User:Lonhart/sandbox

The marine snail Norrisia norrisi is a medium-sized gastropod mollusk within the family Trochidae. It has several common names, including Norris's top snail, Norris's topsnail, norrissnail, smooth brown turban snail, or kelp snail.

Distribution
The species has been found along the Pacific coast of North America from Monterey to Isla Asuncion on the Baja California peninsula in Mexico. Along the coast of California, with the exception of a persistent population in Diablo Cove, Norrisia norrisi primarily occurs south of Point Conception in the low intertidal and shallow subtidal.

Description
Norrisia norrisi has a smooth brown shell that ranges in size from a few mm in juveniles up to 59 mm in adults, as measured across the greatest shell dimension. Similar to other trochid snails, such as the more commonly occurring Chlorostoma species (formerly Tegula), the dextrally coiled shell of Norrisia norrisi is also more globose. Other distinctive features include a smooth, green columella, an open, black-ringed umbilicus, and a round aperture sealed with an operculum made of protein rather than calcium carbonate. The fleshy foot of the snail is a bright reddish orange with black speckling lining the basal margin. Four elongate epipodial tentacles are spaced evenly along both sides of the muscular foot.

Empty shells of Norrisia norrisi are occupied by hermit crabs, using the hard shell to protect their poorly armored posterior.

Habitat
Norrisia norrisi can be found in the lower rocky intertidal zone, where these snails graze on algae, microscopic films, and wrack. More commonly Norrisia norrisi is found in the shallow subtidal, particularly in kelp forests. On Santa Catalina Island off the coast of southern California, Norrisia norrisi is commonly seen crawling up and down stipes of the giant kelp Macrocystis pyrifera.

Feeding
Early studies on the feeding ecology of Norrisia norrisi indicated that these snails preferred to feed on kelps, with a general hierarchy of Egregia > Laminaria farlowii > Macrocystis pyrifera > Eisenia arborea. Using binary choice feeding experiments, Wakefield and Murray (1998) demonstrated that the herbivorous gastropod Norrisia norrisi preferred laminarialean kelps over all other algae tested. When comparing kelps, blades of the giant kelp Macrocystis pyrifera were slightly preferred over the feather boa kelp Egregia menziesii, and both were strongly preferred over sporophylls (i.e. reproductive blades) of the southern sea palm Eisenia arborea. All kelps tested were consistently selected over other algae commonly encountered by Norrisia norrisi (e.g., Halidrys dioica, Dictyota flabellata, and Pterocladia capillacea).

Reproduction
Very little is known about reproduction by Norrisia norrisi. Some marine snails reproduce by broadcast spawning, releasing sperm and eggs into the water column at the same time, and rely on external fertilization to produce the next generation. Other species internally fertilize eggs, then release larvae or lay egg cases containing the larvae. It is not known which method is used by Norrisia norrisi.

Predators
Predators of Norrisia norrisi include sea otters, starfish such as Pisaster ochraceus and Pisaster giganteus, California spiny lobster Panulirus interruptus, and drilling mollusks such as octopus and moon snails. When fleeing a predator on a sloping substrate or while crawling on kelp, a Norrisia norrisi may simply detach itself and roll or fall away from the predator. If detached from a giant kelp or other stipitate alga, Norrisia norrisi will quickly crawl towards another kelp upon reaching the bottom. Mortality on the bottom of the reef is much higher than on the giant kelp.