The Pouch Snails Bladder Snails

THE POUCH SNAILS. BLADDER SNAILS Genus PHYSA, Drap.

Shell sinistral, oblong, thin, polished, of few whorls; aper ture oval, anterior margin not dilated; outer lip acute; inner lip reflexed over columella; foot long, pointed behind; mantle margin fringed, reflected over shell edges; tentacles, long, thread like. , • Distribution world-wide. More active mollusks than the Lirrinxas, both in walking and in gliding with shell downward on the surface of the water. They descend and ascend on threads of mucus.

The best way to study these little pouch snails is to get a few full grown ones in spring, place them in a tumbler or fruit jar of pond water, with a pebbly bottom, and a little pond weed lying on the bottom. The spawn will be extruded, and the young hatched. As they develop they constantly travel about on threads.

A writer in the Quarterly Journal of Conchology makes some interesting observations upon these agile little "bladder snails": Often when two Physe meet upon the same thread they fight as only mollusks of this genus can, and the manoeuvres they go through upon their fairy ladders outdo the cleverest human gymnast that ever performed. I once saw one ascending, and when it was halfway up the thread it was overtaken by another; then came the "tug of war"; each tried to shake the other off by repeated blows and jerks of its shell, at the same time creeping over each others' shell and body in a most excited manner. Neither being able to gain the mastery, one began to descend, followed by the other, which overtook it, reaching the bottom first.

Yet they are not always bent on war, but pass and repass each other in an amicable spirit. One of the most beautiful sights in molluscan economy is to see these little "golden pippins" gliding through the water by no visible means; and when they 293 The Pond Snails fight, to see them twist and twirl, such quick and curious evolutions while seemingly floating in mid-water, is astonishing, even to the patient student of Nature's wonders.

Dr. Jeffreys says that all snails clean each others' shells of confervx, the passive individual remaining patiently quiet while the "operator" goes over the entire surface with its rasping tongue.

P. hypnorum,

Linn., described as a gymnast above, is the most rapid of all aquatic snails. It cleans its own shell to the very apex. European species found also in America.

The Tadpole Pouch Snail (P. gyrina, Say) is an inch long, the last of the six whorls very large, the oval aperture nearly two-thirds the length of the shell. The lip is slightly thickened within, the columella overlaid with a callus.

Habitat.— Vermont and Georgia, westward.

The Jug Physa (P. ampullacea, Gld.) is a shining, delicate, much swollen species, its lip tinged with red. The aperture is wide and about five-sixths the total length of the shell. The columella is deeply excavated anteriorly. Length, l inch.

Habitat.— Oregon, Washington.

P. ancillaria,

Say, has a dainty, flesh-tinted, translucent shell with an inflated body whorl, and an oval aperture a trifle shorter than the shell. Both lips are slightly thickened with a white callus. The apex is blunt and dark.

This species is numerous on piers of wharves in eastern rivers, going up and down with the turns of the tide. It also burrows in mud as soon as the water goes off, reappearing as the water rises. Length, I inch.

Habitat.— New England to Louisiana.

The Physa (P. inicrostoma, Hald.), is a brownish yellow, elliptical, solid shell, with aperture contracted, lip thickened, and columella bearing two pearly teeth. Length, inch.

Habitat.— Kentucky, Ohio.