Cerithidea scalariformis (Say, 1825)
Family: Potamididae
Common names: Ladder Hornsnail
Cerithidea scalariformis image
Cerithidea scalariformis  

Species Description: Cerithidea scalariformis is the largest genus in the Potamidinae, one of two subfamilies of the Potaididae. The other subfamily is the Batillariinae. The subfamilies are distinguished by differences in their radulae, the tooth-like scraping structures used in feeding. In the Potamidinae, the radula lacks cusps on the lower basal plate of the rachidian tooth. A cladistic analysis of this genus, based on morphological distinctions of species within the group is presented by Houbrick (1984).

Regional Occurrence: Cerithidea scalariformis occurs in Georgia, both coasts of Florida, and Cuba. Its limited distribution is probably due to lack of a planktonic larval stage (Houbrick 1984).

IRL Distribution: Although probably occurring lagoon wide, a population of Cerithidea scalariformis was studied at Big Starvation Cove, across the Indian River from Link Port (Houbrick 1984).

Age, Size, Lifespan: Several (4 - 5) weeks after hatching, thousands of juvenile snails 1.1 - 13.0 mm in length were observed in the field, and were most numerous in October and November. By late January, juvenile snails had attained lengths ranging from 2.0 - 8.0 mm and were found in tidal creeks. At this time, adult Cerithidea, with eroded shells and heavily parasitized with trematodes, were beginning to die off. Juvenile snails tend to remain submerged while adults tended to stay above the high water mark occurring along creek banks and can be found a meter above the high water mark on vegetation (Salicornia and mangroves). By early spring, immature snails were half adult size while most adults from the previous generation were gone. By early summer young snails reach adulthood and attain sexual maturity by August - September (Houbrick 1984).

Probable lifespan of Cerithidea scalariformis is 1 to 2 (possibly 3) years. Highest growth rates occur in immature snails (<10.0 mm). The adult snail shows no growth in shell length (Houbrick 1984).

Abundance: Highest abundance observed for Cerithidea scalariformis at Big Starvation Cove (Indian River Lagoon) was 1,100 individuals per square meter. Highest densities are found in the Salicornia zones (Harlos 1976; Houbrick 1984).

Locomotion: Crawls. Hatchlings do not display planktonic stage or swimming behavior.

Reproduction: Cerithidea scalariformis, like all Potamididae, is aphallate and it is thought that spermatophore transfer occurs via the siphons. Spermatophores are held in the spermatophore bursa where they eventually disintegrate, releasing sperm. Sperm migrate to the seminal receptacle where egg fertilization takes place. Eggs are arranged in a loose spiral and encased in long jelly strings, ~51.0 mm long by 1.13 mm in diameter. This "spawn" is deposited in the field (on bark, decaying wood and leaves) from late September through November when hatchlings were also found. A spawn mass can contain up to 350 eggs.

Embryology: Cerithidea scalariformis is a direct developer with no planktonic larval stage (Houbrick 1984). Transparent egg capsules are ~0.37 mm in diameter and the single bright green egg within the capsule is ~0.28mm in diameter. After deposition, cleavage ensues and early embryonic stages appear green. The veliger stage embryo is reached about 5 days after deposition; morphologically, C. scalariformis is typical of direct developers by possessing eyespots, small velar lobes and a large larval shell. Hatchlings emerge 18 - 22 days after deposition, crawl on the substratum and metamorphose into tiny snails within one to two days.

Temperature: C. scalariformis is highly eurythermal, and also is able to tolerate periods of desiccation (Houbrick 1984). Temperatures at Big Starvation Cove (Indian River Lagoon) can vary greatly with sun exposure, and often reach as high as 50.0°C in the summer (N. Smith, pers. obs.).

Salinity: Cerithidea scalariformis is euryhaline, preferring a salinity of 28.0 ppt. However, at Big Starvation Cove (Indian River Lagoon) normal salinity is 33.0 ppt, and varies substantially depending on season. Substrata salinities, more so than predation, probably determine vertical distribution of these snails (Harlos 1976 as cited in Houbrick 1984).

Other Physical Tolerances: Few empty shells of C. scalariformis were found at Big Starvation Cove (Indian River Lagoon),  possibly due to their dissolution in the ambient, low pH environment (Houbrick 1984), which living C. scalariformis tolerate well.

Trophic Mode: Juvenile and adults both feed on detritus and microalgae (N. Smith - pers. comm.).

Habitat: Cerithidea scalariformis leads an amphibious existence in muddy estuarine habitats in tropical and subtropical areas. C. scalariformis occurs in large numbers along tidal creeks in mangrove and salt marsh habitats.

Associated Species: Predator avoidance behavior, i.e., climbing vegetation, is less obvious in Cerithidea scalariformis than in other congeners. At Big Starvation Cove (in the Indian River Lagoon) young snails had nipped tentacles, suggesting killifish predation, as was observed by Harlos (1976). Mud crab predation was also observed, and clapper rails were suspect predators at this later site (Harlos 1976 as cited in Houbrick 1984) Although other potential predators were observed at this site, e.g., wading birds, raccoons opossums and fiddler crabs, Houbrick (1984) observed no visible indications of predation such as drilled or cracked shells. However, Smith (pers. obs.) believes that blue crabs are the main predators of C. scalariformis in the Indian River Lagoon.

Harlos D. 1976. Environmental distribution of Melampus bidentatus (Pulmonata) and Cerithidea scalariformis (Prosobranchia) in a Florida tidal marsh. M.S. thesis. Mississippi State University, MS. 66 pp.

Houbrick RS. 1984. Revision of higher taxa in genus Cerithidea (Mesogastropoda: Potamididae) based on comparative morphology and biological data. Am Malacol Bull 2: 1-20.

Cerithidea scalariformis image
Cerithidea scalariformis  
Cerithidea scalariformis image
Cerithidea scalariformis