New York Natural Heritage Program
Lance Aplexa
Aplexa elongata (Say, 1821)
Gastropods

General Description [-]
Recent studies of anatomy, allozyme frequency and mtDNA have confirmed that Aplexa is the most distinctive of the North American pondsnails (Physidae). In fact, Aplexa is the sister group to all other Physid species, suggesting that it is a very old genus (100s millions of years) (Wethington and Lydeard 2007).

Identifying Characteristics [-]
The shell is elongate, thin, transparent, polished, and oily in appearance. It is light brown colored, up to 20 mm high with a long spire which is pointed and acute, 0.5 times the shell length.

Characters Most Useful for Identification [-]
The long, narrow sinistrial (coiled counter-clockwise when viewed from above) form, polished and blackish surface (when alive) and lack of mantle digitations serve to identify this species positively.

Best Life Stage for Proper Identification [-]
Adult

Behavior [-]
The animals overwinter as juveniles in the frozen soil, growing rapidly in the spring, then reproducing in the late summer or fall. This mollusk moves between suitable habitat patches solely through passive transport, primarily by birds. Physids are Hermaphroditic and generally lay large gelatinous egg masses during winter (Johnson et al., 2013). Juveniles mature rapidly and multiple generations can be produced in a single year (Colburn 2004). Species from northerly latitudes can usually live for two years or more.

Diet [-]
This snail is a strict detritivore (eats decaying vegetation), often hanging upside-down on the water's surface grazing on materials floating on the water and plowing along through silty substrates (Harman and Berg 1971).
Lance Aplexa Images
click to enlarge
The Best Time to See
The activity window is short; this species aestivates in the soil to survive dry periods in summer when vernal pools dry up, and also during winter. In short-cycle vernal pools snails emerge from the sediments upon flooding, grow rapidly to maturation, reproduce, then juvenile members of the next generation burrow into the sediments to aestivate when the pool dries out in summer. In longer cycle pools a second generation may be produced (Colburn 2004). The critical elements for survival during aestivation are water retention and sufficient fuel reserves, thus the ability to survive the dry period could be related to shell size.
J F M A M J J A S O N D
Present Active Reproducing
The time of year you would expect to find Lance Aplexa present (blue shading), active (green shading) and reproducing (orange shading) in New York.
Similar Species
  • Vernal Physa (Physa vernalis)
    Unlike Physa, Aplexa has no finger-like projections on the edge of the mantle.