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Insects and Crustaceans: Phylum Arthropoda

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Insects and Crustaceans: Phylum Arthropoda <br>Source:  PBS.org

The majority of Arthropods recovered at the lower Miocene bed are from various species of crustaceans (lobsters, shrimp, barnacles). Fossils from crustaceans often consist of small body parts such as claws. However, crustaceans such as ghost shrimp (callichirus) tend to construct burrows that resemble lumpy tubes called Ophiomorpha. These corn-stalked resembling tunnels, are created from mud and depository waste to form burrows in which the creatures reside. In comparison to claws and pincher fossils, "trace fossils", such as Ophiomorpha tubes, are often commonly found in greater number than that of various body parts.

Arthropods include an exceedingly diverse group of taxa such as insects, crustaceans, spiders, scorpions, and centipedes. There are more species of arthropods than species in all other phyla combined. The name Arthropod means "jointed foot." All arthropods have segmented bodies and are enclosed in a jointed, protective armor called an exoskeleton. Most arthropods have a pair of compound eyes and one to several simple ("median") eyes or ocelli.

In addition to shrimp and other shellfish, barnacles are commonly found in the lower Miocene bed. Barnacles are separated into two groups sessil and stalked. Both have soft bodies that are protected by an outer wall, which resembles either an acorn (sessil) or stalk. Living in a tight grouping with other barnacles these creatures attach themselves to any suitable surface (rocks, boats, even whales and turtles!) in effort to aid in reproduction.

The trace fossils for Arhtropods found at the Pollock Site include Ophiomorpha nodosa (burrow tubes dug by shrimp) and Skolithos linearis (burrow tubes left by ground-dwelling insects).

Click the image or the link below to view the Arthropod collection.

Reference(s): 

Photographs from DGS Special Publication No. 21, 1998, R.N. Benson, ed.
Top left image: http:/www.pbs.org/kcet/shapeoflife/animals/arthropods4.html

Photo Gallery
Ophiomorpha nodosa specimens preserved in full relief.
Skolithos linearis in channel-margin sands.
A group of burrows likely formed by polychaetes that occur in association with Ophiomorpha.