# Midland Naturalist/Volume 01/Freshwater Life.—1, Entomostraca

Freshwater Life.-1, Entomostraca.
By Edwin Smith, Esq., M.A.
The Entomostraca, though commonly called "Water-Fleas," are not insects, but crustaceans. They breathe by a sort of gills and the general surface of the body. They have two pairs of antennae and mostly more than three pairs of legs, borne by the thorax and abdomen conjointly. They never lave wings, or even traces of wings. Consequently it is incorrect to speak of then as "fleas." They are, in fact, little creatures allied to the shrimp and the lobster. With the exception of Apus, which is 2½ inches, and Chirocephalus, which is one inch long, the Entomostraca are very small animals, yet not too small to be seen with the naked eye. They are readily picked, with a dipping-tube, out of the jar of water containing them, and are more easily managed in the live-box than the strictly microscopic infusoria. On this account they form a capital first study for any one beginning his researches in freshwater life.
About two-thirds of the British Entomostraca inhabit fresh water, the remaining third belay marine: We shall limit our attention at preset to Uwe former. The student who is tolerably persevering will soon make out from his gatherings ten or more genera, comprising about a score species, Which way fairly be considered common. He should plunge his dipping-bottle into every pond in his neighbourhood, particularly into those which are covered with a green mantle of any sort, under which these creatures like to shelter. A still drain is no bad place for search, The rain-filled cart-ruts on the borders of plantations may also be looked into with advantage. I once took up a bottle-full of water from a small pond in North Wales, which had evidently been shrinking in dimensions all through a dry summer, while the life in it ​had been fast multiplying. The water, held up to the light, was literally blood-red. with abundance of Daphnia. Though warm days, especially if little cloudy, are were propitious to the dipping-bottle than cold ones, I have tried my luck with success even in winter, when the ponds were covered with thick ice. A water-trap made in the following way will he found very useful: A glass jar about three inches wile at the tap is fitted with a large bung; the bung has two holes to receive the funnels inserted on opposite sides, one funnel being small enough to go month downwards into the jar, and having its mouth covered with a bit of fine muslin. This acts as a strainer, and keeps back the live objects of as many botties full of water as you choose to pour into the larger funnel.
The Entomostraca are naturally and in the main carnivorous. Indeed, one of their great uses In the economy of nature is to eat up decaying animal matter, which might otherwise taint the air or the water. They appear also to prey upon one another; while they are themselves the load of numerous aquatic animals, beetles, larvæ of insects, and so forth. Common sense will dictate what must be done to keep these little beings in our aquarium for observation, We must retain their food and exclude their enemies. In the struggle for existence amongst themselves the Cyprides appear to have the advantage. Some sprays of Vallisaeria, Anaecharis, or Myriophyllum should always be placed in the tank, to keep the water fresh, and to afford suitable harbour for the Entomostraca, and for their prey.
The Entomostraca have been arranged in four orders, of which we shall take a series of examples:—
* —Ostracoda, such as Cypris, Candona, &c.
* —Copepoda, such as Cyclops, Canthocamptus, &c.
* —Cladocera, such as Daphnia, Chydorms, &c.
* —Phyllopoda, such as Cheirocephalus.
The aquarium is sure to contain, even when other kinds have appeared, swarms of active little specks of a bivalve shape, clustering near the glass, and moving about unceasingly amongst one another. Take one out with the dipping tube; you have almost certainly one of the many species of Cypris. You observe that the body is neatly enclosed in a loose jacket of two valves joined over the back, leaving the animal free to protrude below the bristly organs by which it swims. Taken out of its jacket or carapace, the body seems pinched up about the middle into two halves, the one corresponding to head and thorax, the other to abdomen and tail. There are two pairs of antennæ; the upper pair being employed for swimming only, the lower for both swimming and walking. Next comes the mouth, consisting of an upper and a lower lip, a pair of mandibles, and two pairs of jaws. The number of legs cannot be stated with certainty. I have noticed only two pairs. Then follows the abdomen, with its two lengthened stalks, each terminated by three short hooks. This is the principal swimming organ, being rapidly jerked out behind for that purpose. Breathing is effected by means of gill-plates attached Lo the hinder pair of jaws, with some assistance from the feathered bristles of the larger antennæ and the general surface of the body. But there are no branchial appendages to the legs as there are in Daphnis. Cypris agrees with most other Entomostraca in having only one eye. The species most common in the neighbourhood of Nottingham are Cypris vidua, C. minuta, C. aurantia. If you search carefully the surface of gravel in your aquarium you may chance to see a little oblong horny speck making its way by fitful jerks. This will probably turn out to be a rather large member of the same family, named Condona reptans. It has the comical habit of creeping in preference to swimming. I have found it about here in meadow drains, and have successfully bred it in my aquarium from season to season.
To be continued.
This work was published before January 1, 1930, and is in the public domain worldwide because the author died at least 100 years ago.
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