THE NAKED SEA SLUGS SUB-ORDER NUDIBRANCHIATA. Shell wanting in adults; no proper gills nor osphradium; body soft, worm-like, with many and elaborately branched tentacular processes, called cerata, on the back and sides; skin stiffened by spicules of lime; jaw and radula usually present.
Mollusks live in shallow water, gliding about on stems of sea weeds, feeding on mollusks or anemones, swimming, foot upward, with an undulating motion.
There is not room in a general book on mollusks to describe in detail the families of the sea slugs. A few typical examples must suffice.
The Plumed Sea Slug (/Eolis papillosa, Linn.) is one of the most familiar sea slugs on the North Atlantic shores, American and European both. The back is covered with elongated papilla, like tubular fringes, that fall away from the median line. The foot is squared in front and tapers to a point behind. The head bears two pairs of tentacles. The plumes serve a four-fold purpose: (1) they are breathing organs; (2) they contain stinging threads that the 2olis shoots out at any creature that molests it; (3) they contain branches of the liver, and so help in the digesting of food; (4) they resemble the tentacles of the cave-dwelling anemone (Sagartia) which is distasteful to fish, and thus earn, by deception, immunity from attack. In an extremity the /Eons flings off a bunch of its plumes, and escapes while its pursuer is examining them. It is a small matter to grow new ones in their places.
This creature glides rapidly among seaweeds, or swims in clear water, a thing of grace and beauty, taking on the colqurs of the anemones and algae it feeds upon. Its usual colouring is yellowish gray to orange, with spots of green and purple. The fEolis is a bold creature, never seeming to hide, but evidently trusting that memory of one stinging, bad-tasting sample mouth ful is sufficient to deter a fish from attacking it. The bright 248 The Naked Sea Slugs colouring serves as a danger signal, then, to all sophisticated enemies.
When the /Bolls is full grown it is four inches long. The eggs are laid in a gelatinous cord coiled on rock faces or looped, festoon-like, on seaweeds. The young have glossy shells, coiled like that of the chambered Nautilus, which are soon absorbed. The rasping tongue has but one central row of teeth.
The Slug (Dendronotus arborescens, Mull.) is covered with a forest of miniature tree forms, the elaborately branched cerata, which disguises the creature as it hides among branching corallines and seaweeds whose rosy or brown marbled colouring it imitates faithfully. This is a distinctly edible slug,
from the view point of a fish; therefore protective coloration is its only defence. The adult is a little over an inch in length. No wonder it shrinks from exposure in the clear water where it would be conspicuous.
This is a very desirable addition to a marine aquarium jar. Put in a few pebbles with their tufts of bright coralline, and some ruddy algae with their animated molluscan imitator. It is a marvellously interesting and beautiful study, but you must have a stick to poke up the shy creature.
The grove on its back serves the slug for gills. At the base of each tree is a pouch, a stomach annex, supplied with branches of the liver; here digestion proceeds. The New England coast and opposite, across the Atlantic, is inhabited by this mollusk.
The Sea Lemon or Warty Slug (Doris tuberculata, Linn.) somewhat resembles half a lemon, cut in two lengthwise. The yellowish back is warty and stiffened by limy spicules; there are gill plumes arranged in a rosette on the posterior end of the back; two leaf-like tentacles rise in front. The creature glides slowly on its flat foot, concealed by its resemblance to the crumb-of bread sponges, which are its principal food.
The egg ribbon is wound into a remarkable rosette form, and glued to a rock. Each contains many thousand eggs. The young ones have nautiloid shells. The adults are rarely over three inches long.
The Naked Sea Slugs ish, dotted with black, and often roughly tuberculated. It rarely exceeds three inches in length. Look for it at low tide in shallow pools or in tangles of seaweed. It is worthy of study in a jar of sea water.
It is a diverting thought, and an enlightening one, that these helpless creatures are protected by the expedient of wearing their arborescent "liver and lights" on the outside. Sea ane mones are known as bad-tasting creatures, with projectile stingers which they cast at the least suspicion of attack. Hence, resem blance to anemones is a strong defence to any nudibranch. One little slug carries an anemone on its back. Many feed upon the anemones they imitate, often hiding in the capacious bodies they devour piecemeal. Those that feed upon ascidians, sea fans, hydroids and corals imitate in their branching cerata the tentacles of these creatures, as well as their colouring.