Summarizing Superphylum Ecdysozoa

Summary

Nematodes are pseudocoelomate animals akin to flatworms, yet display more advanced neuronal development, a complete digestive system, and a body cavity. This phylum includes free-living as well as parasitic organisms like Caenorhabditis elegans and Ascaris spp., respectively. They include dioeceous as well as hermaphroditic species. Nematodes also possess an excretory system that is not quite well developed. Embryonic development is external and proceeds via three larval stages. A peculiar feature of nematodes is the secretion of a collagenous/chitinous cuticle outside the body.

Arthropods represent the most successful phylum of animal on Earth, in terms of the number of species as well as the number of individuals. These animals are characterized by a segmented body as well as the presence of jointed appendages. In the basic body plan, a pair of appendages is present per body segment. Within the phylum, traditional classification is based on mouthparts, number of appendages, and modifications of appendages present. Arthropods bear a chitinous exoskeleton. Gills, trachea, and book lungs facilitate respiration. Sexual dimorphism is seen in this phylum, and embryonic development includes multiple larval stages.

Glossary

Arthropoda

phylum of animals with jointed appendages

biramous

referring to two branches per appendage

cephalothorax

fused head and thorax in some species

chelicera

modified first pair of appendages in subphylum Chelicerata

cuticle (animal)

the tough, external layer possessed by members of the invertebrate class Ecdysozoa that is periodically molted and replaced

cypris

larval stage in the early development of crustaceans

hemocoel

internal body cavity seen in arthropods

hermaphrodite

referring to an animal where both male and female gonads are present in the same individual

nauplius

larval stage in the early development of crustaceans

Nematoda

phylum of worm-like animals that are triploblastic, pseudocoelomates that can be free-living or parasitic

oviger

additional pair of appendages present on some arthropods between the chelicerae and pedipalps

pedipalp

second pair of appendages in Chelicerata

uniramous

referring to one branch per appendage

zoea

larval stage in the early development of crustaceans