Amphioxus

Amphioxus

Amphioxus, also known as lancelets, are small, elongated marine animals that belong to the subphylum Cephalochordata. They are considered to be one of the closest living relatives of the vertebrates, making them a significant subject of study in evolutionary biology. Amphioxus are often used as a model organism in research due to their simple body plan and evolutionary significance.

Description

Amphioxus are characterized by their fish-like shape, but they lack the complex structures found in true fish. They have a notochord, a dorsal nerve cord, pharyngeal slits, and a post-anal tail, which are features shared with vertebrates. However, they do not possess a true backbone or vertebrae.

The body of an amphioxus is divided into three main sections: the anterior, middle, and posterior. The anterior end contains the mouth, which is surrounded by oral cirri that help filter food particles from the water. The middle section houses the pharynx with numerous gill slits, which are used for feeding and respiration. The posterior end tapers into a tail fin.

Habitat

Amphioxus are typically found in shallow, sandy environments in temperate and tropical seas. They are benthic animals, meaning they live on or near the seabed. Amphioxus burrow into the sand with only their anterior end protruding, allowing them to filter feed by drawing water through their mouths and out through the pharyngeal slits.

Reproduction

Amphioxus reproduce sexually, with separate male and female individuals. Fertilization occurs externally in the water column. The eggs develop into free-swimming larvae, which eventually settle to the bottom and metamorphose into the adult form.

Evolutionary Significance

Amphioxus are of great interest to scientists studying the evolution of vertebrates. Their simple body plan and genetic makeup provide insights into the early stages of vertebrate evolution. The genome of amphioxus has been sequenced, revealing many genes that are homologous to those found in vertebrates, including humans.

Research and Studies

Amphioxus are used in various research fields, including developmental biology, genomics, and evolutionary biology. Studies on amphioxus have contributed to our understanding of the evolution of the vertebrate nervous system, the development of the notochord, and the origins of the vertebrate immune system.

Also see

• Cephalochordata
• Chordate
• Vertebrate
• Evolutionary biology
• Model organism

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