4. ), which lives along the west coast of the United States, can grow to 1.5 m or more. 6. Body has more than two cell layers, tissues and organs. Eyes may be absent in some gastropods species. Head with numerous retractile tentacular appendages which lack suckers. (A) Caribbean reef squid (Sepioteuthis sepioidea) Image courtesy of Betty Willis, Wikimedia Commons Fig. Phylum Mollusca and Phylum Echinodermata belong to the Kingdom Animalia. These animals lack a calcareous shell, but possess aragonite spicules on their epidermis. 4. Gastropoda includes shell-bearing species as well as species with a reduced shell. Gastropoda 4. A flat creeping ventral foot is present. This class contains the cephalopodscephalopod, member of the class Cephalopoda, the most highly organized group of mollusks (phylum Mollusca), and including the squids, octopuses, cuttlefish, and nautiluses. 2. The heart consists of two auricles and a ventricle. Monoplacophora 2. 3. 5. Upper Cambrian to recent; 25,000 living and 10,000 fossil species. 3. The nervous system is highly developed; the principal nerve ganglia are aggregated around the oesophagus and a cartilaginous skeleton supports and protects the nerve centre. 7. They have a rudimentary mantle cavity and lack eyes, tentacles, and nephridia (excretory organs). Our mission is to provide an online platform to help students to discuss anything and everything about Zoology. 6. Figure from D. R. Prothero, 1998, Bringing Fossils to Life , McGraw-Hill, p. 277; from Clarkson, 1993 - this image from LAB 3 Chapter 8: Phylum Mollusca and Biological Diversity and Evolution through Time Body without cavity. Disclaimer Copyright, Zoology Notes | Exclusive Notes on Zoology for Students, Phylum Mollusca: Features and Classification, 3 Main Classes of Phylum Annelida | Zoology, 2 Main Classes of Phylum Hemichordata | Zoology, Essay on Earthworm: Feeding and Digestion. Amphineura (Gk. The larva passes through trochophore and veliger stages. 11. 7. The mouth and anus are situated at the anteromedian and posteromedian ends of the foot. 249 Phylum Mollusca. The asymmetry of visceropallium is its fundamental feature. The class as a whole has become adapted for a free-swimming existence...... Click the link for more information. Content Guidelines 2. This video explains the characteristics and Classes of the Phylum Mollusca. 4. The foot is ventral and plough-shaped. The rectum pierces the pericardium and the ventricle, and opens in the exhalant siphon. Phylum Mollusca Classes: Gastropoda, Bivalvia, Cephalopoda 2 Who is in phylum mollusca? Their key characteristic is the torsion around the perpendicular axis on the center of the foot that is modified for crawling. A pair of nephridia is present within the mantle cavity. This phylum can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and … The monoplacophorans were believed extinct and only known via fossil records until the discovery of Neopilina galathaea in 1952. The key difference between Mollusca and Echinodermata relies on the habitat of the organisms belonging to these two classes.Molluscs live in both terrestrial and aquatic environments while echinoderms live strictly in marine environments. Mollusks are soft-bodied invertebrates of the phylum Mollusca, usually wholly or partly enclosed in a calcium carbonate shell secreted by a soft mantle covering the body. Many taxa remain poorly studied. (B) The co… Characteristics of Mollusca: Bilaterally symmetrical. Sexes are separate or united; development with a veliger or glochidiam larva. 1. 10. Watch the recordings here on Youtube! Sexual dimorphism is seen in this class of animals. 3. 8. 3. Members of class Scaphopoda (“boat feet”) are known colloquially as “tusk shells” or “tooth shells,” as evident when examining Dentalium, one of the few remaining scaphopod genera. 3. The shell is a curved tube open at both the ends, the opening being wider at the oral and narrower at the other end. Marine, found in shallow (Neomenia) and deep sea (Chaetoderma), feeding upon hydroids, corals, etc. Members of class Gastropoda have an asymmetrical body plan and usually have a shell, which can be planospiral or conispiral. The LibreTexts libraries are Powered by MindTouch® and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. 