Finding More Than You Are Looking For

This has been a fun spring because I had the opportunity to get out with a student intern and coworker.  They were continuing a project that our Office started a few years ago, which was to investigate reproductive timing of the western pearlshell mussel.  The project was conducted in a local stream, and involved inspecting adult mussels for signs of spawning and drift samples for larval mussels (i.e., glochidia, see previous blog for more on the life cycle of mussels).  Because glochidia are really small, around 1/20^th of a millimeter, we use a very fine-mesh net to collect drifting material that is then preserved in alcohol.  The real work starts in the lab where we look for glochidia by picking through all the preserved material under a dissecting microscope.  Although this is often like “looking for a needle in a haystack” when a needle may not be there, the net collects other organisms, which makes the work interesting.

Below is what the material typically looks like magnified 20X.  Where’s “Glochido,” and can you identify some of the other organisms?

This is an early instar (i.e., stage) of a mayfly (Family—Baetidae).  These insects will grow a lot and emerge as winged adults that live for just a couple days or so.

This is the larvae of a small fly called a midge (Family—Chironomidae).  Midges are an extremely diverse group.  Because they are usually very abundant, larval and adult midges are a major source of food for aquatic and terrestrial predators.

The oval object with a black dot is actually a seed shrimp (Class—Ostracoda).  Seed shrimp are crustaceans (large group that includes crabs, crayfish, shrimp, and barnacles) whose two-part shell makes them resemble miniature mussels.

Here are two types of fly larvae, a midge (upper left) and black fly (lower center; Family—Simuliidae).  Black fly larvae have mouth parts with fan-like structures that are used to strain microscopic food particles from flowing water.

There’s “Glochido” (lightest object slightly up and left of center, no stripes or glasses).  This glochidia is about 0.06 mm long and appears small even when magnified 40X (same magnification used for all photos except the first one).  A key characteristic is the faint line appearing horizontally on it at this angle.

Submitted by Sam Lohr