Rethymno, sponges (08-12a#28-1)

Rethymno (Greek: Ρέθυμνο, [ˈreθimno], also Rethimno, Rethymnon, Réthymnon, and Rhíthymnos) is a city of approximately 40,000 people in Greece, the capital of Rethymno regional unit in the island of Crete. It was built in antiquity (ancient Rhithymna and Arsinoe), even though was never a competitive Minoan centre. It was, however, strong enough to mint its own coins and maintain urban growth. One of these coins is today depicted as the crest of the town with two dolphins in a circle.

Sponges are animals of the phylum Porifera ( /pɒˈrɪfərə/; meaning "pore bearer"). Their bodies, which are full of pores and channels allowing water to circulate through them, consist of jelly-like mesohyl sandwiched between two thin layers of cells. While all animals have unspecialized cells that can transform into specialized cells, sponges are unique in having some specialized cells, but can also have specialized cells that can transform into other types, often migrating between the main cell layers and the mesohyl in the process. Sponges do not have nervous, digestive or circulatory systems. Instead, most rely on maintaining a constant water flow through their bodies to obtain food, oxygen and remove wastes. The shapes of their bodies are adapted for maximal efficiency of water flow. Water enters through the central cavity, deposits nutrients, and leaves through a hole called the osculum. All sponges are sessile aquatic animals. Although there are freshwater species, the great majority are marine (salt water) species, ranging from tidal zones to depths exceeding 8,800 metres (5.5 mi).