Polycladida

Common Names

Polyclads are commonly referred to as flatworms or marine flatworms. Due to their often vibrant coloration, they are sometimes also called sea slugs or ribbon worms.

Characteristics

Polyclads are characterized by their flattened, often elongated body shape, which typically ranges in size from a few millimeters to several centimeters in length. They possess a simple, unsegmented body structure with a distinct head region and a ventral surface covered in cilia, which aid in locomotion. Polyclads lack specialized respiratory or circulatory systems, relying on diffusion for gas exchange.

One of the most notable features of polyclads is their diverse and striking color patterns. Many species display intricate markings, ranging from vibrant hues of red, orange, and yellow to more subdued greens and browns. This coloration serves a variety of functions, including camouflage, warning coloration, and attracting mates.

Environments

Polyclads are found in a wide range of marine environments, including:

• Intertidal zones: They are often found under rocks, seaweed, and other debris in the intertidal zone.
• Subtidal zones: Polyclads can also be found in deeper waters, often living on coral reefs, seagrass beds, and rocky substrates.
• Deep sea: Some species inhabit the depths of the ocean, where they may play an important role in the marine food web.

References

• Polycladida: A Review of the Recent Literature - NCBI
• Polycladida - ScienceDirect
• Polycladida - WoRMS