Skip to content

SYNOPTIC DESCRIPTION OF THE PHYLUM MOLLUSCA

SYNOPTIC DESCRIPTION OF THE PHYLUM MOLLUSCA (LINNAEUS 1758)

EUKARYA> UNIKONTA> OPISTHOKONTA> ANIMALIA> METAZOA> BILATERIA> PROTOSTOMATA> SPIRALIA> TROCHOZOA> EUTROCHOZOA> MOLLUSCA
MOLLUSCA LINKS

Introduction

Hierarchical Classification

The following information came from Margulis and Schwartz (1998), Buchsbaum (1938), Barnes (1980), Barnes (1984), Brusca and Brusca (2003), Hickman (1973), Meglitsch and Schramm (1991), Nielsen (2001), Ruppert and Barnes (1991), Storer and Usinger (1965), and Tudge (2000).

I. SYNONYMS: mollusks, shell fish

II. NUMBER: > 100,000 species known.

III. PHYLUM CHARACTERISTICS:

  • A. Structure
    • Symmetry: Bilateral; sometimes distorted.
    • Body Cavity: No body cavity; do have large sinuses in the open circulatory system that may act as a hydrostatic haemocoel.
    • Body Covering: Epidermis and mantle (text with tooltip) The mantle is the tissue that lies next to (and secretes) the shells of mollusks. Similar tissue underlies the shells of barnacles (arthropods) and brachiopods. that usually secretes a calcium carbonate shell of 1-8 plates. Many groups like clams and snails have a pallial line (text with tooltip) The pallial line is the line on the inside of the mollusk shell that delimits the portion of the shell to which the mantle is attached. , the line which marks the extent of the attachment of the mantle to the shell.
    • Support: Hydrostatic skeleton and shell.
    • Digestive System: Complete tube.; mouth with jaws and the buccal region with a radula (text with tooltip) The radula is a rasping tongue-like structure in the mouths of various mollusks. .
    • Circulatory System: Open with a heart and a pericardial (text with tooltip) The pericardial cavity is the fluid-filled sac that surrounds the heart. cavity.
    • Locomotion: Varies, usually associated with a modification of the muscular foot.
    • Excretory System: 1 pair of metanephridia.
    • Nervous System: Several paired ganglia (text with tooltip) A ganglion (ganglia, pl.) is a cluster of nerve cells. A brain is an enlarged ganglion. attached to a ladder-like ventral nerve cord. This may be highly reduced. Some with sophisticated sensory organs for sight.
    • Endocrine System: None.
  • B. Reproduction:
    • Reproductive System: Most separate or hermaphroditic (text with tooltip) An animal that bears both male and female gonads. , usually external fertilization.
    • Development: Zygote develops by spiral cleavage (text with tooltip) Spiral cleavage is typical of the Protostomata and is characterized by the division planes of early cytokinesis products of the zygote being oblique to the plane of the polar axis. This produces unequal cells in the developing blastula. Usually spiral cleavage is determinant. and form a trochophore larva (text with tooltip) The trochophore larva is a distinctive larval form of an assortment of protostomes (e.g. annelids, mollusks, bryozoans). Commonly found in the marine plankton, the trochophore is top-shaped with a marginal ring of cilia pygidium and a ciliary tuft near the mouth. (and often a veliger (text with tooltip) An veliger is a mollusk larval stage that develops from the trochophore. ; Figure H). No asexual reproduction.
  • C. Ecology: Enormous variation; they range from marine to fresh water and terrestrial. Sedentary, benthic (text with tooltip) A benthic (adj.) organism is one that lives in or on the bottom of marine or freshwater environments. , creeping or pelagic. May be filter-feeders, grazers, or active predators.
LITERATURE CITED

Barnes, R. D. 1980. Invertebrate Zoology. Saunders College/Holt, Rinehart and Wilson, Philadelphia.

Barnes. R. S. K. 1984a. Kingdom Animalia. IN: R. S. K. Barnes, ed. A Synoptic Classification of Living Organisms. Sinauer Associates, Inc., Sunderland, MA. pp. 129-257.

Brusca, R. C. and G. J. Brusca. 2003. Invertebrates. Sinauer Associates, Inc. Sunderland, Mass.

Buchsbaum, R. 1938. Animals Without Backbones, An Introduction to the Invertebrates. The University of Chicago Press. Chicago.

