Visitors to Koh Tao who are new to scuba diving might mix up flatworms and nudibranchs. Flatworms are more primitive and lack the distinctive features of nudibranchs. Unlike nudibranchs, flatworms don’t have rhinophores (sensory tentacles) or external gills. They are generally flatter and less colorful. Yet, marine flatworms are intriguing creatures with unique adaptations that help them thrive in their underwater habitats.
Body Structure:
Marine flatworms (Platyhelminthes) have a flattened, ribbon-like body that is bilaterally symmetrical. They lack a coelom (body cavity) and possess a simple body structure. Unlike more complex animals, marine flatworms do not have segmented bodies or specialized appendages, making their form quite basic but effective for their lifestyle.
Sensory Organs:
Flatworms have basic eyespots that can detect light and dark but don't form complex images. These eyespots help them sense changes in their environment. Additionally, marine flatworms have sensory cells scattered across their bodies that aid in detecting touch and chemical signals. These sensory organs work together to help the flatworms navigate, find food, and avoid predators.
Feeding and Pharynx Details
Flatworms have a specialized feeding structure called a pharynx, which is a muscular tube that extends out of their mouth. This pharynx can be everted, or turned inside out, to help them suck in food. Once the food is engulfed, it moves through the pharynx into the digestive cavity. Depending on the species, their digestive system might be quite simple, with just one opening serving as both mouth and anus, or it might be more complex.
These flatworms primarily feed on small invertebrates, detritus (decomposing organic material), and microorganisms like algae and bacteria. They play a crucial role in cleaning up the marine environment and recycling nutrients. To find food, marine flatworms crawl over surfaces using their ciliated ventral surface, relying on their sense of touch and chemical signals to locate their next meal.
Reproduction:
Many flatworms are hermaphroditic, meaning they have both male and female reproductive organs within the same individual. This allows them to reproduce sexually by exchanging sperm with another flatworm. In addition to sexual reproduction, they can also reproduce asexually through fragmentation. In this process, if a flatworm breaks into pieces, each piece has the potential to regenerate into a new, fully functional flatworm. This ability to reproduce in multiple ways helps them adapt to different environments and conditions.
Regeneration:
Flatworms are well-known for their impressive regenerative abilities. They can regenerate lost body parts, and in some cases, even entire new individuals can grow from a single fragment of their body. This regenerative power is due to the presence of specialized stem cells called neoblasts, which can differentiate into various cell types required for rebuilding tissues and organs. This capability is a key feature of many flatworm species and plays a role in both healing and asexual reproduction.
In Koh Tao, you can encounter few types of flatworms:
- Pseudobiceros Bedordi (Persian Carpet Flatworm) is one of the marine flatworms most frequently encountered by divers in Koh Tao.
- Thysanozoon nigropapillosum (Gold speckled Flatworm)