Zoology Chapter 7

Describe the different types of coral reefs.

-Fringing reefs are directly attached to land shore. -Barrier reefs are separated from shore by a deep channel. -Atoll reefs are circular in shape. -Patch reefs have no specific shape or location. They are the youngest stage of atoll reefs.

Be able to identify structures of the common jellyfish Aurelia.

-Lappets (white outline) are sensory structures used to pick up gametes, food, and detect water conditions. -Gastric pouches with gonads and gastric filaments store information. -The statolith is responsible for orientation.

Describe the process of sexual reproduction in hydras.

-Ovaries or testes appear in fall when fertilization usually occurs. -Eggs mature, then are shed. -Cyst (test) forms around egg for overwintering -Hatch in spring (when prey and resources are abundant)

Briefly describe the structure of a polyp and a medusa.

A polyp has a tubular body that attaches to substratum via a pedal disk. Polyps have an upward facing mouth and tentacles. A medusa is bell or umbrella shaped. Medusas have a downward facing mouth and tentacles.

Draw and label the basic structure of the "typical" hydra.

A typical hydroid has a base, a stalk, and one or more terminal polyps (zooids).

Be able to identify the main structures of Metridium.

Anatomical structures of metridium include an oral disc, stalk, discs, siphon, pharynx, gastrovascular cavity, septa, and septal filaments.

What are the general characteristics of the class Anthozoa?

Anthozoa means "flower animals". They are all marine and can be found in both shallow and deep water. They are monomorphic, only having a polyp stage. If they are solitary, they are referred to as sea anemones (usually larger). If they are colonial, they are referred to as corals (polyps are small).

Briefly describe the ways hydras reproduce.

Asexual reproduction occurs via budding. Buds grow hydras. Sexual reproduction involves releasing eggs once conditions are right and water is moving. In hydras, this is called broadcast spawning.

How are medusa and polyps similar, despite appearing very different.

Both medusas and polyps retained the saclike body plan basic to the phylum. A medusa is essentially an unattached polyp with the tubular portion widened and flattened into the bell shape. (p. 145)

To which class do the true jellyfish belong?

Class Scyphozoa

In what type of habitat do you find cnidarians?

Cnidarians can most commonly be found in shallow, tropical, marine waters. Some can be found in freshwater, but none are terrestrial.

What is the most distinguishing characteristic of the cnidarians?

Cnidarians contain cnidocytes and colloblasts (stinging cells).

How is the nerve net of cnidarians similar and different from the human nerve network?

Cnidarians have slow, bidirectional neurotransmitters. No other animals have this. Cnidarians don't have a central nervous system like humans do, their nerve net is much simpler.

Where are cnidocytes located in a cnidarian?

Cnidocytes are located in the tentacles as well as the epidermis of the bell (of a jellyfish).

How can cnidocytes be triggered?

Cnidocytes are triggered when the cnidocil (ciliated chemo- mechano- receptor) detects tactile stimulation. Examples of triggers: -vibration frequency of swimming prey -high osmotic pressures -typical touch and chemical triggers

Describe the main parts of a cnidocyte.

Cnidocytes contain an operculum (door that opens when something is getting stabbed by the barbs), cnidocil (trigger or sensor), nematocyst (cell itself/needles), filament and barbs (spine that stab prey and inject venom).

Describe comb plates. What is the function of comb plates?

Comb plates are longitudinal rows of transverse plates bearing long, fused cilia. The beating of the cilia in each row starts at the aboral end and proceeds along the rows to the oral end, thus propelling the animal forward. All rows beat in unison. Ctenophores are the largest organisms to have locomotion by cilia alone (eight comb plates).

What are dactylozooids responsible for in Physalia?

Dactylozooids are responsible for locating prey and capturing/delivering them with the tentacles.

Is dimorphism or polymorphism more common in cnidarians?

Dimorphism is more common in cnidarians.

Explain the difference between dimorphism and polymorphism.

Dimorphism refers to two different stages of body type (polyp and medusa). Polymorphism refers to multiple stages, including polyp and medusa. These stages also include a larval, fixed polyp, and metamorphosis stage.

How are some of these groups thriving, and what are the causes of some failing?

Example: Coral Reefs Coral reefs are failing because they are suffering from the effects of global warming. The highly beneficial symbiosis between corals and zooxanthellae is threatened by coral bleaching.

What are gastrozooids responsible for in Physalia?

Gastrozooids are responsible for digestion and tentacles are attached to them.

What is unique about the genus Gonionemus?

Gonionemus use adhesive pads or disks to help move. They move around by stick to vegetation, rather than swimming.

What are gonophores responsible for in Physalia?

Gonophores are responsible for reproduction.

Describe the life cycle of Aurelia and how gametes are transferred.

Males release the sperm and females ingest them with oral arms-lappets. Lappets release and collect gametes, and also, pick up chemical cues. Planulas (zygotes with cilia) develop and disperse to the sea floor. A polyp develops and later turns into a medusa (driven by nutrients).

Which of the dimorphic forms is considered a complete and typical cnidarian?

Medusa

Is the nerve net the same as the central nervous system? Explain.

No, the nerve net is the simplest form of a nervous system. Unlike central nervous systems, neurons found in nerve nets are spread apart. In central nervous systems, neurons are grouped together.

What are the different types of polyps on Physalia?

Physalia (Portuguese man-o-war) is a colony of jellyfish. The polyps on it are pneumatophores, gastrozooids, dactylozooids, and gonophores.

What are pneumatophores responsible for in Physalia?

Pneumatophores are responsible for floatation and movement.

Which of the dimorphic forms is considered a persistent larval or juvenile stage?

