pods. A few species of nerites and periwinkles are known to ascend trees near the seashore, although tree-dwelling is best known among certain tropical land snails. In the tropics, the Tectarius prickly-winkles habitually live in or near splash pools along the rocky coast where spray from the waves and drenching rains are constantly changing the temperature and salinity. When the pools are dry the snails are often able to withstand weeks of hot sun and parched conditions.
Three kinds of snails in American waters are forever destined to wander at large on the surface of the open ocean. The purple Janthina snails are born, live and, in most instances, die at sea. These pelagic snails live upside down and remain at the surface by means of a small raft of bubbles. Small bubbles of air are entrapped in a special mucus secreted by the animal. This clear fluid congeals upon contact with salt water and air, and it adheres to the foot. The entire float has much the appearance of crumpled cellophane. The female attaches her small eggs to the underside of the float where they are partially shaded from the sun’s rays. The Janthinas live off the coasts of our southern states, and during certain seasons they are commonly cast ashore in California, Florida and the Gulf States. Specimens have been blown off their Gulf Stream course and been washed ashore in New England and even the British Isles.
As is the case with so many other pelagic creatures, the shell surface of Janthina which faces downward (the spire of this upside down shell) is colored a light, milky blue. This is probably a protective coloration which blends with that of the surface of the sea, which to an underwater observer is similarly colored. For some unknown reason Janthinas are completely blind.
Two other groups of gastropods live at the surface of the ocean and, like Janthina, live an upside down existence. These are the tiny brown Litiopa snails which adhere to floating sargassum seaweed by means of a silken thread of mucus, and the heteropods or fin-footed sea snails which remain afloat by paddling a wide, fin-shaped foot. The latter group includes the rare and highly prized Carinaria, the Atlanta shells and the shell-less Firoloida.
Not all pelagic mollusks live solely at the surface. The transparent, delicate-shelled sea butterflies or pteropods (pronounced tero-pods) remain several fathoms below the surface during the daylight hours but move upward toward the surface at night. In many equatorial areas pteropods exist in great numbers, and the steady rain of the sinking shells of the dead mollusks litter the ocean’s bottom many feet deep. Among the sea slugs, one species of nudibranch (Scyllaea) is always pelagic, while the small and beautiful Bat Sea Slug, Gastropteron rubrum, makes nocturnal trips from the bottom of the shallow bay to the surface. The two pancake-shaped lobes of
