Slide 1: 1 BEATIFUL SEA LIFE Dr. R. K Pillai, Dept of Zoology, Hindu College, Moradabad
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Diversity in Living World Phylum Mollusca General Characters : 2 General Characters 1. Number of species about 93,000 (living) and 70,000 (extinct) (the second largest phylum in number of species, the first being Arthropoda).
2. The term Mollusca (L., mollis, soft) was originally proposed by Jonston (or Jonstonus) in 1650 for cephalopods and barnacles.
3. De Blainville (1825) altered the name Mollusca to Malacozoa which was not popular among scientists
4. Malacology is the study of Mollusca and Conchology is the study of shell of Mollusca .
5. Mollusca comprises some of the best known invertebrates like, snails, slugs, clams, squids and octopuses.
6. Molluscs are triploblastic, bilaterally symmetrical (or secondarily asymmetrical ), unsegmented, coelomate protostomes.
7. Coelom limited to small spaces around nephridia, heart and part of intestine.
8. Principal body cavity is a haemocoel (open circulatory system). Numbers of species : 3 Numbers of species Mollusca - Second largest phylum Slide 4: 4 Myxozoa Arthropoda Annelida Mollusca Lophophores Hemichordata Vertebrata Other
pseudocoelomates Nematoda Porifera Ctenophora Cnidaria Placozoa Platyhelminthes Nemertea Ciliophora Sarcomastigophora Microspora Apicomplexa Mesozoa Echinodermata Crustacea Chelicerata Uniramia Other Chordata Generalized Mollusc : 5 Generalized Mollusc Body Plan : 6 Body Plan Mantle cavity Ctenidium Pericardial cavity Metanephridium Radula Gonad Stomach and digestive gland Foot Slide 7: 7 9. Heart lies in pericardial chamber and composed of separate ventricles and atria.
10. The body is covered by a skin fold mantle with shell glands which secrete calcareous spicules, shell plates or shells.
11. Most molluscs secrete a shell of calcium carbonate that protects and supports their soft tissues.
12. The body is organized into three general regions: head, foot and visceral hump.
13. The head bears the mouth and sense organs.
14. The muscular foot is primitively used for locomotion, crawling in snails and digging in mussels, but in squid it is modified into tentacles for capturing prey.
15. The visceral hump contains the digestive tract and other visceral organs.
16. Digestive system complete with a digestive gland or liver
17. Molluscs typically employ a rasping organ called radula which is armed with rows of chitinous teeth. Slide 8: 8 18. The radula is protruded from the mouth and worked back and forth to rasp the food into fine particles.
19. Blood with amoebocytes, respiratory pigment is copper containing haemocyanin dissolved in plasma.
20. Respiration by ctenidia (gills) , lungs or both; sometimes direct.
21. Excretion by large, complex metanephridia (Kidneys, Organ of Bojanus).
22. Nervous system with paired ganglia, commissures and connectives.
23. Sense organs include eyes, statocysts and osphradia (a chemoreceptor to test chemical nature of water).
24. Reproduction sexual, dioecious or monoecious.
25. Fertilization is generally external, development direct or through free larval forms like trochophore, veliger, glochidium, etc.
26. Most molluscs are marine, some freshwater and few terrestrial.
27. Most molluscs are herbivores, but some (e.g., squid) are active predators. Classification : 9 Classification Molluscs are classified mainly based on shell and foot. There are seven classes of molluscs:
2. Polyplacophora (Amphineura)
5. Gastropoda (Univalvia)
6. Pelecypoda (Bivalvia)
7. Cephalopoda Class I Aplacophora (Gr., a, without; plak, plate; phoros, to bear) : 10 Class I Aplacophora (Gr., a, without; plak, plate; phoros, to bear) 1. Also called solenogasters.
