BIOLOGY/PART 5

Pelecypodsmove rapidly by digging with their Believe-It-Or-NotMollusk Facts muscular,hatchet-shaped foot. Almost all of 'themlive ~ Thereare over f00,000 of mollusks.That buriedin the sea floor. There are giant in the makesit thesecond largest phylum on earth. Arthrop- tropics,but they close their shells very slowfy. oda,the phylum containing insects, has the most Pelecypodsareeaten all over the world, and some species are harvested for pearls. ~ Theradula and mantleare found in noother phylum. C/assCephatopoda: head-foot ~Slugs can crawl over the edge of a razorwithout be- ~ commonnames., , chambered ingcut. This is because their foot is protected by ~ commonfeatures: no radula, captures food with tentaclesand arms; well-developed head and eyes; specialslime. muscularfoot has become arms and ; uses ~ Giantclams may be fivefeet long and weigh 500 ink as an escapemechanism pounds. Cephalopodsaresome ofthe fastest moving and ~ Onlyone in 1,000wild contain a pearl, mostintelligent inthe ocean. An octopus has noshell, but it hasa beakthat it usesto biteand eat ~ Inf860, a giantsquid was found whose body, not itsprey. have an internal shell called the gladius, includingthe arms, was 50 feet long and 20 feet in orpen. The chambered nautilus has a beautifulexter- diameter.It was estimatedto weighttwo tons, nalshell with internal chambers filled with gas to help ~ TheIndians of NewEngland used shells for themfloat and swim. Unlike gastropods, thenautilus is beadsand shells for money. It wascalled notcoiled up intothe shell. It livesonly in the last "wampum." chamber. ~ Untilplastic was invented, many buttons were made of shell.

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ACTIVITY 3 Designinga Dichotomous Key

Purpose informationabout the changes that have occurred Toteach students how to set up and use a overtime. Classification is not a fixedabsolute, but dichotomouskey. rathera dynamicsystem that can change with new knowleclgeorwith the changes thatoccur inorgan- StudentBackground isms over time. Youmay have learned about Linnaeus's system Whenyou want to organize your record albums at beforetoday. Even ifyou haven' t,you' ve probably home,you have to develop a system ofclassification. seena productaf it the scientificname. Scientific Thissystem must be consistent, easy to useand namescome from the last two categories: and basedon important common characteristics. Yau species.Homo sapiens ismade up of the genus cauld,for example, arrange your records according to nameand species name of humanbeings. I ions are thecolor of the cover. Ifyou tried it thisway, you would inthe genus Felis and the species leo, so their scien- runinto some problems. First, most album covers are tificname isFelrs lea. Notice how the name iswritten. manydifferent colors. How are you going to decide Thegenus iscapitalized; thespecies isnot. The entire whichcolor to file the album under? And does the nameshould always be italicizedar underlined. All colorof the cover really make a differencetoyou organismshave scientific names. whenyou' re looking formusic taplay? A betterway Scientistscalled taxonornists putliving things into mightbe to organize thealbums according tothe type a systemof classification and give them names based of music:country, jazz, rack, etc. animportant characteristics. Theyplace organisms Biologistsneeda systemtoorganize living things. intogroups that have clear-cut similarities. Think about Whenyou go to thezoa, you don't find birds on theclass, mammals. Youshould be able to point out displaywith monkeys orsnakes slithering around with theimportant characteristics thatall mammals share. lions.The animals arearranged ina particularway. Andyou should beable to point out why something Whenyou open a biologybook, the chapters onplants likea toadis nota mammal. andanimals are arranged ina certainorder. That' s Naminga creature isone thing, but figuring out becausescientists usethe Linnaean System ofClassi- whatthat name is when you' re not a taxonomistre- fication.This system hasseven categories: kingdom, quiresa key.A keyallows you to retrace the steps that phylum,class, order, family, genus and species. a taxonomisttookto classify an organism. Itleads you Originally,organisms were classified andorgan- througha seriesofchoices until you get to a final izedto make them easier tastudy and to simplify choicethat points to thescientific name of the communicationwith scientists worldwide. It was an at- organismyou wanted to identify.Because there are at temptto create order out of chaos and to develop an leasttwo choices at everystep, these devices are understandingaf relationships. calleddichotomous keys di- means two, whatomous Withour understanding ofevolution, genetics and meansbranched! see Figure 1!. biochemistry,many other characteristics arecon- sideredwhen placing an organism ina groupwith MaterialslEquiprnent similarorganisms, Several changes inthe placement of organismshave occurred since researchers dis- an assortmentof seashells Use whatever shells are coverednew ways of assessingsimilarities, differences available,such as , rnussels, cockles, andrelationships. Currently, theclassification system ,penwinkles, clams, oysters, , moon representsevolutionary relationships andcan give us snailsor slippershells.! rulers string balance hand lens

