Diploblasts: Cnidarians and Ctenophores

Gonozooid

Gonozooids develop reproductive structures called gonophores.

How does Hydra reproduce sexually without a medusa?

Hydra mostly reproduce asexually by producing buds on the body wall. ... They release sperm into water to fertilize eggs of another hydra. Fertilized eggs give rise to tiny planula larvae, which attach themselves and develop into polyps.

Nematocyst

Stinging organelle of cnidarians

Epidermis

The outer, nonvascular layer of skin of ectodermal origin; in invertebrates, a single layer of ectodermal epithelium

Scyphistoma

The polyp form of a scyphozoan.

Manubrium

The portion projecting from the oral side of a jelly medusa, bearing the mouth; oral cone

Gonophore

Sexual reproductive structure developing from reduced Medusae in some hydrozoans; it may be retained on the colony or released.

Gastrovascular cavity

space that functions like stomach and circulatory system. • Circulation • Skeletal system • Excretion • Digestion

Scyphozoan medusae

Moon jellies

Planula larva

Free-swimming, ciliated larval type of cnidarians; usually flattened and ovoid, with an outer layer of ectodermal cells an inner mass of endodermal cells

Gastric filaments

In scyphozoans, a row of filaments on the surface of the gastric cavity which function to kill or paralyze live prey taken into the stomach.

Ocelli Medusae

photosensitive

Classes

- Anthozoa - Scyphozoa - Hydrozoa All in the phylum Cnidarians

Diploblasts

- Germ layers - Gut

Describe the life cycle of Aurelia, naming all the life stages

- Sperm and Egg - Zygote (develops on arms of female) - Ciliated planula larva - Planula settles - Scyphistoma (polyp) - Early strobila - Strobila - Ephyra - Medusa

Hydrozoan medusae

- hydras - Man-of-war - hydroids

Germ layers

1. Diploblastic: Radiata; endoderm and ectoderm only 2. Triploblastic: Bilateria; endoderm, mesoderm, and ectoderm

Cnidocyte

A cnidocyte is an explosive cell containing one giant secretory organelle or cnida that defines the phylum Cnidaria (corals, sea anemones, hydrae, jellyfish, etc.). Cnidae are used for prey capture and defense from predators. - contain nematocysts specialized for prey capture and defense

Medusa

A jellyfish, or the free swimming stage in the life cycle of cnidarians.

Velum

A membrane on the subumbrella surface of jellyfish of class Hydrozoa.

Strobila

A stage in the development of the scyphozoan jellyfish.

Gonad

An organ that produces gametes (ovary in the female and testis in the male)

Comb rows

Any of various, mostly small marine invertebrates of the phylum Ctenophora, having transparent, gelatinous bodies bearing eight rows of comblike cilia

How is the life cycle of Ctenophores different from Cnidarians?

Ctenophores do not have a polyp stage Ctenophores spawn these eggs and sperm freely into the sea, where the sperm must first find the eggs, and the eggs are then fertilized. Fertilized eggs develop through a larval stage that hatches out of the free-floating fertilized egg and gradually grows into an adult ctenophore (the planktonic larvae of benthic ctenophores settle to the bottom before taking on their final adult form).

Focusing on our three taxa, what synapomorphies separate the clade containing Hydrozoa and Schphozoa from Anthozoa?

Hydrozoa and Schphozoa - Primary polyp tentacles hollow - Medusoid body form - Motor nerve net Anthozoa - tentacles solid

Explain the life cycle of Hydrozoa (Cnidarians)

In Obelia, the most conspicuous stage is the polyp. This stage of the Obelia life cycle is actually a colony of many interconnected polyps that share a single gastrovascular cavity. In the Obelia colony, the polyps take on different functions. Some have stinging tentacles that are specialized for capturing prey and feeding, while others are specialized for reproduction. 1. The reproductive polyp produces—by asexual means—tiny medusa body forms. These medusae grow and bud off from the parental tissue. The medusae nearest the tip of the polyp are the most mature and are the first to leave the parent animal. Because they can swim, the medusae help disperse the species in the sea. 2. A medusa may be male or female. Male and female medusae have gonads which produce sperm and eggs, respectively. The medusae reproduce sexually by releasing their sex cells into the water. The sperm cells meet and fertilize the eggs, which become the single-celled zygotes of the next generation. 3. A zygote begins to divide and develops into an immature larval stage, called a planula. A planula, which is covered with cilia, swims to a substrate and settles there. It grows and develops into the polyp body form. A single polyp of Obelia becomes a colony of polyps through asexual budding. Some of the polyps differentiate into the reproductive forms that, in turn, bud off medusae. The medusae will swim away and begin another round of the cnidarian life cycle.

