The Planted Tank Forum - View Single Post - Macro photos of freshwater amphipods
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post #6 of (permalink) Old 01-16-2013, 07:14 PM Thread Starter
Planted Member
Join Date: Aug 2010
Location: Vancouver, Canada
Posts: 177
Hi all, and thank you for the kind words.

The mystery of the amphipod with the red spot has been turns out that the red spot was actually an acanthocephalan (thorny-headed or spiny-headed worm) parasite called Polymorphus. Acanthocephalans are parasitic and donít have a digestive tract; they are basically a sack containing reproductive organs and musculature with a spiny proboscis that can stick out of one end. The proboscis is used to stab into and attach to the gut of its host (the animal in which it is living and feeding from). They ingest nutrients directly through their body surface.

The cool thing is how Polymorphus alters the behaviour of the host amphipod. Gammarus lacustris are preyed upon by ducks (amongst other predators). Needless to say they generally try to avoid being eaten and tend to avoid light and stay away from the surface (where ducks are). However, Polymorphus eventually causes its host to becomes attracted by light and swim towards the surface to increase the likelihood of being eaten by a duck. The bird then becomes infected by the parasite...

Below Iíve uploaded a tightly cropped version of the red-spot photo. Now Iím wondering what the little clump is that is growing on the back of the amphipod (in the upper right corner of the photo)?

www.macrocritters.wordpress .com

amphipod red spot very tight crop_filtered by ernie.cooper, on Flickr
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