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Balanoglossus, an example of a Hemichordata, represents an "evolutionary link" between invertebrates and vertebrates. In addition to the simple observation that the dorsoventral axes of protostomes and chordates appear to be inverted with respect to each other, molecular biology provides some support for the inversion hypothesis.
Among terrestrial invertebrates there are a number of leg forms. The arthropod legs are jointed and supported by hard external armor, with the muscles attached to the internal surface of this exoskeleton. The other group of legged terrestrial invertebrates, the velvet worms, have soft stumpy legs supported by a hydrostatic skeleton.
The vertebrates share one body plan, while invertebrates have many. This term, usually applied to animals, envisages a "blueprint" encompassing aspects such as symmetry, layers, segmentation, nerve, limb, and gut disposition. Evolutionary developmental biology seeks to explain the origins of diverse body plans.
Vertebrates (/ ˈ v ɜːr t ə b r ɪ t s,-ˌ b r eɪ t s /) [3] are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebrata with some 65,000 species, by far the largest ...
Invertebrates cells fire in response to similar stimuli as mammals, such as tissue trauma, high temperature, or changes in pH. The first invertebrate in which a neuron cell was identified was the medicinal leech, Hirudo medicinalis. [14] [15] Learning and memory using nociceptors have been described in the sea hare, Aplysia.
Edwin H. Colbert, (1969), Evolution of the Vertebrates, John Wiley & Sons (2nd ed.) Edwin H. Colbert, Michael Morales, Eli C. Minkoff, 2001 Colbert's Evolution of the Vertebrates: A History of the Backboned Animals Through Time, 5th Edition, Wiley, ISBN 0-471-38461-5; Publisher's Website and Book Overview
Agnatha (/ ˈ æ ɡ n ə θ ə, æ ɡ ˈ n eɪ θ ə /; [3] from Ancient Greek ἀ-(a-) 'without' and γνάθος (gnáthos) 'jaws') is a paraphyletic infraphylum [4] of non-gnathostome vertebrates, or jawless fish, in the phylum Chordata, subphylum Vertebrata, consisting of both living (cyclostomes) and extinct (conodonts, anaspids, and ostracoderms, among others).
Marine invertebrates are invertebrate animals that live in marine habitats, and make up most of the macroscopic life in the oceans. It is a polyphyletic blanket term that contains all marine animals except the marine vertebrates , including the non- vertebrate members of the phylum Chordata such as lancelets , sea squirts and salps .