Houbrick (1993) considers the genus Bittiolum to be a sister genus of Bittium
The grass cerith, Bittiolum varium, is a small cerithiid gastropod
with an elongate, turreted shell consisting of around 10 whorls. The
aperture is notably rounded, with a smooth lip and a short, distinct
siphonal canal. The intersections of the spiral lines and axial ribs form
raised nodules. Color is highly variable, ranging from light to dark brown
to gray-white to bluish black to reddish, sometimes with darker flecks or
mottling. The soft tissues of the animal itself are often colored
similarly to the shell and the sole of the foot is white with opaque spots.
The operculum is light brown and translucent (Qurban 2000, STRI undated,
Potentially Misidentified Species
A number of cerithid gastropods co-occur with Bittiolum varium. The
descriptive information provided above should be sufficient to allow
amateur naturalists to identify specimens with a reasonable degree of
HABITAT AND DISTRIBUTION
Bittiolum varium occurs along the east coast of the Americas from
Maryland to Brazil, along the Gulf coast to Texas, and throughout much of
the Caribbean (Houbrick 1993, Rosenberg 2005).
The species occurs throughout the lagoon.
LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan
The maximum confirmed reported size for this species is 6.5 mm, although
unconfirmed reports of 10 mm specimens exist (Rosenberg 2005).
Marsh (1976) reports the life span of Bittiolum varium is around 1.5
years, although typically many individual do not survive to this age.
Bittiolum varium has been reported to be often abundant (1.7
individuals per square cm) in the summer, and considerably more rare during
the winter (Qurban 2000). Mikkelsen at al. (1995) report that Bittiolum
varium was the most frequently collected and numerically abundant
mollusc of the Indian River Lagoon, based on collection and literature
resources dating primarily from 1974 to 1982.
Brewster-Wingard et al. (2001) report that Bittiolum varium is one
of the two most numerically abundant molluscs in vegetated habitats of
Florida Bay. It and the bivalve mussel Brachidontes exustus
together accounted for 95% of live molluscs sampled during this study.
Core studies indicate Bittiolum varium has been a dominant component
of molluscan assemblages in Florida Bay for the last 200 years (Trappe and
Bittiolum varium is a dioecius (separate sexes) and fertilization is
internal, although males lack a functional penis. Sperm from males may
instead be taken into females via inhalent water currents (Webber 1977).
The species is oviparous, with females depositing egg masses onto a variety
of suitable substrata, including seagrass blades, drift algae, and rock
surfaces. In the IRL, eggs are deposited from spring through early fall
Marcus and Marcus (1963) and Thiriot-Quievreux (1979) describe Bittiolum
varium larvae as planktotrophic, with a small, transparent shell and a
pale, colorless velum.
Planktonic larval Bittiolum varium persist within the water column
for more than three weeks before metamorphosis and settlement to the
benthos. B. varium water column larvae in the IRL were most
abundant in the spring through early fall, becoming increasingly rare in
late fall and winter (Qurban 2000).
Pronounced annual abundance peaks are reflective of seasonal high rates of
recruitment. Size-frequency analysis of IRL B. variolum by Qurban
(2000) revealed the presence of distinct cohorts that could be tracked as
they entered into and matriculated through the population.
The warm-temperate to subtropical/tropical range of this species may be
temperature-driven. Marsh (1973, 1976) noted the presence of large numbers
of individuals within bottom sediments during winter months, possibly as an
avoidance response to cold temperature.
Miller et al. (2007) report a low salinity limit of 10 ppt for Bittiolum varium.
Cote et al. (2001) identify Bittiolum varium as a micrograzer. Van
Montfrans et al. (1982) report the species is seasonal grazer on diatoms,
coralline algae, and other epiphytes of seagrass blades in Chesapeake Bay.
During periods of peak abundance, competition for spatial and dietary
resources may conceivably occur.
Juvenile blue crabs (Calinectes sapidus) inhabiting seagrass
nursery habitats consume large numbers of Bittiolum varium and
other micrograzing snails, and may influence the population dynamics of
prey species (Wright, R. A., Crowder 1996, Cote et al. 2001). Field and
laboratory studies indicated that blue crabs preferentially consumed B.
varium over the gastropod Astyris lunata (Cote et al. 2001).
