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Early deuterostomes and their modern counterparts. Bilateria, one of the five major lineages of animals, is split into two groups; the protostomes and deuterostomes. Deuterostomes consist of chordates (which include the vertebrates) and ambulacrarians. [20] It seems likely that the Kimberella was a member of the protostomes.
The majority of animals more complex than jellyfish and other cnidarians are split into two groups, the protostomes and deuterostomes, the latter of which contains chordates. [43] It seems very likely the 555 million-year-old Kimberella was a member of the protostomes.
The embryological origin of the mouth and anus is an important characteristic, and forms the morphological basis for separating bilaterian animals into two natural groupings: the protostomes and deuterostomes. In animals at least as complex as an earthworm, a dent forms in one side of the early, spheroidal embryo.
Two extinct taxa of uncertain placement, Vetulocystida and Yanjiahella, have each been proposed as either stem-group echinoderms [9] [10] or stem-group ambulacrarians. [11] [12] Vetulocystids have also been tentatively proposed as the basal-most stem-group chordates, [13] while Yanjiahella has also been proposed to be a stem-group hemichordate ...
Order Pterocliformes, sandgrouse (this enigmatic group was traditionally treated as a family in any of three different orders: Charadriiformes, Ciconiiformes, and Columbiformes) Order Columbiformes, doves, pigeons and dodos; Order Psittaciformes, parrots and allies; Order Cuculiformes, cuckoos; Order Strigiformes, owls
Bilateria has traditionally been divided into two main lineages or superphyla. [27] The deuterostomes traditionally include the echinoderms, hemichordates, chordates, and the extinct Vetulicolia. The protostomes include most of the rest, such as arthropods, annelids, molluscs, and flatworms.
Deuterostomes are therefore known as enterocoelomates. Examples of deuterostome coelomates belong to three major clades: chordates ( vertebrates , tunicates , and lancelets ), echinoderms ( starfish , sea urchins , sea cucumbers ), and hemichordates ( acorn worms and graptolites ).
A cell can only be indeterminate (also called regulative) if it has a complete set of undisturbed animal/vegetal cytoarchitectural features. It is characteristic of deuterostomes—when the original cell in a deuterostome embryo divides, the two resulting cells can be separated, and each one can individually develop into a whole organism.