CLASS APLACOPHORA; 2 SUBCLASSES, EACH WITH A SINGLE ORDER)

• Vermiform, laterally compressed, marine; without a shell; with mantle enveloping body except for a longitudinal ventral pedal groove, mantle with one or more layers of calcareous bodies; preoral sense organ in front of subterminal ventral mouth; ventrosubterminal posterior mantle cavity without ctenidia (text with tooltip) Ctenidia (ctenidium, sing.) are comb-like structures that function as respiratory organs in mollusks. Ctenidia can also be applied to the rows of fused cilia in ctenophores that form the ctenes. , sometimes with secondary gills; without excretory organs, some without radula; ganglia fused, with both ventral and dorsolateral longitudinal nerve cords; hermaphrodite; eat and often live on cnidarians. ~300 extant species.

• Subclass Chaetodermomorpha:
  • Chaetoderma, Falcidens, Limifossor, Psilodens, Scutopus.

• Subclass Neomeniomorpha:
  • Chevroderma, Dondersia, Epimenia, Kruppomenia, Neomenia, Proneomenia, Pruvotina, Rhopalomenia, Spengalomenia.

CLASS MONOPLACOPHORA (1 ORDER)

• Small, deep sea, almost bilaterally symmetrical; with single cap- or cone-shaped dorsal shell; body with distinct head and radula, without eyes or sensory tentacles (except around the mouth); foot weakly muscular; anus median, posterior; mantle cavity large, extending laterally and posteriorly around the foot with 5-6 pairs of ctenidia; 8 pairs of pedal-retractor muscles; 6 metanephridia; sexes separate; fertilization external. ~20 extant species known, but many more are presumed to occur in the deep oceans.
  • Laevipilina, Micropilina, Monoplacophorus, Neopilina, Rokopella, Vema.

CLASS POLYPLACOPHORA (3 ORDERS)

• Elongate or oval, dorsoventrally flattened, bilaterally symmetrical, marine; with dorsal shell of 8 transverse, serially overlapping plates embedded in, and sometimes covered by, a girdle; cuticle of girdle spines, scales or bristles; large, muscular, ventral foot; poorly-differentiated head without eyes or tentacles; mantle cavity a groove around foot, with 6-88 pairs of ctenidia; anus subterminal; radula present; without jaws; sexes separate; mostly with larval stages. ~800 extant species.
  • Chloriplax, Lepidochiton, Lepidopleurus, Oldroydia.
  • Callistochiton, Chaetopleura, Ischnochiton, Katharina, Lepidozona, Mopalia, Placiphorella, Schizoplax, Tonicella.
  • Acanthochitona, Chitona, Cryptochiton, Cryptoplax.

CLASS GASTROPODA (15 ORDERS IN 3 SUBCLASSES)

• Asymmetrical; with single, often spiral coiled shell into which body can retract (shell lost in some); during development, visceral mass and mantle rotated relative to head and foot through 180o, so mantle cavity anterior and gut and nervous system in U-shape; head with tentacles and eyes, with jaws and radula; muscular creeping foot (modified in some); mantle cavity with 1 pair of bipectinate ctenidia, often reduced or lost; hermaphroditic or with separate sexes; planktonic larvae or direct development; fertilization external or internal. Probably 60,000 extant species, but estimates range from 40,000 to 100,000.

• Subclass Prosobranchia:
  • Perotrochus, Pleurotomaria, Scissurella, Haliotis, Diodora, Fissurella, Lucapinella, Puncturella, Acamea, Collistella, Lottia, Calliostoma, Margatites, Patella, Tegula, Trochus, Astrea, Nerita, Theodoxus, Alcidia, Helicinia, Crepidula.
  • Hydrobia, Viviparus, Littorina, Turitella, Caecum, Serpulorbis, Tripsycha, Vermetus, Vermicularia, Cerithium, Liocerithium, Cerithidea, Strombus, Epitonium, Janthina, Hipponix, Capulus, Calyptraea, Crepidula, Crucibulum, Carinaria, Natica, Polinices, Erato, Trivia, Cypraea, Jenneria, Ovula, Simnia, Malea, Cassis, Ficus.
  • Buccinum, Cantharus, Macron, Metula, Anachis, Columbella, Mitrella, Nassarina, Pyrene, Strombina, Coralliophila, Latiaxis, Fasciolaria, Fusinus, Leucozonia, Troschellia, Harpa, Garnula, Melongena, Mitra, Subcancilla, Cerastoma, Hexaplex, Murex, Phyllonotus, Pteropurpura, Pterynotus, Acanthina, Morula, Neorapana, Nucella, Purpura, Thais, Nassarius, Cymbium, Lyria, Voluta, Admete, Cancellaria, Conus, Crassispira,Terebra.

