Norrisia norrisi

Norrisia norrisi
A live individual of Norrisia norrisi, its shell encrusted with barnacles (upper left) and an encrusting coralline alga (lower right part of the shell). The snail is on the giant kelp, species Macrocystis pyrifera
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Gastropoda
(unranked):	clade Vetigastropoda
Superfamily:	Trochoidea
Family:	Trochidae
Subfamily:	Tegulinae
Genus:	Norrisia
Species:	N. norrisi
Binomial name
Norrisia norrisi (G. B. Sowerby II, 1838)
Synonyms
Turbo rotelliformis Jay, J.C., 1839

The marine snail Norrisia norrisi is a medium-sized gastropod mollusk within the family Trochidae. ^[1] It has several common names, including Norris's top snail, Norris's topsnail, norrissnail ^[2], 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.^[3] 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. ^{[3] [4]}

Description

Norrisia norrisi shell with a slipper shell Garnotia norrisiarum attached.

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.^[5] 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.^[6] 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.^[5]

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

Ecology

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.^{[7] [5]}

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.^[8] 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).^[9]

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 ^[10], California spiny lobster Panulirus interruptus,^[11] and drilling mollusks such as octopus^{[7] [12]} 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.^{[7] [5]} Mortality on the bottom of the reef is much higher than on the giant kelp. ^[7]

References

1. ^ Williams S.T., S. Karube and T. Ozawa. 2008. Molecular systematics of Vetigastropoda: Trochidae, Turbinidae and Trochoidea redefined. Zoologica Scripta 37(5): 483-506.
2. ^ http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=70013
3. ^ ^{a b} Lonhart, S.I. and J.W. Tupen. 2001. New range records of 12 marine invertebrates: the role of El Nino and other mechanisms in southern and central California. Bulletin of the Southern California Academy of Sciences 100(3):238-248.
4. ^ Morris, R.H., D.P. Abbott and E.C. Haderlie. 1980. Intertidal Invertebrates of California. Stanford University Press: Stanford, CA.
5. ^ ^{a b c d} Lonhart, S.I. 1996. The vertical distribution and diel migration of Norrisia norrisi on Macrocystis pyrifera at Santa Catalina Island. Master of Science thesis, California State University at Long Beach. 103 pages.
6. ^ Keen, A.M. and E. Coan. 1974. Marine molluscan genera of western North America. Second edition. Stanford University Press: Stanford, CA.
7. ^ ^{a b c d} Schmitt, R.J., C.W. Osenberg and M.G. Bercovitch. 1983. Mechanisms and consequences of shell fouling in the kelp snail, Norrisisa norrisi (Sowerby) (Trochidae): indirect effects of octopus drilling. Journal of Experimental Marine Biology and Ecology 69:267-281.
8. ^ Leighton, D.L. 1966. Studies of food preference in algiverous invertebrates in southern California kelp beds. Pacific Science 20:104-113.
9. ^ Wakefield, R.L. and S.N. Murray. 1998. Factors influencing food choice by the seaweed-eating marine snail Norrisia norrisi (Trochidae). Marine Biology 130: 631-642.
10. ^ Leighton, D.L. 1971. Grazing activities of benthic invertebrates in southern California kelp beds. In: W.J. North (editor), The biology of giant kelp beds (Macrocystis) in California. Beihefte zur Nova Hedwigia, Heft 32:1-600.
11. ^ Engle, J.M. 1979. Ecology and growth of juvenile California spiny lobster, Panulirus interruptus (Randall). Doctoral dissertation, University of Southern California.
12. ^ Ambrose, R.F> 1984. Food preferences, prey availability, and the diet of Octopus bimaculatus (Verrill). Journal of Experimental Marine Biology and Ecology 77:29-44.

Gallery

• 

  Norrisia norrisi feeding on a blade of the giant kelp Macrocystis pyrifera. Snails use a radula to rasp away the upper layers of kelp tissue.

• 

  Norrisia norrisi new recruit at 5.5 mm. Note the shell morphology of juveniles differs by having a set of ridges along the whorl.

• 

  Norrisia norrisi climbing up the giant kelp Macrocystis pyrifera at Pumpernickel Reef on Santa Catalina Island, CA.

External links

• Photo of shell and operculum at gastropods.com