4. Cnidarians & Ctenophores

Dimorphism

Presence of two distinct body forms in cnidarians: polyp and medusa.

Gastrovascular Cavity

Incomplete gut in cnidarians for digestion and nutrient distribution.

Mesoglea

Jelly-like extracellular matrix between the epidermis and gastrodermis in cnidarians.

Epidermis

Outer cell layer in cnidarians derived from ectoderm.

Gastrodermis

Inner cell layer lining the gut cavity in cnidarians, derived from endoderm.

Statocysts

Sensory organs in cnidarians for balance and orientation.

Ocelli

Photosensitive organs in cnidarians for light detection.

Velum

Shelflike fold of tissue in hydrozoan medusae that aids in propulsion.

Hydromedusae

Medusae of class Hydrozoa; have a velum.

Scyphomedusae

Medusae of class Scyphozoa; lack a velum.

Polymorphism

Presence of different types of polyps within a cnidarian colony, each specialized for different functions.

Zooids

Individual polyps in a cnidarian colony, specialized for functions like feeding or reproduction.

Planula

Free-swimming larval stage in cnidarians after fertilization.

Zygote

Fertilized egg that develops into a motile planula larva in cnidarians.

Polyp

Sessile stage in the cnidarian life cycle, characterized by a tubular body and a mouth surrounded by tentacles.

Medusa

Free-swimming stage in the cnidarian life cycle, often bell-shaped with tentacles hanging down.

Asexual Reproduction

Reproduction without the involvement of gametes, including budding and strobilation.

Strobilation

A method of asexual reproduction where a polyp produces a series of immature medusae.

Dioecious

Organisms with separate sexes, meaning each individual has either male or female reproductive organs.

Cnidocyte

Specialized cell in cnidarians that contains cnidae, such as nematocysts, used for prey capture and defense.

Cnidae

Organelles within cnidocytes, including nematocysts, used for stinging or attachment.

Nematocyst

Type of cnida that discharges a coiled thread to inject toxins into prey or for defense.

Cnidocil

Triggerlike structure on cnidocytes that stimulates nematocyst discharge.

Epitheliomuscular Cells

Cells in cnidarians that function as both the epidermis and muscle for contraction.

Digestive System

Includes extracellular digestion in the gastrovascular cavity and intracellular digestion in gastrodermal cells.

Nerve Net

Diffuse network of nerve cells in cnidarians that controls reflexes and simple behaviors.

Rhopalia

Sense organs in medusae that contain chemoreceptors, statocysts, and ocelli.

Neuromuscular System

Combination of nerve net and contractile cells in cnidarians that coordinates movements.

Hydrozoa

A class of cnidarians that typically includes both an asexual polyp stage and a sexual medusa stage.

Hydroid Colonies

Colonial forms of Hydrozoa with a base, stalk, and terminal zooids, including feeding polyps called hydranths.

Hydrorhiza

Rootlike stolon of a hydroid colony that attaches to the substrate.

Hydrocaulus

Stalk of a hydroid colony that supports individual zooids.

Coenosarc

Living cellular part of the hydrocaulus, surrounding the gastrovascular cavity.

Perisarc

Nonliving chitinous sheath covering the hydrocaulus.

Hydranth

Feeding polyp in a hydroid colony, equipped with a mouth and tentacles.

Gonangium

Reproductive polyp in a hydroid colony that produces medusae.

Medusa Bud

Free-swimming medusa formed by budding from a reproductive polyp.

Manubrium

Tube-like structure in medusae that extends from the mouth to the stomach.

Entocodon

Ectodermal derivative in medusa buds that differentiates into muscles.

Craspedacusta sowberii

Freshwater medusa with a tiny, simple polyp stage.

Hydra

Freshwater hydrozoan with a simple body plan, typically solitary.

Hypostome

Conical elevation on a hydra where the mouth is located.

Nutritive-Muscular Cells

Cells in hydras that aid in digestion and movement.

Siphonophora

Order of Hydrozoa with specialized colonies including floating and swimming forms.

Physalia

Portuguese man-of-war, a siphonophore with a gas-filled float and stinging tentacles.

Pneumatophore

Gas-filled float of the Portuguese man-of-war.

Scyphozoa

Class of cnidarians including most large jellyfish, characterized by a prominent medusa stage.

Cyanea

A genus of large scyphozoan jellyfish with bell diameters exceeding 2 m and long tentacles.

Rhopalium

Sense organ in Scyphozoa with a statocyst for equilibrium and sensory pits.

Gastric Filaments

Tentacle-like projections in Scyphozoa's gastric pouches that help subdue prey.

Cassiopeia

Scyphozoan known as the "upside-down jellyfish" with a unique mouth structure and symbiotic dinoflagellates.

Staurozoa

Class of cnidarians with stalked polyps that resemble medusae but lack a medusa stage.

