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 Crepidula atrasolea
  formerly Crepidula cf. plana

 
Several Crepidula atrasolea on a clam shell.  From this dorsal view, it is impossible to distinguish between C. atrasolea and C. depressa.   Photo courtesy R. Collin, Smithsonian Tropical Research Institute.

Close-up ventral view of Crepidula atrasolea.   Photo courtesy R. Collin, Smithsonian Tropical Research Institute.

 
C. atrasolea with a full brood of capsules located between the propodium and the neck.  Large, individual eggs can be seen within each capsule.  Photo courtesy R. Collin, Smithsonian Tropical Research Institute.
 

Species Name: 
Crepidula atrasolea Collin 2000;  formerly Crepidula cf. plana Say, 1822.

Common Name:
Eastern white slipper shell

Species Description:
The family Calpytraeidae is made up of three genera: Crepidula (slipper shells), Crucibulum (cup and saucer shells) and Calyptraea (hat shells).  All of the species have limpet-shaped shells with an internal shelly septum.  The genera are distinguished by shell morphology.  In Crepidula the shell apex is directed posteriorly and the internal septum is a flat shelf that attaches along both sides of the shell.  In Crucibulum the shell is conical with a central apex and a cup-shaped internal septum.  In Calyptraea the shell is conical with a central apex but the internal shelly septum is a coiled ramp.  Shells are often not diagnostic on the species level.  Cryptic species often co-occur but they can usually be distinguished on the basis of developmental characters and body pigmentation.  There are 6 species of Crepidula, one Crucibulum and one Calyptraea reported from Florida: Crepidula ustulatulina, C. depressa,  C. atrasolea, C. aculeata,  C. maculosa and C. fornicata, Crucibulum auriculum, and Calyptraea centralis.

Crepidula atrasolea (formerly C. cf. plana) can be distinguished from other Crepidula species by the following suite of characters. The flat white shell ranges from recurved to somewhat convex depending on the habitat of the individual.  Animals from exposed substrates are often oval and convex with a more robust shell.  The shelf is flat in convex shells and convex in recurved shells,

 
with a notch on the right side where it attaches to the shell and also a depression in the center of the shelf margin.  Muscle scars are absent.  Apex at the shell margin usually directly posterior, sometimes slightly recurved to the right.  The shell is white, inside and out.  The shell is 5 - 8 mm in length.  There is no sculpture other than growth lines.   There is diffuse to intense sooty black pigmentation over the foot, mantle, and neck.  There are yellowish blotches on the mantle edge in some live animals. The sooty pigmentation is retained in recently preserved animals, but the yellow color is lost.

Synonomy:
Crepidula cf. plana Say, 1822

Potentially Misidentified Species:
Crepidula atrasolea is easily confused with 2 congeners, C. depressa and C. plana;  both of which occur in the North Atlantic.   C. atrasolea co-occurs with C. depressa along the coast of Florida and can be distinguished from C. depressa by the black pigmentation on the foot and direct development.  C. plana has a white foot and planktonic larvae, like C. depressa but occurs from Nova Scotia south to Georgia and its range may extend into Florida.  These three North Atlantic species cannot be distinguished on the basis of adult shell morphology.  Species with similar shells also occur in California, Chile, New Zealand, and the Mediterranean.  C. atrasolea has both a flat, white shell and a black or sooty foot.

II.  HABITAT AND DISTRIBUTION 

Regional Occurrence:
Crepidula atrasolea occurs on both the Gulf and Atlantic coasts of Florida, including the Florida Keys, and extending north to north through the Carolinas to eastern Canada.

IRL Distribution:
Crepidula atrasolea is distributed throughout the Indian River Lagoon. 

III. LIFE HISTORY AND POPULATION BIOLOGY

Age, Size, Lifespan:
Males of Crepidula atrasolea (formerly C. cf. plana) are characteristically smaller than females. Minimum, typical and maximum sizes for males are: 1, 5 and 8 mm respectively; for females, these sizes are: 5, 10 and 16 mm.  Longevity for males is typically 6 months but females can live for 2 years. However, the size and sex change of Crepidula atrasolea  often depends on the social structure of a population as well as on environmental conditions.

Locomotion:
Crawls.  Hatchlings have no swimming stage.

Reproduction:
All calyptraeids are protandric hermaphrodites.  Small, young animals are males that  later change to females as they grow.  All species copulate.  Females are able to store sperm for several months.  The females deposit eggs into transparent capsules that they brood between the neck and the propodium.  In some species, swimming larvae hatch from the capsules;  in others, benthic juveniles crawl away from the capsules. Crepidula atrasolea has as many as 6 reproductive periods per year, producing from 100 to 200 young. Reproductive seasonality peaks during the summer for this species.

Embryology:
Eggs in Crepidula atrasolea are brooded. Typical larval development time is 21 days, but can range from 14 to 28 days.  Development is direct.  Uncleaved eggs average 335 mm in diameter and there are usually fewer than 20 eggs/capsule.  Hatchlings with mean shell length of 1.02 mm crawl away from the mother.

IV.  PHYSICAL TOLERANCES

Temperature:
Crepidula atrasolea is considered eurythermic.  Temperature ranges, recorded from a data logger in the Indian River Lagoon show that C. atrasolea tolerates a temperature range between  5 - 35 °C.

Salinity:
Crepidula atrasolea is oligohaline to euryhaline.  Salinity ranges, recorded from a data logger in the Indian River Lagoon show that this species tolerates salinities between 15 - 38 ppt.  

Other Physical Tolerances: 
C. atrasolea prefers well oxygenated conditions.

V.  COMMUNITY ECOLOGY

Trophic Mode:
Species in all three genera of the Calyptraeidae are suspension feeders. They collect phytoplankton on mucus covering the gills.  Phytoplankton are then transported to the mouth on a mucus string along the dorsal right side of the neck.  The string is drawn into the mouth by the radula.

Habitat:
Crepidula atrasolea prefers epibenthic habitats in shallow oyster reefs, often near mangroves.  It is most common intertidally to subtidally, but prefers slow moving waters with with low wave exposure.  Typical maximum water depth is to at least 20 m,   In the Florida Keys, it is commonly found subtidally in shells inhabited by hermit crabs.

VI. SPECIAL STATUS

Special Status:
None

Economic Importance:
None

VII. BIBLIOGRAPHY

Collin, R.  2002.  Another last word on Crepidula convexa and a description of
     C. ustulatulina sp. nov. (Gastropoda:  Calyptraeidae) from the Gulf of
     Mexico.  Bulletin of Marine Science 70:  177-184.

Collin, R.  2001.  The effects of mode of development on phylogoegraphy and
     population structure of North Atlantic Crepidula (Gastropoda: 
     Calyptraeidae).  Molecular Ecology.  10:  2249-2262. [This includes, C.
     atrasolea, C. depressa and C. ustulatulina]

Collin, R.  2000.  Phylogeny of the Crepidula plana (Gastropoda: 
     Calyptraeidea) cryptic species complex in North America.  Canadian Journal
     of Zoology.  78:  1500-1514. [This includes C. depressa and C. atrasolea]

Report by:  R. Collin, Smithsonian Tropical Research Institute
and T. Griffin, Florida Institute of Technology
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Page last updated: Jan 2,  2005