Sub-Order 1. Rhynchobdellae.—Hirudinea with an exsertile proboscis, without jaws, and with colourless blood.
Fam. 1. Ichthyobdellidae.—Body formed of two regions, a narrower anterior portion and a wider "abdomen," both anterior and posterior suckers distinct from the body.
These leeches are parasites of fishes and of some other animals such as tortoises. The family contains a number of genera. Branchellion (Fig. 204) has a series of leaf-like branchiae on both sides; in Cystibranchus the respiratory organs are reduced to a series of round vesicles. The latter genus occurs in Europe and North America, and is parasitic upon marine and fresh-water fishes. Piscicola is a common leech which confines its attacks to the inhabitants of fresh water. Pontobdella (Fig. 210) is marine, and affects rays and sharks; the best known species, P. muricata, is usually of a green colour.
To the family Ichthyobdellidae also belongs the large Chilian leech Macrobdella valdiviana, of which there is or are also species in North America. Philippi's figure of this leech[[465]] shows the distinct neck; and as it has no jaws, it should be referred to the present family. It has got an undue reputation for size, 2½ feet[[466]] having been assigned to it. As a matter of fact Philippi's illustration depicts an Annelid of about 7 inches in length, with a greatest diameter of about an inch. But doubtless when extended in walking it would be longer—1½ feet, Philippi thinks. It has no eyes, a failing which is not unusual among the leeches.
Fam. 2. Glossiphoniidae.—Anterior sucker fused with the body, posterior sucker distinct. No cocoon.
Fig. 210.—Pontobdella muricata. × 1. (After Bourne.)
The members of this family all inhabit fresh water; they have the habit of depositing the eggs separately, which are then fixed to the ventral surface of the body, and the young when hatched are still protected by the parent, returning to its body for shelter. The type genus Glossiphonia ( = Clepsine) is common in Europe, and has many species. The Mexican and Amazonian Haementeria contains a number of species, of which the Mexican H. officinalis is used in medicine; but according to Miguel Jimenez, its use is apt to be attended with unpleasant symptoms. Drowsiness, a buzzing in the ears, and the development of a painful rash are some of the effects produced by its bite. It is disputed whether the animal's saliva or foreign matter introduced by it into the wound are the cause of the symptoms.
Mesobdella of Blanchard[[467]] is said to be intermediate between this family and the next. Each segment has three annuli, as in this family, but the leech has three jaws, as in Hirudo.
Sub-Order 2. Gnathobdellae.—Hirudinea without a proboscis, generally with jaws; the blood is red; the eggs are invariably deposited in cocoons.