Star Tunicate

Overview

The Star Tunicate (Botryllus schlosseri) is a colonial marine invertebrate belonging to the phylum Chordata, making it a distant relative of vertebrates. It is widely recognized for its unique, star-shaped colony patterns and its ability to thrive in diverse marine environments across the globe.

Appearance

This species forms fleshy, encrusting colonies that can grow as sheets or lobes on various surfaces. The colony consists of numerous individual zooids, each typically 2–4 mm in size, arranged in distinct, flower-like or star-shaped clusters. These zooids are embedded within a common, gelatinous matrix and share a central exhalant siphon. The colony's coloration is highly variable, often featuring contrasting hues of yellow, orange, white, purple, or brown against the surrounding tunic.

Distribution & Habitat

Originally native to the Mediterranean and parts of the North Atlantic, the Star Tunicate is now considered a cosmopolitan species found in shallow, temperate, and subarctic waters worldwide. It frequently colonizes hard substrates, including rocks, docks, boat hulls, and submerged vegetation like algae and seagrasses. It is highly adaptable and often persists as an invasive species in new regions.

Biology & Behavior

As a filter feeder, the Star Tunicate extracts phytoplankton, zooplankton, and organic particles from the water column. The colony undergoes a fascinating life cycle characterized by periodic "takeover" phases, where adult zooids degenerate and are replaced by new buds. It is a popular model organism in scientific research due to its complex allorecognition system, regenerative capabilities, and its unique ability to reproduce both sexually and asexually.