Cubozoa

Class of cnidarians with cube-shaped medusae, known for their potent venom and advanced sensory organs.

Pedalium

Flattened blade at the base of each tentacle in Cubozoa that aids in swimming.

Velarium

Inward-folding structure in Cubozoa that increases swimming efficiency.

Tripedalia cystophora

A Cubozoan species with a tiny, solitary polyp that metamorphoses directly into medusae.

Myxozoa

Parasitic class with a life cycle involving fish and annelid hosts, causing diseases like whirling disease.

Whirling Disease

Condition caused by Myxobolus cerebralis, affecting fish with skeletal deformities and abnormal behavior.

Tetracapsuloides bryosalmonae

Myxozoan responsible for whitefish population declines in Yellowstone River.

Polypodium hydriforme

Freshwater cnidarian with a free-living phase resembling medusae, infects fish oocytes.

Polar Capsule

Structure in Myxozoa resembling nematocysts, used to attach to gut lining of hosts.

Anthozoa

Marine polyps with no medusa stage; includes sea anemones and corals.

Hexacorallia

Subclass of Anthozoa with sea anemones and hard corals; features hexamerous symmetry.

Cerianthipatharia

Subclass of Anthozoa; includes tube anemones and thorny corals.

Octocorallia

Subclass of Anthozoa; includes soft corals like sea fans and sea pens; features octomerous symmetry.

Septa (Mesenteries)

Inward extensions of the body wall that partition the gastrovascular cavity.

Siphonoglyph

Ciliated groove in sea anemones that creates a water current into the pharynx.

Pedal disc

Structure sea anemones use to attach to surfaces.

Acontia

Threads in sea anemones that aid in prey capture and defense.

Zooxanthellae

Symbiotic dinoflagellates living within coral tissues, aiding in nutrient provision and calcium carbonate deposition.

Coral bleaching

Loss of zooxanthellae from corals due to increased water temperatures, leading to coral death.

Fringing reef

Reef type close to shore with no or narrow lagoon.

Barrier reef

Reef running parallel to shore with a wider and deeper lagoon.

Atoll

Reef that encircles a lagoon but not an island.

Patch reef

Reef occurring in lagoons of barrier reefs or atolls.

Reef crest

Shallow, wave-exposed top of a reef front.

Reef flat

Area of the reef sloping into the lagoon, accumulating calcareous material.

Ctenophora

Phylum of marine invertebrates known as comb jellies or sea walnuts, characterized by eight rows of ciliary comb plates.

Comb Plates (Ctenes)

Rows of ciliated structures used for locomotion in ctenophores.

Pleurobrachia

A representative ctenophore species, 1.5 to 2 cm in diameter, with two tentacles and eight comb rows.

Colloblasts

Adhesive cells on tentacles of ctenophores used for capturing prey.

Gastrovascular System

Digestive system of ctenophores, including mouth, pharynx, stomach, and branching canals.

Monoecious

Organism having both male and female reproductive organs; characteristic of most ctenophores.

Cydippid Larva

Free-swimming larval stage of ctenophores that develops into an adult without metamorphosis.

Beroe

A type of ctenophore with a large, conical body, no tentacles, and a network of canals.

Venus' Girdle (Cestum)

Long, band-like ctenophore adapted for locomotion with sinuous movements.

Ctenoplana and Coeloplana

Disc-shaped, creeping ctenophores adapted for slow movement rather than swimming.

Mnemiopsis

Common ctenophore with laterally compressed body and unsheathed tentacles, known for bioluminescence.

Bioluminescence

Emission of light by ctenophores, often visible at night.

Diploblasts

Animals with two embryonic tissue layers: ectoderm and endoderm.

Cnidarians

Phylum of radially symmetrical animals with nematocysts, including jellyfish, corals, and sea anemones.

Ctenophores

Phylum of marine animals with biradial symmetry and comb plates used for locomotion, known as comb jellies.

Ectomesoderm

Gelatinous middle layer in some diploblastic animals that may have mesoderm-like functions.

Striated Muscle

Muscle type with sarcomeres and Z-discs, found in some cnidarians and ctenophores, evolved independently in several lineages.

Mesoderm

Middle embryonic tissue layer found in triploblastic animals, absent in diploblasts like cnidarians and ctenophores.

Hox Genes

Genes that determine body axis and morphogenesis; cnidarians have homologs of anterior and posterior Hox genes.

Polytomy

A phylogenetic term describing unresolved relationships among taxa.

Medusozoa

Taxon including cnidarian classes with a medusa stage in their life cycle.

Anthozoa

Cnidarian class without a medusa stage, considered the sister taxon to other cnidarians.

Adaptive Diversification

Evolutionary process leading to a wide variety of forms and functions in organisms, such as cnidarians' diverse feeding strategies and colonial life.