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Crustaceans vs. Molluscs: Know the Difference

Shumaila Saeed
By Shumaila Saeed || Updated on December 25, 2023
Crustaceans are aquatic animals with exoskeletons and segmented bodies, like crabs and lobsters, while molluscs are a diverse group including snails and clams, often with soft bodies and sometimes shells.
Crustaceans vs. Molluscs

Key Differences

Crustaceans are a diverse group of arthropods that include creatures like crabs, lobsters, and shrimp, characterized by their chitinous exoskeletons and jointed limbs. Molluscs, on the other hand, are a large phylum of invertebrates ranging from slugs and snails to octopuses and clams, often distinguished by a soft body and, in many cases, a calcium carbonate shell.
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Dec 16, 2023
The body structure of crustaceans is segmented and often divided into a head, thorax, and abdomen, with a variety of specialized appendages for different functions. Molluscs display a more varied body structure, ranging from the segmented anatomy of cephalopods like squid to the simple, unsegmented bodies of gastropods like snails.
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Crustaceans typically breathe through gills and are mostly aquatic, living in both marine and freshwater environments. Molluscs have diverse respiratory systems; some, like bivalves and gastropods, have gills, while others, like terrestrial snails, have adapted to breathe air.
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Reproduction in crustaceans often involves complex mating rituals and direct fertilization, whereas molluscs exhibit a wide range of reproductive strategies from direct fertilization in cephalopods to external fertilization in many bivalves.
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The sensory organs of crustaceans, which include compound eyes and antennae, are adapted for their aquatic life. In contrast, molluscs have varied sensory structures, with cephalopods like octopuses having highly developed eyes and nervous systems, while others may have simpler sensory organs.
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Comparison Chart

Body Structure

Segmented with exoskeleton
Often soft-bodied, some with shells
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Habitat

Primarily aquatic
Aquatic and terrestrial
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Respiratory System

Gills
Gills or lungs
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Reproduction

Mostly direct fertilization
Ranges from direct to external fertilization
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Sensory Organs

Compound eyes, antennae
Varied, from simple to complex
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Crustaceans and Molluscs Definitions

Crustaceans

Members of the class Crustacea, including lobsters, crabs, and shrimp.
Lobsters are large crustaceans known for their delicious taste.
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Dec 04, 2023

Molluscs

Soft-bodied invertebrates, often with a shell, like snails and clams.
Snails, a type of mollusc, are known for their slow movement and spiral shell.
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Crustaceans

Creatures within the arthropod phylum that typically have a carapace.
The hermit crab, a unique crustacean, uses discarded shells for protection.
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Molluscs

Members of the phylum Mollusca, including squid, octopuses, and slugs.
Octopuses, intelligent molluscs, are famous for their eight arms and camouflage skills.
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Crustaceans

Marine and freshwater organisms with a chitinous shell.
Shrimp, small crustaceans, are a popular seafood choice.
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Molluscs

A diverse group of animals, from sea slugs to bivalves.
Sea slugs, colorful molluscs, are known for their striking appearance.
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Crustaceans

Arthropods characterized by segmented bodies and antennae.
The crayfish, a freshwater crustacean, resembles a small lobster.
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Molluscs

Organisms in the Mollusca phylum, characterized by a muscular foot and radula.
The garden snail, a common mollusc, uses its muscular foot to glide over surfaces.
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Crustaceans

Aquatic arthropods with jointed limbs and a hard exoskeleton.
Crabs, a type of crustacean, are commonly found along the shoreline.
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Molluscs

Invertebrates with a mantle, which may produce a hard calcium carbonate shell.
Clams, molluscs that live buried in sand, filter feed through their siphons.
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Crustaceans

Plural of crustacean
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Molluscs

Any of numerous chiefly marine invertebrates of the phylum Mollusca, typically having a soft unsegmented body, a mantle, and a protective calcareous shell, and including the snails, clams, and squids.
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Molluscs

Variant of mollusk.
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Molluscs

Plural of mollusc
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Repeatedly Asked Queries

What is a common feature of molluscs?

Molluscs are characterized by their soft bodies, which are often protected by a hard shell.
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What defines a crustacean?

Crustaceans are arthropods with hard exoskeletons, segmented bodies, and jointed appendages.
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Are crustaceans considered intelligent?

Crustaceans are not typically known for high intelligence, but some species show complex behaviors.
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What is the habitat of most molluscs?

Molluscs are found in diverse habitats, including both marine and terrestrial environments.
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How do molluscs sense their environment?

Molluscs have varied sensory organs, from simple tentacles to complex eyes in cephalopods.
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What is the lifespan of crustaceans?

The lifespan of crustaceans varies widely among species, from a few years to over a decade.
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What is the largest group of molluscs?

The largest group of molluscs is the class Gastropoda, which includes snails and slugs.
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Are crustaceans used in human cuisine?

Yes, many crustaceans like shrimp, crabs, and lobsters are popular in human cuisine.
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How do crustaceans reproduce?

Most crustaceans reproduce sexually with direct fertilization.
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Can crustaceans live out of water?

Some crustaceans can survive out of water for short periods, but most are aquatic.
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How do crustaceans protect themselves?

Crustaceans use their hard exoskeletons for protection and can also use camouflage and defensive behaviors.
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Can crustaceans regenerate lost limbs?

Many crustaceans can regenerate lost limbs, although this ability varies among species.
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Do crustaceans have a social structure?

Some crustaceans exhibit social behaviors, but many are solitary.
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How do molluscs feed?

Molluscs have varied feeding habits, from filter feeding in bivalves to hunting in cephalopods.
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Do molluscs play an ecological role?

Yes, molluscs play significant roles in ecosystems, such as nutrient cycling and as food sources.
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What is the economic importance of crustaceans?

Crustaceans are economically important as seafood and in aquaculture.
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Are molluscs important in research?

Yes, molluscs like squid and snails are important models in neurological and environmental research.
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What is unique about cephalopod molluscs?

Cephalopod molluscs like octopuses are known for their intelligence, complex behavior, and ability to change color.
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What are the conservation concerns for molluscs?

Many mollusc species face threats from habitat loss, pollution, and climate change.
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How do molluscs contribute to biodiversity?

Molluscs contribute significantly to biodiversity, with a wide range of forms and ecological roles.
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About Author
Shumaila Saeed
Written by
Shumaila Saeed
Shumaila Saeed, an expert content creator with 6 years of experience, specializes in distilling complex topics into easily digestible comparisons, shining a light on the nuances that both inform and educate readers with clarity and accuracy.

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