Polycladida - Marine Flatworms

BULNES

The invetebrates of the Chilean Fjords

Nature in Focus

Lugar: Santiago, Chile; Año: 2009; p. 355 - 368

The marine flatworms, also known as polyclads, are colourful and delicate leaf-shaped animals that inhabit the bottom of the sea. The name “Polycladida”, which means ‘many branches’, is a reference to the shape of the intestine in these animals. Even though there are over 900 described species, little is known about their physiology, ecology or biogeography.The marine flatworms are considered to be an ancient group of invertebrates, possibly originating in the western Indo-Pacific region. The majority of the species inhabit waters between the latitudes 30° north and 30° south. They are animals that primarily live in warm water environments and the number of species diminishes in colder water areas. Similarly, the species that inhabit warmer waters are very colourful and eye-catching, whereas in the colder water zones they go unnoticed by possessing more homogenous colours. They are active predators that feed on oysters, clams, corals, ascidians, etc.Until 1882, when Ludwig von Graff created the order Polycladida, these animals were described as organisms belonging to Turbellaria, Planaria, Vermes, etc. In 1884, Lang published a book on the polyclads of the bay of Naples, which is a detailed account of this group from the waters of the Mediterranean Sea. After this very important contribution, many authors continued the work of Lang on this group. Ernst Marcus (1947–1954) and Eveline Du Bois-Reymond Marcus (1955–1968) studied polyclads on the coasts of Brazil; this is the most important contribution on the knowledge of this group in South America. In the 1980s, Faubel (1983; 1984) and Prudhoe (1985) published a series of contributions that set the basis for the current systematics of the flatworms.The most important study on the polyclads in Chile was performed by Marcus (1954b), based on the specimens collected during the Lund University Chile Expedition. The previously cited faunistic studies of the group in Chilean territory (see bibliography) were based on the species gathered during different expeditions to Antarctica, the Magellan Region, Juan Fernández and Easter Island. More recently, Baeza et al. (1997) described a new species from Chile, demonstrating the growing interest of scientists in exploring the fauna inhabiting the Chilean coastal waters. Nevertheless, almost all the scientific contributions for the polyclads are descriptive accounts of the morphology, taxonomy and systematics of the flatworms and less is known about the biology, ecology and biogeography of this group in the Chilean territory. Nineteen species are described for the Chilean fjord region (See Appendix 2 for the complete list). During the process of making this book, five species of Polycladida were collected. These will be morphologically characterised in detail in this chapter.