Animal Kingdom Classification and Body Plans

Vocabulary terms regarding animal kingdom classification, levels of organization, symmetry types, coelom structures, and evolutionary body plans.

Protoplasmic level

A level of organization where unicellular organisms, such as Amoeba, perform all body functions within a single cell.

Cellular level of Org.

A multicellular organization where organisms lack coordination because they possess no sensory cells or nerve cells.

Tissue level of Organisa

An organization level in diploblastic organisms, such as Cnidaria and Ctenophora, where cells are grouped together to form tissues.

Organ level of Organ

An organization level where tissues join to form organs; it is first exhibited by the phylum Plathyhelminthes.

Organ system level

The level of organization found in triploblastic, bilateral organisms such as Nematodes or Aschelminthe.

Symmetry

The geometrical arrangement of body parts such that when an animal is cut through the principal axis, the resulting halves (antimeres) are identical.

Antimeres

The identical and symmetrical halves of an animal resulting from a division plane passing through the centre.

Assymmtry

A lack of definite shape where an organism cannot be cut into two identical halves through any plane passing through the centre, as seen in Porifera Sponges.

Radial Symmetry

A type of symmetry where any plane passing through the central principal axis results in two identical halves, typical of sessile or planktonic organisms like Cnidaria.

Pentamorous radial symmetry

A specific type of radial symmetry exhibited by starfish.

Bilateral Symmetry

A type of symmetry where an animal is divided into two identical halves specifically by a median sagittal plane, allowing for cephalochord and directed stimuli.

Coelom

A term given by Hackel for the body cavity present between the ectoderm and endoderm.

Acoelom

A condition where there is no body cavity between the ectoderm and endoderm, and the space is filled with mesenchyme derived from mesoderm.

Pseudocoelom

A body cavity not lined with mesodermal epithelium and filled with pseudocoelomic fluid, which acts as a hydrostatic skeleton.

Hydrostatic Skeleton

A skeletal system provided by the pseudocoelomic fluid in organisms like Nematoda and Rotifers.

Eucoelom

A true body cavity between the ectoderm and endoderm where the gut is lined by visceral peritoneum and the body wall is lined by parietal peritoneum.

Retroperitonium

A term used to describe the location of organs like the kidney in relation to the peritoneum.

Schizocoelom

A true coelom formed by the splitting of mesodermal blocks or cells, characteristic of Annelids, Arthropoda, and Mollusca.

Protostomians

Organisms in which the first formed opening, the blastopore, becomes the mouth; they exhibit spiral and determinate cleavage.

Archentron

The first formed gut in a developing embryo from which mesodermal pouches or blocks may derive.

Enterocoelom

A coelom formed from mesodermal pouches that originate from the archentron, seen in Echinodermata, Hemichordata, and Chordata.

Deuterostomians

Organisms in which the blastopore becomes the anus and the opposite opening becomes the mouth; they exhibit radial and indeterminate cleavage.

Tube within tube body plan

A body plan found in pseudocoelomates and coelomates that allows for continuous body activity and organ specialization.

Blind sac

A body plan with an incomplete gut that has only one opening acting as both mouth and anus, found in Plathyhelminthes and Cnidaria.

Solid body plan

A body plan where the cavity between the ectoderm (pinacoderm) and endoderm (choandorm) is filled with mesophys, as seen in Porifia.