Lancelet
A lancelet is a small, elongated, translucent marine chordate belonging to the subphylum Cephalochordata. Also known as amphioxus, they are considered to be among the closest living relatives of the vertebrates. Lancelets inhabit shallow coastal waters and are found in temperate and tropical regions worldwide, typically buried in sand or other substrate with their anterior end exposed to filter feed.
Description:
Lancelets are characterized by their slender, fish-like bodies which typically reach a length of around 5-7 centimeters. They lack a distinct head, jaws, or paired fins. A key feature is the presence of a notochord that extends the entire length of the body, providing structural support. They possess a dorsal nerve cord, pharyngeal gill slits used for filter feeding, and a post-anal tail – all defining characteristics of chordates. The body is segmented, evident in the arrangement of the muscle blocks (myomeres). Lancelets have a simple circulatory system without a heart, relying on contractile vessels to circulate blood. They lack specialized respiratory organs, relying on diffusion across their body surface for gas exchange.
Classification:
- Kingdom: Animalia
- Phylum: Chordata
- Subphylum: Cephalochordata
Ecology and Behavior:
Lancelets are filter feeders, drawing water into their mouths with cilia and filtering out microscopic plankton and organic particles using their pharyngeal gill slits. The filtered water exits through the atriopore, an opening on the ventral side of the body. They are benthic organisms, typically found buried in the sand with their anterior end exposed. Lancelets exhibit avoidance behavior when disturbed, quickly burrowing into the substrate.
Significance:
Lancelets are important in evolutionary studies as they provide insights into the origins of vertebrates. Their relatively simple body plan and the presence of chordate features make them a valuable model for understanding the evolution of the vertebrate body plan. They are also used in developmental biology research.