Sphaeriidae

Definition

Sphaeriidae (also known as pea clams or fingernail clams) is a family of small, freshwater bivalves in the order Sphaeriida and consist of 10 genera with 154 species. They are both hermaphrodites and ovoviviparous, giving birth to young that resemble miniature versions of adults [1].

Taxonomy

Kingdom: Animalia

Phylum: Mollusca

Class: Bivalvia

Subclass: Heterodonta

Order: Sphaeriida

Family: Sphaeriidae

Multiple specimens of Sphaerium corneum, the European fingernail clam, found on Goliad Farms in Texas.

Habitat and Range

In North America, native species of sphaeriid have a broad distribution often ranging from the Atlantic to Pacific coast. Introduced species, such as Corbicula fluminea which originates from southeast Asia, also exhibit widespread distribution [2]. Many of these species occur in ephemeral ponds, small, variable flow streams, and profundal regions of lakes [3]. The preference of sphaeriids for these regions of low water flow, high silt, and large organic loads may reflect their lifestyle of sediment detritus feeding [4]. Species diversity in the genus Pisidium has also been shown to increase with decreasing particle size, indicating substrate preferences among sphaeriids possibly linked to their sediment feeding mechanisms [5]. Many sphaeriids are tolerant to air exposure which they achieve through unique emersion adaptations [6].

Life History

Sphaeriids display large variations in life history strategies on both an intra- and interspecific level [7]. They exhibit traits commonly associated with unstable habitats (short life spans, early maturity, small adult size, and increased energetic allocation to reproduction) as well as traits associated with stable habitats (slow growth rates, low fecundity, and release of large, fully developed young) [8]. All species exhibit viviparous reproduction with embryos developing in specialized chambers from outgrowths of the inner demibranch gill filaments. The internal gestation of young lead to sphaeriids having the largest young out of any freshwater bivalves with newborns measuring 0.6 to 4.15 mm and having a biomass of 0.6 to 4.6% that of adults [9] [3]. Seasonal water availability fluctuations and hypoxia associated with their habitats have also influenced the development of developed juveniles as they are more susceptible to environmental stress. This means that sphaeriids dedicate more energy into fewer offspring than those produced by other freshwater bivalves [3]. This initial head start in development in juveniles also leads to faster maturation to a reproduction before the start of seasonal stress. The term “bet hedging” has been used to describe the mixture of r- and K-selective traits allowing for increased fitness in environments with periodic, predicable stress [10].

A Pea Clam, Pisidium adamsi, attached to the hindfoot of a Blue-spotted salamander, Ambystoma laterale (Photo by R.E. Merrick).

Research

Since sphaeriids are hermaphrodites they have an invasive dispersal pattern as only one individual is theoretically needed to establish a population. Mechanisms for aiding in dispersal include juveniles clamping down on parts of other organism such as aquatic insects, water fowl, and salamanders [3] [11]. They effectively use the other organism as transport to a new environment where they can detach. Some can even survive digestion by ducks allowing for dispersal over a longer distance [3].

References

1. Allaby, Michael. A Dictionary of Zoology, Oxford University Press, Incorporated, 2020. ProQuest Ebook Central, https://ebookcentral-proquest-com.gate.lib.buffalo.edu/lib/buffalo/detail.action?docID=6230105.
2. McMahon, Robert. (2000). Invasive characteristics of the freshwater bivalve Corbicula fulminea. Nonindigenous Freshwater Organisms: Vectors, Bilogy, and Impacts (2000), pp 315-343. https://search.lib.buffalo.edu/permalink/01SUNY_BUF/r66d6a/alma990020146270204803.
3. Burky, A. J. 1983. Physiological ecology of freshwater bivalves. in: Russell-Hunter, W. D., Ed. The Mollusca. Vol. 6 : Ecology. Academic Press, New York, pp. 281 – 327. https://search.lib.buffalo.edu/permalink/01SUNY_BUF/r66d6a/alma990002424480204803.
4. Lopez, G. R., Holopainen, I. J. 1987. Interstitial suspension-feeding by Pisidium sp. (Pisididae: Bivalvia): a new guild in the lentic benthos? American Malacological Bulletin 5:21 – 30. https://www.biodiversitylibrary.org/page/45940177.
5. Kilgour, B. W., Mackie, G. L. 1988. Factors affecting the distribution of sphaeriid bivalves in Britannia Bay of the Ottawa River. Nautilus 102:73 – 77. https://www.biodiversitylibrary.org/page/8276899.
6. Byrne, R. A., McMahon, R. F. 1994. Behavioral and physiological responses to emersion in freshwater bivalves. American Zoologist 34:194 – 204. https://www-jstor-org.gate.lib.buffalo.edu/stable/3883685.
7. Holopainen, I. J., Hanski, I. 1986. Life history variation in Pisidium . Holarctic Ecology 9:85 – 98. https://www-jstor-org.gate.lib.buffalo.edu/stable/3682082.
8. Sibly, R. M., Calow, P. 1986. Physiological ecology of animals: an evolutionary approach. Blackwell, London. https://www.jstor.org/stable/2829513.
9. Mackie, G. L. 1984. Bivalves. in: Tompa, A. S., Verdonk, N. H., van der Biggelaar, J. A. M. Eds. The Mollusca. Vol. 7: Reproduction. Academic Press, New York, pp. 351 – 418. https://search.lib.buffalo.edu/permalink/01SUNY_BUF/r66d6a/alma990002424480204803.
10. Stearns, S. C. 1980. A new view of life-history evolution. Oikos 35:266 – 281. https://doi-org.gate.lib.buffalo.edu/10.2307/3544434.
11. Davis, D. S., Gilhen, J. 1982. An observation of the transportation of pea clams, Pisidium adamsi, by bluespotted salamanders, Ambystoma laterale. The Canadian Naturalist 96:213 – 215. https://www.biodiversitylibrary.org/page/28008061.