Corals vs. Sponges
Corals and sponges are types of marine invertebrates that belong to two different phyla. Corals are part of phylum Cnidaria, while sponges belong to the phylum porifera. Corals can be found in subtropical and tropical waters around the world. They usually reside in shallow, coastal water on a depth of 200 feet (some species can be found on a depth of 9800 feet). Sponges can survive both in the freshwater and in the sea, from few-feet-deep water to a depth of 29000 feet. Many types of corals and sponges are beautifully colored and unusually shaped. Despite morphological similarities, corals and sponges have little in common. They have different:
Sponges consist of two layer of cells and gelatinous matrix (called mesohyl) in between. They have small, needle-like structures made of calcium carbonate (or silicon dioxide) which act as inner skeleton. Sponges do not have nervous, respiratory, circulatory and digestive system. Their body has many pores surrounded with flagellated cells which facilitate extraction of food from the water. Constantly circulating water also provides oxygen and eliminates waste products. Corals have more complex body structure than sponges. They secrete calcium carbonate which creates firm skeleton. Corals have central opening which serves both for feeding and for elimination of the waste. They have true gut and tentacles around central opening which play important role in feeding. Each coral head consists of numerous genetically identical individuals, better known as polyps.
Sponges filter food particles from the water which circulates through their body. Polyps actively hunt small fish and zooplankton using stinging cells on their tentacles. Many corals live in symbiosis (mutually beneficial relationship) with algae which perform photosynthesis (convert solar energy, carbon dioxide and water into sugar) and provide food for corals. That's why many corals grow in shallow and well-lit waters and have beautifully colored body (thanks to algal pigments).
Corals and sponges reproduce both sexually and asexually. Most corals produce both male and female reproductive cells (eggs and sperm cells) and release them into the water. Elliptical-shaped larvae, called planula, emerges from fertilized egg, settles on the sea floor and transforms into coral head. It slowly increases its size by producing new, genetically identical polyps from adult polyps in a process called budding or through division of formed polyps. Division and budding are types of asexual reproduction. Sponges produce both types of reproductive cells, but usually release only sperm cells. Water brings sperm cells into the sponge's body, where they merge with eggs and form fertilized eggs. Eggs usually stay inside the "mother's" body until they hatch. Sponges also reproduce asexually via fragmentation of the body or by forming internal buds (budding).
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