids have none.
Exoskeleton and moult
A hard cuticle is shed in moults so the animal can grow — soft-shell crabs are recently moulted.
Crab versus lobster
Crabs typically have a short abdomen tucked under; lobsters have a long muscular abdomen used for swimming.
Krill schools
Krill are small swimming crustaceans that form vast aggregations — whale food at planetary scale.
The confusion pairs
Horseshoe crab versus true crab: horseshoe crabs are chelicerates more closely related to spiders. Hermit crab versus true crab: hermit crabs use borrowed shells.

9 crustaceans guides

Search or filter by conservation status. Every guide carries sourced facts, IUCN status and FAQs.

Showing 1-9 of 9 animals

Animal group
Atlantic horseshoe crab with a domed shell and long pointed tail on a sandy beach
Vulnerable

Invertebrates

A

Atlantic Horseshoe Crab

Limulus polyphemus

The ancient living fossil with blue blood

Oceans · North America

Open guide
Blue crab with bright blue claws and a broad shell on a sandy estuary bottom
Least Concern

Invertebrates

B

Blue Crab

Callinectes sapidus

The swift swimming crab of Atlantic estuaries

Oceans · North America

Open guide
Coconut crab climbing a palm tree trunk at night showing its large orange-brown body and powerful claws
Vulnerable

Invertebrates

C

Coconut Crab

Birgus latro

The world's largest land arthropod and tree-climbing island giant

Asia · Oceans

Open guide
A shore crab on wet sand, its broad hard shell, stalked eyes and two front pincers clearly visible as it walks sideways.
Most species Not Evaluated

Invertebrates

C

Crab

Infraorder Brachyura

Ten-legged, sideways-walking crustaceans found in nearly every watery habitat on Earth.

Oceans worldwide · Coastlines and estuaries

Open guide
Hermit crab peeking out of a spiral snail shell on wet sand
Least Concern

Invertebrates

H

Hermit Crab

Paguroidea

The crustacean that wears borrowed shells

Oceans

Open guide
Dense pink swarm of Antarctic krill underwater in cold blue Southern Ocean water with diffuse sunlight from above
Least Concern

Invertebrates

K

Krill

Order Euphausiacea — Antarctic krill Euphausia superba dominates Southern Ocean biomass

The crustacean swarm that feeds the whale — and the fishery that watches the same stock.

Southern Ocean around Antarctica · Krill orders also occur in all other oceans

Open guide
A clawed lobster (family Nephropidae) on the rocky sea floor, showing its two large front claws, long antennae and segmented exoskeleton.
Not a threatened group; some species data deficient

Invertebrates

L

Lobster

Family Nephropidae

The armoured, blue-blooded crustacean that moults to grow, regrows lost claws and can live for decades.

North Atlantic Ocean · Eastern North America

Open guide
Peacock mantis shrimp with iridescent carapace at a reef burrow
Order page

Invertebrates

M

Mantis Shrimp

Order Stomatopoda — around 500 species, including Odontodactylus scyllarus

A punch that boils water, and eyes that see in ways nothing else does.

Tropical and subtropical shallow seas worldwide · Reefs, rubble and burrows in soft sediment

Open guide
Red sea urchin with long pale spines and dark red test on a kelp forest rocky seabed
Class page

Other animals

S

Sea Urchin

Class Echinoidea — over 950 described species in regular and irregular forms

Spiny echinoderms that graze kelp forests — and some species barely seem to age at all.

All oceans from intertidal to deep sea · Rocky reefs, kelp forests and seagrass beds

Open guide

Conservation: what this group faces

Crustacean fisheries remove huge biomass; krill fishing sits at the base of polar food webs. Warming and acidification shift ranges and moulting success, so stock collapses can arrive faster than management cycles.

Fund invertebrate & habitat protection Current appeals

Crustaceans: frequently asked questions

What is a crustacean?
An arthropod that typically lives in water, moults a hard exoskeleton and has two pairs of antennae — crabs, lobsters, shrimp and krill are familiar examples.
Is a horseshoe crab a crab?
No. Horseshoe crabs are chelicerates, more closely related to spiders and scorpions than to true crabs.
Why do whales need krill?
Many baleen whales filter vast numbers of krill. Southern Ocean food webs are built around krill abundance.
What is a mantis shrimp?
A stomatopod crustacean with raptorial limbs that strike prey at extreme speed — not a true shrimp in the everyday grocery sense.
Are lobsters immortal?
No. They grow by moulting and can live many decades, but they are not immortal; disease, predation and fishing kill them.
Why are some crabs endangered?
Overharvest, habitat loss in mangroves and reefs, and bycatch reduce populations; island endemics are especially vulnerable.

Other types of invertebrates

All invertebrate guides Animals A–Z