Flatworms – Plathelminthes
The flatworms are a phylum of animals. In the sea, they are usually known for their colourfulness. However, tapeworms also belong to the phylum of flatworms. Many of them are parasites, but some have specialised as predators.
Since some of the Plathelminthes are very different species, I’m more interested in the marine species.
Anatomy & Characteristics
Flatworms are bilaterally symmetric. This means that they have a main axis, the sides of which are constructed in the same way and a main direction of movement. Accordingly, they have a head area in which nerve cells concentrate and form a simple brain. During embryonic development, they form a third germinal sheet, which enables them to develop complex organs and real muscle tissue.
Plathelminthes have a skin muscle tube which ensures the body’s stability. This consists of the epidermis, an outer ring musculature and an inner longitudinal musculature. Usually there are two layers of crossing diagonal muscle fibres between the two muscles.
Habitat & Distribution
Of all the flatworms, about a quarter live freely. These are the species we find all over the world on reefs in the sea. The other part lives parasitically on or in the host’s body.
The marine species live mainly benthic, i. e. they are bound to the seabed. In the Canary Islands we usually find them on lava reefs. So far I haven’t been able to find any species on sandy ground.
Species of Flatworms on the Canaries
I have not yet discovered many types of flatworms on the Canary Islands. This is perhaps also due to the fact that they are very small and usually well camouflaged.