Phylum Mollusk

Phylum Mollusk/Mollusca is under the kingdom Animalia and considered as the second largest invertebrate group along with other invertebrates groups like Phylum Porifera, Phylum Cnidaria, and Phylum Platyhelminthes. Mollusks mostly are marine organisms but some are terrestrial like those under the class Gastropoda. Phylum Mollusk is the second most diverse next to phylum Anthropoda. Organisms like snails, octopuses, oysters, scallops, slugs, and clams belong to phylum Mollusk; organisms have fleshy soft bodies that some have shell secreted by mantle that covers the body of the organism.

Organisms live in terrestrial and water areas primarily in oceans. Four major classes under the phylum mollusk are named such as class Scaphopoda, class Gastropoda, class Bivalvia and the class Cephalopoda. The Scaphopods also known as “tusk shells” are slightly curved shells making it look like a tusk. Mantle tissue of organisms under phylum mollusk is significant for their protection and respiration. Tusk shells are obtaining oxygen from seawater through their mantle tissue. The class Gastropoda includes organisms such as snails and slugs, just like Scaphopods, gastropods also use their muscular foot to move and search.

Gastropods are considered by many as the largest group of the phylum mollusk ranging 40,000 living species. According to the University of California Museum of Paleontology, Gastropods are also terrestrial habitats, they are abundant as 60-70 species may coexist in a single habitat and abundance in leaf litter that exceed more than 500 individuals in four liters of litter. However the class Bivalvia also known as Pelecypods considered as the second largest group after Gastropods. About 15,000 Pelycypods exist in marine and freshwater all over the world.

Bivalves have two-part shells, both valves are symmetrical and completely living in freshwater. Bivalves are also unique for lacking a radula which is used by other mollusk organisms for feeding, instead they bivalves use tapping and cleaning huge particles from the water surrounding them. Cephalopoda means “head foot”, organisms under this class has the most complex and large brain, developed senses which many considered cephalopods as the most intelligent invertebrates. Cephalopods also exclusively live in water and can found in oceans, around 786 living species have been identified living in different bodies of water including oceans.

Studies said that Organisms under phylum Mollusk undergo feeding evolution, where there are various ways to acquire food. The taxonomic diversity of Molluscans remained low until the Ordovician (the second period of six of the Paleozoic), when gastropods, bivalves, and cephalopods diversity show a remarkable increase. For their reproduction, female and male Molluscans release gametes into the water, these gametes will merge then fertilization takes place. In the case of gastropods, mostly internal fertilization happens, where male gastropod inserts sperm directly into the body of a female gastropod.

Human beings benefit from these Molluscans by giving them food and livelihood. For instance, Cephalopods have economic significance to human beings in which octopuses and most especially squids are eaten by people and nautilus shells are used for making and selling decorations. Works Cited “Bivalvia” 2002. Animal Diversity Web. 21 February 2009 <http://animaldiversity. ummz. umich. edu/site/accounts/information/Bivalvia. html>. Mulcrone, R. “Scaphopoda” 2005. Animal Diversity Web. 21 February 2009 <http://animaldiversity. ummz. umich. edu/site/accounts/information/Scaphopoda.html>.

Myers, P. and J. Burch. “Gastropoda” 2001. Animal Diversity Web. 21February 2009 <http://animaldiversity. ummz. umich. edu/site/accounts/information/Gastropoda. html>. Bunje, Paul. “The Mollusca: Sea slugs, squid, snails, and scallops” 2003. University of California Museum of Paleontology. 21 February 2009 <http://www. ucmp. berkeley. edu/taxa/inverts/mollusca/mollusca. php>. Wheeler, K. and D. Fautin. “Cephalopoda” 2001. Animal Diversity Web. 21 February 2009 <http://animaldiversity. ummz. umich. edu/site/accounts/information/Cephalopoda. html>.

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