CNIDARIA

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Questions and Answers

What is the characteristic of the mesoglea in hydrozoan medusa?

It is a non-cellular layer and thicker in hydrozoan medusa. (correct)
It is a layer of cells between the epidermis and gastrodermis.
It is a non-cellular layer and thinner in hydrozoan medusa.
It is a layer of cells between the endodermis and gastrodermis.

What is the function of statocysts in medusa?

They are responsible for forming images.
They are involved in digestion.
They help in movement and protection.
They are used for balance and orientation. (correct)

What is the origin of cnidoblasts in cnidarians?

They develop from the epidermis. (correct)
They develop from the endodermis.
They develop from the gastrodermis.
They develop from the mesoglea.

Which of the following is a characteristic of the class Hydrozoa?

They have a life cycle with both polyp and medusa stages. (B) Signup and view all the answers

What is the function of epitheliomuscular cells in Hydra?

They are involved in movement and protection. (A) Signup and view all the answers

What is the characteristic of the gastrovascular cavity in Hydrozoa?

It is not divided by mesenteries. (B) Signup and view all the answers

What is the characteristic of interstitial cells in Hydra?

They are totipotent cells that can specialize into other cells. (B) Signup and view all the answers

Which of the following is a characteristic of the medusa stage in Hydrozoa?

It has a velum and statocysts. (C) Signup and view all the answers

Which of the following classes within the Phylum Cnidaria is characterized by a dominant polyp form?

Anthozoa (C) Signup and view all the answers

What is the characteristic of Cubozoa and Scyphozoa that distinguishes them from other classes within the Phylum Cnidaria?

Segmented body (B) Signup and view all the answers

What is the function of the vellum in Hydrozoa?

Site for reproduction (D) Signup and view all the answers

Which of the following classes within the Phylum Cnidaria has a life cycle with both polyp and medusa forms?

Hydrozoa (A) Signup and view all the answers

What is the basis of the relatedness of Scyphozoa and Hydrozoa according to Cladogram B?

Mitochondrial protein-coding genes (D) Signup and view all the answers

What is the characteristic of the medusa form in Medusozoa?

Dominant medusa form (A) Signup and view all the answers

What is the function of the mesentery in Anthozoa?

Divides the gastrointestinal cavity (B) Signup and view all the answers

What is the characteristic of the Cubozoa and Scyphozoa that allows them to move vertically and horizontally?

Large size (D) Signup and view all the answers

What is the function of the hydrotheca in Obelia?

To provide protection to the gastrozooid (A) Signup and view all the answers

What is the type of larva characteristic of Cnidaria, including Obelia?

Planula (A) Signup and view all the answers

What is the function of the gastrozooid in Obelia?

Nutrition (A) Signup and view all the answers

What is the term for the clusters of cnidoblasts in Obelia?

Batteries (D) Signup and view all the answers

What is the term for the living part of the covering of Obelia?

Coenosarc (C) Signup and view all the answers

What type of polyp contains a gonophore in Obelia?

Gonozooid (C) Signup and view all the answers

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Study Notes

Cnidarian Evolutionary History

Cnidarian medusa is present in most species, with Hydra being mostly polyp in its life cycle.
Trachylina is mostly medusa in its life cycle.

Characteristics of Hydrozoa

Life cycle with both polyp and medusa stages in many species.
Gastrovascular cavity is not divided by mesenteries.
Medusa stage has a velum.
Nematocysts are ectodermal (limited to the outside, epidermis).
Gonads are ectodermal (develop from cells of the epidermis).
Medusa usually has statocysts (for balance) and ocelli (cannot form images).

Structure of Hydrozoan Polyp

Mesoglea is a non-cellular layer between the endodermis and gastrodermis.
Column is the body of Hydra.
Epitheliomuscular cells are for protection (epithelial) and movement (muscular).
Interstitial cells are totipotent cells that can specialize into other cells and make new cnidocytes.
Cnidocyte is a stinging cell.
Gastrodermis lines the gastrovascular cavity in Hydra and is involved in digestion.

Systematics of Cnidaria

Cnidaria is divided into five classes: Hydrozoa, Cubozoa, Scyphozoa, Staurozoa, and Anthozoa.
Cladogram A shows phylogenetic relationships of classes within the Phylum Cnidaria based on form.
Cladogram B shows phylogenetic relationships based on mitochondrial protein-coding genes.
Cubozoa and Scyphozoa are more closely related and are true jellyfishes.
Hydrozoa and Scyphozoa are related based on mitochondrial protein-coding genes.

Hydrozoa

Hydrozoa has a life cycle with both polyp and medusa stages.
Vellum is a shelf-like structure in Hydrozoa that is absent in Scyphozoa.
Obelia is a colonial hydrozoan (unlike the solitary hydra).
Planula larva is a general type of larva in cnidaria that is ciliated and swims for a couple of days before settling and developing into a young hydrozoid.

Obelia

Gastrozooid is a feeding polyp enclosed by a hydrotheca that is in charge of nutrition.
Hydrotheca is an exoskeleton that encloses the gastrozooid for protection and is non-living.
Perisarc is the outermost covering of Obelia that is continuous with the hydrotheca and makes the obelia pliant and flexible.
Coenosarc is the living part of the covering that is continuous with the gastrovascular cavity.
Gonozooid is a reproductive polyp that contains gonophore.
Batteries of cnidoblasts are clusters of cnidoblasts that help in capturing prey.

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