Species Description: The cross-barred venus, Chione cancellata, is a small clam belonging to family Veneridae. The cloudy white to yellow-white shells are highly distinctive, with raised, bladelike concentric ridges superimposed on strong radial ribs and giving the shells their characteristic cancellate (crisscrossed) appearance. Zigzag purplish brown patterns are often present and the interior of the shell usually has some purple (Rothchild 2004, Abbot and Morris 1995).
Stanley (1981) notes that experiments have demonstrated that the raised ridges of C. cancellata shells hinder burrowing, but reduce scour of sand from around the shells of partly exposed animals.
Some authorities recognize two distinct subspecies, Chione cancellata cancellata and Chione cancellata mazycki. Additionally, Roopnarine and Vermeij (2000) suggest specimens occurring along the eastern United States and Central America south to Belize are a separate species, Chione elevata, based on morphometric analysis.
Potentially Misidentified Species: Although many of the approximately 23 recognized species in the genus Chione occur in Florida, the distinctive raised cross-bar pattern and the other features noted above should allow a degree of certainty in species-identification.
Regional Occurrence: This subtropical species from North Carolina to Florida, Texas, and the West Indies (Abbot 1974, Abbot and Morris 1995).
IRL Distribution: Chione cancellata occurs throughout the IRL.
Age, Size, Lifespan: Chione cancellata is a small bivalve, attaining a maximum shell length of a little over 3 cm (Abbot and Morris 1995).
Reproduction: Cross-barred venus clams reproduce sexually. Sexes are separate and fertilization is external via broadcast spawning of gametes. Individuals reach maturity at around 15 mm shell length, at which time they become reproductive males or females at a ratio of approximately 1:1 (Rothchild 2004).
Embryology: Laboratory-based rearing studies reveal embryonic development from fertilization to straight-hinge D-stage veliger larvae occurs in just 24 hours at 25°C. At this time the larvae possess a calcified shell, a poorly developed digestive tract, an apical sense organ, a single mantle fold, and a functional velum equipped with four ciliary bands (Moueza and Frenkiel 2006).
A study by LaBarbera and Chanley (1970) revealed lab-reared C. cancellata larvae settled out of the water column when individuals reached a size of 170-196 µm. D'Asaro (1967) reports larval duration as typically being around 11 days from hatching to settlement.
Temperature: The distribution of this species is limited to warm-temperate and subtropical/tropical locations, likely due to intolerance to colder waters.
Salinity: Chione cancellata is a moderately euryhaline bivalve. Rothchild (2004) reports can tolerate salinities as low as 18 ppt. LaBarbera and Chanley (1970) collected animals from oceanic salinities.
Trophic Mode: Chione cancellata is a suspension feeder on water column phytoplankton.
Predators: Whelks (e.g., Busycon spp., Busycotupus spp.), horse conchs (Pleuroploca gigantea), tulips (Fasciolaria spp.), murex (Murex spp.), and moon snails (Polinices spp.) are among the major gastropod predators of Chione cancellata (Paine 1963). Haefner (1990) indicates C. cancellata are also a prey resource for the portunid crab Callinectes ornatus in Bermuda. Cate and Evans (1994) notes that black drum (Pogonias cromis) in lower Corpus Christi Bay, TX, consume cross-barred venus as well. The shallow burrowing habits of the species leave it fairly vulnerable to such predators (Rothchild 2004). Peterson (1982) notes that C. cancellata is more susceptible to predation than the hard clam, Mercenaria mercenaria.
Associated Species: The shallow burrowing tendencies of Chione cancellata often leave the shell posterior exposed at the sediment surface, offering a colonization site for epibiotic macroalgae and polydorid polychaetes (Rothchild 2004).
Habitats: Chione cancellata is a shallow-water species that occupies shallow soft sediments to a typical sediment depth of 15 cm or less. It can be found in both vegetated and unvegetated areas, but is usually more abundant within vegetation (Abbot and Morris 1995, Rothchild 2004). Orth et al. (1984) found a greater than 25-fold increase in seagrass-associated versus bare substratum-associated C. cancellata in North Carolina. The seagrass root and rhizome systems offer a partial predation refuge for the species.
Special Status: None.
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