The Sea Shore

by William S. Furneaux

The first of these includes only a few species, one of which is found in our seas, and will receive a short notice here. The fishes will, of course, demand a fair share of our attention. Amphibians and reptiles have no British marine representatives, and are therefore quite excluded from this work. As to the birds, although there are so many that live entirely on the sea and in its immediate neighbourhood, these have been so ably dealt with by Mr. Hudson in one of the books of this series that it would be superfluous to mention them. The mammals include a considerable number of marine species, but as only one of these—the Porpoise—is really commonly observed round our coasts, it alone will be selected for description.

Lampreys and their few allies were formerly classified with fishes, but are now made to form a small class by themselves; and there is abundant reason for the separation. It will be remembered that vertebrates, in the early stages of their development, are characterised by a cartilaginous rod running through the dorsal region of the body, below the central cord of the nervous system, and that they possess a series of slits opening into the sides of the pharynx. Now, while these characteristics are usually only transitory in the vertebrates, the Lampreys and their relatives are the only animals in which they persist throughout life, and it is for this reason that they are exalted to the dignity of a class under the title Cyclostomata.

This name signifies ‘round-mouthed,’ while the Lampreys themselves form the still smaller division Marsipobranchii, which means ‘pouch-gilled,’ these two being among the most evident characters of the creatures concerned. They have no true jaws, the circular mouth being supported by a ring of cartilage, and provided with a rasp-like tongue that enables them to divide their food. They have no true bone in their bodies, the simple skeleton, without limbs and ribs, being entirely cartilaginous, and the rudimentary skull is not movable on the dorsal cartilage. Their bodies are elongated and eel-like, with a single medial fin, supported by fine cartilaginous rays, and with seven little slits on each side of the neck, communicating with as many gills in the form of little pouches. The mouth is suctorial, presenting, when open, a circular adhesive disc, by which the animals can attach themselves to any solid object, but assumes the form of a mere slit when closed. The young differ from the adult in a few points of structure. Thus they have no eyes, and the long fin, divided in the adult, is continuous. With the above characteristics in mind, there will be no danger of confusing the lampreys with the eels and other similar fishes.

There are three or four British lampreys, two or three of which inhabit fresh water. Their habits do not seem to be well understood, but it appears certain that the Sea Lamprey (Petromyzum marinus), which reaches a length of from one to two feet, ascends rivers to spawn, while the smaller River Lamprey (P. fluviatilis) has been caught in the sea; and it is probable that the migrations of both, together with the sojourn of the young of the former for a longer or shorter period in fresh waters, have been the cause of the widespread confusion between species.

Lampreys are carnivorous creatures, and attach themselves to fishes by their suctorial mouths, and rasp away the flesh. They have also been known to attack bathers.

Fig. 226.—The Sea Lamprey

Passing now to the true fishes, we must first study the general features of the group by which they are to be distinguished from other animals. Since there are so many creatures outside this class that are more or less fishlike in some respects, it becomes no easy matter to give a concise definition of a fish, and the shortest satisfactory description must necessarily include several points of structure. Thus, we may define a fish as a cold-blooded vertebrate that does not undergo metamorphoses, with limbs modified into fins, possessing also median fins on the dorsal and ventral surfaces, having distinct jaws, a heart with two chambers, and breathing by gills. To this we may add that the young are generally produced from eggs, and that the skin is covered with scales or bony plates, or is naked.

But let us now look more closely into the structure of fishes, so that we may be enabled to see how marvellously they are adapted to their aquatic life, and in order that we may become acquainted with the few technical terms which will, as a matter of convenience, be used in the descriptions of species.