ANIMALIA

1. KINGDOM ANIMALIA PHYLUM MOLLUSCA Deanne L. de Asis Jessica Consad

2. introduction Definition Diversity content Life History and Ecology Taxonomy Morphology conclusion Evolution Relations with Humans

3. introduction

4. MOLLUSCA • is one of the most diverse groups of animals on the planet. It includes familiar organisms like snails, octopuses, squid, scallops, oysters and chitons.. • is the largest marine phylum, comprising about 23% of all named marine organisms. • Numerous mollusks also live in freshwater and terrestrial habits. • also includes some lesser known groups like the monoplacophorans, a group once thought to be extinct for million of years until one was found in 1952 in the deep ocean of the coast of Costa Rica. • they are a clade of organisms that all have soft bodies which typically have a “head” and a “foot” region. Often their bodies are covered by a hard exoskeleton, as in the shells of snails and clams or the plates of chitons. • they have been important to humans throughout history as a source of food, jewelry, tools and even pets. • their shells are considered quite beautiful and valuable. • they can also be nuisance, such as the garden snail; and they make up a major component of fouling communities both on ducks and on the bulls of ships. • they also have a very long and rich fossil record (more than 550 mya), making them one of the most common types of organism used by paleontologists to study the history of life.

5. MOLLUSCA Definition • Molluscs and mollusks are words derived from the French mollusque, originated from the Latin molluscus, from mollis which means soft. • Malacology is the scientific study of molluscs. • The most general characteristics of molluscs is that they are unsegmented and bilaterally symmetrical. • The following characteristics are present in modern molluscs: • the dorsal part of the body wall is a mantle (pallium) which secretes calcareous spicules, plates or shells. • the anus and genitals open into the mantle cavity. • there are two pairs of main nerve cords. Fig. 1 Dorsal view of a chiton with a spike bearing mantle.

6. MOLLUSCA Diversity • In 2001, Haszprunar estimated about 93,000 named species which include 23% of all named marine organisms. • In 2009, Chapman estimated the number of described living species at 85,000. • Molluscs have more varied forms than any other animal phylum. The majority of the species still live in the oceans, from the seashores to the abyssal zone, but some form a significant part of the freshwater fauna and the terrestrial ecosystems. They are extremely diverse in tropical and temperate regions but can be found at all latitudes. • Freshwater and terrestrial molluscs appear exceptionally vulnerable to extinction. • Estimates of the number of non-marine molluscs vary widely. However, in 2004 the IUCN (International Union for the Conservation of Nature and Natural Resources) Red List of threatened Species included nearly 2,000 endangered non-marine molluscs. Fig. 2 About 80% of all known mollusc species are gastropods (snails and slugs), including the cowry(a sea snail) pictured here.

7. content

8. MOLLUSCA Life History and Ecology • In terrestrial communities, gastropods can achieve reasonably high diversity and abundance: as many as 60-70 species may coexist in a single habitat and abundance in lead litter can exceed more than 500 individuals in four liters or litter, • Marine molluscs occur on a large variety of substrates including rocky shores, coral reefs, mud flats and sandy beaches. • Gastropods and Chitons are characteristic of these hard substrates and Bivalves are commonly associated with softer substrates where they burrow into the sediment. • TridacnaGigas are the largest living bivalve. It lives on coral reefs and many bivalves (e.g., mussels and oysters) attach themselves to hard substrates. • Some microscopic gastropods live interstitially between sand grains. Fig. 3 Many marine molluscs emerge from their eggs as planktonictrocophore larvae, however Sinistral Pond Snails (Physellasp) emerge from their eggs as young snails the whitish, jellybean-shaped organisms are ostracodes (crustacenans). Fig 4 TridacnaGigas

