appendiculares

Appendicularia, commonly known as larvaceans, is a class of small, pelagic tunicates within the subphylum Urochordata. They are found in oceans worldwide and are notable for retaining a larval-like body into adulthood, a developmental pattern known as neoteny that distinguishes them from many other tunicates.

Adults are transparent, tadpole-shaped organisms with a flexible notochord and a muscular tail that provides propulsion. They secrete a mucus-based house around their body which functions as a filtration system; the house is periodically renewed when it becomes clogged.

Water is drawn through the mucous house by ciliary action, concentrating phytoplankton and small particles that are captured in the mucus mesh and ingested. The house is shed and rebuilt on short timescales, often every few hours, allowing rapid turnover of feeding filters and continuous feeding.

They inhabit the upper layers of the open ocean, from tropical to temperate waters, and can occur at depths reaching several hundred meters. By exporting organic matter through daily house production and shedding, they contribute to marine carbon cycling and serve as prey for larger zooplankton and fishes.

Most appendicularians are hermaphroditic; fertilization is external, with eggs and sperm released into the surrounding water. Embryos develop into free-swimming, larva-like juveniles that resemble adults, continuing the neotenic life-style characteristic of the group.

Appendicularia is one of the three traditional tunicate classes, alongside Ascidiacea and Thaliacea. Molecular studies have refined their relationships within Tunicata, but some aspects of their early evolution remain debated.