The phylum echinoderms is divided into five extant classes: Asteroidea (sea stars), Ophiuroidea (brittle stars), Echinoidea (sea urchins and sand dollars), Crinoidea (sea lilies or feather stars), and Holothuroidea (sea cucumbers). The most well-known echinoderms are members of class Asteroidea, or sea stars.

First, they all possess five-part radial symmetry around a central disk. Second, they all possess a very unique water vascular system (vascular system based on water). These unique characteristics distinguish echinoderms from other animals in the animal kingdom.

In traditional taxonomy, there are five classes of living echinoderms: Crinoidea (sea lilies), Asteroidea (starfish), Ophiuroidea (brittle stars or snake stars), Echinoidea (sea urchins and sand dollars), and Holothuroidea (sea cucumbers).

Many crinoid traits are like other members of their phylum. Such traits include tube feet, radial symmetry, a water vascular system, and appendages in multiples of five (pentameral). Most of the Paleozoic crinoid species attached themselves to substrates on the ocean floor.

about 450 million years ago

Ammonites were marine animals belonging to the phylum Mollusca and the class Cephalopoda. They had a coiled external shell similar to that of the modern nautilus. In other living cephalopods, e.g. octopus, squid and cuttlefish, the shells are small and internal, or absent.

Parapuzosia seppenradensis

When did they live? Trilobites first appeared during the Cambrian Period (about 520 million years ago) and disappeared at a major extinction event at end of the Permian Period (about 250 million years ago).

Permian mass extinction event

First, we have to define bite. If that definition includes any mention of a jaw structure, then the answer is no, you have nothing to worry about. Jaws, like humans have, did not evolve until 440 million years ago in the Placoderms. Trilobite did not have jaws the way humans or fish or dogs do.

All Trilobites have three lobes, a left pleural lobe, Axial lobe, and a right pleural lobe. Trilobites are Arthropods. They look like little hard shelled insects, and are often nicknamed “bugs” by fossil collectors, but they are not related to insects. Trilobites are an extinct clade of Arthropods (like crustaceans).

When danger struck, some trilobites could ball themselves up like underwater pill bugs, with their rear end flexed under their head. Specimens dating as far back as the late Cambrian have been found in this defensive position.

Trilobites have been extinct since before the age of Dinosaurs (about 251 million years ago), but some living creatures bear such close superficial resemblance to trilobites that they cause great excitement when encountered. Alas, no living trilobite has ever truly been documented.