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References A adhesive organ 1. An organ present at the anterior end of ascidian larvae, serving to attach the larva to the substrate during its metamorphosis. It is usually made of three papillae. 2. The individual papillae. atrium atrial pore atrial siphon Also excurrent siphon or exhalant siphon. Opening through which water exits the branchial basket in ascidians. B blastozooid Sexual ...
A tunicate is an exclusively marine invertebrate animal, a member of the subphylum Tunicata (/ ˌ tj uː n ɪ ˈ k eɪ t ə / TEW-nih-KAY-tə).This grouping is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (including vertebrates).
A chordate (/ ˈ k ɔːr d eɪ t / KOR-dayt) is a deuterostomal bilaterian animal belonging to the phylum Chordata (/ k ɔːr ˈ d eɪ t ə / kor-DAY-tə).All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics (synapomorphies) that distinguish them from other taxa.
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.
The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals.It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for special senses such as vision, hearing and olfaction.
The dorsal nerve cord is an anatomical feature found in chordate animals, mainly in the subphyla Vertebrata and Cephalochordata, as well as in some hemichordates.It is one of the five embryonic features unique to all chordates, the other four being a notochord, a post-anal tail, an endostyle, and pharyngeal slits.
[73] [74] More recently, the fundamental symmetric and twisted development of vertebrates is the topic of the axial twist theory. According to this theory, there is a deep agreement between the vertebrates and cephalochordates, and even all chordates. [75] [76]
The heads of vertebrates are complex structures, with distinct sense organs for sight, olfaction, and hearing, [12] and a large, multi-lobed brain protected by a skull of bone or cartilage. [13] Cephalochordates like the lancelet ( Amphioxus ), a small fishlike animal with very little cephalization, are closely related to vertebrates but do not ...