Zebra mussel
The zebra mussel (Dreissena polymorpha) is a small bivalve mollusk native to the Ponto-Caspian region of eastern Europe and western Asia, including the drainages of the Black, Caspian, and Aral Seas.[1] [2] First detected in North America in 1988 within the Great Lakes basin, likely transported via ballast water from transoceanic vessels, it has proliferated across numerous freshwater systems, establishing dense populations that filter vast quantities of plankton and attach to submerged surfaces using byssal threads.[3] [4] Named for the distinctive alternating dark and light bands on its triangular shell, which typically reaches 2–3 cm in length, the species exhibits high reproductive output, with females capable of producing over one million eggs annually during planktonic veliger larval stages that facilitate rapid dispersal.[1] [2] As a prolific filter feeder, the zebra mussel clears water of phytoplankton and suspended particles at rates exceeding those of native species, often resulting in increased water clarity but disrupting aquatic food webs by depriving zooplankton and native bivalves of primary production, thereby favoring certain predatory fish while harming others.[5] [6] Its colonization of hard substrates, including water intake pipes, power plant cooling systems, and boat hulls, has inflicted billions in economic damages through biofouling and maintenance costs across invaded regions.[6] [7] Despite control efforts involving chemical treatments and physical removal, the species' resilience and passive spread via human-mediated vectors continue to challenge eradication, underscoring its status as one of the most impactful aquatic invasives in North America.[4] [8]Taxonomy and description
Morphological characteristics
The zebra mussel (Dreissena polymorpha) is a small dreissenid bivalve with a distinctive shell morphology adapted for attachment to hard substrates. The shell is triangular to wedge-shaped, measuring up to 50 mm in length and 20 mm in width, though adults typically range from 20 to 40 mm.[9][10] It features a sharply pointed umbo positioned anteriorly, a keeled ventral margin for enhanced stability, and a strong inward curvature along the ventroposterior edge.[11] The valves are asymmetrical, with the right valve smaller and more concave than the left, and their edges align symmetrically in lateral view to form a straight line.[11] The exterior surface is smooth, bearing concentric growth rings and subtle wrinkles, while the interior displays a nacreous layer.[9][10] The periostracum exhibits variable coloration, most commonly yellowish-brown with dark zigzag stripes that inspired the species' vernacular name, but ranging from solid light yellow to dark brown or even unpatterned white shells depending on age, habitat, and genetics.[9][10] Attachment occurs via a bundle of proteinaceous byssal threads secreted from a byssal gland located in the foot, which emerge through a ventral groove between the valves and anchor the mussel firmly to rocks, shells, or artificial structures.[9] Juveniles utilize the muscular foot for limited crawling prior to byssus-mediated settlement.[9] Internally, the zebra mussel possesses distinct inhalant and exhalant siphons protruding from the posterior end, facilitating filter-feeding on phytoplankton and detritus; these siphons are often visible in live, open specimens.[9] The gills serve dual roles in respiration and particle capture, supporting high filtration rates characteristic of the species.[9]
Taxonomic classification
The zebra mussel (Dreissena polymorpha) is a bivalve mollusk classified in the kingdom Animalia, phylum Mollusca, class Bivalvia, subclass Autobranchia, infraclass Heteroconchia, subterclass Euheterodonta, cohort Imparidentia, order Myida, superfamily Dreissenoidea, family Dreissenidae, genus Dreissena, and species D. polymorpha.[12] This placement reflects molecular and morphological analyses aligning Dreissenidae with myid clams, distinct from earlier assignments to Veneroida in some databases like ITIS, which used Order Veneroida based on pre-2010 classifications.[13] [12] The species was originally described by Peter Simon Pallas in 1771 as Mytilus polymorphus, with the basionym reflecting its initial grouping among marine mytilids before recognition as a distinct freshwater dreissenid.[14] The genus Dreissena encompasses three extant species, including D. polymorpha and the congeneric quagga mussel (D. rostriformis bugensis), all endemic to Ponto-Caspian drainages and characterized by byssal attachment and filter-feeding adaptations.[12] Taxonomic revisions, informed by phylogenetic studies, confirm D. polymorpha's monophyly within Dreissenidae, supported by 18S rRNA and mitochondrial DNA sequence data.[2]| Taxonomic Rank | Classification |
|---|---|
| Domain | Eukaryota |
| Kingdom | Animalia |
| Phylum | Mollusca |
| Class | Bivalvia |
| Order | Myida |
| Superfamily | Dreissenoidea |
| Family | Dreissenidae |
| Genus | Dreissena |
| Species | D. polymorpha |