Exercise 5 - Mollusca

• Phylum Mollusca is the second most diverse group of animals on the planet with over 93,000 described species.
• Molluscs are soft-bodied unsegmented schizocoelous protostomes.
• What are the 8 classification of Mollusca?

  1. Caudofoveata
  2. Solenogastres
  3. Monoplacophora
  4. Polyplacophora
  5. Scaphopoda
  6. Gastropoda
  7. Bivalvia
  8. Cephalopoda
• Class Caudofoveata - Wormlike marine molluscs; their body covered by calcareous scales or spicules rather than shells; radula present but reduced in some forms.
• Class Solenogastres - Similar features with members of Class Caudofoveata, however, radula and gills are usually absent. These molluscs have ventral longitudinal groove that runs nearly the length of the body.
• Class Monoplacophora - Small with low, rounded shell and a creeping foot; body characterized by extensive serial repetition (e.g. gills).
• Class Polyplacophora - bilaterally symmetrical; with broad ventral foot and eight overlapping plates; with ctenidia.
• Class Scaphopoda - Ctenidia present; cylindrical and pointed with opening at the apex; head with specialized tentacles (captula).
• Class Gastropoda - Asymmetrical; well - developed head and foot, usually with a single spirally coiled shell.
• Class Bivalvia - Bilaterally symmetrical; buccal mass absent; enlarged ctenidia and labial palps; feeding through a siphon; two valves connected by a single ligament.
• Class Cephalopoda - bilaterally symmetrical;  with  oral  arms  and tentacles equipped with suckers around head.
• What are the samples under class Polyplacophora?

  Acanthozostera and Cryptoplax
• Acanthozostera - This Chiton has an oval body with eight overlapping uniform calcareous dorsal plates. The lateral margin or girdle is covered bands of black and gray spines. A single muscular foot can be found ventrally surrounded by a mantle groove, a depression accommodating the ctenidia.
• Cryptoplax. The body of this chiton is long and vermiform. The eight dorsal plates are very small and not overlapping. The girdle has a wide band covered with very small spines while gill rows along the mantle groove are restricted to the posterior third of the foot.
• Class Scaphopoda

  Dentallium - The shell of this mollusc is slightly curved and open at both ends which became the basis of its common name as tooth shell or elephant’s tusk shell. The shell has ribs (protrusion) and has light blue green coloration.
• The head has modified tentacles known as captacula for capturing food.
• What is the subclasses under class Gastropoda?

  Subclass Prosobrachia, Opisthobranchia, and Pulmonata
• Subclass Prosobrachia - Spirally coiled shelled marine, freshwater and terrestrial molluscs with anterior mantle cavity. Head region with tentacles bearing basal eyes and with calcareous operculated creeping foot.
• What are the specimens under subclass prosobrachia?

  1. Acmaea
  2. Haliotis
  3. Tonna
  4. Conus
  5. Lambis
  6. Oliva
  7. Cypraea
  8. Pomacea canaliculata
• Acmaea - This limpet attached with its powerful foot to rocks along the tidal marks. Its solid conical apex shell is open on its base. The shell has 7-8 prominent ribs. The interior of the shell has distinctive muscle scar.
• Haliotis - Also known as abalone, it has a cup-shaped shell with body whorl making up most of its shell. The spire is very low. A row of holes is arranged on the lateral side of the body whorl. The interior of the shell is shiny, marking the nacreous layer.
• Tonna - This tun shell has large, globular and inflated body whorls with very wide aperture with scalloped margins. The body whorl has prominent varices and can vary in color.
• Conus - This cone shell has low spire and conical body whorl. Its aperture is long and narrow. The body whorl has inverted triangle configuration. This animal is considered as one of the venomous because of its conotoxins. Currently, such biochemical compounds are studied for their potential role in medicine.
• Lambis - Commonly known as spider or scorpion shell, this mollusk can be readily identified by the processes projecting from the aperture lip margin. The body whorl is expanded while the spire is very low.
• Oliva - This olive shell has distinctive cylindrical body whorl with a very low spire. The color varies from deep green to dark brown with unique patterns specific for a species. The aperture is long and narrow.
• Cypraea. This cowry has a globular dorsal shell flattened at the ventral aspect and superficially resemble as bilateral due to the complete enclosure of the body whorl with the previous and thus hiding the spire. Cypraea tigris is the tiger cowry with dark brown spots on its shell.
• Pomacea canaliculata - Known as the golden apple snail, this agricultural pest has globular shell concentrated on its body whorl. Shell color ranges from light to dark brown.
• What are the specimens under subclass Opisthobranchia?

  Dolabella and Chromodoris (nudibranch)
• Dolabella - This sea hare has a triangular body with two pairs of tentacle, the rolled- up rhinophores and oral tentacles located on either side of the mouth. This species together with its relative Aplysia is widely used in comparative neurobiology and animal behavior because of their large and easily dissected nerve cells.
• Chromodoris (nudibranch) - This shell - less marine mollusk has exposed gills and bears a pair of rhinophores, which are chemosensory organs that is uses to detect food. It has vivid coloration when alive from reds to blues enabling it to advertise itself as a very poisonous animal.
• What are the specimens under subclass pulmonata?

  1. Radix quadrasi
  2. Ryssota otaheitana
  3. Helicostyla rufogaster
  4. Achatina fulica
• Radix quadrasi - This freshwater lymnaeid snail has no operculum and with thin subglobular shell. It has a single pair of tentacle and eyes located at its base. It has a pointed spire and an enlarged body whorl. Shell color ranges from light to dark brown.
• Ryssota otaheitana - This endemic and edible land snail locally known as bayuko has thick discoidal shell with laterally projecting body whorl which is also oriented downward. Shell periostracum color is light brown that is easily removed exposing the white inner prismatic layer.
• Helicostyla rufogaster - This is the largest helicostylid land snail of Mt. Makiling and locally known as bayukong tulis. It has conical brown shell with a blunt spire and marked white oblique bands. The aperture is wide with dark rounded thickened lips.
• Achatina fulica - Known as Japanese Garden Snail, it is an introduced mollusk to the country. Initially used as delicacy, this snail later became an invasive species. It has a brown conical shell with pointed spire. The body whorl is expanded with white bands. The aperture is wide with thin lips.
• What are the specimens under class Cephalophoda?

  1. Loligo
  2. Nautilus
  3. Argonauta
  4. Octopus
• Loligo - The squid is a cephalopod with a modified head-foot region.
• Nautilus - This chambered nautilus has shell oriented in a single plane and is marked with red or brown bands.
• Argonauta - This unchambered paper nautilus has scalloped edges and prominent ribs on its very thin shell which are spirally arranged. The shell has white to light brown coloration. The thin shell occurs only in females and functions as an egg case.
• Octopus - This is a well-known cephalopod with globular head and eight oral arms. It has prominent lateral eyes analogous to those of vertebrates. Locate the mouth and note that it is equipped with beaks for crushing hard prey such as shelled molluscs and crustaceans.