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Advances in confocal microscopy technology led to the discovery of embryonic cleavage patterns, which differs between the annelids and arthropods. [5] Annelids show spiral cleavage, meaning that each embryonic cleavage occurs at progressive 90-degree angles with respect to the animal–vegetal axis. Arthropods, on the other hand, display a ...
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 ...
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]
The arthropod head problem has until recently been predicated on the Articulata theory, i.e. that the arthropods and annelids are close relatives. Although arthropods are essentially direct developers that do not possess a trochophore -like larva , the annelids do.
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
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 ...
Dunn et al. in 2008 suggested that the tardigrada could be grouped along with the nematodes, leaving Onychophora as the sister group to the arthropods. [11] The non-panarthropod members of Ecdysozoa have been grouped as Cycloneuralia but they are more usually considered paraphyletic in representing the primitive condition from which the ...
Additional support comes from work on the development of the polychaete annelid Platynereis dumerilii, another protostome. Even more so than Drosophila, its pattern of central-nervous-system development is strikingly similar to that of vertebrates, but inverted. [3] There is also evidence from left-right asymmetry.