2. Benthic, marine, vermiform molluscs.
3. No shell, epidermis secretes aragonite (calcareous) spicules or scales.
4. Mantle cavity rudimentary, without eyes, tentacles or nephridia.
5. Surface dwellers on corals and other substrates and are carnivorous, frequently feeding on cnidarian polyps.
6. Approximately 120 species (Neomenia, Chaetoderma, Falcidens, Scutopus, etc.) Class II Polyplacophora (Gr., polys, many; plak, plate; phoros, to bear) : 11 Class II Polyplacophora (Gr., polys, many; plak, plate; phoros, to bear) 1. Commonly called chitons, inhabitants of hard substrates in intertidal shallow marine water.
2. Head reduced, body flattened, elongated, with broad ventral foot.
3. Without eyes and tentacles.
4. Mantle forms thick girdle that border shell plates.
5. About 1000 described species (Choriplax, Chiton, Katharina, Mopalia, Tonicella, etc.) Chiton Class III Monoplacophora (Gr., mono, one; plak, plate; phoros, to bear) : 12 Class III Monoplacophora (Gr., mono, one; plak, plate; phoros, to bear) Known only from fossils until 1952, when first living species Neopilina galatheae was discovered by Danish Galathea Expedition from 3,570 meters in the Pacific off Costa Rica.
The most primitive mollusc having characters of annelids.
3. Only mollusca having segmentation (internal) or metamerism
4. A ‘living fossil’, a connecting link between annelids and molluscs. Slide 13: 13 5. With a single cap-like shell.
6. Mantle cavity shallow, around foot enclose 3-6 pairs of ctenidia, 2 pairs of gonads, 3-7 pairs metanephridia.
7. Head small, tentacles present only around mouth.
8. About 25 described species, most live at considerable depth (Neopilina, Monoplacophorus, Rokopella, Vema) . Class IV Scaphopoda (Gr., scapha, boat; podos,foot) : 14 Class IV Scaphopoda (Gr., scapha, boat; podos,foot) 1. Commonly called tooth shells or tusk shells.
2. The most distinctive characteristic is a tubular shell that opens at both ends.
3. The head and foot project from wider end of the shell.
4. With proboscis, radula and clubbed contractile tentacles (captacula).
5. Live mostly buried in the substrate feed on foraminiferans.
6. Nearly 900 living species (Dentalium, Pulsellum, Cadulus, Gadila, etc.). Slide 15: 15 Scaphopod Anatomy Class V Gastropoda(Gr., gaster, belly; podos,foot) : 16 Class V Gastropoda(Gr., gaster, belly; podos,foot) 1. Largest and most varied molluscan class comprising snails and slugs.
2. Terrestrial molluscs found only in this class.
3. Asymmetrical with single, usually spirally coiled shell.
4. During development, visceral mass and mantle rotate 90-180o on foot, a phenomenon called torsion.
5. Head with statocyst, eyes, 1-2 pairs of tentacles.
6. Foot large and flat.
7. About 70,00 living species (Pila, Aplysia, Doris, Patella, Limax, etc.). Snail Slide 17: 17 Snail Slug Limpet Slide 18: 18 Torsion in Gastropoda Class VI Pelecypoda ( = Bivalvia ; = Lamellibranchiata)(Gr., pelekus, hatchet; podos, foot) (L. bis, twice; valva, leaf) : 19 Class VI Pelecypoda ( = Bivalvia ; = Lamellibranchiata)(Gr., pelekus, hatchet; podos, foot) (L. bis, twice; valva, leaf) 1. The second largest molluscan class comprising clams, mussels, oysters , scallops and shipworms.
2. Laterally compressed, shell typically of two valves.
3. Head rudimentary, without eyes or radula.
4. Foot laterally compressed, usually without a sole.
5. Mostly filter feeding, usually dioecious, veliger or glochidium larva. Slide 20: 20 6. Mostly marine, few fresh water.
