Biology: Phylum Mollusca and Phylum Annelida

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Table of Contents

Phylum Mollusca
Phylum Annelida
Work Cited

Phylum Mollusca

Class Gastropoda

Snail, Sea slug, Shag-rug Aeolis

Gastropoda is one of the classes in the phylum Mollusca. The key characteristics that define organisms in this class are they live in land, aquatic or marine environment, they have eyes, mouth, tentacles, and spiraled shells (Crawley and Pendarvis 56)

Class Bivalvia

Clam, Muscle, Oyster, Scallop

Bivalvia forms another class of mulluscs with unique attributes that differentiate them from other organisms in the same phylum. These attributes are they comprise two shells (bi-valves), have mantle that secretes shells, respire using ctenidia, live in marine or fresh water. Mulluscs also have filter feeders, microphagous, and visceral mass in their internal organs (Crawley and Pendarvis 66).

Class Cephalopoda

Squid, Nautilus, Octopus, Cuttlefish

One of the classes in the phylum Mollusca with unique characteristics that differentiate them from other organisms. Squid, octopus, nautilus, and cuttlefish are some of the organisms in class Cephalopoda. These organisms live in the marine environment, they possess internal or external shells while some do not have them. They also have differentiated sexual parts in males and females with direct form of development.

Class Polyplacophora

Chitons

Major characteristics of organisms in class polyplacophora are dorsoventrally fattened bodies with bilateral symmetry, eight plates of shell, and muscular foot on the ventral side. As an example of organisms in class polyplacophora, chitons have open blood system with heart, rudimentary nervous system, sensory organs on shell valves, and kidneys (Crawley and Pendarvis 61)

Phylum Annelida

Class Polychaeta

Nereis (Sandworm), Amphitrite (tubeworm)

Organisms in the phylum Annelida are unique because they have long segmented bodies with bilateral symmetry. Their bodies have thin cuticle covering differentiated body cavity with definite organs. The class Polychaeta is in the phylum Annelida characterized by bristles on their bodies. Organisms in class Polychaeta have elongated cylindrical bodies with differentiated dorsal, ventral, posterior, and anterior parts (Crawley and Pendarvis 48)

Class Oligochaeta

Earthworm

Class Hirudinae

Leech

Earthworm and leech are examples of organisms in the phylum Annelida and classes of Oligochaete and Hirudinae, respectively. Organisms in the class Oligochaeta have long segmented bodies with differentiated body organs in coelom and bristles covering their bodies. In contrast, organisms in class Hirudinae do not have bristles (setae) on their bodies but have posterior suckers for attachment and feeding (Crawley and Pendarvis 42)

Work Cited

Pendarvis, Murray, and John Crawley. Exploring Biology in the Laboratory. 3rd ed., Morton Publishing Company, 2018.

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