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Monday, June 18, 2018

Under a rock

Recently, Eric turned over a low intertidal cobble and noticed this interesting isopod.  It didn't seem like a familiar species, so we took a closer look.

[Isopods are crustaceans that are somewhat shrimp-like, but they are flattened dorso-ventrally, i.e., from top-to-bottom.  You might be familiar with terrestrial isopods found under woodland logs, also known as "pill bugs" or "roly-polies."]

This isopod had beautiful stripes and subtle speckling along its back:

Also noticeable were the white segments near the outer tips of the antennae:

And here's a close-up of the telson, the last abdominal segment:

When identifying marine isopods, the shape of the telson can be an important character.

For example, review illustrations of different species of local isopods (below).  Look at the shapes of the telsons the tip of the telson is especially useful, e.g., how pointed it is, the angle of the edges to either side of the point, and whether the corners are rounded or squared.  Then compare the telson shapes below to the photo above.  Which species is the best match? 

Isopods of the Bodega Bay region belonging to the Family Idoteidae: (A) Pentidotea wosnesenskii, (B) Pentidotea stenops, (C) Pentidotea resecata, (D) Pentidotea aculeata, (E) Idotea urotoma.  Figure modified from the Light & Smith Manual (2007).

Did you pick Isopod E?  Yes!   We've observed the other four species previously,  but this is the first time we've documented Idotea urotoma on Bodega Head.

P.S.  Nice spotting, Eric!

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