Animal Parasites and Messmates

by P. J. van Beneden

Any one who has remained for some time on the coast of Brittany, especially at Concarneau, and who does not look with indifference on the many superb fishes which are taken every day, cannot fail to have been struck with the presence of a rather large crustacean,

which clings to the sides of several kinds of Labra, especially the smaller species. This crustacean is an Anilocrian so common that we can scarcely imagine it to have escaped the attention of any naturalist. Nevertheless, no work makes mention of the regular attendance on the Labra by the Anilocra, which bears, we know not why, the specific name of Mediterranean. Rondelet was probably acquainted with it, when he spoke of the fish-lice, which do not derive their birth from these fishes, but from the sea mud. We often see males by the side of females on the same individual.

Some years ago a school of large cetaceans, known under the name of Grindewhalls or Globicephalæ were pursued in the Mediterranean, and those which were captured contained in the cavity of their nostrils, isopods closely allied to the Cirolana spinipes, if not identical with it. Till then the isopods had only been found on sea fishes; fresh-water fish are not, however, entirely exempt; in fact, a species of Œga (Œga interrupta of Martens) has just been found on the skin of a fresh-water fish of Borneo, the Notopterus hypselonotus. This same genus includes a species (Œga spongiophila) which lives in the magnificent sponge, the Euplectella. We know also a certain number of isopods which prefer the interior of their neighbour’s body, and instal themselves in the cavity of the mouth, either to fish at the same time as their host, or to seize the food on its passage; others are of such a cruel nature, that they make no scruple to establish themselves in the stomach of a peaceable white fish. Without injuring any important organ, they penetrate in couples between the intestines, and, concealed in this retreat, they seize by the narrow

entrance door, which they keep half open, all the little animals which are sufficiently bold to pass by. The cruelty of these beings knows no bounds. To instal themselves conveniently, they pierce the body of their host, skilfully open his stomach, and live there as Sybarites; their lodging is in future assured to them, and their fate is bound up with that of their host. Dr. Herklots, who has unfortunately been recently lost to science, communicated in 1869, to the Academy of the Netherlands, a very interesting memoir on two crustaceans of a new species, the Epichtys giganteus, which lives on a fish of the Indian Archipelago, and the Ichthyoxenus Jellinghausii, which lodges in a fresh-water fish of the Island of Java. It is to the latter that we refer here, and it seems that in this species we are approaching the limits at which commensalism commences.

The Cymothoes constitute another category of very interesting Isopods; they lodge with their female in the cavity of a fish’s mouth. Dr. Bleeker, who has so successfully explored the Indian seas, obtained more than twenty species of these; but unfortunately he has not made a note of the fishes which harbour them. He has, however, made one exception with regard to a fish from the roadstead of Pondicherry, which is two feet long, and is called a Bat. It is known to naturalists under the name of Stromatea Nigra; its flesh is much esteemed, and it carried in its mouth a Cymothoe called by Dr. Bleeker Cymothoe Stromatei. A cymothoe has also been observed in the mouth of an Indian Chetodon. De Kay found one in a Rhombus in the United States, and De Saussure saw another at Cuba; and lately, Mons. Lafont discovered one in the Bay of Arcachon, on

the Boops, and on the Trachina vipera. These cymothoes are about fifteen millimetres in length, and often fill all the cavity of the mouth. The most curious of all is that which is found in the mouth of the flying-fish, a kind of herring with elongated fins, which it uses as wings to rise into the air, when too closely pursued in the water. My son, when examining these fishes, in his passage from Cape Verd to Rio de Janeiro, found in the cavity of their mouth an enormous female, firmly wedged in the branchial arches, with its head inclined outwards, and the male, which was rather smaller, installed at her side. Their dwelling thus by pairs, as well as the entire conformation of the animal, plainly shows that these crustaceans make themselves at home, and live as true messmates. Cunningham has given them the name of Ceratothoa exoceti. A short time since, these Cymothoes were only known on marine fishes, but it appears from recent observations, that fresh-water fish are far from being exempt from them. Mons. Gertsfeld has recently noticed some on the Cyprinus lacustris of the river Amour, and another in the Rio Cadea in Brazil, on a Chromida. Other isopods also resort to fishes, and to animals of their own class, but they live as true parasites, and change their form as soon as they have chosen a resting-place. We shall return to this subject again. Some which are very common on prawns, are known under the name of Bopyrus.

An interesting division of amphipods have received the name of Hyperinæ. These crustaceans generally swim with facility, but walk with difficulty. They therefore usually have recourse to fishes, or even to medusæ, in order to gain support. We find on our own coasts the

Hyperina Latreillii, lodged in the superb Rhizostoma, which regularly appears in the later season of the year on the coast of Ostend; and a long time since, in 1776, O. F. Müller gave to a species of this genus the name of Hyperina medusarum. Mr. Alexander Agassiz once found a Hyperina on the disc of an Aurelia. The medusa, when extended, forms for them a balloon with its parachute, which supports and conveys them with greater or less rapidity. Professor Möbius has but lately remarked the presence of Hyperina galba, Mont., in the Stomobrachium octocostatum, Sars, a small species of medusa which appears in the Bay of Kiel in October and November. This naturalist supposes that these messmates at first inhabited the Medusa aurita, and then migrated into this species.

Besides these, there are Gammari, which, according to Semper, live in the Avicula meleagrina (pearl mussel), and are perhaps the principal manufacturers of fine pearls. The immense buccal cavity of the fishing-frog (Lophius piscatorius) is the abode in the Mediterranean of an Apterychta, and in the Northern Ocean of a curious amphipod of the ordinary size of the Gammarus, which takes a voyage without expense, and with no fear of wanting provisions. My son discovered it at Ostend, and proposes the name of Lophiocola to distinguish it. The Gammari give lodging themselves to a great quantity of parasites, which they must introduce into the bodies of those to whom they serve as food. It has been long known that whales have lice, to which naturalists have given the name of Cyami. They are found on the whales of both hemispheres, and on some other cetaceans. It is very remarkable that they are

seen on the true whales of the north and of the temperate regions, on the Megaptera, and on several Catodonta, and that none are found in the Balenoptera. Mr. Dall has just noticed some on the singular Grey Whale of California. In general, we may say that each cetacean which harbours them, has its own species. Are they parasites or messmates? If we are to believe Roussel de Vauzème, they feed on the skin itself of the whale, the remains of which, it is said, are found in their stomach. According to this naturalist, the parts of the mouth are not adapted for suction, and the stomach contains ruminating apparatus. We think that a fresh examination is necessary before this question can be determined. The Cyami seem to us to live on the whale, as the Arguli and the Caligi do on fish; and if these living creatures derive their nourishment only from the mucous products secreted by the skin, we may ask whether they ought not to be classed in a separate category, for they ought not to figure on the list of paupers. We have found the orifice of the Tubicinella covered with cyami of every age, and their abundance in this place seems to indicate that their food was not supplied to them by the skin of their host. Mons. Ch. Lutken has recently published a very interesting monograph on these curious animals; according to him the Cyamus rhytinæ, which was thought to proceed from a piece of the skin of a Stellerus, appears to have been found on the skin of a whale.