7.+Mollusca

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Mollusca  - Akhila Sangadi ======



1. Classification/Diagnostic characteristics: Monplacophorans: - 4 clades: Chitons, Bivalves (clams, oysters, Mussels), Gastropods (snails, slugs, limpets), cephalopods (squids, octopuses, nautiloids) - most diverse group of lophotrochozoans - all share the same major body components: foot, visceral mass, and mantle
 * Protostomes: **Mollusks
 * Approximate Number of Living Species Described: **100,000
 * Major Groups: **

Foot: a muscular structure that originally was both an organ of locomotion and support for internal organs -- in cephalopods feet became arms and tentacles on the head or sensory organs or can become a burrowing organ, or the size can be greatly reduced.

- heart, digestive, excretory, and reproductive organs are concentrated in centralized, internal visceral mass - mantle - fold of tissue that covers the organs of the visceral mass; secretes hard, calcareous shell - in most extends beyond visceral mass to form a mantle cavity

Chiton - characterized by 8 overlapping calcareous plates, surrounded by a structure known as a girdle - protect chiton's internal organs and muscular foot <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- bilaterally symmetrical and the organs, particularly, the digestive and nervous system, is simple <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- marine omnivores that scrape algae, bryozoans, and other organisms from rocks with radula <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- spends most of its life clinging to rock surface with its large, muscular, mucous covered foot

<span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">Gastropods - <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">most species- rich and widely distributed molluscs have nearly 70,000 living species <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- i.e. snails, whelks, limpets, slugs, nudibranchs (sea slugs), abalones <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- only ones to live in terrestrial environments are land snails and slugs <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- here, the mantle tissue is modified into a highly vascularized lung <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- vascularized means filled or lined with blood vessels

<span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">Bivalves <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- clams, oysters, scallops, mussels <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- 30,000 species found in marine and freshwater environments <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- small head, hinged, two-part shell that extends over the sides of the body as well as top <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- the foot is used to burrow into mud and sand

<span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">Cephalopods <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- 800 living species <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- squids, octopuses, nautiluses <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- extra current syphon allows the animal to control the water content of mantle cavity <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- major marine predators <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- have a chambered external shell divided by partitions penetrate by tubes through which gases and liquids can be moved to control buoyancy <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- nautiluses have external and squids and octopuses have internal, this allows them to squeeze through tight spaces

<span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">2. <span style="font-family: Impact,Charcoal,sans-serif; font-size: 150%; vertical-align: super;">Relationship to Humans <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">Humans have relied on mollusks as a significant source of food and nutrition, particularly in coastal areas where mollusks are more abundant, and have also used mollusks in economic trade such as using the shells of mollusks as currency (e.g. the Algonquin Indians who use to thrive in New England used the shell of the great whelk and quahog to make Wampum their currency) and by turning pearls and shells into valuable jewelry. Today, humans study molluscs to identify changes to ecosystems and environments and to potentially utilize some chemicals produced by molluscs such as neurotoxins in medicine.

<span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">3. <span style="font-family: Impact,Charcoal,sans-serif; font-size: 150%; vertical-align: super;">Habitat and Niche <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">- a wide range of aquatic and terrestrial environments. They have adapted to terrestrial, marine and freshwater habitats all over the world. Even though most molluscs are marine, nearly 80% of known molluscs are gastropods. <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">- Cephalopods are found throughout the ocean. They can be found in warm water in the tropics, near-freezing water at the poles, wave-swept intertidal region, to the ocean abyss. With a few exceptions, cephalopods are marine creatures and they cannot tolerate brackish water.

<span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">4. <span style="font-family: Impact,Charcoal,sans-serif; font-size: 150%; vertical-align: super;">Predator avoidance <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">- some have shells <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">- some have nudibranchs that are aposematic, meaning to warn potential prdeators of toxicity <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">- they are very good at camouflaging by using a combination of pigmentation, iridescence, transparency, and light scattering of their skin. This form of camouflage is their primary method of avoiding predators. <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">- Some squids can change color by controlling the size of their chromatophores, which are cells that contain sacs full of pigement, using their muscles and nerves. When a chromatophore is compressed, the pigment is pushed to the surface of the squid, making it seem brighter. Some squids also have iridophores, which contain stacks of reflective plates that produce iridescence, and some have leucophores, which refelct the squids's surroundings in order to camouflage it better <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">- most cephalopods squirt ink as a defence mechanism. The ink sac is between the gills in the mantle cavity and ink is released into the exhalent jet of the syphon; they release large quantities of ink while gettinga way which in turn numb the sense of smell of the attacker <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">- the mimic octopus utilizes chromatophores but also alters its behaviour to resemble various species that predators will avoid

<span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">5. <span style="font-family: Impact,Charcoal,sans-serif; font-size: 150%; vertical-align: super;">Nutrient Aquisition <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">- the gills are also used as filter-feeding devices <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">- others feed using a rasping structure called a "radula" to scrape algae from rocks <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">- the radula is a ring of sharp teeth supported by a muscular structure - this is commonly referred to as the sharp "beak" on many cephalopods <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">- cephalopods capture and subdue prey with tentacles <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">- bivalves feed by taking water in through incurrent syphon and filtering food using gills <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">-Food is transported into the stomach after which the bolus is transported into the caecum for digestion.

