pygidium

[ pahy-jid-ee-uh m ]

/ paɪˈdʒɪd i əm /

any of various structures or regions at the caudal end of the body in certain invertebrates.

Origin of pygidium

1840–50; < New Latin < Greek pȳg(ḗ) rump + -idion diminutive suffix

py·gid·i·al, adjective

Posterior part of the thorax and pygidium, showing endopodites and exopodites projecting under the dorsal test.

The Appendages, Anatomy, and Relationships of Trilobites |Percy Edward Raymond
It and the pygidium are due solely to functional requirements.

The Appendages, Anatomy, and Relationships of Trilobites |Percy Edward Raymond
The number of segments in the pygidium was therefore not fixed and was on the average higher than in earlier periods.

The Appendages, Anatomy, and Relationships of Trilobites |Percy Edward Raymond
He stated that one of these belonged to the cephalon, nine to the thorax, and the remaining sixteen to the pygidium.

The Appendages, Anatomy, and Relationships of Trilobites |Percy Edward Raymond

Appendages of the thorax and pygidium, seen from the dorsal side.

The Appendages, Anatomy, and Relationships of Trilobites |Percy Edward Raymond

pygidium

/ (paɪˈdʒɪdɪəm, -ˈɡɪd-) /

the terminal segment, division, or other structure in certain annelids, arthropods, and other invertebrates

pygidial, adjective

C19: from New Latin, from Greek pugē rump