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[Kingdom: Animalia] [Phylum: Arthropoda] [Clade: Pancrustacea] [Subphylum: Crustacea]
Estimates vary, but research suggests there are around 68,000 different species of small marine crustaceans living in the seas and oceans.
Sea crustaceans vary in size from as little as 0.1 mm (e.g. Stygotantulus stocki) to almost four metres long (e.g. the Japanese spider crab).
In simple terminology, invertebrate crustaceans are a diverse group of aquatic arthropods.
This generalised characterisation usually combines a hard exoskeleton (made of chitin), a segmented body, and jointed appendages.
The common and economically important saltwater crustaceans are:
This group is made up of around 25,000 different species. The hard exoskeleton helps to protect their segmented body (e.g. the head, thorax, and abdomen).
Even though the external skeleton does not grow, it actually molts periodically and therefore must be replaced by a new one.
Key takeaways:
The eyes are often extended on stalks and consist of multiple lenses (known as "compound eyes"). Two pairs of extended antennae operate as feelers and sensory organs.
Appendages on the abdomen, thorax, and tail are used for walking, grabbing, and for swimming (in some species). Saltwater crustaceans reproduce eggs that hatch into minute larvae that differ from the adult form.
Tasty seafood crustaceans such as lobsters, shrimps, and crabs are farmed or caught for consumption. The edible scavengers are important as a human food source and a delicacy in some countries.
Fish and other marine animals eat small crustacea rich in nutrients - known as copepod crustaceans or krill. Thus, copepods and other planktons are important tiny organisms (sometimes parasites) that exist in the aquatic food chain.
Copepods are a diverse group of microscopic aquatic crustaceans. Yet, almost all of the 12,000 different copepod species measure less than two (2) millimetres in size.
This guide highlights some of the key facts about copepod crustaceans and the pivotal role they have in healthy marine ecosystems.
There are more than seven thousand (7,000) different species of crabs, and most of them are members of a select group known as decapod crustaceans.
Even though humans eat a lot of seafood animals, including the blue crab, this section contains information about invertebrate crabs that scuba divers see living in the seas and oceans.
The marine species of shrimps have five (5) pairs of fragile legs known as 'swimmerets or pleopods' which they use to swim and perch.