Polyp

Individual of the phylum Cnidaria

Gastrodermis (endoderm)

Lining of the digestive cavity of cnidarians - absorbs nutrients and facilitates gas exchange.

What are similarities and differences between the structure of cnidarians and ctenophores?

Many ctenophores have two long tentacles, but some lack tentacles completely. Ctenophores, variously known as comb jellies, sea gooseberries, sea walnuts, or Venus's girdles, are voracious predators. Unlike cnidarians, with which they share several superficial similarities, they lack stinging cells.

Nerve Net

Nerve net - loose network of neurons in gastrodermis and epidermis • Muscle cells derived from ectoderm allow polyp and medusa to contract - Cnidarians have neurons but no centralized brain.

Comb plate

One of the plates of fused cilia arranged in comb rows for ctenophore locomotion.

Ephyra

Refers to castelike appearance. Medusa bud from a Scyphozoa polyp.

Gastrozooid

The feeding polyp of a hydroid; a hydranth

Mesoglea

The layer of jelly-like or cement material between the epidermis and gastrodermis in cnidarians and ctenophores. - Mesoglea is not a tissue; it is an acellular matrix with some free-floating cells.

Gastric pouch

The scyphozoan gastric cavity is divided into 4 gastric pouches that contain a tentacle-like projection of gastrodermis called a gastric filament which contain numerous gland cells that secrete digestive enzymes.

Nerve net

Unlike central nervous systems, where neurons are typically grouped together, neurons found in nerve nets are found spread apart. This nervous system allows cnidarians to respond to physical contact. They can detect food and other chemicals in a rudimentary way. While the nerve net allows the organism to respond to its environment, it does not serve as a means by which the organism can detect the source of the stimulus. For this reason, simple animals with nerve nets, such as Hydra, will typically produce the same motor output in response to contact with a stimulus regardless of the point of contact.

Corals

a. colonial polyps b. sessile c. symbioses - Zooxanthellae (dinoflagellates) e. calcium carbonate endoskeleton/skeleton of CaCO3 in hard corals • gastrovascular cavity continuous with other polyps • no medusa stage - polyp produces gametes

Anemones

a. solitary b. some mobility c. hydrostatic skeleton - d. symbioses - Damselfish - Clownfish - Hermit crab - Zooxanthellae (dinoflagellates)

Anthozoa

anemones and corals 1. life cycle - medusa lacking 2. Asexual and sexual reproduction, polyp produces gametes 3. structure - septa, gonads in bottom of gastrovascular cavity Sea anemones reproduce by lateral fission (in which an identical animal sprouts out of the anemone's side) and by sexual reproduction (in which anemones release eggs and sperm, producing free-swimming larvae).

Ctenophora

comb jellies • Ctenophora = 'comb bearing' comb jellies, sea walnuts • 8 rows of ctenes/combs • no polyp stage • complete gut • colloblasts (used to capture prey) • Reproduction - sexual; monoecious

Gut

distinguishes Cnidarians from Ctenophores 1. Blind gut - entrance and exit same 2. Complete gut - separate entrance and exit

What are Statocysts in Medusae used for?

equilibrium

Hydrozoa

hydrozoans; which stage is dominant? Polyp 1. life cycle - small polyps solitary or colonial, medusa lost in some (differs by species) 2. structure - colonial groups have multiple types of polyps; typically small medusa has a velum 3. Hydra - solitary; medusa entirely absent. 4. Obelia - colonial with sexual (medusae produce gametes in linear gonads) and asexual (polyps ) reproduction

Scyphozoa

jelly fish 1. life cycle - small, solitary polyps and typically large medusa; medusa stage is dominant 2. structure 3. reproduction - medusae produce gametes in horseshoe- shaped gonads • polyps reproduce asexually 4. symbioses • symbiotic zooxanthellae • commensalism with fish • parasitized by amphipods and gooseneck barnacles - presence of amoeboid cells and fibers in the mesoglea - lack of a velum (a rim of tissue around the margin of the bell)

What is the role of the ctenes?

locomotion tiny comb-like projections set up in rows along the animal

Ctenophora Feeding

two tentacles, When prey is swallowed, it is liquefied in the pharynx by enzymes and by muscular contractions of the pharynx. The resulting slurry is wafted through the canal system by the beating of the cilia, and digested by the nutritive cells.

Feeding Cnidarians

• food: tentacles-->mouth-->manubrium--> gastrovascular cavity (breakdown starts)--> cells (digestion completed) • symbiotic dinoflagellates in some

Economic importance

• tropical waters are nutrient poor • coral reefs provide habitat for diverse organisms • nutrients get recycled on reefs, making them relatively nutrient rich • valuable for important fisheries and for tourism