9. MOLLUSCA Life History and Ecology • Large concentrations of gastropods and bivalves are found in hydrothermal vents in deep sea. For example, the fauna of Paleozoic hydrothermal vent communities includes the molluscan groups Bivalvia, Monoplacophora and Gastropoda as well as the outgroupsBrachiopoda and Annelida. • Based on current understanding of relationships the earliest molluscs grazed on encrusting animals and detritus. Herbivorous grazers are relatively rare and are limited to some polyplacophorans and a few gastropod groups. • Most chaetodermomorphaplacophorans, monoplocophorans and scaphopods feed on protists and/or bacteria while neomemiomorphaplacophorans graze on cnidarians. • Cephalopods are mainly active predators as are some gastropods, while a few chitons and septibranch bivalves capture microcrustaceans. • Most bivalves are either suspension or deposit feeders that indiscriminately take in particles, typically assimilating bacteria, protists and diatoms. Fig 5 The freshwater Sinistral Pond Snail (Physellasp.) scrapes algae from the glass with its radula. Fig. 6ChitonOlivaceous: West Indian Chiton

10. MOLLUSCA Taxonomy Scientific Classification Kingdom: Animalia Superphylum: Lophotrochozoa Phylum : Mollusca (Linnaeus, 1758) Classes Aplacophora Helcionelloida Bivalvia Monoplacophora Polyplacophora Caudofoveata Cephalopoda Rostroconchia Scaphopoda Gastropoda

11. MOLLUSCA Class: Aplacophora • is an informal group of smalll, deep-water, exclusively benthic, shell-less marine mollusks found in all oceans of the world. • They are cylindrical and worm-like, and most very small, being no longer than 5 cm (2 in), some species, however, can reach a length of 3ocm(12 in) • They mainly burrow into the substrate in water regions deeper than 20m (66 ft). They are typically either carnivores or detritivores. • This class was once classified as sea cucumbers in the echinoderms. In 1987, they were officially recognized as molluscs and given their own class. This class is polyphletic , and consists of two clades: the Solenogastres and Caudofoveata,

12. MOLLUSCA Class: Bivalvia • The approximately 7, 500 living species of bivalves include each common animals as clams, oysters, scallops and mussels. • Derive their name from the two parts, or valves, into which the shell is divided. One or two large, well-developed adductor muscles are used to close shell swiftly and tightly in times of danger • Abundant in both salt and fresh water , most adult bivalves are sedentary, herbivorous filter feeders, using currents set up by cilia on their gills to bring in food particles, usually microscopic algae. • The bivalves have sensory cells for discrimination of touch, chemical changes, and light. The scallop has quite complex eyes; a single individual may have a hundred or more eyes located among the tentacles on the fringe of the mantle.

13. Most bivalves poses large gills for the purposes of respiration and filtering out of small food partiles Fig.7 Interior view of right valve showing the muscel scars. Fig. 8 Bivalve with left valve and rmantleremoved. Because of this diet and feeding, they lack radula. They poses one or two pairs of gills (ctenida) or branchia for respiration. Fig. 9 Section through the viscual mass showing the internal organs.

14. MOLLUSCA Class: Caudofoveata • Also known as Chaetodermomorpha. • Often combined with Solenogastres and termed Aplacophora. However, such grouping is not monophyletic; molecular data suggests that the Caudofoveata are a sister group to the cephalopods • They are small (1-30 mm),mainly deep sea molluscs. • They are worm-like, lacking shells or distinct muscular feet; they instead have scales and calcareous spines called sclerites, for movement. • They live by burrowing through soft sediment, and feed by lying vertically in the sediment with just the mouthparts exposed and taking in passing organic detritus. • During sexual reproduction, the female produces eggs which are fertilized and brooded, and then the larvae swim freely. Fig. 10 Anterior 1.4 mm of a fixed and stained specimen of Falcidens sp. Fig. 11 MolluschiAculiferi (Caudofoveata) molto piccoli

15. MOLLUSCA Class: Cephalopoda • Greek word “kephalópoda” means “head-feet”. • Characterized by bilateral body symmetry, a prominent head, and a modification of the mollusc foot, a muscular hydrostat, into the form arms or tentacles. • became dominant around Ordovician period. • The class contains two extant subclasses • Coleoidea – mollusk shell has been internalized or is absent; includes the octopus, squid and cuttlefish • Nautiloidea – the shell remains; this subclass includes the nautilus. • Two important extinct taxaare • Ammonoidea – the ammonites • Belemnoidea – the belemnites. • Fishing industry name this class as inkfish, referring to many cephalopods’ ability to squirk ink, • Teuthology – branch malacology. It is the sudy of cephalopods. Fig. 12 Cuttlefish (sepia) seizing a shrimp with the use of its tentacles

