Body (excluding appendages)
Up to 8mm long, usually smaller. Translucent white revealing white blobs of ovotestis [image 4]. Brownish staining, often faint, along flanks and behind rhinophores . Genital opening protrudes from right side behind rhinophore  (many publications replicate mirror image in Alder & Hancock showing it on the left, despite their note about the error.).
Up to 4, rarely 5, single cerata  on each side of body. Connected by brown digestive gland that zig-zags left and right . Translucent white revealing orange-brown  to olive-brown  digestive gland if recently fed. Dark brown pigment marks on surface , and sometimes the white internal cnidosac , is partly concealed by a subterminal brown band.
Smooth, translucent white with brown tinting. Twice as long  as oral tentacles.
Tinted brown behind rhinophores. Opaque white buccal mass visible through almost transparent flesh. Front margin rounded , with bases of translucent white oral tentacles set back from edge.
Translucent white, much narrower than body . No propodial tentacles or lobes, but may widen under head when rest of sole contracted.
Eubranchus exiguus (Alder & Hancock, 1848)
Lower shore and sublittorally to 20m. On hydroids growing on stones, Laminaria fronds, piers, floating structures and ships; even isolated small stones in pools in mud. Zig-zag digestive gland resembles stalk of Obelia geniculata (EML) which is frequently found, with T. tergipes on it, on fronds of Laminaria hyperborea growing in moderate wave exposure. Also on many other hydroids, such as Laomedia flexuosa (WoRMS) on sheltered shores and in estuaries down to 10 ppt salinity. Simultaneous hermaphrodite. Spherical or kidney-shape transparent spawn capsules , each containing about 30 white ova, produced throughout the year. Spawn capsules easier to detect, and about ten times more numerous, than adults. Short veliger stage of about a week before metamorphosis. Matures in 5 weeks, ovotestis developed in 2.5mm long specimens, so many generations p.a..
Atlantic coasts from Iceland and Norway to eastern U.S.A. and Spain, and around Mediterranean. Also recorded in S. Africa and Brazil (GBIF map).
Common all round Britain and Ireland, but overlooked as small size requires inspection of hydroids under magnification. Densities of 500 /m² recorded.