The ecosystem is replete with different kinds of relationships some of which are commensalistic and parasitic while other are symbiotic or mutualistic. Here, we would describe a symbiotic relationship between Convoluta roscoffensis an animal and an algae, Carteria. This relationship is known as Convoluta-Alga relationship and we shall examine the significance of this kind of relationship on the ecosystem. [stextbox id=”info” defcaption=”true” float=”true”]Convoluta roscoffensis now known as Symsagittifera roscoffensis is a small marine turbellarian 3mm long and 0.25mm broad. It is found on the sandy beaches of Normandy and Brittany where the olive-green colonies are conspicuous on the sand just above low-water mark. [/stextbox]At low tide, the animals lie exposed on the surface, but they bury themselves in the sand as soon as it is covered by the incoming tide. The green color is due to regular rows of unicellular green algae which just lie just beneath the surface
The worms are hermaphrodite but cross-fertilized. They produce transparent egg-capsules about the size of a pin’s head, each containing eight of twelve eggs. These capsules are manufactured of slime secreted by epidermal glands around the region where the eggs are extruded. Neither the capsules nor the eggs contain algae at this stage. The larvae hatch in twenty-four to thirty-six hours and move around inside the capsule. Within four days, they possess the alga cells and finally emerge form the capsule in five or six days.
The algae in this relationship belong to the genus Carteria of the Chlamydomonadineae. They possess four flagella, a four flagella, a reticulate chloroplast, a pyrenoid, and a red pigment spot. The main storage product resulting from their photosynthesis is starch: it can be demonstrated as a sheath surrounding the pigment spot. it that these algae are attracted by traces of nitrogenous substances present in the egg capsule. They penetrate into it and form cysts within which multiplication takes place. When the cysts burst, the tiny flagellate cells are taken up by the larvae and thenceforward they multiply in its body by binary fission.
For the animal, the partnership is an obligate symbiosis, but the plant cells can exist free in the water. They secrete droplets of fat and possibly protein also, into the body of the worm, and the oxygen they produce during photosynthesis is also of benefit to the animal unlike all other turbellarian general, Convoluta has no organs for nitrogenous excretion but the algal cells provide an excellent substitute. It may be recalled that nitrogen compounds are in short supply in the sea, and these symbiotic algae find in these animals an adequate supply. The excretory carbon dioxide of the animal is also utilized for photosynthesis by plants.
During its larval stages, the animals ingests a variety of solid food particles, though no true gut is ever present, the mouth and gullet leading into a series of intercellular spaces which serve as digestive vacuoles. When mature, it loses the ability to feed itself and thenceforward it relies entirely upon the algae. In the last phase of existence, it digests its partners and then dies. There is therefore, a true symbiotic union for a limited period during which the animal reproduces prolifically. All the plant cells are inevitably destroyed and thus derive no ultimate benefit from the association. Another turbellarian, Convoluta paradoxa, is found in the same regions as Convoluta roscoffensis, clinging to seaweeds in the near the low-water mark. They are solitary animals, golden-brown in color, about 2.75mm long and 0.75mm wide living symbiotically.
In their bodies, are small brown algal cells, also able to exist independently. Their arrangement I the body of the worm is rather more irregular than that found in Convoluta roscoffensis. Here, the general sequence of events and the nature of the union are much the same except that the worms do not appear to digest the algal cells in natural conditions. Also, Convoluta paradoxa, even when mature, does take in solid food particles. The worm’s dependence on the algae has not advanced as far as the condition found in Convoluta roscoffensis.