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groups.Do not recombineany of the shellsyou divided in step 1. Part 1 3. Once again, divide the shellsin each remain- ing group.By nowyou mayhave categories with only Yourclass should divide itself into groups of four, one shell When this happens, you are ready to name Eachgroup should have a number.Your teacher will that shell. This could be its common name coquina, giveeach group a collectionof different seashells plus disk clam! or a made-up name George,Sue!. some work sheets. 4. Any categoriesthat still havemore than one 1.Separate your shells into two distinct groups. To shell can be divided, named and listed. By now each dothis, pick a characteristicthatlooks important. Look shell should have its own category and name, at the color,size and shape Use a rulerand string, Yourchart representsone form of a dichotomous scale or hand lensto identifyIgniffcant differences key.At eachstep, there are two choices. You could ~n theshells. You want to find onecharacteristic haveeasily created a differentform by makingdif- thatwill divide all your shells into two categories. For ferent choices. Therefore, taxonomic keys are reffec- example,shells with hinges and shells without hinges tions of individual choices that are arbitrary in natura typicallysnails]! NOTE: Be sure not to usewords When the class has completed their charts, switch such as clamand .These words assume too charts and shells with another group. Using a stop- much. watch,your teacher will thentime how long it takesfor 2. Separateeach of your large categories into eachgroup to correctlyidentify the shellsusing your smallerones, using dividing characteristics. For exam- chart.The group that is fastesthas the bestkey, To be ple,hinge at center of topand hinge off to oneside.! sure, switch again. Rememberyou are dividing two already separate

Figure1 Dichotomouskey chart

G

ALL SHELLS

hinge no hinge T whorls hinge hinge whorls not connected center off-center connected T v F Wormshell narrow even elongated wide ears no ears cavity for extension A rounded irregular cavity for , animal, B shape shape no knobs G 0 knobs Scallolfi E Quahog C Olive Clam L Ighthlllg Vlfhelk Shell BIOLOG Y/PART 5

ACT VASTY 2 Using8 DichotomousKey

Purpose yourshell. When you select a description,follow the Toteach students howto use a dichotomouskey dottedline to see where you should go next. lf you're not sure about some ofthe words used Mate riats inthe choices, use the glossary and Figure 2.Occa- sionally,none of the choices seem right. In this case, an assortment of shells eitherstart over orpick a choicetosee ifit leads you copyof the dichotomous keychart Figure 1! toa descriptionthatsounds like your shell. You must be patient. Procedure Onceyou reach a scientificname for your shell, Dividestudents into groups of four or five. The checkit by looking it up in a fieldguide with photo- teacherwill give each student a collectionofshells graphsordrawings. Your teacher willonly allow you to anda dichotomouskey of seashells. checkyour shell when you have a possiblename. Examinethe key and notice how it differsfrom the And,it's not fair to leaf through the guide to find the oneyou made in Part1. It hasno boxes, but the nghtpicture and then look for the name. categoriesarearranged insequence oneach page. Tryto properly identify allthe shells given toyour Seehow each number has at least two choices, Pick group.When you' re finished, test each other on the upone of your shells and try to work through the key commonand scientific names. Next time you go to untilyou get to its scientific name. Be sure to read all thebeach, you' ll bea realexpert. thechoices before picking one that seems closest to

Figurv'.2 Parts of shells Gastropods Unlvalves! Pefecypads Bivalves!

