Atrina zelandica
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| Atrina zelandica | |
|---|---|
 | |
| A partly broken shell of Atrina zelandica | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Bivalvia |
| Order: | Pteriida |
| Family: | Pinnidae |
| Genus: | Atrina |
| Species: | A. zelandica |
| Binomial name | |
| Atrina zelandica | |
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Atrina zelandica, one of several species known as the horse mussel, is a large species of saltwater clam. It is found around New Zealand.[2]
The shell of Atrina zelandica is triangular, elongate and blackish, while the inside is pearly purple.[3] The valves are convex with rather close longitudinal ribs and semi-cylindrical hollow spines.[3] The body of Atrina zelandica is 280 mm long.[4] Atrina zelandica is the largest of all bivalve species in New Zealand, with some individuals of Atrina zelandica growing up to 400 mm in length.[5] Most individuals of Atrina zelandica are between 30-260 mm long and 100-110 mm wide.[5]
The shell of Atrina zelandica has a crenellated posterior edge that extends a few centimeters above the substrate.[5] This helps keep the water intake clear of surface deposits but also provides a surface for various algae and invertebrates to attach to it, such as sponges and sea squirts.[6]
Geographic distribution
Atrina zelandica is native to New Zealand.[2] They inhabit depths of up to 50 m, primarily in muddy sand in the intertidal and subtidal zones in sheltered waters, and are widely distributed across the country.[5]
However, Atrina zelandica has experienced frequent die-offs in the Rangitoto Channel. Populations of 200-300 individuals per square meter have decreased to just 1-35 individuals per square meter over a period of 2-3 years.[5][7] Possible explanations include damage caused by storms, shell damage leading to increased predation and over harvesting.[5][7]
Life cycle
Atrina zelandica are classified as dioecious broadcast spawners.[5] Atrina zelandica spawns during the summer months but there is currently no available research on the age or sizes that Atrina zelandica begins breeding.[5] Atrina zelandica grows rapidly during the first few years of life, sometimes up to 40 mm a year, but once shells exceed 166 mm long their growth slows significantly.[7] Individuals mature between 5 years and 15 years old.[7]