Summary of Ecdysozoa and Arthropods

Ecdysozoa Overview Ecdysozoa includes diverse species such as Nematoda (roundworms) and arthropods. Key characteristics are the presence of a tough cuticle or exoskeleton, which protects against water loss and predators. Members of this group undergo molting, shedding their old exoskeleton to allow for growth.

Arthropods Arthropods represent one of the most successful animal clades, with over a million documented species. They feature a chitinous exoskeleton, jointed appendages, and have adapted to various habitats including terrestrial, aquatic, and aerial environments. The five subphyla include Trilobita (extinct), Chelicerata (spiders and horseshoe crabs), Myriapoda (millipedes and centipedes), Crustacea (crabs and lobsters), and Hexapoda (insects).

Morphology of Arthropods Arthropods possess jointed appendages often paired for specialized functions such as sensing (antennae) and feeding (mandibles). Their bodies consist of segmented regions called tagmata. The chitinous exoskeleton comprises two layers: an outer epicuticle and a stronger procuticle. The hemocoel is the body cavity for circulatory fluid movement, and their nervous systems feature segmentally distributed ganglia.

Respiratory Systems Insects and myriapods have tracheae for gas exchange directly with body cells, opening at spiracles on the cuticle surface. Aquatic crustaceans utilize gills, while chelicerates have book lungs or gills depending on their habitat.

Subphyla Details Chelicerata: Includes horseshoe crabs and spiders; characterized by two tagmata and chelicerae as specialized appendages. Myriapoda: Terrestrial arthropods with numerous legs; includes centipedes (predators) and millipedes (herbivores). Crustacea: Dominant aquatic arthropods with two pairs of antennae and biramous appendages. Hexapoda: The largest arthropod class, insects possess three tagmata and either undergo complete or incomplete metamorphosis. They often play essential roles in pollination and are capable of eusocial behavior.