16. Fig. 15 Nautilus: the only shelled cephalopod Fig. 13 Dorsal view of a squid (loligo) in swimming position. The tentacles and arms are held together and functions as a rudder. Fig.14 Sagital section of nautilus. Most of cephalopods are active and predatory swimmers pressing jaws and radula. They poses eyes as complex as those of humans, and a greater capacity of learning than any other invertebrates.

17. MOLLUSCA Class: Gastropoda • a class of animals that are more commonly known as snails and slugs. • contains a vast total of named species, second only to the insects in overall number. • The fossil history of this class goes all the way back to Late Cambrian. • There are 611 families of gastropods, of which 202 families are extinct, being found only in the fossil record. • they are previously known as univalves and sometimes spelled Gasteropoda. • They are a major part of Mollusca and are the most highly diversified class in the phylum, with 60,000 to 80,000 living snail and slug species. • Representatives live in gardens, woodland, deserts and mountains; small ditches, great rivers and lakes; estuaries, mudflats, rocky intertidal, the sandy subtidal, in the abyssal depths of the oceans including the hydrothermal vents, and numerous other ecological niches, including parasitic one. • Gastropods without shell, with only a very reduced or internal shell are known as slugs. • Marine shelled species of gastropod include edible species such as abalone, conches, periwinkles, whelks, and numerous other sea snails with coiled seashells.

18. Fig. 16 Gastropod anatomy Fig. 17 Sea slug • Prosobranchia – they have a spiral shaped shell, well developed head that poses tentacles, radula, and a large flat foot for motion. • The primitive members are herbivores (rasp seaweeds and micro algae). • The advanced forms are predators (poses a long proboscis and cylindrical siphon). • Opisthobranchia (sea slugs, sea hares, nudibranches etc.) have forsaken their gills and shells. It has been speculated that their ancestors were sand-burrowers, for whom these would have been a hindrance. Fig. 15 Air-breathing land gastropod Helix pomatia, the Roman snail

19. MOLLUSCA Class: Helcionelloida • an extinct group of ancient molluscs. • the oldest known conchiferanmolluscs, that is, they had a mineralised shell. • They were mistaken for Monoplacophorans. • They were untorted and they had coiled, cone-shaped shell. • Modern reconstructions depict them as resembling snails. • They possessed a “snorkel”-like opening which was most likely used for breathing. Latouchellacostata Yochelcionella, a member of the small shelly Fauna of the Tommotian.

20. MOLLUSCA Class: Monoplacophora • Means “bearing one plate” • a class of mollusks with a cap-like shell, living on the bottom of deep sea • have known as a recent class since 1952; previously they were known from the fossil record. • Geographically widespread component of the benthos. Most are known from deep water (1800-6500 m), although several species are found shallower waters ranging up to 200 m. • They graze on microscopic organisms in mud or bottom detritus • They have a single, flat, rounded bilateral shell that is often thin and fragile; ranges in size from 3-30 mm • The heart is divided into two equal halves, each with its own auricle, ventricle and aorta. • The nervous system has small ganglia around the esophagus from which two pairs of main nerve cords run through the body; one pair supplying the foot, and the other the visceral organs. • There are two pairs of gonads, which release gametes into the water through one of the pairs of nephridia. Sexes are separate and fertilization is external.

21. Ventral view of the (fossil) shell of TryblidiumreticulatumLindström, 1880. There are visible muscular attachment scars. Head region is on the upper part of the drawing. The shell region is up to 43mm. Dorsal view of the shell of Tryblidiumreticulatum. Drawing of the shell of Pilina unguis. Head region is on the left.

