Nerites are small rounded snails belonging to the family Neritidae, and most are ideally suited to aquariums because of their small size, herbivorous diet, and long life. Some nerites are not suitable for aquariums, however, because they live just above the tide line, venturing below the water surface only briefly to feed on various types of algae. The main diet of most nerites is diatoms that grow as a film coating rock surfaces in the intertidal zone. Nerites also feed on filamentous and film-forming cyanobacteria, and filamentous green algae.
Their appetite for these algae makes them a good choice as a herbivore in marine reef aquariums, even though most species don’t occur on reefs per se. Nerites generally occur in the intertidal zone on rocky shores, in tidepools, and on reef flats. A few species can be found on mangrove roots, some on seagrasses or mudflats, and there are also brackish and freshwater species. While any of the nerites may be active during the day, most Nerita species are more active at night. Some species congregate in clusters during the day and disperse at night to feed. The congregation behavior appears to be a means of preventing desiccation in the hot afternoon sun.
Marine nerites have adapted to living in the intertidal zone where the tides rise and fall causing areas of the shoreline to be either covered with water or exposed to air. The change from a marine environment to a terrestrial one can place stresses upon the organisms located within the intertidal zone (Denny and Paine 1998). The stresses include temperature extremes in air and water, desiccation, and periodically rough wave action.
Unlike many snails that spawn by releasing gametes into the water, Nerites reproduce by having sex! The male has a penis and the female has an organ to store sperm. The eggs are laid in small white capsules. see: http://habitatnews.nus.edu.sg/news/chekjawa/ria/text/402.htm
The white egg capsules look like sesame seeds and are commonly seen on the glass or live rock in aquariums with nerites. They often generate “what is that?” remarks from observers. Just say they’re sesame seeds and watch how the subject gets changed. Though these egg capsules are laid prolifically, I have so far not seen an example where new nerites appeared. Apparently the larval period and requirement for planktonic food limits the successful recruitment of nerite larvae. There may also be a special requirement that the egg capsules be exposed with the change of the tides, or rainfall and salinity change may be necessary for some species.
There are numerous freshwater Nerites, but only one of them is common in the aquarium trade. The Olive Nerite, often referred to as Neritina reclivata (Say, 1822) but correctly,_Vittina usnea_ (Roding, 1798) is a brackish water snail from Florida, the Caribbean and Gulf of Mexico sometimes called by the common name “Black marble snail.” It has a thick, relatively heavy shell that is dark green with numerous, narrow black stripes. They are occasionally available in pet shops or through online vendors. See http://www.azgardens.com/index2.htm and look under algae eaters to find them. Clithon spp. are exquisite freshwater nerites from the Indo-Pacific region._Theodoxus danubialis is another freshwater nerite, from rivers in Europe, and it bears remarkable resemblance to the zebra nerite, Puperita pupa_. see photos: http://www.capricornica.com/world_shells/Neritidae/Neritidae.html
There are numerous species of nerites from tropical and temperate marine shores. Following is a survey and description of some that I have collected and maintained in aquariums, with observations regarding their longevity, husbandry, and natural habitat.
Zebra Nerite, Puperita pupa
The Zebra Nerite is a beautiful little snail that occurs in rocky tidepools under full sun in the Caribbean and Bahamas. It is reported to occur in Florida, but there it does not typically have the distinct zebra stripping. Instead the Florida snails more closely resemble the very similar Virgin Nerite, Neritina Vittina virginea. While the latter is more common on mudfalts and seagrass at the low tide mark, both can live together in tide pools. Where they are found together, the form of Puperita becomes more like N. virginica, dark and variable, and it was described as a separate form, Puperita pupa (Linnaeus, 1767) form tristis (d’Orbigny, 1842). Puperita is active during the day when it is submerged, and feeds mainly on diatoms. At low tide if the tide pools become dry or exceptionally hot, Puperita may stop feeding and congregate out of water in a stationary mass with others of its kind. In aquariums the Zebra nerite actively feeds on diatoms or cyanobacteria. Unfortunately, in aquarium the lovely striped shell soon becomes coated with pink coralline algae. The life span in captivity is typically about one year.
The Virgin Nerite, Neritina Vittina virginea
Virgin nerites occur in the Caribbean, Gulf of Mexico including Texas, Florida, and the South Atlantic. The color and pattern in Neritina Vittina virginea is extremely variable. Colors include purple, red, orange, gray, black, white and patterns with checkers, triangles, or stripes. There are numerous Neritina species found in coastal habitats in tropical and temperate locations all over the world, and many of them are superficially identical to N. virginea. Neritina communis (Quoy & Gaimard, 1832), now known as Vittina waigiensis (Lesson, 1831) from the Philippines and western Pacific is even more colorful than the Virgin Nerite and just as variable in pattern. The Virgin nerite occurs at the low tide mark on mudflats and Halodule spp. seagrass beds, often in areas with brackish water. It also occurs in tidepools along with the similar looking Puperita pupa tristis. The operculum in the Virgin nerite is darker than the operculum in Puperita, otherwise they can be difficult to distinguish. The diet and husbandry requirements in captivity are the same as for Puperita. The life span in captivity is also typically about one year. Other species in the genus Neritina may live for longer periods of time. Vittina luteofasciata, from the central American Pacific coast lives at least three years in captivity (pers. obs.). It has recently been imported to the USA for the aquarium trade.
