LESSON 8: MOLLUSCS

• • Second largest group of animals where 31% is found in the Philippines
  • 50% of 1294 Philippine land snails are in Luzon
• Ecological Significance

  • indicators of a healthy ecosystem
• Anthropogenic Significance

  • agricultural pets

  Economic Significance

  • Pearl farming

  Medical Significance

  Other Significance

  • ornaments and tools
• Sources of natural products

  • Conus is one of the richest source of bioactive peptides
  • potential molluscicides
  • insecticides
  • antimicrobial agents
• Cosmeceutical potential of land snails

  • Lissanta fulica (Giant african snail)
  • introduced to the PH in 1942 during WWII
  • viable candidate for snail farming due to their large size and adaptability to a wide range of food and environmental conditions
• Land snails as part of Filipino diet

  A) marida

  B) berber

  C) talkok

  D) bayuko

  
• Position of Molluscs in the Animal Phylogeny

  • Lopotrochozoa
  • trocophore larvae
  • spiral cleavage
  • Molluscan origin hypotheses
  • flatworm ancestor
  • non segmented coelomate ancestor
  • segmented ancestor
  • Potential sister groups
  • Sipuncula
  • Annelida

  
• General body plan

  A) visceral mass

  B) radula

  C) mouth

  D) mantle

  E) foot

  
• Defining Characteristics

  1. Dorsal epithelium forms a mantle, which secretes calcareous spicules or one or more shells
  2. Cuticular band of teeth (radula) in the esophagus
  3. Ventral body wall develops into a locomotory or clinging foot.
• Layers of the Shell

  1. Periostracum - outer organic layer
  2. Prismatic - thick, middle calcite prisms
  3. Nacreous - thin, innermost calcareous tablets (nacre)

  A) periostracum

  B) prismatic layer

  C) nacre

  
• Method of feeding

  • R: Radula
  • O: Odontophore - radular assembly with complex musculature
  • M: Mouth
  • E: Esophagus
• Types of radulae

  A) docoglossan

  B) rhipidoglossan

  C) taenioglossan

  D) stenoglossan

  E) toxoglossan

  F) sacoglossan

  
• Molluscan circulatory system

  • hemoglobin and hemocyanin
  • Scapophods lack heart
  • Closed in cephalopods
  • Open circulatory system with large sinuses
• What is the classification of the class Aplacophora?

  Not shell bearing
• How many plates do organisms in Class Polyplacophora have?

  1. 8 plates
• What is the defining feature of Monoplacophora?

  One shell bearing
• What does the term "stomach foot" refer to in Class Gastropoda?

  It refers to their unique locomotion mechanism
• What type of shell do gastropods have?

  Univalve shell
• What are the three subclasses of Class Gastropoda?

  Prosobranchia, Opistobranchia, Pulmonata
• What characterizes the subclass Prosobranchia?

  Anterior gills; snails
• What organisms are included in the subclass Opistobranchia?

  Sea hares, sea slugs, bubble shells
• What is the defining feature of the subclass Pulmonata?

  Lung; land snails and slugs
• What is the common name for Class Bivalvia?

  Hatchet foot
• What are the three subclasses of Class Bivalvia?

  Protobranchia, Lamellibranchia, Septibranchia
• What characterizes the subclass Lamellibranchia?

  Plate gill; mussels
• What is the defining feature of the subclass Septibranchia?

  Fence gill; shipworms
• What is the common name for Class Scapophoda?

  Spade foot; tusk shell
• What is the defining feature of Class Cephalopoda?

  Head foot; squids, octopi, Nautilus
• What are the main classes of taxa in the classification system provided?

  • Class Aplacophora
  • Class Polyplacophora
  • Class Monoplacophora
  • Class Gastropoda
  • Class Bivalvia
  • Class Scapophoda
  • Class Cephalopoda
• Class Aplacophora

  • cylindrical, vermiform
  • 300 species in the deep ocean
  • unsegmented body with numerous calcareous spines embedded in the outer cuticle
  • with radula
• Class Polyplacophora

  • shells form a series of 7-8 articulating plates
  • 800 species
  • intertidal; on rocks
  • Aesthetes - organs derived from mantle extending from holes of plates (light receptors)
  • Pharyngeal/sugar glands - release amylase-containing secretions into the stomach
• Class Monoplacophora

  • 3-6 pairs of ctenidia; multiple pairs of pedal retractor muscles; 6-7 pairs of nephridia
  • 20 extant species; all marine collected at 2,000m
  • Single, unhinged limpet-shaped shell
• Class Scapophoda

  • tusk-shaped, conical shell open at both ends; development of anterior thread-like adhesive feeding tentacle (captacula)
  • 300-400 marine species