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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.
The calcichordate hypothesis, formulated by British Museum paleontologist Richard Jefferies, holds that each separate lineage of chordate (Cephalochordates, Urochordates, Craniates) evolved from its own lineage of mitrate, and thus the echinoderms and the chordates are sister groups, with the hemichordates as an out-group. [1]
The lancelets (/ ˈ l æ n s l ɪ t s, ˈ l ɑː n-/ LA(H)N-slits), also known as amphioxi (sg.: amphioxus / ˌ æ m f i ˈ ɒ k s ə s / AM-fee-OK-səs), consist of 32 described species of "fish-like" benthic filter feeding chordates [9] in the subphylum Cephalochordata, class Leptocardii, and family Branchiostomatidae.
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 ...
The endostyle is an organ found in invertebrate chordate species of tunicates, lancelets, and in the larval stage of vertebrate lampreys.It assists in filter-feeding. [1] It has evolved into the thyroid in vertebrate chordates.
Comparative molecular biology has revealed that the Pax 1 and Pax 9 genes (which encode for transcription factors) are expressed in similar patterns between hemichordates and urochordates. In vertebrates, Pax 1 and Pax 9 are expressed in the pharyngeal pouches and are important for thymus development. [ 14 ]
The earliest animals were marine invertebrates, that is, vertebrates came later. Animals are multicellular eukaryotes, [note 1] and are distinguished from plants, algae, and fungi by lacking cell walls. [1]