Cnidaria Lab

Cnidaria Lab


Hydra w.m under microscope 4x

Hydra Nematocysts under microscope 40x

Hydra Budding under microscope 4x

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Hydras are tiny, simple invertebrates that have a circulatory system similar to jellyfish. They are apart of the phylum Cnidaria, order Anthomedusae and class Hydrozoa. Typically found in freshwater ponds, lakes, and streams. They have a fluid-filled gastrovascular cavity where nutrients are absorbed and are atypical because they do not have a medusa (jellyfish) stage as part of their life cycle as do most other cnidarians. Hydras live and reproduce sexually and asexually, and have a nematocysts or cnidae. Nematocysts are microscopic intracellular stinging capsules and are one of the most complex structures in the animal world. They are produced by nematoblasts, or cnidoblasts, and are used for capturing and paralyzing prey or for defense. They are native to the temperate and tropical regions and have an amazing regenerative ability. Hydra can extend their body to the maximum length (four to five times the length of the body) when feeding. Upon contact, they use their nematocysts on their tentacle to fire into preys and then coil their tentacle around the prey. They also have two main body layers, so they are diploblastic. The outer layer is the epidermis, and the inner layer is called the gastrodermis. They do not have a recognizable brain or true muscles. 

Aurelia Scyphistoma under microscope 4x

Aurelia Late Strobila w.m. under microscope 4x

Aurelia Strobila, early form w.m. under microscope 10x

Aurelia Ephyra w.m. under microscope 10x

ephyra anatomy

Aurelia Planulae w.m. under microscope 40x

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Aurelia is in the phylum Cnidaria, order Semaeostomeae, and displays the typical life stages for the class Scyphozoa of invertebrates; planula, the stalked and tentacled scyphistoma polyp, the strobila bud, and the mature medusa stages. Aurelia jellyfishes undergo the ephyra stage. The tiny ephyrae typically swim free from the immobile scyphistoma polyps. During the dispersal stage, the ephyra ensures that the jellyfish travels to a more suitable environment and prevent the jellyfish from laying all its eggs in one place due to environmental changes or catastrophic events. In less than a year, the ephyrae will mature sexually into medusas. During this stage, the larval stage, most of the adult characteristics are present except the gonads.

Obelia: w.m. under microscope 4x

Obelia medusae under microscope 4x

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Obelia is in the phylum Cnidaria, order Leptomedusae, and class Hydrozoa, which consists of marine and some freshwater animals. These animals have both polyp and medusa stages in their life cycle. In coastal and offshore plankton around the world, the medusa stage is very common. Cnidaria species are all aquatic and are relatively simple in structure. Obelia is usually found within 660 ft from the water’s surface, grows in intertidal rock pools and in low water of spring tides. Their polyp colony reproduces asexually. On Obelia mature colony surface, there are individual hydranths called gastrozooids. Gastrozooids can be expanded or contracted and aid in the growth of this organism. They can also be specialized for defense. The physical appearance of the male and female medusae velum are indistinguishable, and can only be determined by observing the inside of the gonads to see if it contain sperm or eggs. However, the medusae reproduce sexually,  it releases sperm and eggs that fertilize to form a zygote. They are diploblastic, with two true tissue layers; an epidermis and a gastrodermis.  They have incomplete digestive tracts where the food enters, is digested and expelled through the same opening and carry a nerve net with no brain or ganglia.




Blue Acropora in the Lizard Island Lagoon by Ryan McMinds is licensed under CC BY 2.0


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