Pterygotids are differentiated from other eurypterids by their flattened telsons (the most posterior segment of the body) and their modified chelicerae (frontal appendages), ending in well-developed chelae (claws).

The Necrogammarus fossil was collected by Humphrey Salwey at Church Hill quarry in Leintwardine, a village in Herefordshire, England.

[1][7] Peach had however never examined the holotype in person (basing his diagnosis on images alone)[1] and some researchers, such as Henry Woods in 1909, noted that its classification was still uncertain.

As the outer segments do not appear to be double nor possess any overlap of segments in addition to the complete lack of evidence of any terrestrial habits, Almond considered the genus to tentatively represent an early aquatic relative of the Uniramia subphylum of arthropods (the group that includes myriapods, hexapods and velvet worms).

[10] Two other pterygotids (and numerous unidentifiable fragments referred to the group) are known from the same locality as Necrogammarus, Pterygotus arcuatus and Erettopterus marstoni.

[13] The chelicerae (the first pair of appendages), typically small and used to aid in feeding in other eurypterid groups, were robust and gigantic in pterygotids, with strong developed teeth on specialized claws.

[15] Other than eurypterids, the Ludlow-aged deposits at Leintwardine have also yielded remains of several genera of extinct microplankton,[16] as well as a diverse fauna of asterozoans (the group that includes starfish and brittle stars) compromising at least 16 distinct species.

[17] The environment appears to have mainly been sub-marine, with deposits indicating that the local fauna lived in channels connected to a larger body of water.