22. MOLLUSCA Class: Polyplacophora • Chitons are small to large, primitive marine molluscs in the class Polyplacophora. • Amphineura – 900 to 1000 extant species of chitons in the class which was formerly known. • Commonly known as sea cradles or “coat-of-mail shells”. • They are also sometimes referred to more formally as loricates, polyplacophorans, and rarely as polyplacophores. • They live worldwide, in cold water and in the tropics. Most of them inhabit intertidal or subtidal zones and do not extend beyond the photic zone. • They live in hard surfaces, such as ion or under rocks or in rock crevices. • They are exclusively and fully marine. A contrast to the valves which were able to adapt to brackish water and freshwater, and the gastropods which were able to make successful transitions to freshwater and terrestrial environments. • They are easily recognizable because of their shells that are split into eight dorsal plates that cover the centre of their bodies.

23. Vental view of a chiton with a spike bearing mantle. Dorsal view of a chiton with a spike nearing mantle. ChitonOlivaceous: West Indian Ocean Respiration occurs through 6-80 pairs of gills in a groove around the foot. Chitonsare herbivores that have strongly toothed radulae. They are chiefly found in shallow coastal waters.

24. MOLLUSCA Class: Rostroconchia • class of extinct molluscs dating from the early Cambrian to the late Permian. • Initially thought as bivalves. • They have a single shell in their larval stage, the adult typically has a single, pseudo-bivalved shell enclosing the mantle and muscular foot. • Rostroconchs probably lived in a sedentary semi-faunal lifestyle. • Heraultipegmais the earliest, very primitive, rostroconch genus dating from the Late Terreneuvian. True Rostroconchsappeared during the Ordovician, • Ribeiroia had a single hinge in which all shell layers covered the dorsal region resulting in a very rigid shell. It’s an early primitive rostroconchs • Conocardium – the outer shell layers do not cross the entire margin, suggesting independent steps towards the bivalve flexible hinge. It is amore advanced Rostroconch. • Some evidences that conocardoidrostroconchs were the predecessors to the Scaphopoda.

25. MOLLUSCA Class: Scaphopodia • also known as tusk shells. A class of shelled marine molluscs. • Scientific name is Scaphopoda, meaning “shovel=-footed”. • Shells of species range from about 15cm to about 5 mm in length. • They live on soft substrates offshore. • Molecular data suggests that the scaphalopods are a sister group to the cephalopods, although higher-level molluscan phylogeny remains somewhat unresolved. • They live in the bottom sediments where they feed on detritus, foramanifera and microscopic animals. • Well-known in the fossil record, with claims that they appeared in the Mid-Ordovician, although the first well-identified fossils date to the Mississippian. • Most closely related to extinct molluscan class Rostroconchia. • Dentaliumhexagonum, a scaphopodmollusc. The shells were strung and used by the natives of the Pacific Northwest as shell money.

26. The shell and mantle are slenderly tubular, slightly curved (shaped like an elephant tusk) and open at both ends. • conical foot protrudes from the larger ventral end of the shell and is used for burrowing. • Delicate ciliated contractile tentacles are found around the mouth to capture food. • The large mantle cavity serves for respiration. • The aragonitic shells of scaphopods are conical and curved in a planispiral way, and usually whitish in color. • the shell resembles a miniature elephant’s tusk. • The shells are hollow and open at both ends; the opening at the larger end is the main or anterior aperture of the shell. The smaller opening is known as the apical aperture. • Some are minute, most are 4-6 cm (1.6 -2.4 in)long; some species reach 15cm (5.9 in) in length. A fossil Dentalium shell from the Pliocene of Cyprus

27. MOLLUSCA Morphology Body Parts and Functions Characteristics • Digestion and Excretion • Nervous System and Sensory Capability • Respiration and Circulation • Locomotion

28. Body Parts and Functions • There are three distinct body zones: • head-foot - contains both the sensory and motor organs • visceral mass - contains the well-developed organs of digestion, excretion, and reproduction • Mantle- a specialized tissue formed from folds of the dorsal body wall, that hangs over and enfolds the visceral mass and that secretes the shell.  • The mantle cavity, a space between the mantle and the visceral mass, houses the gills; the digestive, excretory, and reproductive systems discharge into it.  • Radula - a toothed tongue, composed primarily of chitin. It serves both to scrape off algae and other food materials and to convey them backward to the digestive tract.  In some species, it is also used in combat.

