Snails were one of the favourite foods of the Roman gourmet and they appeared on the menus of feasts marking special occasions. Octopus have eight arms while squid and cuttlefish have eight arms plus two other specialized arms, called tentacles. Very few gastropod species transmit animal diseases; however, the flukes that cause human schistosomiasis use gastropods as intermediate hosts. The group includes more than 800 species (and new species are still being found . Galba longiscata (a basommatophore) from southern England lived in fresh waters during the Palaeogene (Eocene to Oligocene). Hard part morphology: # 486 & unnumbered Fasciolaria. The largest mollusk in the world is a cephalopod, the colossal squid (Mesonychoteuthis hamiltoni), known to grow to between 39 and 45 feet and weigh up to 1,650 pounds. Avoiding the confusion altogether, some scientists refer to all eight armed cephalopods as octopods, reserving the term octopus for only those within the genus Octopus. Uexkull starved a group of octopuses for fifteen days and then presented them with hermit crabs carrying anemones on their shells. Others are carnivores and use the radula to penetrate the shells of their prey. The uncanny similarity between the argonaut egg casing and the nautilus shell indicate itmay be an example of convergent evolution. Opisthobranchs may have a coiled shell, but some have lost the torsion characteristic of gastropods and have become bilaterally symmetrical. But the nautilus uses its chambered shell like a submarines ballast system to pass fluid and gas between the chambers to adjust the internal shell pressure and keep the gas a consistent volume as it swims between varying ocean depths. The soft-tissue mantle covers the internal organs and is used to build the shell (when present). The largest freshwater snails, Pomacea from South America, reach nearly 10 centimetres in diameter, and the largest marine snail, the Australian Syrinx aruanus, occasionally grows to more than 0.6 metre (two feet). The sucker rings of squids are composed of "suckerin" proteins that are similar in strength and structure to the protein found in spiders silk. Identify a fossil as a gastropod or bivalve, and be able to identify bivalves to the order level using the chart provided. arthropods. An octopus is a bit more dexterous than a squid, and uses its arms for a variety of tasks including walking and handling objects. BGS UKRI. Creative Commons, HSP90. Volborthella's classification is uncertain. 1. The Dumbo octopod swims by moving its fins and pulsing its webbed arms. Shell forgo eating and instead spend her time fanning the eggs with water to keep them clean and protect them from predators. The evolutionary relationships 'within' the molluscs are also debated, and the diagrams below show two widely supported reconstructions: Morphological analyses tend to recover a conchiferan clade that receives less support from molecular analyses,[35] although these results also lead to unexpected paraphylies, for instance scattering the bivalves throughout all other mollusc groups. Perhaps, being defenseless, with soft bodies and living in a competitive environment with stronger, more agile bony fish led them to evolve especially sharp minds for problem-solving. Living species of this basommatophorean gastropod are able to secrete threads, which are attached to objects and used by the animal to ascend and descend through the water. Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. (, 2. for snails living in shifting sand or mud, snowshoe projections can stabilize them. Each limpet eats almost 6g of rock a year and when you consider how many millions of limpets there are, this amounts to a lot of chalk! Retrieved from https://www.thoughtco.com/facts-about-mollusks-4105744. where there was a large recess for the clam to retract the Remarkably, coiled cephalopods in the nautiloid group survived the extinction, but the coiled ammonites did not fare so well. lives head-down This powerpoint is split into three sections, so you can cover all the mollusks in one lesson, or split them up. They typically like in rocky environments and clamp onto We don't have any fossil evidence that this particular animal ever existed; the most any expert will venture is that mollusks descended hundreds of millions of years ago from tiny marine invertebrates known as "lophotrochozoans" (and even that is a matter of dispute). BGS UKRI. Soft part morphology. environments: I. The long egg development time is most likely a response to the relatively cold environment of the deep sea. [12], Some analyses of helcionellids concluded these were the earliest gastropods. Othersproduce and store an ammonium-based chemical that makes them neutrally buoyant. During preparation, chefs refused to use iron knives claiming that the metal left an unsavory taste and would instead use special bamboo knives. However, the giant cuttlefish (Sepia apama) experienced a significant decline in numbers during the 1990s. Local divers recall how in an