In Depth

Title: Arthropods: Introducing Other Animal Life Forms

Arthropods are a diverse group of invertebrate animals belonging to the phylum Arthropods are characterised by the following features:. Although insects are arthropods for the purposes of this website insect orders have been given a separate section as they are a large group deserving attention in their own right. In this section the focus is on other ‘insect-like’ animals; arachnids, molluscs and assorted other invertebrate creatures. 

Arthropods are characterised by the following features:

1. Segmented Body: Their bodies are divided into distinct segments, often grouped into regions like the head, thorax, and abdomen.
2. Exoskeleton: They have a tough, rigid outer shell made of chitin (sometimes reinforced with calcium carbonate), which provides protection and support. This exoskeleton is periodically shed in a process called moulting to allow for growth.
3. Jointed Appendages: Their legs and other body parts, such as antennae or mouthparts, are jointed, giving them mobility and flexibility.
4. Bilateral Symmetry: They have symmetrical body plans, meaning their left and right sides are mirror images.
5. Open Circulatory System: Their blood-like fluid, called hemolymph, flows freely through their body cavity.
6. Highly Diverse: Arthropods are the largest phylum in the animal kingdom, with millions of described species. They include insects, spiders, crustaceans, and centipedes.

Arachnids:

Arachnids belong to the class Arachnida, which includes spiders, scorpions, ticks, mites, and several other lesser-known groups. Despite their differences, arachnids share several defining characteristics. Most notably, they possess eight legs—a feature that distinguishes them from insects, which typically have six legs. Additionally, arachnids have two body segments: the cephalothorax (fused head and thorax) and the abdomen.

Spiders, arguably the most well-known arachnids, exhibit remarkable diversity in size, shape, and behaviour. From the minuscule Patu digua, measuring just 0.37 millimetres in length, to the colossal Goliath birdeater tarantula, with a leg span of up to 30 centimetres, spiders occupy a wide range of ecological niches. Their ability to produce silk, used for webs, shelter, and prey capture, is one of their most remarkable adaptations.

Molluscs:

Molluscs belong to the phylum Mollusca and are not actually arthropods! However, they need a home within the Sidmouth Nature project and so they are included here in a section which, in truth, is a ‘catch-all, for minor types of animal encounters on survey expeditions. I am sorry if that offends any ‘professionals’ in the conservation field.

Molluscs comprise an astonishing array of species, including familiar forms such as snails, clams, and octopuses, as well as lesser-known groups like chitons and nudibranchs. With over 100,000 recognised species, molluscs exhibit remarkable diversity in size, shape, habitat, and lifestyle, making them one of the most successful and widespread groups of animals on the planet.

Whilst there are several marine members of Mollusca in the sea off of the coast at Sidmouth the Sidmouth Nature project focuses primarily on land sites rather than species in particular and species of slugs and snails are the most likely to feature. These creatures are often nocturnal, spending the day under stones and in crevices. Finding these creatures in the wild is quite unusual other than some species that like to feed on shrubby plants, notably brambles, and so become more apparent to the passer by.

Arthropods:

This section is devoted to members of the Arthropoda phylum other than insects and arachnids. This means creatures such as wood lice, centipedes and millipedes will be included here however, given the secretive, dark world these animals inhabit they will nor feature in the survey results very often. It is important they are not overlooked so information about them is provided here in the knowledge section.