What kind of intestines do planarians have

Left: Sheep liver fluke Fasciola hepatica stained. Right: Liver fluke preserved. They have no digestive or nervous tissue. Attachment to the intestinal wall is by a scolex , a structure that contains hooks and suckers.

The segments proglottids each contain male and female reproductive organs. Eggs are fertilized from sperm, which often come from other proglottids of the same individual. After fertilization, other organs within the proglottid disintegrate and the proglottid becomes filled with eggs. The intermediate hosts are usually pigs or cattle. They can become infected by drinking water contaminated with human feces.

The photographs below show the scolex and proglottids at increasing distances from the scolex. Those segments closest to the scolex on the left are the smallest. Those furthest away on the right become filled with zygotes, break away, and pass out with the feces.

Figure 5. Left: Taenia pisiformis anterior end. Middle: Taenia pisiformis mid region. Right: Taenia pisiformis posterior end. Skip to main content. Module 8: Invertebrate II. Search for:. Reading: Flatworms This laboratory exercise covers the following animals. The planarian has opposing muscles, circular muscles that extend around the flatworm and longitudinal muscles that extend from anterior to posterior of the flatworm. If the circular muscles contract, the flatworm changes shape to become long and thin.

If the longitudinal muscles contract, the flatworm changes shape to become short and wide. These opposing muscles push against the solid body of the worm. Unlike other animals with opposing muscles, flatworms lack a body cavity coelom. The body, instead, has cells called cellular mesoderm surrounding body organs. The cellular mesoderm provides a structure for the muscles to push against. The second way in which the flatworm moves is through the use of cilia that are located on the ventral surface epidermis.

The cilia beat in a coordinated fashion, and the flatworm is able to glide through the water. The planarian has a nervous system that allows it to respond to the environment. Two clusters of nerve cells called ganglia are located near the anterior of the animals. This pair of ganglia constitutes the brain of the flatworm. Two ventral nerve cords extend from the brain to the posterior of the planarian.

The two ventral nerve cords are connected to one another by smaller nerves. Additionally, the planarian has two visible sensory organs.

The auricles are lateral flaps near the anterior of the animal. The auricles are chemoreceptors and sense chemicals in the water. Also near the anterior are two eyespots. These allow the flatworm to sense whether it is darkness or light. It does not allow to animal to see images. Once a planarian has sensed food, moved to it, and ingested it, the food is digested by both extracellular digestion and intracellular digestion. The lining of the gastrovascular cavity the gastrodermis releases digestive enzymes into the GVC.

The ingested food is broken down to small food particles by this process. The small food particles are then taken into the gastrodermis cells by endocytosis.

Within food vacuoles formed by endocytosis, the food particles are further broken down to food molecules. These food molecules diffuse or are actively transported into the cytoplasm of the gastrodermis cell. Food is distributed from the gastrodermis to other cells of the body by diffusion primarily. Since flatworms are small distribution of food by diffusion is possible.

Food digestion produces digestive waste. This is released from the planarian through the mouth. The digestion of proteins produces nitrogen waste ammonia. The planarian has a system of tubules extending throughout its body from the anterior to posterior on both sided of the body.

These tubules are called protonephridia and they collect both excess water and much of the nitrogen waste. The tubules have pores that lead out of the body. Water and ammonia leaves through these pores. Aerobic respiration produces carbon dioxide as a waste product. This is released from the planarian by diffusion. To carry out aerobic respiration, the planarian must get oxygen to the cells of its body.

Oxygen enters the planarian by diffusion. The special features of the Phylum Platyhelminthes includes the protonephridia. These structures can be considered primitive kidneys. They are unique to the phylum. Planarians are placed in the Class Turbellaria, and these were discussed extensively above. The free-living species of flatworms are predators or scavengers.

Parasitic forms feed on the tissues of their hosts. Most flatworms, such as the planarian shown in Figure 1, have a gastrovascular cavity rather than a complete digestive system. Some species also have an anal opening.

The gut may be a simple sac or highly branched. Digestion is extracellular, with digested materials taken in to the cells of the gut lining by phagocytosis. One group, the cestodes, lacks a digestive system. Flatworms have an excretory system with a network of tubules throughout the body with openings to the environment and nearby flame cells, whose cilia beat to direct waste fluids concentrated in the tubules out of the body.

The system is responsible for the regulation of dissolved salts and the excretion of nitrogenous wastes. The nervous system consists of a pair of nerve cords running the length of the body with connections between them and a large ganglion or concentration of nerves at the anterior end of the worm, where there may also be a concentration of photosensory and chemosensory cells.

Figure 1. The planarian is a flatworm that has a gastrovascular cavity with one opening that serves as both mouth and anus. The excretory system is made up of tubules connected to excretory pores on both sides of the body. The nervous system is composed of two interconnected nerve cords running the length of the body, with cerebral ganglia and eyespots at the anterior end.

There is neither a circulatory nor respiratory system, with gas and nutrient exchange dependent on diffusion and cell-cell junctions.

Most flatworm species are monoecious, and fertilization is typically internal. Asexual reproduction is common in some groups. Platyhelminthes are traditionally divided into four classes: Turbellaria, Monogenea, Trematoda, and Cestoda Figure 2. As discussed above, the relationships among members of these classes is being reassessed, with the turbellarians in particular now viewed as a paraphyletic group, a group that does not have a single common ancestor.

Figure 2. Phylum Platyhelminthes is divided into four classes. Dactylogyrus , commonly called a gill fluke, is about 0. The class Turbellaria includes mainly free-living, marine species, although some species live in freshwater or moist terrestrial environments.

The ventral epidermis of turbellarians is ciliated and facilitates their locomotion. Some turbellarians are capable of remarkable feats of regeneration in which they may regrow the body, even from a small fragment.