Horseshoe crab trilobite larva

 

Horseshoe crabTrilobite larva of the horseshoe crab Limulus

Collected: June 2015, North Inlet, Georgetown, SC.

Notes: Horseshoe crabs mate and lay eggs on sandy beaches near the high tide line. the trilobite larvae emerge after several weeks on a subsequent high tide. These larvae are only in the plankton for a week or less before molting and assuming a benthic lifestyle. These primitive arthropods are not crustaceans. they are almost unchanged for 300 million years and have no close living relatives. They are more closely related to spiders and to the long extinct trilobites. Note the primitive median eye as well as the two lateral eyes. The long telson of the adults will appear in the next few molts.
 The specimen shown is less than 1.5 mm long

Photographed by: W. S. Johnson, Goucher College