Olenelloides
Olenelloides armatus is an extinct, small sized olenelloid redlichiid trilobite arthropod. It lived during the later part of the Botomian stage, which lasted from approximately 524 to 518.5 million years ago. This faunal stage was part of the Cambrian Period. The most conspicuous feature is the hexagonal head shield that carries 6 ray-like spines..
Etymology
The genus is named after its originally supposed close relationship with Olenellus. The species epithet armatus, a Latin adjective meaning 'armoured', is a reference to the fierce looking spines of the head shield.Occurrence
Olenelloides armatus lived during the late Lower Cambrian deposits presumably contemporary with the middle Olenellus-zone, that probably represents the late Botomian, approximately between 519 and 516 million years ago.Distribution
Olenelloides armatus has been collected from the Fucoid Beds, Northern slopes of the Meall a'Ghiubhais, County Ross and Cromarty, Scotland, UK.Description
As with most early trilobites, Olenelloides has an almost flat exoskeleton, that is only thinly calcified, and has crescent-shaped eye ridges. As part of the Olenellina suborder, Olenelloides lacks dorsal sutures. Like all other members of the Olenelloidea superfamily, the eye-ridges spring from the back of the frontal lobe of the central area of the cephalon, that is called glabella.The exoskeleton of Olenelloides armatus is small and narrow.
Its head shield is hexagonal, with three pairs of spines extending from each of the corners of the cephalon, all almost as long as the diameter of the cephalon. The frontal pair have an angle of about 25° to the axis, the middle pair of about 100°, and the rear pair of about 150°. The intergenal spines do not emerge from the cephalic border, but rather from the sides of the 2nd lobe of the glabella from the back - the scientific convention is to count glabellar lobes back to front, giving them the following names: occipital ring or lobe, 1st lobe, 2nd lobe, 3rd lobe, and anterior lobe -. The front side of the cephalon is slightly bulging out forward to accommodate the frontal lobe of the raised central area called glabella. The eye lobes are short, wide and strongly curved, occupying most of the middle rd of the area outside the glabella. The occipital ring is wider than the other glabellar lobes, and carries a node on the rear edge at midline.
The thorax has a wide axis of about of the total width of the thorax, not including the spines, and consists of 9 segments. The frontal 3 are equal in size, but segments further back get smaller at an increasing rate. The thorax segments carry a node on the rear edge at midline, that diminishes towards the back. The 1st, 2nd, 4th and 5th thorax segments do not carry spines, the frontal edge of the outer lobes suddenly angles back at 150° ending in a blunt tip. The 3rd segment ends laterally in a straight spine that angles back at about 150° and extending backwards beyond the axis. The 6th-10th segments carry spines that curve backwards and increasingly inwards to the midline and extending increasingly less far backwards, the 6th ending parallel to the midline and extending as far back as the spine of the 3rd segment.