ak e tee h

should uscle scars ibs pallalial sinus

unule panetal shield Q ribs Kjges

canal width

width

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List of Common North Carolina Shells Aperture:in gastropods,the major openingof the shell. These are the shells that can be found in the Beaded:sculptured so as to resemblebeads or dichotomous key strings of beads. Pelecypods: Beak: smalltip of a pelecypod bivalve!shell, near the Anadora ovalis Ark Shell hinge. Also calledthe "urnbo." Anomieemphippium AtlanticJingle Shell Area zebra Zebra Ark Canal:in gastropods,a narrownotch or tubularexten- Argopectengibbus Calico sion of the aperture. Argopectenirradians AtlanticBay Scallop Crenulations:regular notcheson the edge of a shell. Atrina serrata Pen Shell Chione cancellata Dog Clam Height:see Figure2. Crassostreavirginica EasternOyster Hinge:all the structuresat the dorsalregion of Dinocardium robustum Great Heart Cockle pelecypod bivalve!shells that functionin openingand Dtvalingaquadrisulecata Cross-HatchedLucine closing the shews. Donax variabilrs Coquina Clam Oosinia discus Disk Shell Length: see Figure 2. Macroca!lrsta nimbosa Venus Sunray Clam Lunule:heart shaped area on the dorsal marginof Mercenaria mercenaria Northern Quahog pelecypods. see Figure2!. Mociiolus demrssus Ribbed Mytiluseduiis Common Paftial Sinus: an inward curve of a fai~t line on the in- Placopectenmagellanicus Deep SeaScallop side of pelecypod shells. Pterracolymbus Wing Oyster Shield;a coveringon the inner of a Sprsulasolidissima Surf Clam gastropod see Figure2!. Tagelusdivisus FalseRazor Clam Trachycardiurnegmontianum PricklyCockle Ribs:an external,raised structureon gastropodsand pelecypods,running vertically lengthwise! on bivalves Gastropods: and in al! directions on univalves. Busyconcari ca Busyconcanaliculata Channeled Whelk Ridges:an external,raised structure on pelecypods, Busyconcontranum LightningWhelk running horizontally. Crepidu!afornicata SlipperShell ;the upperwhorls from the top of the shellto the Cypraeacervus AtlanticDeer Cowrie body . Diodoracayenensis KeyholeLimpet Epitonium spp. Wentletrap Whorl.in spiral gastropods,one full turn of the shell. fasciolaria hunteria Banded Tulip Shell The body whorl is the whorl that occupiesthe largest llyanassaobsoleta Mud Snail area of the body see Figure2!. Litton'na irrorata Marsh Periwinkle Nassarius vibax Mottled Dog Whelk Olivasayana Olive Shell Phalium granulatum ScotchBonnet Polinices duplicatus Moon Snail Sinum perspecti vum Baby's Ear Terebra dislocata Atlantic Augur Shell castanea Chestnut Turban

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Questions 9.In which class isa squid?What does the class 1.Place the correct letters next to the following items. namemean? Does a squidhave a shell? Insome cases more than one letter may be right. Polyplacophora= P 10.What kind of mollusks arein the class polyplaco- Gastropod= G phora?Do they havea shell? Pelecypocla= 8 b!valve! Cephalopoda= C 11.In which class would you find bivalves? How would youdistinguish between a bivalveand a univalve? a! radula Makea listof the differences between the two. b! pearls c! lnh 12.What's different about the lifestyle ofa snailand d! trochophorelarva a clam? e! tentacles 13.Mow do you explain the fact that a chambered p! scallops nautilusis notin thesame class as a moonsnail~ 14.Describe two major differences between a scien- j! two a!phone tificname and a commonname.

I! hatchet-foot 15.What do clams eat? m!no head n! two shells 16.Where are found? o! head. loot 17.The Linnaeus Classification hasseven divisions. In 2.Describe what you think isthe best way to arrange order,they are: booksinyour locker or on a shelfathorne. Why do youprefer this way to anyothe' 18.Name several ways inwhich humans use or have used! mollusks. 3.What do we calI the system that biologists useto arrange living things~ 19.Tell the scient!fic name and common name of one molluskthat you identified using the professional 4.What do we call scientists whoclassify living things? dichotomouskey. S.What is a dichotomouskey? 20.Why do you think it's alright for gastropocfs to moveslowly? How do they protect themselves from 6.What are the common features of all mollusM dangerif theycan't run away? 7.What are the four major classes of mollusk@. 21.Explain why you think it is importantfor scientists to havea wayof organizing living things. Give at least 8.In which class is a snail?Describe the main features threereasons. Then tell why it's important foryou to of this class. knowabout this system.

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