Phylum Cnidaria

What are the requirements of the hydrostaic skeleton?

1. Presence of a cavity with an incompressible fluid that transmits pressure changes uniformly in all directions 2. That the cavity be surrounded by a flexible outer membrane, permitting deformations of the outer body wall 3. Two different muscles that orientate in different directions 4. That the volume of fluid in the cavity remains constant

What are the characteristics of Phylum Cnidaria?

1. Radial symmetry or modified as biradial symmetry 2. Diploblastic, tissue - level organization 3. Gelatinous mesoglea between the epidermal and gastrodermal tissue layers 4.Gastrovascular cavity 5. Nervous system in the form of a nerve net 6. Specialized cells, called cnidocytes, used in defense, feeding, and attachment.

Great Barrier Reef

A 1,250-mile chain of more than 2,500 reefs and islands along Australia's northeast coast, containing some 400 species of coral.

cnida

A fluid-filled, intracellular capsule enclosing a coiled, hollow tube.

operculum

A lid or cap-like structure on the top of a nematocyst.

cnidocyte

A specialized cell for which the phylum Cnidaria is named; consists of a capsule containing a fine coiled thread, which, when discharged, functions in defense and prey capture

Cnidarians

An animal characterized by cnidocytes, radial symmetry, gastrovascular cavity, a poly and medusa body form with examples including hydra, jellies, sea anemones, and corals.

diploblastic

An organism whose body is made of only two cell layers, the ectoderm and the endoderm; the two are connected by a noncellular layer called the mesoglea; animal phyla that are this are the Porifera (sponges) and the Cnidaria (jellyfish and hydra).

polyp

Basic body plan in cnidarians such as jellyfish; tubular in shape and typically sessile.

medusa

Body plans of a cnidarians; has a bell-shaped body and is typically motile.

benthic

Bottom of an aquatic ecosystem; consists of sand and sediment and supports its own community of organisms.

cnidocil

Bristle-like structure that extends from one end of a cnidocyte and functions as a trigger.

motile

Capable of movement.

velum

Cnidaria; Hydrazoan; Shelf like projection occuring on the subumbrella surface of the bell.

coelenteron

Cnidarian digestive cavity.

planula

Cnidarian larva, develops from the zygote, and continues to develop into a polyp.

Class Hydrozoa

Cnidocytes present in the epidermis; gametes produced epidermally and always released to the outside of the body; mesoglea is largely acellular; mesoglea usually with a velum; many polyps colonial; mostly marine with some freshwater species. Ex: Hydra; Obelia; Gonionemus; Physalia

Class Anthozoa

Colonial or solitary polyps; medusae absent; cnidocytes present in the gastrodermis; cnidocils absent; gametes gastrodermal in origin; gastrovascular cavity divided by mesenteries that bear nematocysts with wandering mesenchyme cells; tentacles solid; marine. Anemones and corals. Ex: Metridium

gastrovascular cavity

Digestive chamber with a single opening, in which cnidarians, flatworms, and echinoderms digest food.

nutritive-muscular cells

Gastrodermal cells that phagocytize partially digested food and incorporate it into food vacuoles, where digestion is completed.

dioecious

Having male and female reproductive organs in separate animals.

nematocyst

In cnidarians, along, thin, coiled stinger that is used to inject a toxin into prey.

mesoglea

In cnidarians, the jellylike material located between the ectoderm and the endoderm.

gastroderm

In cnidarians, the layer of cells surrounding the digestive tract.

peristalsis

Involuntary waves of muscle contraction that keep food moving along in one direction through the digestive system.

alternation of generations

Life cycle that has two alternating phases- a haploid (n) phase and diploid (2n) phase.

Class Scyphozoa

Medusa prominent in the life history; polyp small; gametes gastrodermal in origin and released into the gstrovascular cavity; cnidocytes present in the gastrodermis as well as epidermis; medusa lacks velum; mesoglea with wandering mesenchyme cells of epidermal origin; marine. Ex: Aurelia

Class Cubozoa

Medusa prominent in the life history; polyp small; gametes gastrodermal in origin; medusa cuboidal in shape with tentacles that hang from each corner of the bell; marine. Ex: Chironex

Class Staurozoa

Medusae absent; develop form benthic planula larvae; eight tentacles surrounding the mouth; attachment to substrate by adhesive disk; sexual reproduction only; marine. Ex: Haliclystis

nerve net

The simplest invertebrate nervous system; a network of nerves that can sense touch.

zooxanthellae

Tiny single-celled algae that live in the tissues of coral polyps. They have a mutualistic relationship with the polyp. They provide the polyp with food and oxygen.

hydrostatic skeleton

Water or body fluids confined in a cavity of the body against which contractile elements of the body wall act.