February 2014

Free ride for a flat worm

The photo attached was taken in Lamington NP of a Blue crayfish. When I examined the picture and the crayfish closely I could see little slug like creatures on its back!

My question is, are the parasites? Babies? Or something else?

Answer

Lamington Spiny Crayfish with friends Symbiotic temnocephalans

The crayfish in your photo is a Lamington Spiny Crayfish (Euastacus sulcatus). The small tentacled animals are a kind of flatworm called temnocephalans. These aren't parasites or young, but are symbionts that live on the crayfish, apparently without affecting them. Temnocephalans feed on any microscopic aquatic animals they can capture, sometimes including other temnocephalans.

An individual crayfish can host many temnocephalans (as seen in your photo), and can even have different species living on different parts of its body.

We sent your photo to Dr Kim Sewell, a former QM staff member and expert on temnocephalans. He identified those in your photo as species of Temnosewellia; the exact species can not be determined without examining them in a laboratory. Dr Sewell added that Lamington Spiny Crayfish can also host species of Temnohaswellia (note the different spelling, members of this genus are distinguished by their white colour and larger number of tentacles) and species of Didymorchis may inhabit the gills.

Australia has more species of temnocephalans than any other part of the world (approximately 90 species are found in eastern Australia). Temnocephalans are also found in South America, South-east Asia and Madagascar.

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