Modulus modulus (Linnaeus, 1758)
Family: Modulidae
Common names: Buttonsnail
Synonyms: Modulus filosus Helbling, 1779,  more...
Modulus modulus image
Modulus modulus  

Species Description: The buttonsnail, Modulus modulus, is a small marine gastropod of the family Modulidae. The shell is top-shaped and low-spired, and is wider than it is high, consisting of 3-4 or 5-6 strongly convex and angulate whorls. The body whorl is disproportionately larger then the other whorls. The margin of each whorl has a ridge or keel formed by a prominent spiral cord and parallel to 3-4 weaker spiral cords. The aperture is nearly round and the lip is moderately thin and crenulate (serrate-scalloped). The columella terminates in a deep notch that accommodates the pallial tentacles of the inhalant siphon. The shell color is usually yellowish white, splotched with purple or brown, although this is often obscured by the periostracum and algal epiphytes in living specimens. The colummela has a purple tinge and the columellar notch has a purple spot. The operculum is round, thin, and horny (Houbrick 1980, Abbot and Morris 1995).

The living animal is light green to mossy green in overall appearance. The head is equipped with a short, bilobe-tipped snout and two thin tentacles. The fully exposed foot is slightly smaller than the shell diameter (Houbrick 1980).

Potentially Misidentified Species: The congener Modulus papei also resides in Florida waters, although it is primarily a rocky intertidal species (USFWS 2007) and is therefore unlikely to occur in the same habitat as M. modulus.

Regional Occurrence: Modulus modulus occurs from North Carolina south to Brazil, and also in Bermuda (Abbot and Morris 1995).

IRL Distribution: Modulus modulus occurs throughout the IRL system.

Age, Size, Lifespan: Modulus modulus is a small gastropod with shell lengths typically ranging around 10-25 mm in length (Houbrick 1980).

Houbrick (1980) determined that the life cycle of M. modulus from the Indian River Lagoon in the vicinity of Fort Pierce lasts for approximately one year.

Abundance: Virnstein and Curran (1986) note that Modulus modulus was the third most abundant seagrass invertebrate in IRL Thalassia testudinum seagrass beds surveyed by these authors. Prager and Halley (1999) indicate that M. modulus densities can peak sporadically, and describe population 'blooms' in the seagrass beds of Florida Bay that appear to be the result of single recruitment events.

Reproduction: Reproduction is sexual. Sexes are separate and fertilization is internal.

In the Indian River Lagoon population studied by Houbrick (1980), mating occurred in early winter and egg mass deposition took place in the spring. Females produce cylindrical gelatinous egg masses that are deposited on seagrass surfaces.

Embryology: Embryonic Modulus modulus exhibit direct development with no planktonic larval stage. Crawl-away juveniles emerge from egg masses after approximately three weeks (Houbrick 1980).

Temperature: The distribution of this species is restricted to warm-temperate and subtropical/tropical locations, possibly because it is intolerant of colder waters.

Salinity: Examination of the NOAA NBI collection records suggests Modulus modulus may occupy a narrower range of salinities than many estuarine species. Collection information from these records indicate that buttonsnails have been sampled from salinities ranging from 23-37 ppt.

Trophic Mode: Buttonsnails are style-bearing, micrograzing herbivores, feeding primarily on diatoms and other seagrass epiphytes (Houbrick 1980).

Predators: Haefner (1990) reports that Modulus modulus dominated the diets of the portunid crab Callinectes ornatus from Mullet Bay, Bermuda.

Walker et al. (2002, after Randall 1967) list a large number of potential fish predators of M. modulus, including various grunts, wrasses, blennies, and puffers.

Habitats: Modulus modulus inhabits shallow vegetated habitats, and is a prominent faunal component of many marine and estuarine seagrass communities (Houbrick 1980, Abbot and Morris 1995). Haefner (1990) notes the species is common on macroalgae in Mullet Bay, Bermuda.

Economic/Ecological Importance: The shells of dead buttonsnail are an ecologically important resource for large numbers of hermit crabs such as Pagurus maclaughlinae (Tunberg et al. 1994, Virnstein and Curran 1986).

Abbot RT and PA Morris. 1995. Shells of the Atlantic and Gulf Coasts and the West Indies. Peterson Field Guides. Houghton Mifflin Company, NY. 350 p.

Haefner PA, Jr. 1990. Natural Diet of Callinectes ornatus (Brachyura: Portunidae) in Bermuda. Journal of Crustacean Biology 10:236-246.

Houbrick RS. 1980. Observations on the anatomy and life history of Modulus modulus (Prosobranchia: Modulidae). Malacologia 20:117-142.

Randall JE. 1967. Food habits of reef fishes of the West Indies. Pp. 665-847 in: Studies in Tropical Oceanography, No. 5. Institute of Marine Sciences, University of Miami, Miami.

Tunberg BG, Nelson WG, and G Smith. Population ecology of Pagurus maclaughlinae Garcia-Gomez (Decapoda: Anomura: Paguridae) in the Indian River Lagoon, Florida. Journal of Crustacean Biology 14:686-699.

U.S. Fish and Wildlife service (USFWS). South Florida Multi-Species Recovery Plan - Ecological Communities: Nearshore and Midshelf Reefs. USFWS South Florida Ecological Service Office. Available online.

Virnstein RW and MC Curran. 1986. Colonization of artificial seagrass versus time and distance from source. Marine Ecology Progress Series 29:279-288.

Walker SE, Parsons-Hubbard K, Powell E, and CE Brett. 2002. Predation on experimentally deployed molluscan shells from shelf to slope depths in a tropical carbonate environment. Palaios 17:147-170.

Modulus modulus image
Modulus modulus