Difference between Crustaceans and Molluscs (Mollusks)

Crustaceans

It is a taxon under the phylum Arthropoda. Crustaceans include lobsters, crayfish, crabs, shrimps, prawns, barnacles, amphipods, copepods, etc. They differ from other arthropods by the presence of biramous limbs. Their larval forms, like the nauplius (copepods), are unique among crustaceans. Also, the crustaceans moult their exoskeleton to grow.

Most of them are free-living aquatic organisms, while some are terrestrial. Their body is segmented into abdomen, thorax and head. Usually, the thorax and head of these crustaceans are fused to form a cephalothorax. This cephalothorax is covered by a carapace. They also have two pairs of antennae.

Arthropods

They are the largest phylum that includes animals with jointed appendages and a chitinous exoskeleton. Arthropods comprise economically important insects like bees, vectors like mosquitoes, pests like locusts, crustaceans like shrimps and living fossils like king crab.

Explore: Phylum Arthropoda

Molluscs

They are the second-largest phylum that includes organisms with an organ-system level of organisation. They can be aquatic or terrestrial. They are triploblastic, coelomate and bilaterally symmetrical animals. The body of a typical mollusc is unsegmented and is covered by a calcareous shell. They have a distinct head, visceral hump and a muscular foot. There is a skin layer over the visceral hump that forms the mantle. The space between the mantle and hump is called the mantle cavity. This cavity has gills that have both excretory and respiratory functions. Their head has sensory tentacles, and also a mouth with a feeding organ called a radula.

Examples – Apple snail, Cuttlefish, Pearl oyster, Squid, etc.

Crustaceans and Molluscs (Mollusks)

Also Read: Phylum Mollusca

Difference between Crustaceans and Molluscs (Mollusks)

Crustaceans

Molluscs

It is a taxon under one of the largest phylums called Arthropoda.

Mollusca is the second largest phylum under the Animal kingdom.

Their body is segmented into abdomen and cephalothorax.

They have soft unsegmented bodies.

They have a chitinous exoskeleton.

They have a calcareous shell.

They have biramous appendages.

They do not have biramous appendages.

They do not have a muscular foot or a visceral hump.

They have a muscular foot and a visceral hump.

They show unique larval stages like the nauplius and zoea.

Their larval stage includes typical trochophore larvae followed by complex veliger larvae.

Examples – Lobsters, Crabs, Shrimps, Prawns, Barnacles, Copepods, etc.

Examples – Apple snail, Cuttlefish, Pearl oyster, Squid, etc.

Frequently Asked Questions on Difference between Crustaceans and Molluscs (Mollusks)

What are copepods?

They are small crustaceans found in both saltwater and freshwater habitats. Most of them live in underwater stream beds or sinkholes. Their larval stage includes the nauplius. Copepods are a subclass under the class Hexanauplia and subphylum Crustacea.

What are cephalopods?

It is a class under the phylum Mollusca. They have advanced vision and a sensory receptor called statocysts. They also have unique muscular hydrostats. Cephalopods include organisms like octopus, cuttlefish and squid.

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