Phacopida

Dalmanites limulurus from the subordination Phacopina

• Worldwide

Phacopida is an order of trilobite that had spread throughout the world and has existed from the Ordovician to the Devonian. The Phacopida trilobites have a highly variable body shape.

Features

The trilobites of this order have 8 to 19 thoracic segments. These segments can have significant budgetary furrows in some species. The Mittellobus is very wide in some species. The glabella on the Cephalon has up to four times joined in a single furrow couples, but do not share the glabella in praise. Compound eyes may be present. Sometimes they contain several thousand individual eyes ( so-called holochroal compound eyes, up to 15,000 closely lined-up eyes) and those which consist of only a few hundred individual eyes ( so-called schizochroal compound eyes, up to 700 large, individually ducted eyes). Front on the bottom may a so-called rostral plate. The pygidium is very small. But there are also species with larger pygidia. On the pygidium praise are sometimes present and it can be prickly or taper.

Submissions

This Trilobitenordnung has three suborders: Calymenina, Cheirurina and Phacopina.

Characteristics of Calymenina

The cephalon is semicircular to triangular and usually has small, holochroal compound eyes. Below is a rostral plate is available. The glabella is narrowed to the front. The thorax typically has thirteen segments with rounded Pleurenenden; sometimes there are also eleven to thirteen segments. The pygidium is semicircular to triangular without spines on the boundary.

See:

• Flexicalymene ouzregui

Characteristics of Cheirurina

The Cephalon has a rostral plate on the bottom. The cheeks are often covered with dimples. The glabella of these animals has up to four furrows and will forward normally wider or it is barrel-shaped. The trilobites have holochroal compound eyes. The thorax consists of 8 to 19 often thorn -like ending segments. The pygidium consists of two to 16 pairs of ribs and sometimes is tapered. Very often these animals are covered with tubercles.

Characteristics of Phacopina

These animals have schizochroal compound eyes. The glabella is widened forward. The free cheeks ( Librigena ) are fused into one piece yoke- and sometimes they have rear-facing spine- like extensions. Some have no rostral plate below. The thorax has ten but typically eleven grooved segments sometimes. The semi-circular, triangular or pointed, tapering pygidium is less than the Cephalon and has either a smooth or a prickly limit.