Overview
Kākahi are New Zealand’s freshwater mussels, but the number of species present and the scientific names to be used for them has been uncertain. They have been known by many different specific names, and referred to multiple genera in several families and subfamilies.
A research programme led by Te Papa’s Bruce Marshall, together with Mark Fenwick (Te Papa, later NIWA) and Peter Ritchie (Victoria University), confirmed that there are three species of kākahi, one of which was new to science and all of which belong to the genus Echyridella.
Echyridella menziesii (Gray, 1843) is the most common and widely distributed kākahi. Because of its variability and over-naming, it had been known by a chaos of no less than 72 scientific names (8 specific/subspecific names combined in 5 genera/subgenera).
Echyridella aucklandica (Gray, 1843) is also widely distributed and occurs with E. menziesii, though it is less common. Less variable than E. menziesii, it has nevertheless been known by at least 33 scientific names (4 specific/subspecific names combined in 2 genera/subgenera). Until the 2014 revision this species was almost completely misclassified and remains relatively little known to field ecologists. Although occurring widely in the North Island with an outlier in the southern South Island, E. aucklandica is evidently more endangered by agricultural and urban runoff than E. menziesii (and E. onekaka), especially in Northland.
Echyridella onekaka Marshall & Fenwick, 2006 is superficially similar to E. menziesii and had long been confused with it in collections. It was recognised during genetic sequencing of kākahi from throughout the country, and proved to be restricted to the north-western South Island, west of a line between Tākaka and Cape Foulwind.
Kākahi are an important indicator of freshwater quality. They feed on food particles filtered from the water, naturally occur in dense aggregations, and contribute to the health of their environment. Regrettably they are susceptible to pollution, notably agricultural and urban runoff, and many populations have vanished or are in decline.
Kākahi belong to the family Hyriidae, a group that provides strong evidence of former land connection between New Zealand, South America and Australia.
Kākahi specimens in Te Papa’s Collections Online.
More on kākahi from Te Papa’s Collections Online.
References:
Marshall BA, Fenwick MC (2006) Unio zelebori Dunker in Dunker & Zelebor, 1866, a form of Cafferia caffra (Krauss, 1848) (Mollusca: Bivalvia: Unionidae). Molluscan Research 26: 19-22. Online abstract.
Fenwick MC, Marshall BA (2006) A new species of Echyridella from New Zealand, and recognition of Echyridella lucasi (Suter, 1905) (Mollusca: Bivalvia: Hyriidae). Molluscan Research 26: 69-76. Online abstract.
Marshall BA, Fenwick MC, Ritchie PA (2014) New Zealand Recent Hyriidae (Mollusca: Bivalvia: Unionida). Molluscan Research 34: 181-200. Online abstract.