Cephalization

Information about Cephalization

Tenia solium, a cestode showing simple cephalization.

Cephalization is an evolutionary trend, whereby nervous tissue, over many generations, becomes concentrated toward one end of an organism. This process eventually produces a head region with sensory organs.

Cephalization is intrinsically connected with a change in symmetry. It accompanied the move to bilateral symmetry made in flatworms, with ocelli and auricles placed in the head region. The cephalization/bilateral symmetry combination allowed animals to have sensory organs facing the direction of movement, allowing a more focused assessment of the environment into which they are moving. In addition to a concentration of sense organs, all animals from annelids on also place the mouth in the head region. This process is also tied to the development of an anterior brain in the chordates from the notochord. A notable exception to the trend of cephalization throughout evolutionary advancement is phylum Echinodermata, which, although having a bilateral ancestor, as evidenced by their embryology, develop into a pentaradial animal with no concentrated neural ganglia or sensory head region. However, some echinoderms have developed bilateral symmetry secondarily.

In neuroembryology, neural induction of the ectoderm forms a neural tube which undergoes cephalization to form initially 3, then 5 vesicles as a developing embryo. It is the internalized ectoderm which goes on to become the central nervous system, peripheral nervous system and epidermis.

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nervous system of an animal coordinates the activity of the muscles, monitors the organs, constructs and also stops input from the senses, and initiates actions. Prominent parts of a nervous system include neurons and nerves, which are used in coordination.
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head of an animal is the rostral part (from anatomical position) that usually comprises the brain, eyes, ears, nose, and mouth (all of which aid in various sensory functions, such as sight, hearing, smell, and taste).
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sensory system: in this case, vision, for the visual system. ]]

A sensory system is a part of the nervous system responsible for processing sensory information.
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Symmetry in biology is the balanced distribution of duplicate body parts or shapes. The body plans of most multicellular organisms exhibit some form of symmetry, either radial symmetry or bilateral symmetry. A small minority exhibit no symmetry (are asymmetric).
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Platyhelminthes
Gegenbaur, 1859

Classes

Monogenea
Trematoda
Cestoda
Turbellaria

The flatworms (Phylum Platyhelminthes from the Greek platy, meaning "flat" and helminth
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ocellus (plural: ocelli) is a type of photoreceptor organ in animals. Also called "simple eyes", ocelli are miniature eyes capable of sensing light but not distinguishing its direction. See also stemmata, which are structurally similar. Ocelli are found in many invertebrates.
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The pinna (Latin for feather) is the visible part of the ear that resides outside of the head (this may also be referred to as the auricle or auricula).

Purpose

The purpose of the pinna is to collect sound.
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Annelida
Lamarck, 1809

Classes and subclasses

Class Polychaeta (paraphyletic?)
Class Clitellata*
Oligochaeta - earthworms, etc.
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In animals, the brain or encephalon (Greek for "in the skull"), is the control center of the central nervous system, responsible for behavior. The brain is located in the head, protected by the skull and close to the primary sensory apparatus of vision, hearing,
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Chordata
Bateson, 1885

Typical Classes

See below

Chordates (phylum Chordata) are a group of animals that includes the vertebrates, together with several closely related invertebrates.
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The notochord is a flexible, rod-shaped body found in embryos of all chordates. It is composed of cells derived from the mesoderm and defines the primitive axis of the embryo.
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phylum (Greek Φῦλον plural: Φῦλα phyla) is a taxon in the rank below kingdom and above class.
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Echinodermata
Klein, 1734

Subphyla & Classes

Homalozoa Gill & Caster, 1960

Homostelea

Homoiostelea

Stylophora

Ctenocystoidea Robison & Sprinkle, 1969

Crinozoa

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Embryology is the study of the development of an embryo. An embryo is defined as any vertebrate in a stage before birth or hatching. Embryology refers to the development of the egg cell (zygote) after fertilization and the differentiation of cells into tissues and organs.
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The ectoderm is the start of a tissue that covers the body surfaces. It emerges first and forms from the outermost of the germ layers.

What forms from it (general)?

Nervous system
Outer part of integument

What forms from it (vertebrates)?

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neural tube is the embryo's precursor to the central nervous system, which comprises the brain and spinal cord. The neural groove gradually deepens as the neural folds become elevated, and ultimately the folds meet and coalesce in the middle line and convert the groove into a
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vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. If there is only one lipid bilayer, they are called unilamellar vesicles; otherwise they are called multilamellar.
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The central nervous system (CNS) represents the largest part of the nervous system, including the brain and the spinal cord. Together with the peripheral nervous system, it has a fundamental role in the control of behavior.
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The Peripheral nervous system resides or extends outside the "CNS" central nervous system (the brain and spinal cord) to serve the limbs and organs. Unlike the central nervous system, however, the PNS is not protected by bone, leaving it exposed to toxins and mechanical injuries.
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Epidermis is the outermost layer of the skin. It forms the waterproof, protective wrap over the body's surface and is made up of stratified squamous epithelium with an underlying basal lamina.
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