area that once saw thousands of the cuttlefish, people are now thrilled to see a couple hundred. A deep-sea octopus, the dumbo octopus uses its ear-like fins to float in the water column. Octopus are famous for their sophisticated intelligence; some scientists even argue that cephalopods were the first intelligent beings on the planet. BGS UKRI. The suckers in some squids are transformed into sharp hooks to better grasp their prey, making squid a formidable underwater predator. Humans have many more, just under 100 billion, but a cephalopod is on par with dogs and some monkeys since they also carry about two-thirds of their neurons in their arms, not their head. Once a female begins to spawn, a small male will dart in and quickly mate with her, a behavior that has earned them the name sneaker males. Snails and slugs, limpets, and sea hares, No. A male sometimes initiates the interaction with a courtship display meant to attract and woo the female, though for most octopuses there is little foreplay. Share this article. A nighttime view of the Gulf of Thailand from the International Space Station. The two terrestrial families, Helicinidae and Hydrocenidae, can be found as far back as the Devonian. GB3D Type Fossils. Some live in shallow waters while others travel to depths over 16,000 feet (5,000 meters). Upon consuming all eight arms by himself, the man fell ill and required the attention of a doctor. When startled, luminescent clouds of mucus are emitted from the arm-tip light organs, leading scientists to think the glowing display is a defense mechanism. External Anatomy. Classification: A new cladistic classification of molluscs was They are also the only terrestrial molluscs, being found in virtually all habitats ranging from high mountains to deserts and rainforest, and from the tropics to high latitudes. Heterobranchia Certain molluscan subgroups secrete noxious chemicals either as a poisonous secretion of the salivary glands or as distasteful acids in mantle cells. Gastropods had colonised marine, brackish and fresh water habitats as well as the land by this time. One, the Ohridohauffenia drimica was last seen in 1983 in springs feeding the River Drim in Macedonia, Greece and was listed as extinct in 1996. They are extremely diverse in size, body and shell morphology, and habits and occupy the widest range of ecological niches of all molluscs, being the only group to have invaded the land. A female argonaut secretes an egg case that not only looks like a nautilus shell but also is used to help with buoyancy. Most marine species as well are nocturnal, and the shells of many of these species are so heavily covered with algae and other encrusting organisms that they may be mistaken for bits of rock. Bottom-dwelling octopuses usually use jet propulsion only as a means of escape, instead relying on their arms to walk across the sea floora few species even walk on two arms. Other species inhabit barren deserts where they must remain inactive for years between rains. The animal lives between, Nautilus - The only representatives of the early, shelled cephalopods that still exist today are. Notice the thickness of the These fast swimmers flourished following the loss of dinosaurs during the KT mass extinction roughly 66 mya. One type of mollusk, the aplacophorans, are cylindrical worms with neither shell nor foot. Answer key shows which groups have which characteristics. It can also cruise along the sand like a flat, banded sole fish or swim up in the water column like the venomous, spiny lionfish. Some were as small as a thumbnail while the largest measured over eight feet (2.5 meters) in diameter, taller than the average, grown man. One way scientists distinguish the nautiloid fossils from their coiled cousins the ammonoids by looking at the siphuncle. This was a time of rapid evolutionary radiation of benthic (bottom-dwelling) species and, starting in the early Eocene, pelagic (swimming) pteropods evolved as well. This would have been impermeable and thus forced the development of more sophisticated respiratory apparatus in the form of gills. Many details of cephalopod evolutionary classification continue to change as scientists find new clues from genetic testing and newly discovered fossils. There is still controversy about the phylogenetic position of some gastropod clades. Bivalves, which include but are not limited to clams, oysters, mussels, and scallops, have two shells, which are joined together at one side by a hinge. When the Sepia is frightened and in terror, it produces this blackness and muddiness in the water, as it were a shield held in front of the body.Aristotle,The History of Animals, Book IV(ca. Carnivorous predators, all cephalopods have evolved special tools to help eat their prey. Fossilized cephalopod shells were quite a mystery to people during ancient times, and are the source of several fantastical tales. This phylum includes gastropods, bivalves, scaphopods, cephalopods, and several other groups. "Rostroconchians" lived in the world's