Amphipoda

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Scheme amphipod anatomy-en

Amphipodredkils (flipped)

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Ampelisca brevicornis

Lepidepecreum longicornis

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Pariambus typicus

Amphipoda is an order within the class Crustacea, comprising more than 9,900 species of small, mostly marine, but also freshwater and terrestrial arthropods. Amphipods are characterized by their compressed bodies and the absence of a carapace, which distinguishes them from other crustaceans. They are commonly referred to as "scuds" or "side-swimmers" due to their distinctive mode of locomotion – they usually swim on their sides by using their pleopods (abdominal appendages) for propulsion.

Description

Amphipods range in size from 1 to 340 millimeters, with most species being less than 10 millimeters in length. Their bodies are divided into three main parts: the head, thorax, and abdomen. The head bears compound eyes, two pairs of antennae (the first pair being usually shorter than the second), and mouthparts adapted for various feeding habits. The thorax has eight segments, each with a pair of appendages, which can be modified for walking, grabbing, or feeding. The abdomen consists of six segments, with the last three segments bearing pleopods for swimming.

One of the most distinctive features of amphipods is their laterally compressed bodies, which allows them to navigate through narrow spaces in the benthic environment. They also have a unique brood pouch (marsupium) where females carry their eggs until they hatch into fully formed juveniles.

Habitat and Distribution

Amphipods are found in almost all aquatic environments, from deep-sea vents and cold seeps to freshwater streams and lakes. They are also present in moist terrestrial environments, such as leaf litter and soil. Marine amphipods are especially diverse in polar regions and are important components of the benthic and pelagic ecosystems, serving as a crucial link in the food web between primary producers and higher trophic levels like fish and whales.

Ecology and Behavior

Amphipods play significant roles in their ecosystems, primarily as detritivores and scavengers, breaking down dead organic matter and recycling nutrients. Some species are herbivores, feeding on algae and phytoplankton, while others are predators or parasites. Their behavior and life history strategies are highly varied, with some species exhibiting complex social behaviors, including territoriality and brood care.

Amphipods are preyed upon by a wide range of animals, including fish, birds, and marine mammals. Their ability to rapidly reproduce and their importance in the food chain make them a key species in assessing environmental health and changes in aquatic ecosystems.

Taxonomy

The order Amphipoda is divided into several suborders and families, reflecting the group's diverse morphologies and habitats. The taxonomy of amphipods is continually being revised as new species are discovered and molecular techniques are applied to understand their evolutionary relationships.

Conservation

While many amphipod species are abundant and not considered at risk, some specialized and habitat-restricted species are vulnerable to environmental changes, pollution, and habitat destruction. Conservation efforts for amphipods focus on protecting their habitats and maintaining the quality of aquatic and terrestrial ecosystems.

In Research and Industry

Amphipods are used in scientific research as model organisms to study toxicology, ecology, and evolutionary biology. They are also important in aquaculture as a source of food for fish and other aquatic animals.