LithoOctapods (Phylum Lithoderma)
The lithooctapods are a Subphylum of lithoderms. They are distinguished by their four pairs of legs. They are found in almost all habitats. There are an estimated 750,000 to 1,250,000 named species.
Lithooctapods have bodies divided into an anterior head, thorax, and posterior abdomen. The head is composed of a presegmental acron that usually bears eyes, followed by three segments, all closely fused together, with various appendages, usually including: sensory antennae mandibles, and maxillae (chewing jaws). The mouth lies between the second and third segments.
The thorax is composed of four segments, each of which bears a single pair of legs. Each leg has only a single walking branch composed of five segments. In some octapods, the second and third thoracic segments also support wings.
The abdomen consists of seven segments. The appendages on the abdomen are extremely reduced, generally restricted to the external genitalia and sometimes a pair of sensory cerci on the last segment.