The Cambrian Explosion: Rotifers and Many other Unfamiliar Animals Note: These links do not work. Use the links within the outline to access the images in the popup windows. This text is the same as the scrolling text in the popup windows.

I. Introduction (Page 1)

Rotifera: http://courses.ncsu.edu/zo495x/common/zo155_site/wrap/cambrian/cambrian_popups/rotifera.html

This photograph is of a typical rotifer. Most have a foot, as seen on the left side of the animal. The animal can attach to the substrate by its foot, or it can detach itself and move freely about. Rotifers are nearly transparent and their internal organs can be seen clearly through the body wall.

Rotifers: http://courses.ncsu.edu/zo495x/common/zo155_site/wrap/cambrian/cambrian_popups/rotifers.html

This diagram shows the anatomy of a typical rotifer. There is a row of cilia around the mouth that creates a current drawing small particles of food, such as yeast cells, bacteria and dead organic particles into the mouth, assisted by a muscular pharynx that sucks the food into the digestive tract. A digestive gland provides enzymes that digests the food in the stomach. The nutrients are absorbed in the intestine and the undigested material ejected via the anus. An ovary produces eggs that are also extruded from the body. The nitrogenous wastes are propelled by the flagella of flame cells through an excretory duct to the exterior of the animal. The nervous system is rudimentary, consisting of a ganglion near the head end and a few nerves leading from it.

Spines: http://courses.ncsu.edu/zo495x/common/zo155_site/wrap/cambrian/cambrian_popups/spines.html

This unusual rotifer has long, stiff spines that give it some protection from being eaten by predators.

Contract: http://courses.ncsu.edu/zo495x/common/zo155_site/wrap/cambrian/cambrian_popups/contract.html

Here are more photographs of rotifers illustrating the variation in shape of different species. Note that the one in the upper left has elongated and extended its body while the one in the lower left has contracted its body nearly into a spherical shape.

By alternately elongating and contracting they can move across a surface.

Colonial: http://courses.ncsu.edu/zo495x/common/zo155_site/wrap/cambrian/cambrian_popups/colonial.html

This is an example of a colonial rotifer. Note that the individuals are radiate from the central point where their feet are attached.

Tubes: http://courses.ncsu.edu/zo495x/common/zo155_site/wrap/cambrian/cambrian_popups/tubes.html

This species of rotifer constructs a tube from bits of debris in its environment and in which it seeks shelter. Here it is seen protruding from its tube. Note the flared mouth with the cilia beating around the edges.

Eggs: http://courses.ncsu.edu/zo495x/common/zo155_site/wrap/cambrian/cambrian_popups/eggs.html

This photograph shows a rotifer in the center and its newly laid egg in the upper left. Note the cilia around the mouth of the adult. II. Pylum Rotifera (Page 2)

III. Phylum Tardigrada (Page 3)

Tardigrada: http://courses.ncsu.edu/zo495x/common/zo155_site/wrap/cambrian/cambrian_popups/tardigrada.html

Tardigrades have eight pairs of legs, three pair along the sides of the body and one pair at the posterior end of the body. Each leg has a set of claws. In some species, the body is covered in heavy plates and there are filamentous projections protruding from between the plates. Some have a pair of eyespots.

Mouthparts: http://courses.ncsu.edu/zo495x/common/zo155_site/wrap/cambrian/cambrian_popups/mouthparts.html

This illustration shows a photograph of a Tardigrade on the left with its mouthparts clearly visible through the body wall. The arrow leads from them to a diagram showing them in more detail. Tardigrades feed by using a pair of stylets, shown her by S, to project a sharp projectile from a tube, labeled T, inside the mouth into the food item. A muscular pharynx, labeled P, then sucks the food into the digestive tract. Most tardigrades are herbivores and may pierce a moss cell and suck out the contents. There are some predatory tardigrades, however, that pierce a prey, such as a nematode or another tardigrade, and suck up its tissues. In that case, the attacking tardigrade digs in with its claws and holds it ground until the skewered, writhing prey is subdued. This has the appearance of a calf-roping contest in a microscopic rodeo.

Tardigrade Eggs: http://courses.ncsu.edu/zo495x/common/zo155_site/wrap/cambrian/cambrian_popups/tardigrade_eggs.html

Here are two examples of tardigrade eggs, one on the left with small mushroom-like protrusions and the one on the right with large folds. Each species has a distinctive egg. Some look like miniature marine mines.

Shrivel Up: http://courses.ncsu.edu/zo495x/common/zo155_site/wrap/cambrian/cambrian_popups/shrivel_up.html

The Tardigrade on the left is in the normal active state. The picture on the right shows it shriveled up in the dormant state.

IV. An unfamiliar fauna (Page 4)

The Minor Phyla: http://courses.ncsu.edu/zo495x/common/zo155_site/wrap/cambrian/cambrian_popups/minor_phyla.html