419 Million B.C.T. - Spiders, Centipedes and Worms

Around 419 Million B.C.T., the ancestors of spiders, centipedes and worms began to inhabit the Earth.

Evidence suggests the presence of predatory trigonotarbid arachnoids (spiders) and myriapods (centipedes) in Late Silurian faeces. Predatory invertebrates would indicate that simple food chains -- food "webs" -- were in place that included non-predatory prey animals. Extrapolating back from Early Devonian biota, a food web based on as yet undiscovered detritivores (worms) and grazers on micro-organisms must have existed.

The Order Trigonotarbida is an extinct group of arachnids (spiders) whose fossil record extends from the late Silurian to the early Permian (c. 419 to 290 million years ago). These animals are known from several localities in Europe and North America, as well as a single record from Argentina. Trigonotarbids can be envisaged as spider-like arachnids, but without silk-producing spinnerets. They ranged in size from a few millimeters to a few centimeters in body length and had a segmented abdomen, with the tergites across the back of the animal's abdomen characteristically divided into three or five separate plates. Probably living as predators on other arthropods, some later trigonotarbid species were quite heavily armored and protected themselves with spines and tubercles. About seventy species are currently known, with most fossils originating from the Carboniferous Coal Measures.

Myriapoda is a subphylum of arthropods containing millipedes, centipedes, and others. The group contains 13,000 species, all of which are terrestrial. Although their name suggests they have myriad (10,000) legs, myriapods range from having over 750 legs (Illacme plenipes) to having fewer than ten legs.

The fossil record of myriapods reaches back into the late Silurian, although molecular evidence suggests a diversification in the Cambrian Period, and Cambrian fossils exist which resemble myriapods. The phylogenetic classification of myriapods is still debated.
The scientific study of myriapods is myriapodology, and those who study myriapods are myriapodologists.

Detritivores, also known as detritophages or detritus feeders or detritus eaters or saprophages, are heterotrophs that obtain nutrients by consuming detritus (decomposing plant and animal parts as well as organic fecal matter). By doing so, they contribute to decomposition and the nutrient cycles. They should be distinguished from other decomposers, such as many species of bacteria, fungi and protists, which are unable to ingest discrete lumps of matter, but instead live by absorbing and metabolizing on a molecular scale. However, the terms detritivore and decomposer are often used interchangeably.

Detritivores are an important aspect of many ecosystems. They can live on any soil with an organic component, including marine ecosystems, where they are termed interchangeably with bottom feeders.

Typical detritivorous animals include millipedes, woodlice, dung flies, slugs, many terrestrial worms, sea stars, sea cucumbers, fiddler crabs, and some sedentary polychaetes such as amphitrites (Amphitritinae, worms of the family terebellidae) and other terebellids.