Notable characteristics of these flatworms are their flat bodies and triangular shaped heads with a clump of light-sensitive cells on each side of the head. Larger planarians may also move as a result of muscular contractions. Planarians have cilia on the underside of their bodies, which they use for movement. They have elongated bodies and most species are brown, black, or white in color. These flatworms are commonly found in freshwater habitats and in moist soil environments. Planarians are free-living flatworms from the class Turbellaria. Eduard Solà / Wikimedia Commons/CC BY 3.0 Asexual specimen from Santa Fe, Montseny, Catalonia. However, these mainly free-living worms have a specialized cavity called a rhynchocoel that some consider to be a true coelom.įlatworm Dugesia subtentaculata.

Ribbon worms of the phylum Nemertea have historically been considered to be acoelomates. Examples of flatworms include planarians, flukes, and tapeworms. Others are parasitic and often pathogenic organisms that live within other animal organisms. Some flatworms are free-living and commonly found in freshwater habitats. Commonly known as flatworms, these invertebrate animals are unsegmented worms with bilateral symmetry. They have a defined head region and display bilateral symmetry, which means they can be divided into two equal left and right halves.Įxamples of acoelomates are found in the kingdom Animalia and the phylum Platyhelminthes. They have sense organs for detecting light and food sources, as well as specialized cells and tubules for eliminating waste. Acoelomates commonly have a single orifice that serves as both an inlet for food and an exit point for undigested waste. Acoelomates commonly possess a simple digestive tract, nervous system, and excretory system. For example, acoelomates lack a cardiovascular system and respiratory system and must rely on diffusion across their flat, thin bodies for gas exchange. In addition to not having a body cavity, acoelomates have simple forms and lack highly developed organ systems. OpenStax, Features of the Animal Kingdom/CC BY 3.0 Pseudocoelomates have a similar body cavity, but it is lined with mesoderm and endoderm tissue. Eucoelomates have a body cavity within the mesoderm, called a coelom, which is lined with mesoderm tissue.

Triploblasts may be acoelomates, eucoelomates, or pseudocoelomates.

Characteristics of flat worms