Introduction The Gastropods - Phylum Mollusca - Second largest class. Includes - sea snails and slugs, as well as freshwater snails, freshwater limpets, and land snails and slugs. The most highly diversified class in the phylum, with 65,000 to 80,000 living snail and slug species. Older classification of the gastropods Opisthobranchia (gills to the right and behind the heart). Gymnomorpha (no shell). Prosobranchia (gills in front of the heart). Pulmonata (with a lung instead of gills).

1. Biology of Gastropods
By Vinod Kumar

2. Introduction
❏ The Gastropods - Phylum Mollusca - Second largest class.
❏ Includes - sea snails and slugs, as well as freshwater snails, freshwater
limpets, and land snails and slugs.
❏ The most highly diversified class in the phylum, with 65,000 to 80,000
living snail and slug species.

3. Taxonomy
Older classification of the gastropods
● Opisthobranchia (gills to the right and behind the heart).
● Gymnomorpha (no shell).
● Prosobranchia (gills in front of the heart).
● Pulmonata (with a lung instead of gills).

4. New Classification of Gastropods
Neritopsina (= Neritimorpha)
● This group includes old gastropods with a long fossil record. They are
known to occur in all shapes and sizes from coiled shells, to limpet-like, to
slugs. This includes terrestrial, freshwater, and marine species.
Vetigastropoda
● This clade includes top shells, abalone, keyhole and slip limpets, and
several other families.

5. Caenogastropoda
● This group is highly diverse and has colonized almost all marine,
freshwater, and terrestrial environments. This clade (large group) consist
of about 60 % of extant gastropods and contains a large number of
ecologically and commercially important marine families such as
Muricidae, Volutidae , Mitridae, Buccinidae, Terebridae ,Conidae ,
Littorinidae, Cypraeidae, Cerithiidae , Calyptraeidae, Tonnidae , Cassidae ,
Ranellidae , Strombidae and Naticidae .

6. Heterobranchia
● This group includes pulmonates (comprises more than 20,000 species)
and opisthobranchs includes sea hares, sea slugs and bubble shells. This
group includes the gastropod groups positioned by Thiele’s taxonomic
scheme into the ‘Opisthobranchia’ and ‘Pulmonata’, as well as some
‘prosobranch’ groups.

7. Patellogastropoda
● This is a major group of marine gastropods that contains true limpets,
traditionally called Docoglossa. Patellogastropods are known to occur
mostly on rocky shores in all continents.
Cocculiniformia
● This group includes white limpets that attach to organic matter in the
deep ocean.

8. Cladogram

9. Structure of Gastropods

11. Anatomy
➢ The body is generally divided into 2 main regions:
(1) head-foot
(2) mantle ; shell, mantle cavity, and visceral mass.
➢ Foot is the locomotion organ; gastropods mainly crawl, attach, or burrow
using the foot.
➢ The head includes sense organs (e.g., tentacles and eyes) and in many
groups is the site of concentration of nerve ganglia and connectives.

12. ➢ The mantle, typical of molluscs, lines the shell internally; its external edge
is the site of shell deposition.
➢ The space between the head-foot and the mantle proper is the mantle
cavity, where the ctenidium (or ctenidia), osphradium, anus,
nephridiopore, and external genitalia are located.
➢ The visceral mass, located in posterior direction, is the location of the
gonads, digestive gland, heart, kidney, and part of the alimentary system.

13. Torsion
➔ Torsion is a gastropod synapomorphy which occurs in all gastropods
during larval development.
➔ Torsion is the anti-clockwise rotation of the visceral mass, mantle, and
shell 180˚ with respect to the head and foot of the gastropod.
➔ This rotation brings the mantle cavity and the anus to an anterior position
above the head.

15. Food and Feeding
➢ The Gastropoda exhibit extremely diversified food habits.
➢ There are predators, scavengers, filter- and deposit-feeders, macro- and
micro-herbivores.
➢ In addition, in order to reach the food source, some gastropods are able
to drill through hard structures (e.g., shells) using the radula.
➢ Predatory carnivorous gastropods : Cone shells, Testacella, Daudebardia,
Ghost slug.

17. Reproduction
➢ From the standpoint of reproduction, gastropods may be dioecious or
hermaphroditic, and may perform internal or external fertilization.
➢ Most gastropods go through pelagic larval development of varied
duration, but some groups are known to have bypassed pelagic
development, undergoing intracapsular (direct) development instead.

19. Habitat
➢ The types of habitats occupied by gastropods are also extremely
diversified
➢ Gastropods inhabit both terrestrial and aquatic environments, and in the
marine environment, can be found from the bottom of the deepest ocean
trenches to the canopies of mangrove forests.

21. Diversity
➢ Described species of Mollusca with accepted names: about 85,000
➢ The total number of Mollusca, including undescribed species, is about
240,000 species.
➢ The estimate of 85,000 molluscs includes 24,000 described species of
terrestrial gastropods
➢ The total number of living species of freshwater snails is about 4,000.

22. Life Cycle
➢ Egg laying.
➢ The embryonic development of gastropods,
➢ The larvae: some gastropods may be trochophore and/or veliger.
➢ Estivation and hibernation (each of these are present in some gastropods
only).
➢ The growth of gastropods
➢ Courtship and mating in gastropods: fertilization is internal or external
according to the species. External fertilization is common in marine
gastropods.

24. Families of Interest
CASSIDAE
● Cassis flammea (Linnaeus, 1758).
● Cassis madagascariensis Lamarck, 1822.
● Cassis tuberosa (Linnaeus, 1758).

25. FASCIOLARIIDAE
● Fasciolaria tulipa (Linnaeus, 1758).
● Pleuroploca gigantea (Kiener, 1840).

26. FISSURELLIDAE
● Diodora listeri (d’Orbigny, 1842).
● Fissurella barbadensis (Gmelin, 1791).
● Fissurella nimbosa (Linnaeus, 1758).

27. MELONGENIDAE
● Busycon perversum (Linnaeus, 1758).
● Melongena corona (Gmelin, 1791).
● Melongena melongena (Linnaeus, 1758).
● Pugilina morio (Linnaeus, 1758).

28. MURICIDAE
● Chicoreus brevifrons (Lamarck, 1822).
● Chicoreus pomum (Gmelin, 1791).
● Stramonita haemastoma (Linnaeus, 1767).

29. NERITIDAE
● Nerita peloronta Linnaeus, 1758.

30. RANELLIDAE
● Charonia variegata (Lamarck, 1816).

31. STROMBIDAE
● Strombus costatus Gmelin, 1791.
● Strombus gigas Linnaeus, 1758.
● Strombus pugilis Linnaeus, 1758.

32. TROCHIDAE
● Cittarium pica (Linnaeus, 1758).

33. TURBINELLIDAE
● Turbinella angulata (Lightfoot, 1786).

34. TURBINIDAE
● Turbo castanea Gmelin, 1791.

35. Red list
Extinct :- 267
Extinct in the wild :- 14
Critically Endangered :- 632
Endangered :- 527
Vulnerable :- 1004