Platyhelminthes
From Microcosm Aquarium Explorer
[edit] The Flatworms & Ribbonworms
Number of Living Species: 18,500.
Common Characteristics: soft-bodied, bilaterally symmetrical, dorso-ventrally flattened; head may or may not carry tentacles and eyes; common mouth/anus and no central body cavity.
Noteworthy Behaviors: most move slowly by using tiny hairlike cilia; large species (polyclad flatworms) propel themselves with muscular undulations; some free-living reef species are flamboyantly pigmented as a warning to predators.
Class Turbellaria (free-living flatworms): 3,000 species
From Reef Life by Denise Nielsen Tackett.
[edit] Aquarium Care
These common hitchhikers often have frilly edges that undulate in waves down the animal as it moves. They often have two small tentacles at the front end, with C-shaped eye spots near the tentacles.
Polyclads are thin (most less than 1 mm thick), oval, rectangular, or somewhat teardrop-shaped. Over 100 described species include some of the most strikingly colored and beautiful marine animals.
Most appear to be predators on tunicates or other sessile animals, and as we are unable to maintain tunicates in the aquarium, we have a long way to go before we can maintain their flatworm predators. Some species, common in reef tanks, prey on snails.
Excerpt from: A PocketExpert Guide to Marine Invertebrates
By Ronald L. Shimek, Ph.D.