Mollusca Lab

Class Polyplacophora (Chiton)

Class Gastropoda (Snails and Slugs)

Subclass Prosobranchia (Sea snails, Land snails, Freshwater snails)

          Subclass Opisthobranchia (the sacoglossans, anaspidean sea hares, pelagic sea                                                                    angels, sea butterflies, and Nudibranchia)

            Subclass Pulmonata (snails and slugs characterized by the ability to breathe air)

Class Bivalvia (Marine and Freshwater Molluscs)

Class Cephalopoda (Octopi and Squid)


  • eight dorsal plates- Chiton
  • foot- In bivalves, the foot is pointed and used for digging. The muscular foot is located on the underside on mollusks.
  • girdle- The girdle is a strong but flexible structure that in most cases encircles the plates, holding them all together.
  • mouth- Most mollusks have radulas, or tonguelike structures covered with interlocking teeth that slice and steer prey down their throat.
  • ctenidia- A respiratory organ or gill.
  • head- The head contains the sense organs and “brain,” while the visceral mass contains the internal organs.
  • tentacles- Used for grasping and feeding and also as sensory organs.
  • eyes-  Molluscs have eyes of all levels of complexity, from the pit eyes of many gastropods, to the pinhole eyes of the Nautilus, to the lensed eyes of the cephalopods. Compound eyes are present in some bivalves, and reflective ‘mirrors’ have been innovated by other lineages such as scallops.
  • siphon- A tube-like structures in which water flows. The water flow is used for locomotion, feeding, respiration, and reproduction. The siphon is part of the mantle of the mollusc, and the water flow is directed to or from the mantle cavity.
  • mantle-The dorsal body wall which covers the organs of digestion, reproduction and movement. The epidermis of the mantle secretes calcium carbonate and conchiolin, and creates a shell.
  •  operculum- Like a “trapdoor”, it allows mollusks to shut themselves in their shell when they feel they are in danger. 
  • byssal threads-They are small proteinaceous “ropes” extending from the muscular foot. Juvenile mussels them like climbing ropes, extending, attaching, and pulling themselves forward in succession.
  • whorls- A complete revolution in the growth of a mollusk shell.
  • spire-A spire is a part of the coiled shell of molluscs. The spire consists of all of the whorls except for the body whorl. Each spire whorl represents a rotation of 360°.
  • apex- The pointed tip of the shell.
  • aperture-This is the main opening of the shell, where the head-foot part of the body of the animal emerges for locomotion and feeding.
  • pneumostome-It is an opening in the right side of the mantle which is part of the respiratory system.
  • radula-Similar to a tongue. It is a  toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food enters the esophagus.
  • gills- Aquatic mollusks use these to breathe.
  • incurrent and excurrent siphons-The mantle of the two sides comes together at the posterior end of the clam to form the incurrent and excurrent siphons.
  • palps-pair of elongated, often segmented appendages usually found near  the mouth.
  • heartIt consists of one or more pairs of atria which receive oxygenated blood from the gills and pump it to the ventricle, which pumps it into the aorta and eventually opens into the hemocoel.
  • adductor muscles- The main muscular system in bivalves. They are located on the anterior and posterior sides. 
  • visceral mass-It generally holds the bulk of the digestive, reproductive, excretory, and respiratory systems.
  • gonads-The reproductive organs.
  • glochidia- The larval stage of some freshwater mollusks.
  • funnel- The single siphon in cephalopods.
  • arms- They have suckers attached to them.
  • fins of the squid- Attatched at the mantle and positioned dorsally.
  • umbo- The most prominent, highest part of each valve of the shell of a bivalve or univalve mollusk.
  • right and left valves- Bivalves have two shells or valves, a “right valve” and a “left valve”, that are joined by a ligament.
  • anterior- Where the foot protrudes from.
  • posterior- Where the siphon protrudes from.
  • ink sac- Expels a cloud of dark ink to scare and get away from predators.
  • branchial hearts- Gill hearts that move blood through the capillaries of the gills.
  • systemic heart- Pumps the oxygenated blood through the rest of the body.
  • Stomach- Found in the middle of the visceral mass.
  • digestive caecum- The pouch at the beginning of the large intestine where most of the digestion and absorption of nutrients takes place.
  • pen- A hard internal body part found in many cephalopods.
  • funnel retractor muscle- Helps control the direction that the squid swims in.
  • “kidney”- It filters waste from the organism from the blood.