<span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%;">6. <span style="font-family: Impact,Charcoal,sans-serif; font-size: 150%;">Reproduction and Life Cycle

<span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">Differentiated into seperate sexes, squid behaves differently and accordingly during reproduction, which the majority of individauls only do once due to their short lifespans. With squid closer to the surface, mating rituals can take place with females initially swimming together in circles until males fall in line, pairing up with mates based on how much interest certain female places in a given male's changing colors (a form of sexual selection). A modified arm called a hectocotylus injects spermatophores into the female head, which holds the coutnerpart female organs. Meanwhile, with squid deeper down the giant squid (//Architeuthis dux)//, a penis stays within the head until intercourse, which is when it more articulately injects spermatophores into the female. With smaller squid with shorter penises and hectocotyli, the male must wrap himself around the female, making her uncomfortable and possibly leading her to reject him. Thus, species like //Onykia ingens// developed a longer penis that becomes erect and inseminate the female from afar, thereby avoiding her wrath. Thus, besides some sessile barnacles, squid exhibit the largest penises in ratio to the rest of the organism's body.



<span style="font-family: Trebuchet MS,Helvetica,sans-serif; vertical-align: super;">Comparison of //<span style="color: #2a2a2a; font-family: Merriweather,serif; font-size: 16px; vertical-align: baseline;">Onyk ////<span style="color: #2a2a2a; font-family: Merriweather,serif; font-size: 16px; vertical-align: baseline;">ia ingens //penis before (A) and after (B) erection

<span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">The difference in mechanism can be easily observed as factor of speciation. Lack of gene flow exists between penile and arm inseminating species due to such a mechanism. In fact, //A. dux// exhibits both structures, although it is unknown wheter the perceived hectocotyli are actually used for spermatophore transfer anymore.

<span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">7. <span style="font-family: Impact,Charcoal,sans-serif; font-size: 150%; vertical-align: super;">Growth and Development

<span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">Unlike most large fish, the squid grows and devleops rapidly. This quick growth is accompanied by a short lifespan, the giant octopus only lives up to three years. They reach maturity at around twelve inches and grow even more to almost sixty feet in a just one year. <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- Most mollusks go through the spinal cleavage <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- the Development of mollusks can proceed directly to the juvenile form, or undergo the swimming trochophore larval stage <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- Mollusks also go through torsion, which include a rotation of the visceral mass that chagnes the relative location of body regions

<span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">8. <span style="font-family: Impact,Charcoal,sans-serif; font-size: 150%; vertical-align: super;"> Integument <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">The system is enclosed in the mantle, which consists of 2 swimming fins for each side. <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">The skin is covered in chromatophores, allowing the squid to change color based on the enviornment. <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">The two sides of the squid are different colors, as the bottom is lighter than the top. This helps provide camoufage from prey and predators. <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">Cephalopod bodies are covered by an enveloping structure, called a mantle or pallium, which in other mollusca species would secrete the hard shell. <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">The skin of differetn cephalopods can have different coverings, such as open-coiled, kinked, twisted, or hooked, and each type of skin covering serves a different purpose specific to that species, such as swimming faster or latching on to prey easier.

<span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">9. <span style="font-family: Impact,Charcoal,sans-serif; font-size: 150%; vertical-align: super;">Movement <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">- chitons move slowly, by means of rippling waves of contraction <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">- gastropods move by gliding on their muscular foot ; in some species (sea butterflies and heteropods) foot is swimming organ that helps animal move through open ocean waters <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">- Squids can rely on their speed of movement to keep them afloat, or they can achieve neutral buoyancy; they do not have to stay afloat since animals like these also move in short bursts when catching prey. (1)

<span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">10. <span style="font-family: Impact,Charcoal,sans-serif; font-size: 150%; vertical-align: super;">Sensing the Environment <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">- in some mollusks, such as the marine cone snails, the radula has been modified into a drill or poison dart <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">-Their eyes function like sophisticated camera to better detect light. <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">- cephalopods have a head with complex sensory organs <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">- head is like large, branched foot that bears tentacles and sipon <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">- large, muscular mantle provides an external supporting structure <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">- Cephalapods are equipped with lights with numerous functions: counterillumination, communication, prey-capture, defense, path-finding and etc... (1) <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">Cephalopods have the most complex nervous systems of all invertebrates. [|Source]