oceans from about 530 to 250 million years ago, and seem to have been ancestral to modern bivalves; "helcionelloidans" lived from about 530 to 410 million years ago, and shared many characteristics with modern gastropods. The Humboldt squid is a particularly fearsome predator that uses the toothed sucker rings to grab its prey. Cuttlefish and a few squid species either undulatetheir fins to hover. For hundreds of years seafarers have regarded octopus and squid with trepidation, fear, and awefeelings that inspired many stories, like 20,000 Leagues Under the Sea, that depict squid as terrifying beasts. However, the first confirmed cephalopod fossil is the Plectronoceras, noted by the presence of a siphuncle used for control of buoyancy. The stout, slightly curved shell shapes of the late Cambrian evolved into a variety of shapes that included coils, straight cones and domes. A number of deep-sea species are known, and a significant snail fauna is associated with hydrothermal vents. Two giant squid are displayed at the museum, the larger of the two measured 36 feet (11 meters) when alive and was probably about 2-3 years old when it became caught in a fishermans net off the coast of Spain. When actively moving, they continuously lose water. Holthuis, B.V. 1995. Life out of the water brought two big problems: how to breathe and how to prevent drying out. unnumbered brown and white: 6. Heterobranchia is a very large group that has only recently been recognized as a clade within Gastropoda. Faced with a pesky damselfish it buries six of itsarms in the sand leaving just two strategically placed and colored to look like the venomous banded sea snake (a predator of the fish). Often, cephalopods are voracious consumers. Most mollusks are marine animals that live in habitats from shallow coastal areas to deep waters. When the muscles contract the sack expands, revealing vibrant pigmentsreds, browns, and yellows. Why would pulmonate snails (Nottingham, UK: British Geological Survey.). For hovering, cephalopods have a couple of different strategies. Over 4 million metric tons of cephalopods are fished from the ocean every year, the same weight as 27,000 adult whales. Travel to the Smithsonians National Museum of Natural History Sant Ocean Hall and you will find the largest cephalopod species in the world. 5. Squid The squids are divided into quite a few groups, with over 300 species worldwide. But octopuses and cuttlefishes are also culinary favorites. Well assume youre okay with this, but you can opt out if you wish. BGS UKRI. Another type of gastropod, the murex, was cultured by theancient Greeks for itsdye, known as "imperial purple," and the cloaks of some rulers were woven from long threads secreted by the bivalve species Pinna nobilis. Between the Cambrian and Devonian, gastropods were entirely marine, but by the (Charles Livingston Bull, Library of Congress), The circles on this piece of sperm whale skin are. The first of these early cephalopod ancestors is likely Tannuella, a mollusk with a chambered shell. Most gastropods have bodies that consist of several basic parts. Octopus, squid, cuttlefish, and nautilus all have differently shaped pupils an octopus has a rectangular pupil, a cuttlefish has a w-shaped pupil, and a squids pupil is circular. As in all molluscan groups except the bivalves, gastropods have a firm odontophore at the anterior end of the digestive tract. At the ocean surface the octopus traps air within its papery shell and then propels itself underwater. Experiments by Roger Hanlon show cuttlefish expertly mimicking mottled textures, stripes, spots, and a black and white checkerboard! Though the earliest nautiloids had straight shells, by the Ordovician, which began roughly 500 mya, their shells began to diversify, some becoming gently curvedand others coiling. Most gastropods have a coiled or conical shell, which may be extremely reduced in some species or lost entirely . The most obvious external molluscan features are the dorsal epidermis called the mantle (or pallium), the foot, the head (except in bivalves), and the mantle cavity. Birds also eat cephalopods. In the paper nautilus, the hectocotylus detaches completely during sex and remains inside the femalethis is what Cuvier mistook as a worm. Cephalopod ink itself is the featured ingredient in Italian risotto nero and Spanish arroz negro. The body cavity is filled with fibrous tissue or fluid-filled spaces (hemocoel), or both. Sperm whales that wash ashore can even have large sucker scars along their body, indicating the whales engage in epic battles with giant squid while eating them. Some mollusks secrete fluids to divert or frighten a predator, to provide camouflage, or to inhibit the predators sense of smell. The cephalopods are a diverse class of mollusks. The mantle, or pallial, cavity is found between the mantle rim and the body. Lakes and rivers are also prone to the introduction of invasive species, particularly mollusks which travel attached to international seagoing ships. The