7. With nearly 20,000 living species of marine or fresh water molluscs (Unio, Anodonta, Mytilus, Teredo, Pecten, etc.)
8. Teredo is commonly known as ‘shipworm’; it is destructive to wood in sea water.
9. Pinctada vulgaris (Indian Pearl Oyster): Pearl is secreted by mantle on some external particles entangled in skin which causes irritation to animal. Pearl Oyster Slide 21: 21 Oysters Pearl formation : 22 Pearl formation Developing pearl Epithelium Shell Irritant lodged between shell and mantle
Layers of nacre secreted around foreign material Shipworms : 23 Shipworms Class VII Cephalopoda (Gr., kephale, head; podos, foot) : 24 Class VII Cephalopoda (Gr., kephale, head; podos, foot) 1. Most specialized molluscs comprising cuttlefish, squids, octopods and nautiloids.
2. Most active molluscs, the foot is located on the head modified in the form of oral arms.
3. Head is distinct and large with well developed eyes and a ring of tentacles.
4. Part of the foot forms, a funnel-shaped siphon.
5. Locomotion is by expelling water in jet through siphon (Jet propulsion). Cuttlefish Slide 25: 25 6. Ink glands in some squids for offence and defence.
7. When the squid is attacked, it emits a cloud of inky fluid through its siphon.
8. This ‘smoke screen’ interferes with the visual and; chemoreceptors of the predator and thereby helps the squid to escape.
9. Cephalopods are exclusively marine and carnivorous.
10. Nautilus has an external shell, but in others the shell has been reduced and enclosed within the body or lost entirely.
11. About 900 species (Sepia, Loligo, Octopus, Nautilus, Spirula, Argonauta, etc.) Octopus Squid : 26 Squid Dorsal Ventral Posterior surface Right Left Slide 27: 27 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cephalopod Eye Nautilus : 28 Nautilus Up to 94 tentacles
Shell with many chambers
Lives in outermost chamber Trochophore Larva : 29 Trochophore Larva A larval form common for annelids and molluscs Phylum Mollusca : 30 Phylum Mollusca Subphylum ACULIFERA
Class Polyplacophora — chitons
Chiton — Sea mica (Mail shell)
Class Scaphopoda — tooth shells, tusk shells
Dentalium— Tusk shell Slide 31: 31 Class Gastropoda — snails and slugs
Patella — Limpet
Fissurella — Keyhole limpet
Trochus — Top shell
Pila — Apple snail
Crepidula — Slipper shell
Cypraea — Cowrie
Natica — Star shell
Buccinum — Whelk
Doris — Sea lemon
Aplysia— Sea hare
Turbo — Cat's eyes
Vermetes— Worm shell Slide 32: 32 Nassa — Mud shell
Conus — Cone shell
Bulla — Bubble shell
Pteropod — Sea butterfly
Littorina — Periwinkle
Philippa — Sundial shell
Janthina — Violet shell
Cyphoma — Flamingo tongue shell
Bursa — Frog shell
Columbella — Dove shell
Helix — Land snail
Limax — Grey Slug Slide 33: 33 Class Pelecypoda (=Bivalvia)
— clams, mussels
Unio — Freshwater mussel
Mytilus — Sea mussel
Dreissena — Zebra mussel
Spondylus — Edible oyster
Pinctada — Pearl oyster
Pecten — Scallop
Teredo — Shipworm
Solen — Razor clam
Tridacna — Giant clam
Mya — Soft shell clam
Pinna — Pen shell
Anomia — Jingle shell Slide 34: 34 Class Cephalopoda (Siphonopoda)
— squid, octopus, cuttlefish
Sepia — Cuttlefish
Loligo — Squid
Octopus — Devilfish Spirula — Ram's horn
Todarodes — Arrow squid
Architeuthis — Giant squid Slide 35: 35 Architeuthis (Giant Atlantic squid)
Largest of all invertebrates, length 20 meter including tentacles, weight exceeding 1 ton.
The eyes are upto 20cm in diameter, the largest animal eye on record. Slide 36: 36 A true Objective Hand Book
“A conscientious teacher of Zoology who has been guiding students for various competitions for last 30 years has put his best in this book” 11th Edition Slide 37: 37 End