<span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">11. <span style="font-family: Impact,Charcoal,sans-serif; font-size: 150%; vertical-align: super;">Gas Exchange <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">- <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 130%; vertical-align: super;">have an open circulatory system <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 130%; vertical-align: super;">- have a blood chamber <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 130%; vertical-align: super;">- have body cavity vestiges for major organs <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 130%; vertical-align: super;">- in the mantle are gills used for gas exchange <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 130%; vertical-align: super;">- when the cilia on the gills beat, a water current is created <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 130%; vertical-align: super;">- vascularized gill tissue takes O2 from water and expels CO2. <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 130%; vertical-align: super;">- in bivalves, gills are a huge source of gas exchange <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 130%; vertical-align: super;">- vascularized means having blood vessels

<span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">12. <span style="font-family: Impact,Charcoal,sans-serif; font-size: 150%; vertical-align: super;">Waste Removal

<span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">Molluscs have kidneys which seperate waste products from water and nutrients. <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">Solid waste is released out of the rectum. Right next to the rectum is an ink sac from where the squid can release black ink.

<span style="font-family: "Trebuchet MS",Helvetica,sans-serif; font-size: 150%; vertical-align: super;">13. <span style="font-family: Impact,Charcoal,sans-serif; font-size: 150%; vertical-align: super;">Environmental Physiology (temperature, water, and salt regulation) <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">All species of Squids are found in salt water at least 1,000 ft below the surface. Squid are able to survive in a wide range of climates, as different species of squid live in Japan, Antartica, and the Gulf of Mexico.

<span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">14. <span style="font-family: Impact,Charcoal,sans-serif; font-size: 150%; vertical-align: super;">Internal Circulation <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">- blood vessels do not form a closed circulatory system <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">- blood and other fluid empty into a large, fluid-filled hemocoel, through which fluids move around animal and deliver oxygen to the internal organs <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">then fluids reenter the blood vessels and are moved by a heart.

<span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 150%; vertical-align: super;">15. <span style="font-family: Impact,Charcoal,sans-serif; font-size: 150%; vertical-align: super;">Chemical Control (i.e. Endocrine System)
 * <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 160%;">Sharks have a pituitary gland in the brain and a thalamus to control homeostasis and sexual activity
 * <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 160%;">squids and octopuses can change color in order to avoid predators
 * <span style="font-family: Trebuchet MS,Helvetica,sans-serif; font-size: 160%;">they do this by controlling the size of the cells in their body and the frequency of the muscle cell contractions

<span style="font-family: Impact,Charcoal,sans-serif; font-size: 19.5px;">Review Questions:

=<span style="font-family: Trebuchet MS,Helvetica,sans-serif;">1. How do Molluscs conduct gas exchange? =

<span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- They have an open circulatory system and vascularized gills that take O2 from water and expel CO2

=<span style="font-family: Trebuchet MS,Helvetica,sans-serif;">2. Generally, how do these organisms move? = <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- they ripple waves for contraction and utilize buoyancy and speed for movement

=<span style="font-family: Trebuchet MS,Helvetica,sans-serif;">3. How do these organisms acquire nutrients? = <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- they use gills as filtering devices and scrape food off surfaces with radula

=<span style="font-family: Trebuchet MS,Helvetica,sans-serif;">4. How many clades of Mollusks are there? What are they? = <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- 4 Clades: Chiton, Bivalves, Gastropods, Cephalopods

=<span style="font-family: Trebuchet MS,Helvetica,sans-serif;">5. What is the integument of the Molluscs are made of? How does it work? = <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif; font-size: 19.5px;">- enclosed system in the mantle with fins on either side - skin is covered in chromatophores that control color - the cephalopod is usually different colors on the top and bottom for camoflauge reasons

<span style="font-family: Impact,Charcoal,sans-serif;">Sources: <span style="background-color: #ffe7af; font-family: 'Times New Roman',Georgia,serif; font-size: 16px;">Hillis, D. M. (2015). //<span style="background-color: #ffe7af; font-family: 'Times New Roman',Georgia,serif; font-size: 16px;">Principles of life //<span style="background-color: #ffe7af; font-family: 'Times New Roman',Georgia,serif; font-size: 16px;">. Sunderland, MA: Sinauer Associates. http://eol.org/pages/2195/details http://eol.org/pages/2195/details#growth http://invertebrates.si.edu/giant_squid/page4.html http://sunny.moorparkcollege.edu/~econnolly/Mollusca.htm https://guides.library.harvard.edu/c.php?g=310450&p=2072051 www.nativetech.org/wampum/wamphist.htm https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4463464/ https://endocrine4lifexhs.weebly.com/chordata.html http://marine-francine.blogspot.com/2007/11/squid.html http://www.squid-world.com/squid-habitat/ http://ocean.si.edu/ocean-news/how-octopuses-and-squids-change-color http://cronodon.com/BioTech/Cepahlopod.html (1) http://www.thecephalopodpage.org/ [] https://www.sciencedaily.com/images/2017/04/170406121601_1_900x600.jpg <span style="color: #252525; font-family: Verdana,Helvetica,Arial,sans-serif;">( [] ) https://academic.oup.com/mollus/article-lookup/doi/10.1093/mollus/eyq019 http://www.squid-world.com/squid-reproduction/