The influence of protostomes on humans Many protostomes are small in size and often overlooked among larger natural features and more charismatic creatures of the surrounding world. However, protostomes have played a variety of important roles in human cultures, economies, and health since ancient times. Some protostome species have instilled a sense of fear in […]


The large number and sheer diversity of protostomes necessitates a restriction on the kinds of behaviors (and species) that can be discussed in this chapter. The behaviors highlighted here are based in part on their importance to the survival of an individual organism. Protostomes are some of the most morphologically complex, ecologically diverse, and behaviorally […]


Introduction Without symbiosis, living organisms would be quite different from what they are today. This is true not only because symbiotic relationships were fundamental to the separation of eukaryotes (organisms whose cells have true nuclei) from prokaryotes (cellular organisms lacking a true nucleus), but also because they represent a unique biological process without which many […]


Introduction Protostomes are one of the most diverse and abundant groups in the animal kingdom. Their distribution, variety, and abundance are largely the result of evolutionary adaptations to climatic changes in their respective environments. At present, they inhabit a wide range of terrestrial and marine environments. Many protostomes are familiar to most people, including spiders, […]

Reproduction, development, and life history

Ontogeny and phylogeny All animals must reproduce, passing copies of their genes into separate new bodies in future generations. These genetic copies may be genetically identical, produced by asexual processes, or genetically distinct, produced by sexual processes. In sexual processes, which are by far the more common among animals, the initial result of reproduction is […]

Evolution and systematics

Roots and methods of systematics and classification There is only one figure in the 1859 first edition of Charles Darwin’s On the Origin of Species; it is what biologists now call a phylogenetic tree. A phylogenetic tree is a diagram that shows how animals have evolved from a common ancestor by branching out from it. […]

What is a Protostome?

Origin of Protostomia The term Protostomia (from the Greek “proto,” meaning first, and “stoma,” meaning mouth) was coined by the biologist Karl Grobben in 1908. It distinguishes a group of invertebrate animals based upon the fate of the blastopore (the first opening of the early digestive tract) during embryonic development. Animals in which the blastopore […]