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Arthropods, on the other hand, display a heterogeneous mix of embryonic cleavage patterns including spiral-like cleavage and radial cleavage patterns. This led researchers to two theories: The first was that the arthropods lineage must have lost the ability to spiral cleave since differentiating from the last common ancestor between annelids ...
Arthropod heads are typically fused capsules that bear a variety of complex structures such as the eyes, antennae and mouth parts. The challenge that the arthropod head problem has to address is to what extent the various structures of the arthropod head can be resolved into a set of hypothetical ancestral segments.
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 ...
Historically, it was believed that only insects had mushroom bodies, because they were not present in crabs and lobsters. However, their discovery in the mantis shrimp in 2017 lead to the later conclusion [2] that the mushroom body is the ancestral state of all arthropods, and that this feature was later lost in crabs and lobsters.
The front end encounters the environment before the rest of the body so sensory organs such as eyes tend to be clustered there. This is also the site where a mouth develops since it is the first part of the body to encounter food. Therefore, a distinct head, with sense organs connected to a central nervous system, tends to develop. [17]
Likewise, the relationships between various arthropod groups are still actively debated. Today, arthropods contribute to the human food supply both directly as food, and more importantly, indirectly as pollinators of crops. Some species are known to spread severe disease to humans, livestock, and crops. (Full article...
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 ...
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 ...