Tergipes tergipes

(Forskål, 1775)

This slender and delicate species may reach 8 mm in length, but is usually smaller, up to 5 mm. It is immediately recognisable because each branch of the digestive gland leads to only a single ceras. A maximum of two cerata, usually only one, originate from the right hepatic lobe; the rest of the cerata spring from the left lobe. Up to eight (rarely ten) cerata may be present in all, the first two opposite, the others alternating. The appearance of T. tergipes is unmistakable and so is its gait, creeping along in a jerky fashion, unlike any other nudibranch. The basic body colour is translucent white, but the undulating digestive gland shows through the skin, greenish in colour. Streaks of red-brown pigment originate on the sides of the head and run posteriorly along each flank. A red-brown streak is usually to be seen at the base of each rhinophore, and this links up with the streak on the flank. Similar red-brown pigment forms a subapical band covering the cnidosac of each ceras (T. tergipes-detail).

This species is common on such as Obelia and Laomedea species, together with Gonothyraea loveni , Aglaophenia pluma , Clava multicornis and Sarsia eximia , often attached to kelp or moored rafts, piers or ships, often in company with the related aeolidacean Eubranchus exiguus .

It is widely distributed through the Atlantic Ocean, from Brazil to Iceland and Norway, the eastern American seaboard and the Mediterranean Sea (Distr. T. tergipes).