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Mollusca comes from the word molluscus which means soft. Thus, Mollusca is a group of animals that have soft bodies. There are approximately 1500 species of Mollusca animals that are scattered in nature. Habitat is in the sea, fresh water, and on land. Some examples of animals from the phylum Mollusca, namely oysters, snails and squids.
Characteristics of the Phylum Mollusca
- Has a soft body
- Does not have the segments on the body
- Included in the triplobastic animal coelomate, meaning that it already has a true body cavity and consists of three body layers.
- Has a variety of sizes and shapes.
- It is bilateral in symmetry, meaning that the body can be divided into two equal parts and symmetrical.
- The body is divided into three main parts, namely the legs, visceral mass, and the mantle (shell / bowl). In the shelled Mollusca, the shell is made of calcium carbonate.
- Has legs that function to move or dig the substrate.
- Has a nervous system in the form of a nerve ring
- His esophagus spread.
- The digestive system consists of the mouth, esophagus, stomach, intestines, and anus.
- Reproduction is done by means of internal fertilization.
- It is a hermaphrodite animal, which means that it has male and female genitals in one individual (one home), but there are some Molluscs who have separate genitals (have two households).
Classification, Reproduction, Examples of Molluscs
Based on its characteristics, Mollusca is divided into five classes, namely:
1. Gastropoda Class
Gastropoda comes from Greek, gaster means stomach and podos means feet. Thus, Gastropods are animals with stomach legs. Gastropods generally have conical and spiral shells. On the head there are long and short tantacles. On the long tentacles there are eye spots that distinguish dark and light. Meanwhile, the short tantacle is used as an organ of smell.
Gastropods have gills, lungs, or skin as a means of breathing. Gastropods already have a complete digestive system and a mouth (radula). Examples of gastropods that live on land are snails, snails (Acathina fulica), greedy snails (Amphidromus); Those that live in water are kreco (Paludina), and rice slug (Limnea javanica).
Gastropods are hermaphrodite animals, but fertilization still occurs by involving other individuals through external fertilization. Gastropods can be used as a source of food and as a beautiful decoration or display. Besides being beneficial, gastropods can also be harmful because they can become pests such as golden snails which are pests of rice.
2. Class Bivalvia / Pelecypoda
Bivalves have two shells that can open or close and are moved by several large muscles. Bivalves’ feet are specialized to live in silt or fine sand. On the posterior side of the Bivalvian shell there are two slits called siphons. The siphon functions as a place for water and metabolic waste to enter and exit.
Generally, Bivalves have only one genitalia, male or female. Bivalves fertilization occurs externally, that is, the sperm and egg are released into the water and fertilization is assisted by currents. If fertilization is successful, the larvae that are formed will swim freely to find a place to settle on the bottom of the water and develop into adults. Bivalves serve as a source of food for humans and can be used as decoration / souvenirs. Examples of Bivalves are, meleagrina (pearl shells), anadonta (mussels, live in fresh water), ostrea (edible oysters, live in the sea), Panope generosa (giant clams), Chlamys opercularis, Pinctada maxima (pearl oysters), and Mytilus. viridis (green clams).
3. Class Cephalopod
Cephalopod consists of the word cephale which means head and podos which means feet. Thus, Cephalopods are animals that use their head as a means of movement (feet). Cephalopods have tentacles on the head that are useful for capturing prey. Cephalopods are carnivores. In the mouth of cephalopods, there are teeth to bite and tear their prey. The skin contains chromatophores, which are pigments that can change skin color.
Cephalopda already have separate genitals, so that they can be distinguished between male and female animals. Reproduction occurs by internal fertilization. Male animals channel sperm cells into the cavity of the female animal’s coat using their tantacles. The ovum will grow and develop in the female’s body, then hatch. After being mature enough, the chicks will come out of the female’s body and live freely. Cephalopods serve as a food source for humans and a link in food webs (which can serve as food for other fish). Cephalopods can be used as a source of food for humans and other living things because they have high nutritional value. Examples of cephalopods are the squid (Loligo), octopus (Octopus), and cuttlefish (Sepia).
4. Scaphopoda class
Scapophoda is an animal that has a sharp, trumpet-shaped shell that opens at both ends. Scapophoda has a high ability to survive because it can adapt to its habitat. Scaphopods live in the deep sea and are buried in sand / mud. Scaphopods already have separate genitals and reproduce by internal fertilization. The eggs will develop into trochophore and veliger larvae. Scaphopods breathe using a mantle and catch prey with a mouth equipped with a capsule. Scapophoda can be used as decoration and become detritivores for other living things in nature. An example of a species from the Scaphopoda class is Dentalium vulgare.
5. Amphineura Class
Amphineura has a flat body shape, the head is not visible, and the dorsal back is protected by a shell arranged like a house roof. On the ventral part of the body there are legs to attach to the substrate. Amphineuran has a food digestive tract consisting of the mouth, radula (tongue), teeth, stomach, intestines, and anus. Amphineura reproduction occurs by internal fertilization. The eggs are removed from the female and grow into tofokor larvae. Amphineura can be used as a food source. An example of a species from the class Amphineura is the Chiton.