Lab Skill 4: Mollusca

LAB SKILL 4 MOLLUSCA I. Basic theory Mollusca are soft animals and do not have segments. The body of this animal is tripoblastic, bilaterally symmetrical, generally has a coat that can produce graft material in the form of calcium carbonate. The graft functions as a house (outer frame) made of limestone, for example clams, oysters, rice snails and snails. However, there are also Mollusca that do not have grafts, such as squid, cuttlefish, octopus or naked snails. Molluscs have muscular structures called legs whose shape and function differ for each class. Molluscs have perfect digestive organs starting from their mouthsradula(scarred tongue) up to the open anus in the mantle cavity area. Apart from that, there are also well-developed digestive glands. This open blood circulation occurs in all classes of Mollusca except classCephalopods. Respiration is carried out using gills or "lungs", the mantle or by the epidermis. The excretory organ is the kidney. The nervous system consists of three pairs of ganglions, namely the cerebral ganglion, visceral ganglion and pedal ganglion, all three of which are connected by longitudinal nerve cords. The reproductive organs are generally separate or united and fertilization is internal or external.Based on body symmetry, leg characteristics and grafts,Molluscadivided into seven classes : 1.1. Aplacophora: approximately 250 types are known, namely molluscs with a wormlike body shape, no head, legs or shell. Example Chaetoderma sp. 1.2. Monoplacophora; There are 6 known types, which are ancient mollusks with cone-shaped shells. Example:Neopilina galateae. 1.3. Polyplacophora (±600 species), characterized by the presence of 8 shell plates with many layered gill fibers, bilaterally symmetrical body. Example :Chiton sp. 1.4. Scaphopoda, elongated shell, shaped like a horn that is open at both ends, tubular mantle, cylindrical or conical legs, no gills, head without eyes. Example Dentalium sp 1.5. Gastropods (±40,000 types), consisting ofMolluscasingleshelled, although there are those without shells. The characteristics of members of this class include: The head is clearly visible, has one or two pairs of tentacles, one pair of which is retractile and is equipped with an eye at the end. Internal organs are contained within the twisted shell. Shells have various variations, the direction of rotation of the shell is generally to the right (dextral) and is generally equipped with an operculum. The type of shell that rotates to the left (sinistral) is mostly found in terrestrial gastropods. The systematics of Gastropods is somewhat confusing and according to Paul Burtsch, the Gastropoda class based on its respiratory organs is divided into 3 orders, namely Prosobranchia, Opisthobranchia and Pulmonata. 1.6. Cephalopods, there are ± 650 types of members of this class, have internal shells or without shells, the body is covered by a thick mantle. The eyes are especially well developed in Loligo. The mouth is equipped with two jaws made of chitin, shaped like a pincer and surrounded by 8 – 10 tentacles. In males, one or more tentacles change shape to become hectococtylus (subclassCeleoidea) and spandix (sub classNautiloidea), which apart from functioning as a means of copulation also to attract female animals. The only one of this class that still has an external shell isNautilus. The Cephalopoda class consists of 2 orders, namely Tetrabranchia and Dibranchia, which are based on the number of gills, tentacles and the presence or absence of shells. 1.7. Pelecypoda (Bivalvia), members of the Pelecypoda class, there are approximately 20,000 types with the followingcharacteristics: Having cupped shells (bivalves) with variations in shape and size. It has no head or mouth, legs are shaped like axes (pelecyphoda), gills are thin and layered(lamellibranchiate) located between the mantle. Both shells can be opened and closed by tightening and relaxing the adductor and retractor muscles. The way of life of this class is diverse, some immerse themselves, attaching themselves to the substrate withbyssusor other adhesives, some even swim actively. Lives in marine, brackish and fresh waters. The classification of Pelecypoda is still very diverse, however, it is generally based on the type of hinge teeth, adductor muscles and gills. Based on these criteria, pelecypods are divided into 4 orders, namely Protobranchia, Filibranchia, Eulamellibranchia and Septibranchia. Some examples of Pelecypoda species that a re widely known and have important economic value include: Mytilus edulis, Margaritifera sp, Pinctada sp, Anadara sp, Tridacna sp. II. Tools and materials Tool : 1. Preparation tank 2. Surgical Tools 3. Blade or razor 4. Glass chip measuring 25 x 10 cm 5. Microscope Material : 1. Snail (Achatina Fulica) Feather 2. shells (Anadara antiquata) Virgin 3. cockle (Anadara granosa) Green 4. mussels (Mytillus viridis) Squid/ 5. Sontong (Loligosp) Blekutak / 6. Cuttlefish (Sepiasp) Octopus ( 7. Octopussp). III. How it works 1. Draw examples of Mollusca species from each class 2. Draw a picture of each specimen above and give a description and make a taxonomic classification 3. Take measurements of the mollusk's body (morphometry). 4. Specifically for cephalopods, observe the differences between squid, blekutak and octopus. 5. Place the snail on the glass plate and let it walk, observe from under the glass how it moves 6. Stimulate by applying a stick touch to the four ends of the tentacles, the medioventral part, around the head and the posterior part. Observe how you react to the stimulus 7. Break the tip of the snail graft that is still alive, take a little of the liquid inside, then dilute it with distilled water, observe with a microscope to see if microorganisms are found.