Are tunicates cephalochordates?
Tunicates or urochordates (appendicularians, salps and sea squirts), cephalochordates (lancelets) and vertebrates (including lamprey and hagfish) constitute the three extant groups of chordate animals.
Why are tunicates closer to vertebrates?
In particular, a close proximity between tunicates and vertebrates suggests that the presence of metameric segmentation classically used to unify cephalochordates and vertebrates might be considered as an ancestral feature that underwent a secondary reduction in tunicates9.
Why Ascidians are called tunicates?
Their name derives from their unique outer covering or “tunic”, which is formed from proteins and carbohydrates, and acts as an exoskeleton. In some species, it is thin, translucent, and gelatinous, while in others it is thick, tough, and stiff.
Do tunicates have direct development?
Tunicates have reduced genomes compared to those of other chordates, with many genes in operons. Unlike other deuterostomes, tunicates have determinate development, with cell fates decided very early.
How do tunicates move?
Tadpole larvae and appendicularians swim by undulating the tail, which contains a stiff notochord. Despite their sessile lifestyles, some adult ascidians can move by attaching with one area of the body and letting go with another. Movement of colonies up to 1.5 centimetres per day has been recorded.
What are urochordates and cephalochordates?
Urochordata consists of a notochord in the posterior part of the body while Cephalochordata consists of a notochord extended to the head region. The main difference between Urochordata and Cephalochordata is the presence of the notochord in the head region.
How do tunicates develop?
Tunicates are generally hermaphrodites that sexually reproduce by cross-fertilization. That means that an individual does not use its own sperm to fertilize its eggs. Instead, they obtain sperm released into the open ocean by other individuals.
How are tunicates different from other chordates?
Tunicates do not have the well-developed secondary body cavity (coelom) of other chordates, but traces of one perhaps are represented by cavities around the heart and by an extension of the gut called the epicardium around some of the internal organs.
What are the difference in characteristics between Urochordata and Cephalochordata?
The main difference between Urochordata and Cephalochordata is that Urochordata consists of a notochord extended in the head region whereas Cephalochordata contains the notochord in the posterior region of the body.