Doliolids

Doliolids are small, pelagic tunicates in the order Doliolida, class Thaliacea, phylum Chordata. They are gelatinous, free-swimming organisms that inhabit open-ocean waters around the world and feed by filtering suspended particles from seawater.

They have a barrel-shaped, transparent body, typically a few millimeters to a few centimeters in length. Water enters and exits through incurrent and excurrent siphons; a pharyngeal basket with slits extracts food particles, aided by a mucous net secreted by the endostyle. A ring of circular muscles powers jet-like locomotion.

Dolioids are planktonic suspension feeders found in both warm and temperate seas, often in nutrient-rich surface layers but occasionally at mid depths. They consume phytoplankton and tiny zooplankton and are themselves prey for many small fish, chaetognaths, and other gelatinous zooplankton.

Doliolids have a complex life cycle typical of thaliaceans, involving alternating generations that can reproduce both sexually and asexually. This can lead to rapid population growth under favorable conditions.

The order includes several genera, such as Doliolum and Dolioletta, with multiple species described in warm and temperate oceans. They are minute to moderate in size and contribute to oceanic food webs and carbon cycling through their delicate bodies when organisms die or are consumed.