Conway Morris, S. and J. S. Peel. 2008. The earliest annelids: Lower Cambrian polychaetes from the Sirius Passet Lagerstätte, Peary Land, North Greenland. Acta Palaeontol. Pol. 53(1): 137-148.

Darwin, C. R. 1881. The Formation of Vegetable Mould, Through the Action of Worms, With Observations on their Habits. John Murray. London.

Frelich, L., C. Hale, S. Scheu, A. Holdsworth, L. Heneghan, P. Bohlen, and P. Reich. 2006. Earthworm invasion into previously earthworm-free temperate and boreal forests. Biological Invasions. 8(6): 1235-1245.

Giribet, G., C. W. Dunn, G. D. Edgecombe, and G. W. Rouse. 2007. A modern look at the Animal Tree of Life. Zootaxa. 1668: 61-79.

Giribet, G., A., A. Okusu, A. R. Lindgren, S. W. Huff, M. Schrodl, and M. K. Nishiguchi. 2006. Evidence for a clade composed of molluscs with serially repeated structures: Monoplacophorans are related to chitons. Proc. Nat. Acad. Sci. USA. 103(20): 7723-7728.

Halanych, K. M. 2004. The new view of animal phylogeny. Annu. Rev. Ecol. Evol. Syst. 35: 229-256.

Halanych, K. M., T. G. Dahlgren, and D. McHugh. 2002. Unsegmented annelids? Possible origins of four lophotrochozoan worm taxa. Integ. and Comp. Biol. 42: 678-684.

Hickman, C. P. 1973. Biology of the Invertebrates. The C. V. Mosby Company. Saint Louis.

Margulis, L. and K. Schwartz. 1998. Five kingdoms, an illustrated guide to the phyla of life on earth. 3rd Edition. W. H. Freeman and Company. New York.

McHugh, D. 1997. Molecular evidence that echiurans and pogonophorans are derived annelids. Proc. Nat. Acad. Sci. USA. 94: 8006-8009.

Meglitsch, P. A. and F. R. Schramm. 1991. Invertebrate Zoology. Oxford University Press, New York, Oxford.

Nielsen, C. 2001. Animal Evolution: Interrelationships of the Living Phyla. 2nd Edition. Oxford University Press. Oxford.

Pechenik, J. A. 2005. Biology of the Invertebrates. McGraw-Hill. New York.

Ruppert, E. E. and R. D. Barnes. 1994. Invertebrate Zoology. 6th edition. Saunders. Ft Worth, TX.

Ruppert, E. E., R. S. Fox, and R. D. Barnes. 2004. Invertebrate Zoology: A Functional Evolutionary Approach. Seventh Edition. Thomson, Brooks/Cole. New York. pp. 1-963.

Siddall, M. E., E. Borda, and G. W. Rouse. 2004. Toward a tree of life for Annelida. In: Cracraft, J. and M. J. Donoghue, eds. Assembling the Tree of Life. Oxford University Press. Oxford, New York. pp. 237-251.

Sigwart, J. D. and M. D. Sutton. 2007. Deep molluscan phylogeny: synthesis of palaeontological and neontological data. Proc. Royal Society B. 274: 2413-2419.

Storer, T. I. and R. L. Usinger. 1965. General Zoology. 4th Edition. McGraw-Hill Book Company. New York.

Struck, T. H., N. Schult, T. Kusen, E. Hickman, C. Bleidorn, D. McHugh, and K. M. Halanych. 2007. Annelid phylogeny and the status of Sipuncula and Echiura. BMC Evolutionary Biology. 7:57 doi: 10.1186/1471-2148-7-57

Tudge, C. 2000. The Variety of Life, A Survey and a Celebration of all the Creatures That Have Ever Lived. Oxford University Press. New York.

Walker, J. C. and D. T. Anderson. 2001. The Platyhelminthes, Nemertea, Entoprocta, and Gnathostomulida. In: Anderson, D.T., ed. Invertebrate Zoology. Oxford University Press. Oxford, UK. pp. 59-85. [L]

Valentine, J. W. 2004. The Origin of Phyla. University of Chicago Press. Chicago. 614 pp.

Zrzavý, J., P. Ríha, L. Piálek, and J. Janouskovec. 2009. Phylogeny of Annelida (Lophotrochozoa): total-evidence analysis of morphology and six genes. BMC Evolutionary Biology. 9:189 doi: 10.1186/1471-2148-9-189
By Jack R. Holt. Last revised: 01/26/2012
Print Friendly, PDF & Email

Document Footer

Skip to toolbar