Freshwater mollusks are pretty sedentary creature, right? They have a foot which they can extend from their body but it is used mainly for burrowing down in the watery bottom or lakes or rivers, not for mobility. So, have you ever wondered why the hard shell mussels are not all piled together? If they are not going anywhere and they simply reproduce in the water, how do their populations spread around? How do mollusks go mobile?
[caption id="attachment_6793" align="aligncenter" width="300"] Life cycle diagram Source: Freshwater Mussels of Iowa[/caption]
Well, it is about the coolest thing ever, really!
Male mussels release their sperm into the water. The females, forever siphoning water in and out, siphon in the sperm which then fertilizes her eggs. These fertilized eggs develop for a few weeks within her gills.[caption id="attachment_6792" align="aligncenter" width="300"] Magnified image of Glochidia. Source: Roger Gordon, U.S. Fish & Wildlife Service[/caption]
They will emerge from her gills as larvae called glochidia. The glochidia release themselves from their mamma and attach themselves to the gills of fish. They are basically parasites at this point, living off their host fish while they continue to develop.[caption id="attachment_6791" align="aligncenter" width="300"] Glochidia on fish gills. Source: Roger Gordon, U.S. Fish & Wildlife Service[/caption]
The fish then are responsible for taking them places. So this is how the mussels get around! On the gills of fish! A few weeks later, these glochidium develop into juvenile mussels and they drop from the host fish. At this point, the juvenile mussels are about .75 mm long, as bog as a pin head.[caption id="attachment_6795" align="aligncenter" width="300"] Juvenile mollusk the size of a pin head. Source: Roger Gordon, U.S. Fish & Wildlife Service[/caption]
Cross your fingers they land in a great spot! This is now their home where they hopefully continue developing and growing until they re mature enough to reproduce! And the cycle continues...
Thank you fish and wildlife for the info and images! Cool science stuff. Wondering what this has to do with pearls? Read my next post on cultured pearls and fish...