Gastropods are the second largest class of animals, with over 40,000 living species. They live in oceans, freshwater, and on land. Their shells vary greatly in size and shape. Gastropods have soft inner parts like gills or lungs and a foot, as well as a hard shell that can have different forms depending on the shape of the whorls and spire. The shell forms include discoidal, trochiform, turbinate, turreted, cylindrical, globular, fusiform, convolute, auriform, conical, vermiform, patelliform, and pupaeform.
3. INTRODUCTION
Gastropods are the Second largest class of Animals (after the Insecta) with 40,000 -90,000 living species
& at least 13,000 extant & fossil general Pender of kindbeg, 2020)- and are also one of the most
evolutionarily successful groups in the variety of coco systems & babitats that they occupy. They live in
the world's oceans, freshwater lakes & streams, & terrestrial ecosystems, including, deserts, mountains,
backyards, & beaches. Their shells range in Size from almost a meter to less than a millimeter.
The name "Gastropoda" Comes from the Greek roots “gastro” (= stomach) & “Pod” (=foot).
Snails were given this name because many have the appearance crawling around on their stomach.
4. MORPHOLOGY
A Gastropods shell is long, conical tube like structure closed at one end open at the other end. The
open anterior end is known as aperture.
Morphology of Gastropods have been divided into two parts;
Soft parts
Hard parts
5. SOFT PARTS
Head with tantacles& eyes
Mouth cavity
Foot
Gills or lungs
Heart
Peristome
Redula
Nervous system
Mantle
Oesophagus
Stomach
6. HARD PARTS
1.Spire:- All The whorls except the last whorl constitute the
spire of the shell.
Protoconch-The closed posterior end is known
asprotoconch.
Suture line - The whorls are separated by a
slightdepression which is known asthe suture.
Apex- The terminal whorl of the spire forms the apex.
7. HARD PARTS
2.Body whorl- The last whorl in which the animal leaves is
known as body whorl.
Aperture- The open anterior end is known as aperture
Peristome - The margin of the aperture is term as
peristome.
Inner lip-The inner part of the peristome is known as inner
lip.
Outer lip - The outer part of the peristome is known as
outerlip.
8. HARD PARTS
Columella- : A central pillar likeaxis extending form apex to
the base of the shell called as columella.
Siphonal canal : The anterior tube is the anterior or siphonal
canal.
Anal canal : The posterior tube is the posterior or anal canal.
Operculum- The aperture ofthe shell may be covered by a
plate known as operculum.
10. FORMS OF THE SHELL
The forms of the shell depend on the
Spire angle
Number the whorl
Shape of the whorl
Size of the last whorl
11. The following are the forms of the shell.
1. Discoidal :-The shell is planispirally coiled. The whorls are
in one plane so that the entire arrangement can be seen eg:
Planorbis.
12. 2. Trochiform- The spire is sharp and acute. the whorl
inthe spire increase in diameter gradually. The body whorl
is small and the base of the shell is Hate, eg: Trochos
13. 3. Turbinate- The spire is sharp and acute. the whorl in the
spire increase in diameter gradually. The base which is
convex. eg- Turbo.
14. 4. Turreted-The spire is long with numerous whorls and
acute sharp apex. The body whorl is very small. eg-
Turritella.
15. 5. Cylindrical-After gradual increase in the diameter
of the spire, the diameter remains containt or it
may reduce near the base. eg-Voluta.
16. 6. Globular-The spire is small and sharp. The body whorl is large. And round with round aperture. Eg-
Natica.
17. 7. Fusiform-The shell is spindle-shaped.
The body whorl is thick. in the middle
and tapering near the bottom and the
top. eg- Fusinus.
18. 8. Convolute-The last whorl of the shell covers all the
previous whorls. The aperture, with crenulated outer lips,
is a long as the shell. ex-Cypraea.
20. 10. Conical-The spire is short, apex is sharp, the
body whorl is large. conical with parallel lips. ex-
Conus.
21. 11. Vermiform-the shell is worm like and twisted.
Ex-vermicularia.
12. Patelliform-The apex is sharp and shell is cap like. Ex-
patella.
22. 13. Pupaeform-the apex is convex and rounded,
whorl increase in size in spire, all whorl are uniform in
in diameter and the aperture is rounded. Ex-Pupa