6. Locomotion in cephalopods is facilitated by ejecting a stream of water for propulsion (“jet” propulsion). Bilaterally symmetrical, free-swimming, marine molluscs. 8. 2. 1. Weird Science: An Inordinate Fondness for Beetles; Activity: Aquatic Invertebrate Behavior; Question Set: Phylum Arthropoda; Further Investigations: Phylum Arthropoda; Phylum Echinodermata. It is estimated that 23 percent of all known marine species are mollusks; there are around 85,000 described species, making them the second most diverse phylum of animals. Subclass i. Aplacophora or Solenogastres: 1. They have die characters of both the phylum Annelida and phylum Mollusca. Some species live quite high in the intertidal zone and are exposed to the air and light for long periods. The bodies are generally very soft and are covered by the hard exoskeleton. Visceral complex usually incorporated into head-foot complex, leading to secondary external bilateral symmetry. 6. Unless otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0. The head bears a pair of large, simple eyes. 2. 5. They are bilaterally symmetrical, triploblastic and coelomate animal. Shell usually symmetrical, with dorsal hinge and ligament, and closed by 1 or 2 adductor muscles. The mouth is bounded by two pairs of labial palps acting as lips. The Phylum Mollusca is considered one of the largest phyla in the animal kingdom.There are at least 100,000 known species. Primarily aquatic gastropods, retaining larval torsion and nervous asymmetry. Example: Nautilus pompilius. The shell consists of eight separate pieces on dorsal surface and studded laterally with scales or spines to form a girdle. Mollusks is one of the most fascinating and diverse animal groups on our planet.. amphi- both + two neuron = nerve): A free-swimming trochophore larva is succeeded by a veliger. 4. Cephalopoda. [ "article:topic", "authorname:boundless", "showtoc:no" ], Differentiate among the classes in the phylum mollusca. 1. The body is covered by a shell made up of calcium carbonate. Examples: Neometiia, Proneomenia, Chaetoderma, etc. The members are known as molluscs or mollusks . The nervous system consists of cerebral, pleural, buccal, pedal, visceral and abdominal ganglia with their connectives and commissures. 3.65). Marine gastropods displaying reduction or loss of shell (shell sometimes internal). These animals bear a single conical shell, which has both ends open. The two subclasses of the class Amphineura sharing a similar primitive nervous system are very different in appearance, habitat and development. Larval stages are trochophore and veliger. Phylum Mollusca is the Large phylum of invertebrates having 100,000 species distributed in 8 classes. 5. This phylum can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda. Welcome to NotesOnZoology.com! These animals do not possess eyes, but they have a radula, as well as a foot modified into tentacles with a bulbous end, known as captaculae. Disclaimer: The Animal Diversity Web is an educational resource written largely by and for college students.ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. 4. The body is divided into head, dorsal visceral mass, and ventral muscular foot and mantle. 10. Head with one or two pairs of tentacles and one pair of eyes. Phylum Mollusca In: Atkinson LJ and Sink KJ (eds) Field Guide to the Ofshore Marine Invertebrates of South Africa, Malachite Marketing and Media, Pretoria, pp. Phylum Mollusca Classification Mollusca (mollusks) are classified into 6 classes according to their symmetry and the characters of food, shell, mantle, … The head is rudimentary and protrudes out of the posterior end of the shell. Very few are terrestrial found in damp soil. 1. 3. The shell of a bivalve is composed of calcium carbonate, and consists of two, usually similar, parts called valves. 1. 5. Classes and General characteristics of Vertebrates. The odontophore is with a simple radula. 2018. There are six classes of which three are more prominent. Members of class Polyplacophora are better known as “chitons;” these molluscs have a large foot on the ventral side and a shell composed of eight hard plates on the dorsal side. Marine molluscs with an elongated, bilaterally symmetrical flattened body and a broad foot ventrally. Class 2. 7. The phylum Mollusca includes a wide variety of animals including the gastropods (“stomach foot”), the cephalopods (“head foot”), and the scaphopods (“boat foot”).