The morphology of the eurypterida is now well understood, due to work carried out by Holm (1898) and later by Wills (1965).  Holm studied a particular species of Silurian eurypterid known as Baltoeuripterus tetragonophthalmus,  looking at fragments of the exoskeleton discovered in the rock.  The morphology is similar to other species in the arthropod family such as trilobites, all of which grow by ecdysis (molting).

The name 'eurypterid' refers to the large 'paddle' structure found on the prosomal appendage of many  eurypterid species.  Which was probably used for swimming, to propel the animal away from potential dangers, or towards potential prey!

The body is divided the prosoma, preabdomen and postabdomen.  The anterior or 'head' end is known as the prosoma and contains the large compound eyes.  Also attached to this region is the mouth and prosomal appendages or 'legs'.  Next follows 12 movable segments, 7 segments in the broad flattened pre-abdomen , and 5 on the more narrower post-abdomen, which terminates in a telson.

The first pair of legs are modified to form anterior chelicerae, the next legs make up the appendages used for walking, balancing, and swimming.  Behind the metasoma is the operculum, which bears the genital appendage.  It is an elongated rod of which 2 kinds may be present in a eurypterid population, which indicates sexual dimorphism.

Eurypterid respiration consisted of a specialised kiemenplatten, this comprised of small cones that hung downwards positioned on the ceiling of the branchial chamber.