invertebratesmost

Invertebrates are animals without a vertebral column. They form the vast majority of animal life on Earth, with insects representing the largest single group of described species. Collectively, invertebrates inhabit virtually every ecosystem, from deep oceans to deserts and high mountains.

Major groups include: Arthropoda (insects, arachnids, crustaceans, myriapods); Mollusca (snails, clams, squids); Annelida (earthworms, leeches); Cnidaria (jellyfish, corals); Echinodermata (starfish, sea urchins); plus numerous phyla such as Nematoda and Platyhelminthes.

Ecological roles of invertebrates are diverse and essential. They pollinate many crops and wild plants; they decompose organic matter and contribute to nutrient cycling; they aerate and structure soils; they serve as both predators and prey in food webs; and some, like corals and termites, act as ecosystem engineers that create or modify habitats.

Anatomy and life cycles vary widely. Many invertebrates have an exoskeleton made of chitin (notably arthropods); bodies can be segmented or unsegmented; sensory and nervous systems range from simple to complex. Reproduction includes sexual and asexual modes; metamorphosis is common in insects and some crustaceans, while others develop directly.

Conservation and study of invertebrates face challenges such as habitat loss, pollution, climate change, and invasive species. Despite being small or inconspicuous, they underpin ecosystem services, biodiversity, and the functioning of natural systems, making their continued study and protection important.