29. MOLLUSCA Characteristics Digestion and Excretion The digestive tract is complete and ciliated, with a mouth, anus and complex stomach. The pattern of the stomach varies according to the mollusks diet.  Food is taken up by cells lining the digestive glands arising from the stomach, and then is passed into the blood.  Undigested materials are compressed and packaged, then discharged through the anus into the mantle cavity and are carried away from the animals in the water currents.  This packaging of wastes in solid form prevents fouling of the water passing over the gills.         Excretory functions are carried out by a pair of nephridia, tubular structures that collect fluids from the coelom and exchange salts and other substances with body tissues as the fluid passes along the tubules for excretion. The nephridia empty into the mantle cavity.

30. MOLLUSCA Characteristics Nervous System and Sensory Capability •  Mollusks have a relatively complex nervous system, which varies from species to species reaching the height of complexity at the octopus. • The octopus is thought to be among the most intelligent of all invertebrates, with a mental capacity likened to that of a domestic cat.  • Sensory ability in some mollusks (notably the cephalopods) is considerable, with a variety of organ systems, as well as large, complex eyes. • The eyes of the giant squid are the largest in the animal kingdom, approaching the size of dinner plates.  It has recently been demonstrated that squid can successfully locate and capture transparent prey in the water by means of a specialized polarization vision.

31. MOLLUSCA Characteristics Respiration and Circulation • Mollusks (excluding cephalopods)have an open circulatory system, the blood does not circulate entirely within vessels but is collected from the gills, pumped through the heart, and released directly into spaces in the tissues from which it returns to the gills and then to the heart.  • Hemocoel ("blood cavity").  In mollusks, the hemocoel has largely replaced the coelom, which is reduced to a small area around the heart and to the cavities of the organs of reproduction and excretion.  • Cephalopods have vigorous activities that require the cells to be supplied with large quantities of oxygen and food molecules. They have a closed circulatory system of continuous vessels and accessory hearts that propel blood into the gills. 

32. MOLLUSCA Characteristics Locomotion • Herbivorous forms are commonly gliders, moving on waves of muscular contraction. • Carnivorous forms have achieved more advanced forms of locomotion. • Cephalopods swim actively by a type of jet propulsion, in which water is rapidly expelled from the mantle cavity via the siphon. • The Cuttlefish and the Sea Hares rely upon undulating lateral fins for highly maneuverable locomotion. • In the bivalves the foot has developed into a tool for burrowing, which can be remarkably rapid for example in the common Razor Shells.  • The three major classes range from: • largely sedentary or sessile filter-feeding animals, such as clams and oyster (class Bivalvia), • through aquatic and terrestrial snails and slugs (class Gastropoda) • to the predatory cuttlefish, squids, and octopuses (class Cephalopoda). 

33. MOLLUSCA Characteristics 1. Body is short and partially or wholy enclosed by a fleshy outgrowth of the body wall called the mantle. Between the mantle and the visceral mass is a mantle cavity containing components of several systems (secondarily lost in a few groups)2. A shell (if present) is secreted by the mantle and consists of one, two or eight parts. the head and the ventral muscular foot are closely allied (the foot being variously modified for burrowing, crawling, swimming, or food capture).3. The digestive canals are complete and intricate with ciliary canals for the sorting of particles. The mouth with a rudula bearing traverse rows of minute chitinous teeth to rasp food , except in Bivalvia. The anus opening in the mantle cavity. A large digestive gland and often salivary glands are present.4. The circulatory system is open, except in Cephalopoda and usually includes a dorsal heart with one or two atria and one ventricle. An anterior aorta and other vessels and many blood spaces (hemocoels) exist in the tissues.

