One very common species of the Blenniidæ differs considerably in general form from the others, its body being elongated and eel-like, but much compressed laterally. We refer to the Butterfish or Butter Gunnel (Blennius gunellus), which is often mistaken for a small eel by young sea-side naturalists. It is exceedingly common under stones at low tide, and may be recognised at once by the light rectangular spots along the flattened sides of the body. It is quite as slippery and as difficult to hold as the eel itself.
It will be interesting to note that the ugly Sea Cat or Wolf-fish (Anarrhichas lupus), which is sometimes sold for food in our large towns, is also a member of the blenny family. It is a powerful, rapacious fish—a veritable wolf of the sea, always ready to attack anything. It feeds on molluscs and crustaceans, the shells of which are easily reduced between the powerful crushing teeth that line the jaws behind the formidable canines.
Fig. 240.—The Butterfish
The Gobies (Gobiidæ) form another interesting family of small littoral fishes, easily distinguished by the fact that the ventral fins are united in such a manner that they enclose a conical cavity. The first portion of the dorsal fin has also six flexible spines. The Spotted Goby (Gobius minutus) is commonly to be found on sand-banks, where it is well protected by the colouring of its upper surface, which closely resembles that of the sand on which it rests. It is said to make a nest by cementing fragments together round some little natural hollow, or to utilise an empty shell for a similar purpose, fixing the shell to the surrounding bed, and constructing a tunnel by which it can enter or leave. The eggs are deposited in this nest, and the male keeps guard over the home. The Black or Rock Goby (G. niger) inhabits rocky coasts, clinging to the rocks by means of a sucker formed of the modified pelvic fins.
A brightly coloured fish known as the Dragonet (Callionymus lyra) is sometimes classed with the Gobies, though its pelvic fins are not united. It is not a well-known species, and is seldom obtained except with the dredge, as it inhabits deep water.
Fig. 241.—The Black Goby