Amphipoda

Many small animals live in the water.

These animals are called amphipods. Most live in the sea. Some live in lakes. A few even live on land.

They have bodies with many parts. They have two pairs of feelers on their heads. They also have special legs for eating. These legs help them grab food.

Most amphipods are scavengers. This means they eat bits of food they find. They help keep the water clean. They can be very tiny. Some can grow quite large too. They are amazing little creatures!

Amphipods are small animals that live in water.

Most live in the sea. Some live in lakes. A few even live on land. There are more than 10,700 known species.

Their bodies have 13 parts. These parts are the head, thorax, and abdomen. The head has two pairs of antennae. Antennae are long feelers used to sense the world. They also have special legs called gnathopods. These legs help them grab food.

Most amphipods are scavengers. They eat bits of food they find. This helps keep the water clean. They can be very tiny. Some are less than 1 millimeter long. Other large kinds can grow to 340 millimeters.

Some amphipods live in caves. These are called troglobitic species. Others live in the deep ocean. Some even live on whales. These are called whale lice. They use strong claws to stay attached to the whale.

Amphipods are a big part of life in the water.

Amphipods are amazing little creatures that belong to a group called crustaceans.

They are found in almost every kind of water on Earth. Most live in the salty ocean, but some live in fresh water. There are even some that live on land in damp places. Scientists have found more than 10,700 different species of them. They play a huge role in keeping water environments healthy.

They often act as scavengers by eating bits of food left behind.

An amphipod's body is divided into thirteen distinct segments. These segments make up the head, the thorax, and the abdomen. The head is attached to the thorax and has two pairs of antennae. It also has one pair of eyes that do not sit on stalks. One of the most special parts is the gnathopods. These are modified legs that they use for feeding. The thorax and abdomen are usually pressed flat from side to side.

This shape helps them move through their watery homes.

Learning about their history helps us see how long they have been around. Scientists think amphipods first appeared during the Lower Carboniferous period. However, it is hard to find their fossils from that long ago. Most of the fossils we know come from much later times. For example, some have been found in Baltic amber from the Upper Eocene. We also have one species from the Lower Cretaceous found in the United Kingdom.

This shows they have survived for a very long time.

Amphipods come in many different sizes and shapes. Some are tiny and less than one millimeter long. Others, like the species Alicella gigantea, can grow very large in the deep ocean. In the Kermadec Trench, some have been seen reaching 340 millimeters in length. Their size often depends on how much oxygen is in the water. For instance, those in Lake Titicaca stay small because of the high altitude. In Lake Baikal, they can grow much larger because of the oxygen levels.

You might recognize some amphipods by the names people use for them. Anglers often call them freshwater shrimp, scuds, or sideswimmers. These names come from the way they swim through the water. Some species even live in a special way with other animals. For example, whale lice live on baleen whales using strong claws. Other types live in dark caves or even in the deepest parts of the ocean.

They are truly a diverse group of living things.

Amphipoda is a large order of malacostracan crustaceans. These animals are vital members of global marine ecosystems. They are found in almost every aquatic environment on Earth. Most species live in the salty ocean. However, about 2,250 species live in fresh water. Some even live on land in damp places like leaf litter. Scientists currently recognize more than 10,700 different species.

The anatomy of an amphipod is quite specialized. Their bodies are divided into 13 segments. These segments form the head, the thorax, and the abdomen. The head is fused to the thorax. It carries two pairs of antennae and one pair of compound eyes. These eyes are sessile, meaning they do not have eyestalks. A unique feature is the gnathopods. These are specialized feeding legs used to grasp food.

An amphipod's body structure also helps it move and breathe. Most species have bodies that are laterally compressed. This means they are flattened from side to side. The thorax contains eight pairs of uniramous appendages. These legs are used for movement and feeding. Gills are located on the thoracic segments to help them breathe. They have an open circulatory system. A heart pumps haemolymph through the body. This fluid uses haemocyanin to carry oxygen to their tissues.

The abdomen is split into two distinct sections. The first is the pleosome, which holds swimming legs. The second is the urosome. The urosome includes a telson and three pairs of uropods. Amphipods are unique because they possess more than one pair of uropods. This distinguishes them from other malacostracan crustaceans. Their size can vary significantly depending on their environment. Tiny species are less than 1 millimeter long.

Environmental factors strictly control how large an amphipod can grow. Dissolved oxygen levels are a major limiting factor. In Lake Titicaca, high altitude limits growth to 5 millimeters. In contrast, amphipods in Lake Baikal can grow much larger. Some deep-sea species are massive. The species Alicella gigantea can reach very large lengths. In the Kermadec Trench, specimens have been photographed at 340 millimeters.

Amphipods have complex life cycles and behaviors. Many species engage in amplexus. This is a behavior where a male grasps a female with his gnathopods. He carries her against his ventral surface for two to fifteen days. This guarding ends when the female molts. Mature females have a marsupium, which is a brood pouch. This pouch holds the eggs until they hatch. There are no larval stages in their life cycle. The eggs hatch directly into juvenile forms.

Feeding habits vary across the order. Most are detritivores or scavengers. They eat dead organic matter or algae. Some species use compensatory feeding. This means they eat large amounts of low-quality food. This behavior might help them avoid predators. Some species, like Ampithoe longimana, are very sedentary. They stay on host plants to minimize risk. Other mobile species can actively pursue better food sources.

The history of amphipod classification is constantly changing. Scientists used to group them into four suborders. Modern research by James K. Lowry and Alan Myers changed this. They used cladistic analysis to create a new system. Now, there are six recognized suborders. The largest is Senticaudata, which includes over 6,000 species. This group contains almost all freshwater species. The fossil record for amphipods is quite meagre. They likely originated in the Lower Carboniferous period.