Bleeding Tooth, Nerita peloronta
The Bleeding Tooth nerite gets its name from a strange formation at the aperture of the snail that looks just like a set of teeth surrounded by a blood red stain. The “blood” is really just iron deposited in the shell, and the function of the teeth is not known, but it seems that the bleeding teeth are intended as a display that makes the snail shell appear to be a mouth. Presumably this would startle potential small predators. The bleeding tooth nerite reaches up to 3 cm in length. Its shell is yellowish with red and dark purple zigzag marks. It is a pretty snail, but unfortunately not suitable for home aquariums. It lives just above the tide line and migrates with the change in the water level. This results in it escaping from the aquarium and ending up somewhere else in your home, attached to a wall, a bedpost, the ceiling. The surprising thing about them is that they can remain out of water for extended periods of time, days at least, possibly weeks. I know this because I at one time attempted to keep a few of them. After a few had become missing in action, when I discovered them more than a week later somewhere in the house, they miraculously came back to life when placed in a cup of saltwater. It might be possible to maintain this snail in a large rocky tidepool exhibit, but the tidal variance should be at least one meter.
The four tooth nerite, Nerita versicolor, is very similar to the bleeding tooth nerite viewed from above, but lacks the “blood” stain on the underside of the aperture. It only reaches 2.5 cm in length. The four tooth nerite has 4 prominent teeth, compared to two or three for the bleeding tooth nerite. It occurs in the same habitat as the Bleeding tooth, but spends more time in the water, and stays lower down on the rocks even when it crawls out. Like the Bleeding tooth it always crawls out of the water, so it is not suitable for most aquariums. Lower down on the rocks and in tidepools in Florida and the Caribbean one may find the checkered nerite, Nerita tesselata, that reaches 2 cm in length. Its shell is checkered black and white and it may have very small, modified teeth (Kaplan 1988). The checkered nerite population includes individuals that frequently crawl out of the water and individuals that rarely do. They are distributed on the rocks and in tidepools according to their preference. To the best of my knowledge no-one has studied the difference in their behavior, but I have observed it because it is my experience that the ones that rarely leave the water are suitable for aquariums while the ones that frequently leave the water are not, even though they are technically the same species. The water-loving form often has coralline algae on its shell, a telltale sign of its preference to remain in the water. It is a good herbivore for marine and reef aquariums.
Another nerite that occurs in Florida and the Caribbean, especially on rocks near mangroves, is Nerita fulgurans. Its shell is black and it has prominent concentric grooves. As with the checkered nerite, some members of a population spend more time in the water than others. In general, however, Nerita fulgurans will eventually migrate out of the aquarium so I don’t recommend it.
Emerald nerite snails Smaragdia viridis
Emerald nerites belong to the genus Smaragdia. They are small and flattened, with thin shells that are translucent and bright green. This color makes them nearly invisible on the seagrass blades where they live. It would be a dream if these exquisite little snails fed simply on epiphytic algal films on the grass, but unfortunately their diet consists not of algal films but of the seagrass itself! They pierce the cells of the grass and draw out the contents, leaving clear spots on the blades. Therefore they are not suitable for most aquariums. Without their seagrass food source they starve within a few weeks.
Nerita picea Recluz, 1841.
In Hawaiian tidepools there is a little black nerite that evolved to match the color of lava. It is a very hardy little herbivore, available to the trade from Indo Pacific Sea Farms. They feed well on diatoms and are active during the day. The lifespan in captivity is typically about 1 year.
Nerita polita and Nerita albicilla from the Western Pacific and Red Sea are occasionally offered for sale to aquarists. They have elongated shells that are colored cryptic shades of gray and brown. Nerita sanguinolenta Red Sea and Eastern Mediterranean is similar. These nerites, which reach a size of about 3 cm are long-lived (3 years or more) excellent herbivores for reef aquariums, feeding even on Derbesia (green hair algae).
While not yet as well established as turban snails for the “cleanup crew” in reef aquariums, nerites do have many fans and are gaining in popularity. Considering how prolific nerites are in their natural habitat and how frequently they lay eggs, they would seem to be an ideal candidate for captive propagation. Tropical mariculture farms have succeeded in culturing turban snails ( Trochus, Turbo, Astraea ) as herbivores for aquariums. It would be worthwhile to investigate the special requirements for successful captive rearing of nerites.
References And Suggested Readings
- Delbeek, J.C. and J. Sprung. 1994. The Reef Aquarium volume one. Ricordea Publishing.
- Etter, Ron J. 1989. Life History Variation in the Intertidal Snail Nucella Lapillus Across a Wave-Exposure Gradient. Ecology. V.70 n. 6. P.1857-1876.
- Helmuth, Brian S. T. and Gretchen E. Hofmann. 2001. Microhabitats, Thermal Heterogeneity, and Patterns of Physiological Stress in the Rocky Intertidal Zone. Biol. Bull. 201:374-384.
- Kaplan, Eugene H. 1988. Peterson Field Guides: Southeastern and Caribbean Seashores. Houghton Mifflin Company. New York.
- Sprung, J. 2002 Algae: A Problem Solver Guide. Ricordea Publishing
- Sprung, J. 2001. Invertebrates: A Quick Reference Guide. Ricordea Publishing