forcibly from the mantle cavity through the funnel, at the same time expelling a cloud of ink from its ink-sac.
 |
Fig. 1.—Sepia officinalis, L., about 12 natural size, as seen when dead, the long prehensile arms being withdrawn from the pouches at the side of the head, in which they are carried during life when not actually in use. a, Neck; b, lateral fin of the mantle-sac; c, the eight shorter arms of the fore-foot; d, the two long prehensile arms; e, the eyes. |
The Sepia feeds principally on Crustacea, and in aquaria has been observed to pursue and capture prawns. The method in which it secures its prey has been carefully observed and described by the present writer, who studied the living animal in the aquarium of the biological laboratory at Plymouth. The prawns support themselves on their long slender legs on convenient points of the rockwork, and the Sepia stalks them with great caution and determination, the rapid play of its chromatophores giving evidence of its excitement. When it has arrived within striking distance, the two tentacular arms are shot out with great rapidity, and the prawn is seized between the two expanded ends, drawn within the circle of short arms, and devoured; unless, as sometimes happens, the prawn springs away and the Sepia misses its aim.
Two species of Sepia occur in British and European waters, including the Mediterranean, namely, S. elegans and S. officinalis. The usual length of the body is about 9 or 10 in. They live mostly between ten and forty fathoms, coming into shallower water in July and August to deposit their eggs, which are about as large as black currants and of somewhat similar colour, and are connected by elongated stalks into a cluster attached to the sea-bottom. Other species occur in various parts of the world, e.g. S. cultrata, which is common on the coasts of Australia. The Sepiidae form the only family of cuttle-fishes in which the shell is calcified. They belong to the tribe Myopsida, characterized by the complete closure of the external corneal covering of the eye outside the iris and the lens.
Sepiola and Rossia belong to another family of the Myopsida. Both are British genera living in shallow water, and entering estuaries. The animals of both genera are small, not more than 2 or 3 in. in length, with the body rounded at the aboral end, and the fins short and rounded, inserted in the middle of the body length, instead of extending from end to end. Sepiola, although it swims by means of its fins and funnel when active, spends much of its time buried in the sand for concealment. Rossia has similar habits. The shell is chitinous and shorter than the body. In other genera of the Sepiolidae the shell is entirely absent. Idiosepius is the smallest of the Cephalopoda, only 1.5 in. in length. It inhabits the Indian Ocean. The body is elongated and the fins rudimentary. In the Sepiadariidae also the shell is absent. The body is short and the mantle united with the head dorsally. The two genera Sepiadarium and Sepioloidea occur in the Pacific Ocean. The common squid Loligo is the type of the only remaining family of the Myopsida. In this species the shell is a well-developed chitinous pen or gladius with a thickened axis narrowing to a point behind, but bearing posteriorly a wide thin plate on each side. The shape closely resembles that of a quill pen with the quill in front. The fins are large and triangular, extending over rather more than half of the length of the body aborally. The tentacular arms are only partly retractile. The body is elongated and conical, and reaches about a foot in length. The squid is gregarious, and forms a favourite food of the larger fishes, especially of conger. All the Myopsida are more or less littoral in habit, and the British forms are familiar in consequence of their frequent capture in the nets of fishermen. The shell, or “bone” as it is commonly called, of the common Sepia frequently occurs in abundance on the shore among the sea-weed and other refuse left by the tide.
 |
Fig. 2.—A, Loligo vulgaris; a, arms; t, tentacles. B, Pen of the same reduced in size. C, Side-view of one of the suckers, showing the horny hooks surrounding the margin. D, View of the head from in front, showing the arms (a), the tentacles (t), the mouth (m), and the funnel (f). |
The Oigopsida, or cuttle-fishes in which the corneal covering of the eye is perforated, are on the whole more oceanic than littoral, and many of the species are abyssal. Ommatostrephes sagittatus is one of the forms that occurs off the British coasts, especially the more northern, e.g. in the Firth of Forth. In general appearance it resembles the common squid, but the fins are broader and shorter, not extending to the middle of the body.
