Key to species of Buccinidae and Colidae found in the GB (see also Bouchet & Warén 1985)

1. Sculpture conspicuous, with definite spiral ridges ........................................................................... 2

– Sculpture attenuated, consisting only of fine spiral grooves ............................................................ 3

2. Sculpture mostly spiral, shell commonly> 5 cm ............................................................................... ........................................................................... Troschelia berniciensis (King, 1846) (Fig. 23J–K)

– Sculpture with conspicuous knobs along the periphery ..................................................................... .................................................................................. Kryptos koehleri (Locard, 1896) (Fig. 23L–M)

3. Protoconch of little more than 1 whorl, with a large nucleus ............................................................. .................................................................................... Colus gracilis (da Costa, 1778) (Fig. 24A–G)

– Protoconch of more than 2 whorls, with a small nucleus ................................................................... .......................................................................... Colus jeffreysianus (P. Fischer, 1868) (Fig. 24H–K)

Remarks

There are two species of Colus Röding, 1798 to be found on GB (Fig. 24), and their correct identification is crucial since they are an important component of the benthic community and food chain. Both have extremely similar shells and their accurate identification relies essentially on the diagnostic character of the protoconch. Colus gracilis is found on the summit platform and the adult is somewhat larger and more solid, whereas C. jeffreysianus has a broad distribution on the deeper part of the slope. Colus aurariae Fraussen, Rosado, Afonso & Monteiro, 2009, described from off Portugal in 200–500 m depth, differs from C. gracilis in having both early whorls and siphonal canal more stretched out; it was not found on GB.