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Thelodonti (from Greek: "nipple teeth") [4] is a class of extinct Palaeozoic jawless fishes with distinctive scales instead of large plates of armor.. There is much debate over whether the group represents a monophyletic grouping, or disparate stem groups to the major lines of jawless and jawed fish.
The roach is a small fish, often reaching no more than about 35 centimetres (14 in); maximum length is 50 cm (20 in). Its body has a bluish-silvery colour and becomes white at the belly. The fins are red. The number of scales along the lateral line is 39–48. [3] The dorsal and anal fins have 12–14 rays.
An insect uses its digestive system to extract nutrients and other substances from the food it consumes. [3]Most of this food is ingested in the form of macromolecules and other complex substances (such as proteins, polysaccharides, fats, and nucleic acids) which must be broken down by catabolic reactions into smaller molecules (i.e. amino acids, simple sugars, etc.) before being used by cells ...
There are three different tracheae supplying oxygen diffusing oxygen throughout the species body: The dorsal, ventral, and visceral. The dorsal tracheae supply oxygen to the dorsal musculature and vessels, while the ventral tracheae supply the ventral musculature and nerve cord, and the visceral tracheae supply the guts, fat bodies, and gonads.
In all vertebrates, these progenitor cells differentiate into all adult tissues and organs. [5] In the human embryo, after about three days, the zygote forms a solid mass of cells by mitotic division, called a morula. This then changes to a blastocyst, consisting of an outer layer called a trophoblast, and an inner cell mass called the embryoblast.
Cockroaches are popularly thought to be an ancient order of insects, with their origins in the Carboniferous. [4] However, since the middle of the 20th century it has been known that the primitive cockroach insects found fossilized in Palaeozoic strata are the forerunners not only of modern cockroaches and termites but also of mantises. [5]
The notum (plural nota) is the dorsal portion of an insect's thoracic segment, or the dorsal surface of the body of nudibranch gastropods. The word "notum" is always applied to dorsal structures; in other words structures that are part of the back of an animal, as opposed to being part of the animal's ventral surface, or underside.
Monotrysian: Primitive groups have a single genital aperture near the end of the abdomen through which both copulation and egg laying occur. This character is used to designate the Monotrysia. [7] Ditrysian: The remaining groups have an internal duct that carry sperm and form the Ditrysia, with separate openings for copulation and egg laying. [7]