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Origins of Mollusca

Origins of Mollusca. By Aliah Marzolf, Lawrence Irvin, Lauren Stagner, . Evolutionary Evidence. According to fossil evidence, molluscs originated in the ocean, most have remained there much of their evolution happened along the shore - due to abundant resources and diversity of habitats

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Origins of Mollusca

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  1. Origins of Mollusca By Aliah Marzolf, Lawrence Irvin, Lauren Stagner,

  2. Evolutionary Evidence • According to fossil evidence, molluscs originated in the ocean, most have remained there • much of their evolution happened along the shore - due to abundant resources and diversity of habitats • only bivalves and gastropods moved into brackish or freshwater habitats • A fossil found in 2012, Kulindroplax, gives good evidence that the more worm-like mollusks evolved from the more anatomically complex shelled mollusks

  3. Abundance of CaCO3 in the Ocean • The ocean is richly abundant with calcium from decomposing organisms and carbonate from the carbon system. • These conditions permitted organisms like Mollusca to evolve and use CaCO3 in their production of a shell. • With the increasing acidification (pH of the ocean is increasing) of the ocean, it is now more difficult to produce a hard CaCO3 shell and previously produced CaCO3 shells are being dissolved. • Scientists hypothesize that the coral reefs and CaCO3 producing organisms in the oceans will be permanently affected within 40 years.

  4. Mantle • dorsal body wall that covers the visceral mass • encloses internal organs Molluscs may have evolved from free-living flatworms. Both flatworms and molluscs are triploblastic, bilaterally symmetric, and cephalized.

  5. The Shell • Polyplacophora plus the group Conchifera developed a concentration of shell glands to produce solid shell(s). • Polyplacophora used this shell gland to make 7-8 segmented shell parts • furthermore, Conchifera is unique with the presence of a single, well-defined shell gland. • after this split the use of this shell gland varies. • Monoplacophora use this shell gland to make a univalve, caplike shell. • Gastropoda and Cephalopoda use this shell gland to make a coiling shell • gastropoda undergoes Torsion • Cephalopoda possess a septate shell • Bivalvia and Scaphopoda underwent the expansion of their mantle (shell gland) to surround their entire body

  6. The Foot • Other than aplacophorans, molluscs all have a muscular structure known as the “foot”. • It is used for a variety of tasks from locomotion, to anchoring in place, to catching prey. In octopi it even specialized into becoming prehensile tentacles for grabbing. • Is a major source for diversity in molluscs. • Original foot was most likely used by a shelled mollusc to remain locked in place to avoid predators.

  7. Sources • "Which Came First, Shells or No Shells? Ancient Mollusk Tells A Contrary Story." ScienceDaily. N.p., 03 Oct 2012. Web. 8 Oct 2013. <http://www.sciencedaily.com/releases/2012/10/121003132326.htm>. • http://eol.org/pages/2195/details • http://co2.cms.udel.edu/Ocean_Acidification.htm

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