Somite


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somite

[′sō‚mīt]
(zoology)

Somite

 

a paired metameric formation in the embryos of such invertebrates as annelids and insects and in the embryos of man and all other chordates. The middle germ layer, or mesoderm, is segmented into somites during embryonic development. The somites are arranged along the longitudinal axis of the body alongside the neural tube and the chorda. The entire mesoderm is segmented in invertebrates, whereas in man and other chordates only its dorsal section is segmented, with the remaining mesoderm forming lateral plates, or splanchnotomes. Segmentation begins from the anterior section of the body and gradually extends to the posterior section. In the process of development, each somite decomposes into a myotome, a sclerotome, and a dermatome, from which are formed, respectively, the truncal musculature, the axial skeleton (in fish, also the skeleton of the fins), and the connective-tissue portion of the skin and its derivatives.

T. A. DETLAF

References in periodicals archive ?
Shh is a gene involved in different processes of embryonic development, as the induction of the neural tube, differentiation of the somites, and regionalization of the intestine (Sadler, 2012), it is also related to a center of signals involved in the anteroposterior formation members design (Johnson et al., 1994; Antonelli et al., 2012).
Higher exposure concentrations resulted in progressively higher GFP expression levels, and a nominal concentration of [EE.sub.2] (10 ng/L; measured concentration, 7.25 ng/L) induced considerable expression throughout the liver; this was accompanied by GFP expression in the muscle (somite and cranial muscle) and heart (Figure 3D).
The focus of these experiments was to achieve survival of the embryos following somite:somite cross-transplantation through 10 days post-surgery, which provides the opportunity for the embryo to complete pattern formation, and establish the basic body plan.
6, A and B): Dorsomedian spines on the 4th, 5th and 6th abdominal somites; one pair of lateral spines on 5th and 6th abdominal somites; one pair of lateroventral spines on the 6th abdominal somite.
Abdomen extremely large, with six somites, and telson free articulated; margin with tomentum, laterally covering ischia and distally buccal cavity and eyes.
acanthitelsonis herein examined, from north and south Atlantic, do not vary in the characters mentioned in the identification key of Crosnier & Forest (1973) presenting: smooth dorsal margin at abdominal somites 3-5; abdominal somite 2 without dorsal carina; long and slender rostrum; and 13-19 pairs of dorsolateral spines at telson.
Nonsignificant malformations (otic vesicle, somite, circulation, pigmentation, swim bladder, notochord distortion, and alterations in touch response) are excluded.
The upper distal borders of the fifth abdominal somite have a spine on each side that was only visible on the right-hand side of the prezoea stage.
Citation: Taketaro Sadahiro et al., Tbx6 Induces Nascent Mesoderm from Pluripotent Stem Cells and Temporally Controls Cardiac versus Somite Lineage Diversification.
(A) Habitus, dorsal view; (B) Urosome showing posterior end of the genital double-somite, the anal somite, and caudal rami, ventral view; (C) Caudal ramus, dorsal view; (D) Leg 5.
The above are in line with the observed complexity of the embryological development of the vertebral skeleton, which encompasses abnormalities that can arise at any stage from the somite development through the ossification of the cartilage anlage (primordium stage of development).
Urosome with four segments, genital double somite subquadrate, lacking lateral medial protrusions and with rounded integumental window on each side of posterior half (arrows in Fig.