radula has many teeth in each row. Scientists often find the tough beaks of squid and octopus in the stomachs of sperm whales and seals. Gastropods and Cephalopods The Molluscs All Molluscs possess some or all of the following characteristics: A muscular foot a visceral mass a mantle a radula a special respiratory gill a shell Gastropods General - snails, limpits, nudibranchs, slugs The largest class of mollusc - over 40 thousand living species "stomach foot" (Jeffrey de Guzman/Natures Best Photography), Glowing photophores are visible on a squid (. They display vivid coloration, typically seen in squids and octopuses which is used for camouflage. shiny line that runs from one muscle scar to the other is the pallial Carboniferous some had entered non-marine waters and land snails may have BGS UKRI. This "snakehead" is from theYorkshire coast of England. siphons. Gastropods The largest group of the mollusks are called the gastropods includes snails, conchs, abalones, whelks, sea slugs, and garden slugs. Brachiopods belong to Phylum Brachiopoda, whereas bivalves belong to Phylum Mollusca, along with snails and cephalopods (e.g., octupuses and squids). The squids are two of only about a dozen giant squids on display at museums around the globe. 1. When fishing dries up in one area the shell buyers move and the fishermen usually follow. What was this The lobes are specialized centers that, among other things, process information from the eyes, controlcamouflage, and store memories. This complexity may have helped with buoyancy control, while the more basic sutures of early ammonoids helped withstand the pressure of deep water. One of these clams was a burrower, and the clam needed a place to pull in its siphons. In combination, these cones allow us to see a wide breadth of color hues. Of the roughly 100,000 known mollusk species, about 70,000 are gastropods, and 20,000 are bivalves or 90 percent of the total. It has a trochiform shell. At the top is the Pacific flying squid, in the middle is the angle squid, and at the bottom is the rams horn squid. Finally, is it octopi or octopuseshow do you know which one is correct? This group was also previously included within the "Archaeogastropoda." Some scientists argue that the acidic ocean waters following the extinction-causing meteor crash dissolved the delicate shells of baby ammonites that lived near the ocean surface, and the deeper dwelling cephalopods remained out of harms way. In 2014, cuttlefish fishing was banned from the area and there is hope that the stricter regulations will help them rebound. In bivalves a dorsal hinge ligament joins two shell valves, which are further held together by two adductor muscles with attachment points on the inner aspect of each valve. Within each chromatophore is an elastic, pigment-filled sac that is connected and controlled by several muscles and nerves. Caenogastropods have only one gill, one kidney, one auricle in the heart and sometimes a siphon and proboscis. A study of the California two-spot octopus found that an 80 percent decline in the octopus population spurred a 500 percent explosion of their prey populations, gastropods (snails and slugs) and hermit crabs. The highly varied evolutionary development of basic molluscan features has left only a few characters that may be taken as typical. A highly intelligent group of ocean dwelling creatures, the living cephalopods include the eight-armed octopuses, the ten-armed squids and cuttlefishes, and the shelled chambered nautiluses. Archaeogastropods have distinctive gills, two auricles in the heart and some have paired gills and kidneys. of the animals. In general, evolution occurs through a series of incremental changes in the DNA codea mutation occurs in DNA, which then is transcribed in the instructional RNA, which then tells the cell how to build an altered protein. The Vetigastropoda is a diverse group that includes the keyhole and slit-limpets (Fissurellidae), abalones (Haliotiidae), slit shells (Pleurotomariidae), the top shells (trochids), and about 10 other families. The cup-shaped sucker connects to the squid arm or tentacle via a thin stalk. 2. Apart from members of the Neogastropoda, the radula usually has only seven teeth in each row. "Mollusk Facts: Habitat, Behavior, Diet." The biggest living gastropod is the sea hareAplysia californicus, which is found off California and known to gt to over 7kg. Most gastropods have a coiled or conical shell, which may be extremely reduced in some species or lost entirely as in slugs. A 2018 study on cuttlefish found that once the papillae extend they become locked in place, enabling thecuttlefish to effortlessly hold their textured disguise while expending minimal energy. Cephalopods are a class of shell-bearing animals as well as mollusks with a reduced shell. on land and nudibranchs and sea hares in the ocean. By comparison, the 27cm-long African giant snail Achatina fulica, the largest land snail, weighs only 0/5kg. Fewer than 10 species live in the same area together