A multicellular organism whose mouth develops from a primary embryonic opening, such as an annelid, mollusk, or arthropod.
- ‘In the complementary category, the protostomes, which includes annelids and arthropods, the blastopore develops into the mouth.’
- ‘These animals are all protostomes - the mouth develops before the anus in the young embryo - and they have long been recognized as belonging together as a group.’
- ‘Arthropods are bilaterally symmetrical protostomes with strongly segmented bodies.’
- ‘Once this had appeared, the protostomes could develop.’
- ‘If the ancestor of protostomes displayed a segmentation comparable to annelids and arthropods, this necessarily means that segmentation was lost independently in different protostome lineages.’
1950s: from proto- primitive + Greek stoma mouth.