GASTROPODA Shelby Lynch, Gillian Johnstone

Anik Obomsawin, Chantalle Byron

INTRODUCTION • Snails and Slugs

• Class consisting of around ~65 000 species • ~30 000 ocean living• ~30 000 land on living • ~5 000 fresh water living

• Herbivores, carnivores (ex. Moon snail) and scavengers

4 DEFINING CHARACTERISTIC • Developed head – tentacles

• Foot used for motion

• Coiled shell

• Asymmetrical organism

*organs twisted in figure 8

*coils to right or left

*torsion in larval stage

CHARACTERISTICS

DEVELOPED HEAD• Tentacles

• Pigment eyes

• Central nervous system

TORSION & DEVELOPMENT

• During Veliger stage

• 180o turn and upward twist of the posterior- reposition it over the head

• Anus, mantle cavity, and gills above head

SPECIALIZED SHELL

• Asymmetric helical coiling

• Helps with protection

• Sealed off with operculum

SPECIALIZED RESPIRATION

• thin skin permeable for water- breathe through skin

• originally breathe by gills situated in the pallial cavity

SPECIALIZED RESPIRATION

• Loss of gills, and developed a vascularised lung from the mantle cavity

• Varied gill arrangement and respiration method

LIFE CYCLE

LIFE CYCLE

• Mating • Hermaphroditic species

• Fertilization

• Development• Trochophore Larval Stage• Veliger Larval Stage

EVOLUTION

• Basic Trends:• Changes in radula and shell morphology

• Loss of organs

• Changes in diet (herbivorous to carnivorous)

• Changes in habitat (seawater – freshwater – terrestrial life)

• Adoption of slug-like form

*changes occurred independently, at several times in gastropod history

EVOLUTION

PROSOBRANCH •Diotocardia: this species has two sets of mantle organs; most similar to generalised gastropod structure

•Trochacea & Neritacea: gradual loss of set of mantle organs on the right side of the body occur

•Monotocardia: only has one set of mantle organs; has fewer radula teeth; shift in diet, from algae and fungi to consumption of larger sessile organisms.

•Neogastropoda: peak of prosobranch evolution; marine predators with modified radular teeth, poison glands to aid catching prey, and reduction and loss of right mantle organs, more efficient respiration.

EVOLUTION

OPISTHOBRANCH

•Arose from an unknown primitive prosobranch group

•Show reduction of visceral hump and shell

•In some forms: an external cerata develops to provides a respiratory surface

•This replaces lost mantle-cavity surface and ctenidia

EVOLUTION

PULMONATES •Varying degrees of adjustments to freshwater and landlife

•Union of male and female gonoducts (more prevalent in advanced groups)

•More sophisticated means of water consumption

•Some pulmonates are predators of snails or earthworms

FACTS • On average they have a speed of 8cm per

minute • Radula- ribbon of teeth helping with food

consumption • Can store digested food in its liver for use

during inactive times• Warning coloration (bright shells) is present

in carnivore snails which produce poisons when catching prey • Range from 600mm to 0.5mm in size

SOURCES

• J. Mollus. Stud. (1988) 54 (4):367-441.doi: 10.1093/mollus/54.4.367

http://mollus.oxfordjournals.org/content/54/4/367.abstract

• http://www.ucmp.berkeley.edu/taxa/inverts/mollusca/gastropoda.php

• http://www.britannica.com/EBchecked/topic/226777/gastropod/35728/Evolution-and-paleontology

• http://www.nhc.ed.ac.uk/index.php?page=24.25.312.328.352

SOURCES• Solem , G. A. (2012, April 17). gastropod. Retrieved from

http://www.britannica.com/EBchecked/topic/226777/gastropod/35728/Evolution-and-paleontology

• (n.d.). Retrieved from http://www.ento.csiro.au/education/allies/gastropoda.html

• Nordsieck, R. (n.d.). Retrieved from http://www.molluscs.at/gastropoda/index.html?/gastropoda/morphology/respiration.html

• Myers, P., & Burch, J. B. (n.d.). Retrieved from http://animaldiversity.ummz.umich.edu/accounts/Gastropoda/

• (n.d.). Retrieved from http://shells.tricity.wsu.edu/ArcherdShellCollection/Gastropoda/Pulmonates.html