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Guide to New Zealand's freshwater invertebrates
Estuarine mud crabs
(
Varunidae
: Helice
)
Diagnostic features
Helice is the most common crab in our upper estuaries. They are much more strongly armoured than the freshwater crab Amarinus, and the cephalothorax is roughly rectangular (round in Amarinus). Helice is much more likely to be found in areas of regular tidal salinity than Amarinus.
Typical habitats
Helice is found in abundance in muddy estuaries, and the tunnels of these crabs can be used as an indication of the extent of seawater influence into streams and rivers.
Feeding
They are opportunist detritivores, scavengers and predators with the ability to feed on many forms of organic matter settling on mudflats.
Indicator value
Helice are indicators of tidal influence. They are found in pristine estuaries, but also estuaries with sediments contaminated by urban runoff. They have been assigned a soft bottom tolerance value of 6.6 (no hard bottom value has been assigned).
