Agraulos

Agraulos Temporal range: 510–499 Ma PreЄ Є O S D C P T J K Pg N Middle Cambrian
Agraulos ceticephalus, Cambrian, Jince Formation, Czech Republic
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Trilobita
Order:	Ptychopariida
Superfamily:	Ptychoparioidea
Family:	Agraulidae
Genus:	Agraulos Hawle & Corda, 1847
Species
A. ceticephalus (Barrande, 1846) = Arion ceticephalus, Arionides ceticephalus, Arionellus ceticephalus
Synonyms
Arion Barrande, 1846 non Arion Férussac, 1819 Arionides Barrande, 1847 Arionellus Barrande, 1850 Proampyx Agrauloides

Agraulos is a genus of trilobite that lived during the Middle Cambrian in North America and Europe, particularly the Czech Republic. A. ceticephalus grew to approximately 1 inch or 2.5 centimetres.

Etymology

Agraulos is derived from the Greek Ἄγραυλος, "country woman" after a mythological figure that committed suicide after ignoring a warning from the goddess Athena and is a reference to the fact it is extinct. The species epithet ceticephalus is the contraction between κῆτος (Kētos), "whale", "large fish" or "sea monster", and Κέφαλος (Kephalos), "head", so "whale head" for the rounded rather effaced headshield that may be thought to look like a sperm whale.^[1]

Distribution

• A. ceticephalus occurs in the Middle Cambrian of the Czech Republic (Jinče Formation).^[2]

Description

The exoskeleton of Agraulos is approximately inverted egg-shaped, about 1½× longer than wide, with the maximal width across the tips of the genal spines. The headshield (or cephalon) is ⅜ of the total body length and is approximately semicircular although almost flat on the front and with two short spines pointing backward and about 35° outward. The central raised area of the cephalon (or glabella) tapers forward, is truncated at its front, weakly defined, and about ⅔× the length of the cephalon. Most specimens are found without the free cheeks. As in all trilobites, the natural fracture lines that aided in molting (or sutures) follow the inside of the visual surface of the eye, and from the back of the eye cut to the back of the cephalon (a state called opisthoparian) with a gentle curve outwards and increasingly more backward. From the front of the eye the suture curves initially forward and eventually fully inward, coinciding with the frontal margin. This makes the remaining so-called cranidium weakly clock-shaped. The eyes are about ¼× as long as the glabella with its front aligned with the front of the glabella. Eyes, border furrow and furrows crossing the glabella are almost fully effaced. The articulate middle part of the body (or thorax) has 16 segments and the axis is about the same width as the ribs (or pleurae) to its right and left, and these have rounded tips. The tailshield (or pygidium) is very small, rectangular, about 15% of the width of the frontal segment of the thorax, 3½× wider than long, and the axis reaching slightly beyond the pleural fields.^[3]

References