across most of North America. A study by scientists at the Nagahama Institute of Bio-Science and Technology, The pharaoh cuttlefishs chosen disguise is just as impressive, University of California Museum of Paleontology, The University of Michigan Museum of Zoology, Curiouser and Curiouser--Octopus's Evolution Is Even Stranger Than Thought, Polarized Display Sheds Light on Octopus and Cuttlefish Vision-and Camouflage, is a Just-Discovered Underwater City Engineered by Octopuses, The Cuttlefish, a Master of Camouflage, Reveals a New Trick, Other Minds: The Octopus, the Sea, and the Deep Origins of Consciousness, Octopus - There are roughly 300 species of octopuses swimming around in the ocean today, though the exact number is continuously changing as new species are discovered. #1242: III. confuse these with some kinds of cephalopods, but the shell on Gastropods and bivalves may be the most common mollusks, but cephalopods (the family that includes octopuses, squids, and cuttlefish) are by far the most advanced. Another defense includes the ability of most solenogasters and chitons to roll the body up. The octopus is attracted to the beautiful cowrie shell and the promise of a tasty meal but upon attack they are scooped up by Hawaiian fisherman. The shell is nacreous in many of these taxa and an operculum is usually present. The land snail Helix nemoralis (a pulmonate stylommatophore) from the Quaternary of Cambridgeshire was active in cool, wet periods, but sheltered in damp soil or in shade during hotter, drier times. The largest family, Neritidae, includes many marine, brackish, and freshwater lineages. #592 While most squid have a flattened shell remnant called a pen, the ram's horn squid has an internal coiled shell that they use to control buoyancy like the nautilus. The cephalopods are a diverse class ofmollusks(a group that also includes snails and bivalves) that emerged during an explosion of animal diversity in the oceans during the Cambrian period, over 500 million years ago (mya). the rocks. However, the evolutionary history both of the emergence of molluscs from the ancestral group Lophotrochozoa, and of their diversification into the well-known living and fossil forms, is still vigorously debated. Humans have three different types of cones: one that detects red wavelengths of light, one that detects blue, and one that detects green. The cephalopods are a diverse class of mollusks (a group that also includes snails and bivalves) that emerged during an explosion of animal . Images of octopuses appear on pottery dated from 2000 BCE during the Minoan period and theres even an Egyptian hieroglyphic in the shape of a squid. The higher content of PFOA for bivalves and gastropods in the BS and YS were mainly attributed to its contents in environmental media, as mentioned above. More on morphology Neritopsina Once the sun comes up they make their way down to deeper, darker water. Of these two groups only the Neogastropoda remains as a monophyletic group. . The largest bivalve is the giant clam (Tridacna gigas), which reaches a length of four feet and weighs 500 pounds. In the early 2000s on the Philippine island of Bohol, fishermen caught up to 200 nautilus a day, but now they may only pull up a few. In the presence of ink the California market squid will begin to swim, and the Caribbean reef squid will initiate camouflage coloring. $4.00. cross-sections, and flat bottoms that clamp down effectively on rock: The organism Diet: Some gastropods are herbivores using the radula to scrape off food particles. Some authors believe, however, that they are members of the Neritopsina. When observed in 2014 during NOAA's Okeanos Explorer's Gulf of Mexico expedition, this dumbo had a never before seen coiled leg body posture. The Mollusk visceral mass includes body organs - the digestive tract, renal and reproductive organs. This one is covered in encrusting spnge (red) and These marine invertebrates have astonishingly complex nervous systems, which allows them to engage in elaborate camouflage and even display problem-solving behaviorfor example, octopuses have been known to escape from their tanks in laboratories, squish along the cold floor, and climb up into another tank containing tasty bivalves. BGS UKRI. shell, then digesting the contents. ), Aplacophorans(spicule-covered, worm-like), The phylogeny (evolutionary "family tree") of molluscs is a controversial subject. Upon coming in contact with an object, like a tasty crab or rocky ledge, the sucker surface creates a seal with the object. This method would take quite a bit of processing power compared to a multi-cone eye and can help explain why a cephalopod has such a large brain. Now scientists and governments are coordinating to try and save this ancient animal. Throughout time, over 10,000 different species swam in the ocean, though today only the seven species of chambered nautiluses remain. Gastropod shells take on a variety of shapes. Because of that, these bivalves usually build shells . Food and