Cryptocelididae Family of Flat Worms

California Flatworm, Hylocelis californica. A representative of the Cryptocelididae Family of Flatworms.

Phylogeny:  The Marine Flatworms are members of the Cryptocelididae Family are within the Phylum Platyhelminthes (Flatworms) and the Cryptocelilidae Flatworms are in the subphylum Rhabditophora. They are the simplest of the worm group and range in size from microscopic to several feet long; they are all very thin. They can be free-living or parasitic, and are found in both fresh and marine environments. The most well-known family member is the parasitic tape worm, which lives in humans and is capable of reaching several feet in length. They are in the Class Monogenea and the  Order Polycladida.

Distribution:  Cryptocelidid are found in all tropical and substropical seas. There are twenty members of the Cryptocelididae Family of which four are round along the Pacific Coast of Mexico. They are found from the intertidal zone to very deep water, including deep sea thermal vents on hard substrates and on thick stands of algae.

Morphology:  The Flatworms are are oval, to elongate oval in shape and flattened dorsally. They are unsegmented, soft-bodied invertebrates that are bilaterian, meaning they are equal on both sides of their centerline. They have lamellated rhabdites, rod-like granules in the cells of the epidermis. A second characteristic is that they have a duo-glandular adhesive system. This allows them to secrete an adhesive that attaches anchor cells to the substrate, allowing the animal to cling to the substrate. They also possess a substance that releases the anchor cells from the substrate allowing them to either cling to the substrate or become free swimming. The body has a high surface to volume ratio and has no skeletal structure. The bodies are elliptically shaped and are a tan olive color blending into their backgrounds. They possess highly branched digestive tracts of chocolate brown or dark green that form highly visible zigzag lines radiating from the central main intestine to the periphery. They are triploblastic, indicative that they are composed of three fundamental cell layers – outer ectoderm, middle mesoderm, and inner ectoderm. They have no body cavities (acoelomates) other than the gut, and they lack an anus. The same pharyngeal opening takes in food and expels waste. The gut is highly branched to allow intracellular food transport to all parts of the body with no cell being too far from the outside, making a flat shape a necessity. They take in oxygen but have no formal respiration system. The nervous system is very simple, being composed of two nerve cords running down each side of the body; they have two simple brains called ganglia, that are bundles of nerves. They do not have formal eyes but have two eyespots, which allow them to sense light. They move via tiny bristles called cilia and two layers of muscles under the skin. In an emergency they are capable of swimming via rhythmic muscular contractions. They are often associated with ascidians, bivalves and sponges. The Marine Flatworms can reach 15 cm (5.9 inches) in length. Some are brightly colored and contain toxic materials to help avoid predation.

Ecosystems Role:  Cryptocelidid are either diurnal or nighttime predators that prey upon ascidians, insects, mollusks, small worms, and microscopic matter. They are utilized by the aquarium trade on a limited basis and as lab animals, but otherwise are not significant to humans.

Reproduction: The marine flatworms are hermaphroditic with each individual producing both eggs and sperm. They lay eggs in cases that contain a single egg that are attached to the undersides of rocks. The eggs hatch in several weeks and quickly settle out benthically. They have the ability to regenerate missing body parts with ease