Tergipes tergipes (Forsskål, 1775)

Tergipes tergipes

Description: A tiny aeolid with single cerata arranged alternately along the sides of the body. The body is translucent white with red markings on the sides of the head and just behind the rhinophore bases. The digestive gland is grey in colour, and shows through the back as a branching vessel. The cerata are swollen in shape, and have large white cnidosacs at the tips. The oral tentacles are short but the rhinophores are long and tapering. Only 6-8mm in length when fully grown.

Habitat: Feeds on several species of Obelia but especially Obelia geniculata (normally found on kelp fronds). The spawn consists of small white capsules.

Distribution: Widespread and common throughout the British Isles, but frequently overlooked because of its small size.

Similar Species: Eubranchus exiguus is often found with Tergipes tergipes, and is equally small. It may easily be distinguished with a hand lens or low-power microscope by the more numerous cerata and dark rings on the rhinophores.

Key Identification Features:

• Cerata single, not in rows, along each side of the body.
• Red streaks on the head.

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