feeding. The rest of the cephalopods have complicated eyes. Gastropods have figured prominently in paleobiological and biological studies, and have served as study organisms in numerous evolutionary, biomechanical, ecological, physiological, and behavioral investigations. The tentacles and suckers of squid come in many shapes and sizes. Gastropods cemented) of each bivalve and the morphological evidence These cuttlefish are quite famous for their annual breeding aggregations off the coast of Australia in the Spencer Gulf, a phenomenon that attracts scientists, filmmakers, tourists, and fishermen. The septa-shell edge is called a suture, and as the ammonoids evolved the suture became increasingly intricate. A coiled shape strengthens the shell, increases maneuverability, increases the ability to cut through the water, and lowers the energy required to maintain buoyancy. Habitat: They are found in both salt (marine) and freshwater habitats and on land. Gastropods have a fossil record that extends back over 500 million years. shell is calcite. At the end of this lab, you should be able to: II. The ancestral state of this group is clearly bilateral symmetry (e.g., chitons, cephalopods, bivalves), but gastropod molluscs twist their organ systems into figure-eights, differentially develop or lose organs on either side of their midline, and generate shells that coil to the right or left. As a Greek word, the plural should be octopodes, but as Merriam Webster points out, whenever a foreign word is assimilated into the English language it assumes the English pluralityso octopuses it is. Cephalopods are famous for their eyes. The siphon is part of the mantle of the mollusc, and the water flow is directed to (or from) the mantle cavity. They occupy all marine habitats ranging from the deepest ocean basins to the supralittoral, as well as freshwater habitats, and other inland aquatic habitats including salt lakes. BGS UKRI. Ph.D. thesis, University of Washington. Diacria trispinosa, a pteropod that swam in the ocean waters of the North Atlantic during the Quaternary. After the winner was named the octopuses were released back into the ocean. Author of. The maximum development of the gastropods has been in the last 65 million years following the end-Cretaceous mass extinction event. Conchs are sometimes called univalves. Surprisingly, though, octopuses are not the best when it comes to tackling mazesthey fail to even remember a simple sequence of turns. However, most of what we know about them comes from their shellsmost belemnites had a solid tip beyond the chambered shell called a rostrum that was easily fossilized. [18] However, the shell-less Coleoidea (squid, octopus, cuttlefish) are abundant today.[19]. It is likely the acquisition of buoyancy that spurred diversification from these ancestral molluscs, since cephalopods were freed from a bottom-dwelling existence and could explore the open water column. Octopus, squid, cuttlefish, and nautilus all have differently shaped pupils an octopus has a rectangular pupil. At this stage of life, the squids light organ is not fully developed but small hairs along the photophore sweep the bacteria closer, and a molecular deterrent prohibits all bacteria except Vibriofischeri from entering. Mollusk Powerpoint Notes. Every animal in the group has one shell except for slugs because they don't have a shell. Albatrosses will plunge up to 32 feet (10 meters) deep to snatch a squid beneath the waves. ThoughtCo, Feb. 16, 2021, thoughtco.com/facts-about-mollusks-4105744. A 2006 study suggested that octopuses will play with blocks as well. In general, oceanic gastropods are most diverse in number of species and in variety of shell structures in tropical waters; several hundred species (each represented by a small number of individuals) can be found in a single coral reef habitat. The Gastropoda This is in contrast to the Arctic or subarctic coasts, where the few species present are represented by many individuals. The discovery of a mass squid graveyard off the coast of California indicates that once the female squid successfully reproduce, they dieand sink to the bottom of the ocean to over 3,300 feet (1,000 m) where they become food for deep-sea scavengers. Over and above their historical importance as a food sourceespecially in the far east and the Mediterraneanmollusks have contributed in numerous ways to human civilization. There are so many lineages and types of fossils that even cephalopod specialists often debate how they are related. evolved by the late Carboniferous. They change texture by controlling the size of projections on their skin (called papillae), creating surfaces ranging from small bumps to tall spikes. You may have noticed that throughout this website the plural of octopus is octopuses. The mantle in caudofoveates and solenogasters is covered by cuticle that contains scales or minute, spinelike, hard bodies (spicules), or both (aplacophoran level). and the pallial line runs around the edge of the shell from muscle scar