There are over 1,100 species that are found worldwide in intertidal zones as well as deep waters. The digestive system breaks down food into nutrients such as carbohydrates, fats and proteins. The flatworms are acoelomate, so their bodies contain no cavities or spaces between the outer surface and the inner digestive tract. Incomplete digestive systems only have one opening for food intake and waste removal. When the reproductive buds mature, they break off and become free-swimming medusa, which are either male or female (dioecious). The nervous system is primitive, with nerve cells scattered across the body. - Definition & Factors, What is Epidermis? The Sea Cucumber is a soft-bodied invertebratethat is related to the starfish and sea urchins. According to Ayurveda indigestion means the state of an incomplete process of digestion. In Platyhelminthes, however, this space is filled with mesenchymal tissue. This website helped me pass! Cnidaria Respiratory System | Overview, Process & Examples, Four Stages of Food Processing | Overview, Steps & Examples, CSET Science Subtest II Life Sciences (217): Practice Test & Study Guide, UExcel Anatomy & Physiology: Study Guide & Test Prep, High School Biology: Homework Help Resource, DSST Principles of Physical Science: Study Guide & Test Prep, Principles of Physical Science: Certificate Program, UExcel Basic Genetics: Study Guide & Test Prep, UExcel Weather and Climate: Study Guide & Test Prep, Create an account to start this course today. The proglottid detaches and is released in the feces of the host. The stomach is a saclike organ that secretes gastric digestive juices. The ecdysozoan phyla have a hard cuticle covering their bodies that must be periodically shed and replaced for them to increase in size. Want to cite, share, or modify this book? The other is the anus. Subphylum Myriapoda includes arthropods with legs that may vary in number from 10 to 750. - Functions & Explanation, What is Angiogenesis? All cnidarians have two membrane layers in the body: the epidermis and the gastrodermis; between both layers they have the mesoglea, which is a connective layer.