In addition to blue crabs, Martin et al. (1989) considered spot
(Leiostoma xanthurus) to be a major predator of B. varium.
Bittiolum varium is a widespread epifaunal inhabitant of marine and
estuarine seagrass beds and is a dominant faunal component of Indian River
Lagoon seagrass and drift algal communities (Houbrick 1993, Qurban 2000).
Ferguson (2005) notes that Florida Bay B. varium shows increased
abundance in Halodule wrightii (= wrightii) beds compared
to Thalassia testudinum beds.
Wells (1961) and Rothchild (2004) report the species as an oyster
associate, and it has also been observed on hydroid-covered algae in
shallows near shore (STRI undated).
In at least some portions of the IRL, juveniles and adults appear to
overwinter in greater numbers within unattached benthic ÒdriftÓ macroalgae
than among seagrass blades, and few adults overwinter within the sediment
Due to their seasonal high abundance, B. varium is an important
grazing faunal community component. When abundant, the species is also
important as a dietary resource for benthic predators.
Bailey-Matthews Shell Museum. Undated. Bittiolum varium species
profile. Available online.
Brewster-Wingard GL, Stone JR, and CW Holmes. 2001. Molluscan faunal
distribution in Florida Bay, past and present: An integration of down-core
and modern data. Bulletins of American Paleontology, special
Cote J, Rakocinski CF, and TA Randall. 2001. Feeding efficiency by juvenile
blue crabs on two common species of micrograzer snails. Journal of
Experimental Marine Biology and Ecology 264:189-208.
Ferguson CA. 2005. The appearance of change: Searching for an environmental
transition in an accumulating subfossil assemblage. Abstract presented at
the 2005 Geological Society of America annual meeting, Salt lake City, UT.
Houbrick R. 1993. Phylogenetic relationships and generic review of the
Bittiinae (Prosobranchia: Cerithioidea). Mlacologia 35:261-313.
Marcus E and E Marcus. 1963. Mesogastropoden von der kusts von saoPaulo.
Abhandl. Math. Nnaturwissensch. Klasse akad. Wiss. and Lit. Mainz. 1:1-105.
Marsh G. 1973. Zostera epifaunal community in the York River
Virginia. Chesapeake Science 14:87-97.
Marsh G. 1976. Ecology of the gastropod fauna of eelgrass in a Virginia
estuary. Chesapeake Science 17:182-187.
Martin TH, Wright RA, and LB Crowder. 1989. Non-additive impacts of blue
crabs and spot on their prey assemblages. Ecology 70:1935-1942.
Mikkelsen P, Mikkelsen PS, and DJ Karlen. 1995. Molluscan biodiversity in
the Indian River Lagoon, Florida. Bulletin of Marine Science 57:94-127.
Miller AW, Ruiz GM, Minton MS, and RF Ambrose. 2007. Differentiating
successful and failed molluscan invaders in estuarine ecosystems. Marine
Ecology Progress Series 332:41-51.
Rosenberg G. 2005. Malacolog 4.1.0: A Database of Western Atlantic Marine
Mollusca. Available online.
Rothschild SB. 2004. Beachcomber's Guide to Gulf Coast Marine Life: Texas,
Louisiana, Mississippi, Alabama, and Florida. Taylor Trade Publications,
MD. 200 p.
Smithsonian Tropical Research Institute (STRI). Undated. Bittiolum
varium species profile. Bocas del Toro Species Database. Available
Thiriot-Quievreux C. Identification of some planktonic prosobranch larvae
present off Beaufort, North Carolina. Veliger 23:1-9.
Trappe CA and GL Brewster-Wingard. 2001. Molluscan fauna from core 25B,
Whipray Basin, central Florida Bay, Everglades National Park. Open-File
Report 01-143. U.S. Geological Survey OFR-01-143. U.S. Geological Survey,
Van Montfrans J, Orth RJ, and SA Vay. 1982. Preliminary studies of grazing
by Bittium varium on eelgrass periphyton. Aquatic Botany 14:75-89.