Note From the Editor:

This is a companion article to the one we did on copepods a couple of weeks ago. Aquarists tend to refer to copepods, amphipods, and isopods in one breath, yet they are actually quite different creatures. Amphipods share the same kingdom, phylum, and subphylum, Crustacea, but beyond that, they diverge. We will address isopods separately in a future article.


The Amazing Amphipods

What are these fascinating creatures? The amphipods are tiny crustaceans related to prawns and crabs. They most resemble tiny shrimp. There are an incredible 9,900 species of amphipods at the time of this writing. You can find these animals in freshwater, saltwater, and the saltwater aquarium. Like copepods, they have been found at every depth and salinity in the ocean that has been explored. They are exceptionally abundant!

Many sea animals feed on amphipods, and because of this, most of them like to hide. Birds and different kinds of fish eat amphipods for their survival. You can find these creatures under seaweed, leaf litter, or below the rocks.

Are amphipods harmful? Not really. They are good at controlling brown algae and are usually scavengers, although some are predators of smaller crustaceans.

Regarding mating, males are very clingy to the females. Females prefer keeping their young ones in a little pouch like kangaroo!

At 600 feet below the Antarctic Sheet, a special camera designed by NASA's Jet Propulsion Laboratory caught a photo of an unexpected visitor: an amphipod.

This photo is courtesy of NASA, and used with permission following their guidelines.

The Etymology of Amphipods

The name amphipod is derived from the Latin word, Amphipoda. This is in connection with the two types of legs that amphipods possess.

The Taxonomy of Amphipods

According to the research done by the University Students of Tasmania in Australia, the taxonomical classification of Amphipods is as noted below. Go through this meticulous scientific survey done by the Australian scholars.


Phylum: Arthropoda

Subphylum: Crustacea

Class: Malacostraca

Superorder: Peracarida

Order: Amphipoda

The Anatomy of Amphipods

Amphipod anatomy.

This diagram is courtesy of © Hans Hillewaert and is borrowed from Wikimedia. It is used with permission through Creative Commons License 4.0.

An amphipod is divided into thirteen segments. They can be grouped into head, abdomen, and thorax.

The Head

The head of this creature is attached to the thorax. According to the research that has been done to date, the head has one pair of sessile compound eyes, and two pairs of antennae. The head carries the mouthparts, which are mostly concealed.

The Abdomen

The abdomen of the amphipod is divided into two parts.

These are:

Pleosome: this comprises the swimming legs

Urosome: it bears three pairs of uropods and a telson

The Thorax

The thorax of amphipods comprise eight (8) pairs of uniramous attachments. The first attachment is used as accessory mouthparts, the next four (4) pairs are pointed forward, and the last three pairs are directed backward.

The gills of amphipods are found on the thoracic segments, and amphipods also have an open circulatory system with a heart. The respiratory system of this pretty animal has haemocyanin, which carries oxygen in haemolymph to the tissues. The digestion and defecation of salts are regulated by specific glands on the antennae.

The Difference between Amphipods and Copepods

Most folks confuse these creatures. Amphipods and copepods share primary crustacean features and look similar in physical appearance. These two creatures are both sea animals that are commonly kept in salt water tanks. Because of their small size, most of the time, laymen cannot differentiate between them correctly.

The Amphipods

Amphipods are tiny crustaceans of Amphipoda group. According to the research that has been done by the Amphipodologists, it appears that Amphipoda are typically (0.0394-13.4 inches) in length. The creatures are flat and have numerous appendages which include thoracic legs, antennae, and gnathopods. Amphipods present as handy food in a salt water tank for the larger fish.

The Copepods

Copepods are typically smaller than amphipods. A copepod is usually 0.04-0.08 inches in length. They are difficult to notice in a saltwater aquarium unless they appear in large numbers. A copepod has a single eye at the center of the head unlike Amphipoda which have paired eyes.

Copepods do not have a complex respiratory system. They take oxygen in their bodies through diffusion. Amphipods have a heart and gills for their circulatory system.


Isopods, unlike amphipods and copepods, have a cephalon, a pereon with 8 segments, and a pleon with 6 sections, some of which may be attached. Isopods are typically even smaller with an approximate length of about 0.3mm although larger ones do exist. Isopods are regularly recognized because of their dorsoventral appearance. This is a distinguishable feature from other sea creatures. The above characteristics are the ones that distinguish amphipods from isopods.

An amphipod, Gammarus locusta, a benthic amphipod from the North Sea.

This photo is courtesy of © Hans Hillewaert and is borrowed from Wikimedia. It is used with permission through Creative Commons License 4.0.

Benefits of Amphipods in a Saltwater Tank

A lot of people may ask themselves, ‘’are amphipods useful in a saltwater tank?’’ The answer is YES!

Many individuals try to keep ample amphipods in their aquarium purposely for feeding other kinds of livestock in the saltwater tank. These creatures can also be kept in a saltwater tank for aesthetic purposes. Amphipods are eye-catching animals that like moving up and down in the saltwater tank.

Wrapping Up

Amphipods, like copepods, are interesting sea creatures. Since they are larger than copepods, they are easier for the aquarist to see and useful to have in your tank.

We've looked at amphipod etymology, taxonomy, and anatomy and briefly looked at the differences between amphipods, copepods, and isopods. References are listed below for further information.


Barnard, J.L. and Barnard, C.M. 1983a. Freshwater Amphipoda of the World. I. Evolutionary Patterns. Hayfield Associates, MtVernon, Virginia: 1–358, pls. I–XVII.

Friend, James Anthony 1980 , 'The taxonomy, zoogeography and aspects of the ecology of the terrestrial amphipods (Amphipoda: Talitridae) of Tasmania', PhD thesis, University of Tasmania.

J. M. Guerra-García & I. Takeuchi (2004) The Caprellidea (Crustacea: Amphipoda) from Tasmania, Journal of Natural History, 38:8, 967-1044, DOI: 10.1080/0022293021000054497


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Author Profile: Joseph Keenman

Harvard-educated Joseph Keenman is a freelance science and business writer based in the UK.