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GASTROPODS

GASTROPODS. GASTROPODS. CLASS: Gastropoda As a class they are long lived, some appeared in the Cambrian and at the present day they are the most abundant molluscs.

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GASTROPODS

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  1. GASTROPODS

  2. GASTROPODS • CLASS: Gastropoda • As a class they are long lived, some appeared in the Cambrian and at the present day they are the most abundant molluscs. • They occupied a number of life modes, most lived in water: typically shallow marine areas but they can also live in fresh water and some forms survive on dry land.

  3. GASTROPODS • Modern day forms include: • Marine: • Limpets • winkles. • Dry land: • Snails • slugs (shell less).

  4. MORPHOLOGY: • Copy diagrams in Black page 53.

  5. SOFT PARTS: • The most striking feature is the coiled shell, forms because the internal organs are twisted. • The soft body parts are lined throughout the shell and sections could be extended at will: Head, foot and siphons. • The HEAD extended out of the ANTERIOR END and a FOOT extended out of the majority of the shell APERTURE. • The head consists of TENTACLES for sensing and below this is the MOUTH.

  6. SOFT PARTS: • The foot is a muscular organ, which allows movement. • Terrestrial forms secrete mucus to aid their movement. • Other soft body parts are concentrated in the anterior end where the shell is often at it's widest. • The ANUS is also at the anterior end. • Water living forms contain GILLS and some have a SIPHON that can be extended.

  7. HARD PARTS: • It has one valve = UNIVALVE and is coiled vertically and usually spirals to the right (dextral). • The shell is mostly made of calcite or aragonite. • In simple terms the shell is a conical tube closed at the pointed end (apex). • This end is also called the POSTERIOR. • The shell is secreted by the MANTLE and grows along the aperture.

  8. HARD PARTS: • Each completed coil is called a WHORL. • The line along which the whorls meet is called the SUTURE. • The LAST WHORL is called just that the rest are the SPIRE. • The spire may be high, pointed with many whorls or short with a few whorls. • Sometimes the shell can be flattened giving a planispiral form (similar to ammonites).

  9. HARD PARTS: • The size of the last whorl varies sometimes being slightly bigger than the previous one but sometimes it is much larger. • A SIPHONAL CANAL may extend the aperture at the anterior end. • This varies in length and is used to support the siphon (that takes in water). • Sometimes the INNER LIP of the aperture can appear thickened and almost folded back as it grew = CALUS.

  10. HARD PARTS: • In some genera a type of lid mechanism can be used to shut off the aperture when the soft parts were withdrawn called the OPERCULUM. • The SHELL ORNAMENT varies: smooth, fine, coarse ribs, tubercles or sometimes spines. • Because of the coiling muscle scars are not usually visible. • Most genera coil right handed (dextral) and therefore the aperture is on the right. Only a very few are sinistral.

  11. MODE OF LIFE: • See reef video from Discovery. • Generally the marine gastropods living in the shallowest water had the thickest shells (littoral zone) e.g. the cap shaped limpets. • Gastropods with an aperture with siphonal canal were usually carnivores and lived on soft sediment (e.g. ate bivalves and other gastropods). • The gastropods without a siphonal canal were generally herbivores.

  12. MODE OF LIFE: • They did not burrow and therefore lived on hard surfaces. • They crawled when necessary. • The freshwater forms generally had thinner shells.

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