endostilo

The endostyle is a ciliated groove found in the floor of the pharynx of filter-feeding chordates, including tunicates, lancelets, and acorn worms. Its primary function is to secrete mucus, which traps food particles from the water drawn into the pharynx for ingestion. The cilia within the endostyle then move this mucus-laden food towards the esophagus.

This structure plays a crucial role in the feeding apparatus of these animals, enabling them to efficiently filter small food items from their environment. In some chordates, like the tunicate tadpole larva, the endostyle also has endocrine functions, producing iodinated compounds, similar to the thyroid gland in vertebrates. This has led to the hypothesis that the endostyle is a precursor to the vertebrate thyroid gland.

The morphology and activity of the endostyle can vary between different taxa. In tunicates, it is a prominent feature of the pharyngeal basket. In lancelets, it is a more spiral structure. While its primary role is food trapping and transport, its homology with the thyroid gland remains a significant area of study in evolutionary biology.