Polyp

How are reefs constructed?

Reefs are constructed when conditions are ideal. They require hard substrate, warm/tropical/shallow waters, high salinity, clear water, sunlight, and waves. Waves oxygenate water, bring in nutrients, and aid in dispersal of coral (fragments).

Why does your text believe that the Cnidarians and Ctenophores may not have a shared ancestry with bilateral animals?

Researchers found differences in the ways striated muscle cells were assembled in cnidarians and bilaterians, suggesting convergent evolution, not shared ancestry.

Describe some of the symbiotic relationships of the sea anemone.

Sea anemones have symbiotic relationships with algae, crabs, and fish. Detailed example: The clownfish cleans the tentacles of the anemone, draws in prey, and provides moving water. In return, the anemone provides the clownfish with protection. This type of symbiotic relationship is called mutualism.

Which jellyfish from the class Cubozoa is considered to be of extreme importance and why?

The Irukandji (ear-a-con-jee) is important to note because they are extremely small and their bell possesses stinging cells, not just their tentacles. There are also no treatments for their stings.

What are the general characteristics of the class Cubozoa?

The class Cubozoa is classified by a cubed, medusa shape. They are very small, only found in warm waters, and are typically dimorphic (though the polyp stage is not very noticeable). The base of each tentacle is flattened (pedalium), and they are very dangerous. Note: They have multiple active eyes (first we've seen).

The class Myxozoa are what type of parasites? What is unique about them?

The class Myxozoa are parasites of fish, making them a major concern for commercial and sports fisheries. They can live in soil for decades before needing a host, making them hard to eliminate. Note: They have mitochondrial DNA, but no mitochondria (lost during evolution). Also, a species of this class was the first to lose the ability to breathe oxygen.

Cnidocil

The cnidocil is the modified cilium that acts as the trigger or sensor of a cnidocyte.

Describe the different types of cells found in the epidermis and gastrodermis of the hydra.

The gastrodermis has muscular, interstitial, nerve, and gland cells. The epidermis has cnidocytes (stinging cells).

Explain the difference between the two different classes found in the phylum Ctenophora.

The main difference between the two is whether they have tentacles or not.

What are the main parts of a Hydroid colony, and what are their functions?

The main parts of a hydroid colony, based off of obelia, are the hydrocaulus (stock), hydranths (gastrozooid), and gonangia (gonozooid).

Explain the relationship between a cnidocyte and a nematocyst.

The nematocyst is an organelle inside of the cnidocyte. The nematocyst consists of the ejectable thread and toxins that are injected into prey.

Where is the nerve net located in the cnidarians?

The nerve net is located at base of ectoderm and endoderm in cnidarians.

Operculum

The operculum is a door that opens when something is getting stabbed by the barbs of a cnidocyte.

Give the general characteristics of the phylum Ctenophora.

The phylum Ctenophora is an old, small phylum consisting of sea walnuts or comb jellies. They are known for their bioluminescence in their digestive canals. They have comb rows used for free-swimming locomotion. They have an anal opening and complete digestive tract. They have a medusa-like body with (bi)radial symmetry. They have no nematocysts, but they have adhesive structures called colloblasts. They are monomorphic and only have a medusa stage.

What does the siphon do in metridium?

The siphon helps to push and pull water in and out.

What is the function of the statocyst?

The statocyst is a balance sensory receptor. It lets the jellyfish know where they are oriented, whether its upside down or sideways.

Nematocyst

The stinging cell of a cnidocyte.

What are the similarities and differences between Ctenophores and Cnidarians?

They both have (bi)radial symmetry. Cnidarians are dimorphic, having medusa and polyp stages. Ctenophores don't have a polyp stage, only a medusa one. Ctenophores cast out tentacles to capture prey, while Cnidarians have stinging cells to intoxicate and capture their prey.

What are the major characteristics of cnidarians and ctenophores?

They have (bi)radial symmetry, lack organ systems (simple organization), contain a statocyst (sensory organ), contain mesoglea (hydrostatic skeleton), and are all found in marine habitats.

What type of symmetry do cnidarians and ctenophores have? How is this type of symmetry and advantage for these organisms?

They have radial symmetry which allows them to react to their environment in every direction.

What is unique about Turritopsis dohrnii?

Turritopsis dohrnii ("immortal jellyfish") can revert to an earlier developmental stage if it is injured or otherwise threatened. It does this thought the process of transdifferentiation, reverting the cells back to a cyst of undifferentiated cells.

Describe the different types of movements that occur among hydras.

Types of movements of hydras include gas bubble (unique to hydras), looping, somersault, climbing, and inverted-hand stand.

Describe the significant ecological and human impacts of Cnidaria.

When congregating, Jellyfish can devastate prey and dog fish nets can trigger eutrophication. Global climate change is causing this to occur more often. Many biochemicals come from marine life, meaning many pharmaceuticals are created from them. Coral reefs contribute to tourism and have a significant impact on commercial and sport fisheries.

Which type of reproduction is more common in the winter among hydras? Why?

When food is scarce, hydras reproduce sexually. This is usually when winter is approaching. This is so that eggs can hatch in the spring when the water is warmer and prey are more abundant.

Briefly describe what occurs when a cnidocyte is triggered.

When triggered, cnidocytes shoot out a discharge thread which can entangle and/or poison it's intended prey.

Explain the difference between Zoantharian and Octocorallia corals.

Zoantharian corals (Hexacorallia) are known as "stony or true corals". Their skeleton is made up of calcium carbonate and their septa is arranged in multiples of six (hexamerous). Octocorallia are known as "soft or horny corals". They have an internal skeleton and they have body plans in multiples of eight (octamerous).