34. MOLLUSCA Characteristics 5. Respiration occurs via one to many uniquely structured ctenidia (gills) in the mantle cavity (secondarily lost in some), by the mantle cavity, or by the mantle.6. Excretion by kidneys (nephridia), one or two or six pairs, or only a single one. They usually connect to the pericardial cavity and they exit in the mantle cavity. The coelom is reduced to the cavities of the nephridia, gonads and pericardium.7. The nervous system is typically a circumesophageal nerve ring with multiple pairs of ganglia and two pairs of nerve cords (one pair innervating the foot and another the visceral mass). 8. The sexes are usually separate(some are monoecious, a few are protandric). Gonads add up to four, two or one, all with ducts. Fertilization occurs externally or internally. Egg cleavage determinate, spiral, unequal and total (meroblastic in Cephalopoda). Trochophores and veliger larvae form, or a parasitic stage occurs(Unionidae), or the development is direct (Plumonata, Cephalopoda).9. Unsegmented (except Monoplasophora). Symmetry bilateral or asymmetrical. 

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36. MOLLUSCA Evolution Fossil Record • The Mollusca include some of the oldest metazoans known. • Late Precambrian rocks of southern Australia and the White Sea region in northern Russia contain bilaterally symmetrical, benthic animals with a univalved shell (Kimberella),resembles those of molluscs. • The earliest unequivocal molluscs are helcionelloidmolluscs that date from Late Vendian rocks. • In the Early Cambrian the Coeloscleritophora are also present (gastropods, bivalves, monoplacophorans, and rostroconchs) • Cephalopods are first found in the Middle Cambrian. • Polyplacophorans in the Late Cambrian. • Scaphopoda in the Middle Ordovician. • Late Vendian-Early Cambriantaxa bear little resemblance to the Cambrian-Ordoviciantaxa (most of which remain extant today). On the left is Inoceramus sp., a bivalve from the Cretaceous of Alameda County, CA. At right is Turritellaandersoni, a gastropod from the Eocene of Ventura County, CA.

37. MOLLUSCA Evolution Phylogeny • The phylogeny (evolutionary "family tree") is a controversial subject. • Molluscs are generally regarded members of the Lophotrochozoa , a group defined by having trochophore, larvae and, in the case of living Lophophorata, a feeding structure called a lophophore. • The other members of the Lophotrochozoa are the annelid worms and seven marine phyla.  • The molluscan shell appears to have originated from a mucus coating, which eventually stiffened into a cuticle. • An analysis in 2009 that used both morphological and molecular phylogenetics comparisons concluded that the molluscs are not monophyletic. • A 2010 analysis similarly concluded that the molluscs are not monophyletic, this time suggesting that solenogastres are more closely related to the non-molluscantaxa used as an outgroup than to other molluscs.

38. MOLLUSCA Relations with Humans Uses by Humans • Bivalves such as clams and mussels, have been an important food source since at least the advent of anatomically modern humans—and this has often resulted in over-fishing. • bivalves and some gastropods whose shells are lined with nacre are valuable.The best natural pearls are produced by pearl oysters Pinctadamargaritifera and Pinctadamertensi, which live in the tropical and sub-tropical waters of the Pacific Ocean. Natural pearls form when a small foreign object gets stuck between the mantle and shell. • Mollusc shells were used as a kind of money in several pre-industrial societies. When used for commercial transactions they functioned as commodity money.

39. MOLLUSCA Relations with Humans Threats to Humans • STINGS AND BITES • When handled alive, a few species of molluscs can sting or bite and with some species, this can present a serious risk to the human handling the animal. • All species of cone snails are venomous and can sting when handled (carnivorous gastropods that feed on marine invertebrates ). Their venom is based on a huge array of toxins, some fast-acting and others slower but deadlier—they can afford to do this because their toxins require less time and energy to be produced compared with those of snakes or spiders • PESTS • Schistosomiasis(also known as bilharzia, bilharziosis or snail fever) is "second only to malaria as the most devastating parasitic disease in tropical countries. The parasite itself is not a mollusc, but all the species have freshwater snails as intermediate hosts. • snails and slugs, can be serious crop pests and when introduced into new environments can unbalance local ecosystems.

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