Clavelina lepadiformis (O F Müller, 1776)

Light bulb tunicate

Clavelina lepadiformis

Description: Colony consists of free zooids loosely attached by creeping stolons or basal test material. Zooids are transparent, with delicate cream or white lines delineating the endostyle and dorsal lamina and forming a white ring at the top of the branchial sac (peri-pharyngeal band). In some specimens there may be additional white pigment at the edge of each siphon, forming two additional rings. Zooids 20mm long x 5mm diameter.

Habitat: From low water mark to about 50m. One of the commonest ascidians in shallow rocky sublittoral habitats, usually on vertical rock faces, sides of boulders, etc. but also found on stones, shells and seaweeds. Tolerant of a wide range of exposure but most abundant in moderately exposed sites in the infralittoral zone.

Ecology: Clavelina lepadiformis shows a yearly cycle of growth beginning in January when new zooids start to grow from the overwintering base, with larval production in late summer (June to September) followed by disintegration of the zooids leaving an overwintering bud.

Distribution: Common and widely distributed in British waters, elsewhere from Norway to the Mediterranean.

Similar Species: The only other British species with similar white markings in a transparent zooid of this size is Diazona violacea. In Diazona the zooids are more closely united in a common test and there is a series of six white spots around the exhalant siphon. In the Mediterranean Sea there is an almost identical cryptic species which is distinguished on DNA evidence.

Key Identification Features:

• Colonies of free transparent zooids.
• White markings of rings and lines in zooid.

Distribution Map: NBN map : National Biodiversity Network mapping facility, data for UK.

WoRMS: Species record : World Register of Marine Species.

iNaturalist: Species account : iNaturalist World Species Observations database