CLASS: Gastropoda

1
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.

2
GASTROPODS

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

3
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.

4
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.
• the shell is a conical tube closed at the pointed
  end (apex).
• The shell is secreted by the MANTLE and grows
  along the aperture.

5
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).

6
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.

7
HARD PARTS

• The SHELL ORNAMENT varies smooth, fine, coarse
  ribs, tubercles or sometimes spines.
• Most genera coil right handed (dextral) and the
  aperture is on the right.
• Only a few are sinistral.

8
MODE OF LIFE

• Generally the marine gastropods living in the
  shallowest water had the thickest shells
  (littoral zone)
• 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.

9
MODE OF LIFE

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