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Segmentation in animals typically falls into three types, characteristic of different arthropods, vertebrates, and annelids. Arthropods such as the fruit fly form segments from a field of equivalent cells based on transcription factor gradients. Vertebrates like the zebrafish use oscillating gene expression to define segments known as somites
Annelids are members of the protostomes, one of the two major superphyla of bilaterian animals – the other is the deuterostomes, which includes vertebrates. [68] Within the protostomes, annelids used to be grouped with arthropods under the super-group Articulata ("jointed animals"), as segmentation is obvious in most members of both phyla ...
[1] [2] Well-known examples of protostomes are arthropods, molluscs, annelids, flatworms and nematodes. They are also called schizocoelomates since schizocoely typically occurs in them. Together with the Deuterostomia and Xenacoelomorpha, these form the clade Bilateria, animals with bilateral symmetry, anteroposterior axis and three germ layers ...
Well-known phyla of invertebrates include arthropods, mollusks, annelids, echinoderms, flatworms, cnidarians, and sponges. The majority of animal species are invertebrates; one estimate puts the figure at 97%. [1] Many invertebrate taxa have a greater number and diversity of species than the entire subphylum of Vertebrata. [2]
Most living animal species belong to the infrakingdom Bilateria, a highly proliferative clade whose members have a bilaterally symmetric and significantly cephalised body plan, and the vast majority of bilaterians belong to two large superphyla: the protostomes, which includes organisms such as arthropods, molluscs, flatworms, annelids and ...
A chaeta or cheta (from Ancient Greek χαίτη (khaítē) ' crest, mane, flowing hair '; pl. chaetae) is a chitinous bristle or seta found on annelid worms, although the term is also frequently used to describe similar structures in other invertebrates such as arthropods. Polychaete annelids (polychaeta literally meaning "many bristles") are ...
Some key events in the evolution of the arthropod body resulted from changes in certain Hox genes' DNA sequences. The trunks of arthropods comprise repeated segments, which are typically associated with various structures such as a pair of appendages, apodemes for muscle attachment, ganglia and (at least embryologically) coelomic cavities.
Mushroom bodies visible in a Drosophila brain as two stalks. From Jenett et al., 2006 [1]. The mushroom bodies or corpora pedunculata are a pair of structures in the brain of arthropods, including insects and crustaceans, [2] and some annelids (notably the ragworm Platynereis dumerilii). [3]