The Sea Shore

by William S. Furneaux

1. The spined sea screw (Dexamine spinosa). 2. Westwoodia cœcula. 3. Tetromatus typicus. 4. The sandhopper (Orchestia littorea). 5. Montagua monoculoides. 6. Iphimedia obesa. All enlarged

The above and other isopods feed on various animal and vegetable substances, some species being quite omnivorous in habit. Most of them are eagerly devoured by birds and fishes.

The Amphipods, six species of which are shown in the above illustration, include the Sandhoppers or Beach Fleas, so numerous on our coasts that it is almost impossible to go any distance without making their acquaintance. They are invaluable as scavengers, as they rapidly devour decaying sea weeds, and will speedily reduce the body of any animal washed on the beach to a clean skeleton. Although they are all small creatures, they make up in numbers for any deficiency in size; and though devoured in enormous quantities by the various shore birds, they multiply so prodigiously that they are never lacking wherever there is decomposing organic matter to be consumed.

The bodies of these animals are usually flattened from side to side, very distinctly segmented, and have a well-developed abdomen. The head is furnished with two pairs of antennæ and a pair of sessile eyes, though some species possess only one pair of antennæ, while others have four eyes. The limbs of the thorax are used either for walking or for swimming, and give attachment to the gills. The abdomen has generally six pairs of appendages, the foremost three pairs of which are usually small, and employed in swimming, while the others are stronger and directed backwards, and are often adapted for jumping.

It is very interesting to observe the habits of the Sandhoppers and other Amphipods both on the sandy beach and in the water, and the student will find that certain species burrow into the sand with considerable agility, and live principally at the extreme high-water mark, where they feed on the organic matter washed in by the breakers at each high tide, while others dwell almost exclusively in the water, among weeds and stones, and should be searched for at low water. The latter may be kept alive for some time in the aquarium providing they are the only occupants, but a little experience will show that these and all other Amphipods are readily devoured by many marine creatures, and consequently they are of real value to the aquarium keeper as food for other animals.

We now come to the Stalk-eyed Crustaceans (Podophthalmata), which contain those members of the class most generally known, such as crabs, lobsters, shrimps, and prawns. In these the eyes are mounted on movable pedicels, the head and thorax are generally covered by a large shield called the carapace, and the appendages are adapted partly for seizing and masticating, and partly for locomotion.

The group includes two orders—the Stomapoda or Mouth-footed crustaceans, so called because some of the limbs are crowded round the region of the mouth; and the Decapoda, or Ten-footed crustaceans.

The Stomapods, though very abundant in tropical seas, are not often met with on our own shores. However, since a few interesting species are inhabitants of our seas we will briefly describe the distinguishing characteristics of the group.

We have just mentioned the fact that the head and thorax of a decapod is usually covered by a large shield—the carapace. Now, the general character of this carapace may be seen at once in either the shrimp or the lobster. In these animals the segments that form the head and the thorax are all fused together, and are completely covered by the protective buckler of hardened skin; but in the Stomapoda the carapace is much smaller in proportion, and a few of the segments of the thorax, instead of being fused into the general mass of the cephalo-thorax, are quite distinct from it. The abdomen, also, is large and strongly formed in these animals. Five pairs of the thoracic limbs are directed forwards, and are adapted both for catching food and for climbing, while others are used in walking. The limbs of the abdomen generally number six pairs, of which the first five bear feathery gills.