Sea squirt

Sea Squirt

Sea squirts, also known as ascidians, are marine invertebrates belonging to the subphylum Tunicata within the phylum Chordata. They are notable for their sac-like body structure and their ability to filter feed by drawing water through their bodies. Sea squirts are found in oceans worldwide, from shallow waters to the deep sea.

Anatomy and Physiology

Sea squirts have a simple body plan characterized by a tough outer covering called a tunic, which is composed of a cellulose-like carbohydrate. The body is divided into two main parts: the siphons and the pharyngeal basket.

Siphons

Sea squirts possess two siphons: the incurrent siphon, through which water enters, and the excurrent siphon, through which water exits. These siphons are used for feeding, respiration, and excretion.

Pharyngeal Basket

The pharyngeal basket is a large, perforated structure that filters food particles from the water. Cilia on the pharyngeal basket create a current that draws water in through the incurrent siphon. Mucus secreted by the endostyle traps food particles, which are then transported to the digestive tract.

Life Cycle

Sea squirts exhibit a complex life cycle that includes both sexual and asexual reproduction. They are hermaphroditic, possessing both male and female reproductive organs.

Larval Stage

The larval stage of sea squirts is free-swimming and resembles a tadpole. This stage is crucial for dispersal and settlement. The larvae possess a notochord, a dorsal nerve cord, and a post-anal tail, which are characteristic features of chordates.

Metamorphosis

After a brief planktonic phase, the larvae settle onto a substrate and undergo metamorphosis. During this process, the notochord and tail are absorbed, and the organism transforms into its adult form.

Ecological Role

Sea squirts play a significant role in marine ecosystems as filter feeders. They help maintain water quality by removing suspended particles and plankton. Additionally, they serve as a food source for various marine predators, including fish and sea stars.

Research and Biomedical Applications

Sea squirts are of interest in scientific research due to their evolutionary significance and potential biomedical applications. They are considered a model organism for studying chordate development and evolution. Compounds derived from sea squirts have shown promise in cancer research and drug development.

Also see

• Tunicata
• Chordata
• Filter feeding
• Marine invertebrates