• Subclass Opisthobranchia:
  • Acochlidium, Unela.
  • Acteon, Aglaja, Bulla, Chelidonura, Haminoea, Navanax, Retusa, Rictaxis, Scaphander.
  • Ilbia, Runcina
  • Berethellina, Elysia, Oxynoe, Tridachia.
  • Aplysia, Dolabella, Stylocheilus.
  • Clio, Limacina.
  • Clione.
  • Berthellina, Gymnotoplax, Pleurobranchus, Tylodina.
  • Acanthodoris, Aegires, Aeolidia, Aeolis, Armina, Cavolina, Chromodoris, Corambe, Coryphella, Dendrodoris, Dendronotus, Diaulula, Doris, Embletonia, Fiona, Glaucus, Hermisenda, Hexabranchus, Hopkinsia, Limacina, Janolus, Phidiana, Philine, Phyllidia, Platydoris, Pneumoderma, Polycera, Rostanga, Scyllaea, Tambja, Trinschesia

• Subclass Pulmonata:
  • Cassidula, Ellobium, Otina.
  • Bulinus, Carychium, Chilina, Lanx, Physa, Planorbis, Polygyra, Siphonaria, Trimusculus.
  • Achatina, Arion, Bulimulus, Cepaea, Haplotrema, Helix, Liguus, Limax, Megaspira, Oreohelix, Pupilla, Rachis, Succinea, Vertigo.
  • Onchidella, Onchidium, Rhodope.

CLASS CEPHALOPODA (5 ORDERS IN 2 SUBCLASSES)

• Bilaterally symmetrical with linearly-chambered shell with characteristic sutures (text with tooltip) A suture is an immovable joint (e.g. in the bones of the vertebrate skull and the shells of chambered cephalopod mollusks). between the chambers, often the shells are reduced or lost; when external shell present, animal inhabits last chamber, a thin filament of living tissue (the siphuncle (text with tooltip) The siphuncle is a thin strand of living tissue in nautiloids that connects the animal's body to the chambers of the shell. ) extending through older chambers; head with large, complex eyes and circle of prehensile tentacles around mouth; mouth with a radula and a beak; mantle muscular, large ventral cavity present with gills, with opening beneath head; reduced foot forming a siphon (text with tooltip) A siphon is a funnel-shaped tube that connects the mantle cavity to the outside in marine mollusks. through which water forced by contraction of mantle, providing jet propulsion; sexes separate, some tentacles of male modofied for copulation; benthic or pelagic marine. ~700 extant species (>10,000 extinct taxa known).

• Subclass Nautiloidea (also called Tetrabranchiata):
  • Nautilus.

• Subclass Coleoidea (also called Dibranchiata):
  • Rossia, Sepia, Spirula.
  • Architeuthis, Bathyteuthis, Chiroteuthis, Doryteuthis, Dosidiscus, Gonatus, Histioteuthis, Illex, Loligo, Lycoteuthis, Octopoteuthis, Ommastraphes.
  • Argonauta, Octopus, Opisthoteuchis, Stauroteuthis.
  • Vampyroteuthis.

CLASS SCAPHOPODA (2 ORDERS)

• Bilaterally symmetrical, with an elongate body in tubular 1-piece shell, that is tapered and open at each end; often the shell is curved like an elephant-tusk; mantle cavity large, extending along whole ventral surface, without gills; head without eyes, with radula, and paired clusters of clubbed contractile tentacles (capitula), head projecting from larger aperture of shell; foot cylindrical; sexes separate; fertilization external; benthic marine. ~500 extant species.
  • Dentalium, Fustiaria, Laevidentalium, Pulsellum, Annulipulsellum, Cadulus, Gadila.

CLASS BIVALVIA (ALSO CALLED PELECYPODA OR LAMELLIBRANCHIATA; 10 ORDERS IN 6 SUBCLASSES)

• Bilaterally symmetrical; laterally compressed body enclosed within 2 calcareous, lateral shells, each usually with a beak-like umbo (text with tooltip) An umbo is the beak-like structure on a bivalve shell and the swollen part of the cone scale. , hinged dorsally by an elastic ligament and closed by large adductor muscles (text with tooltip) Adductor muscles are pillar-like muscles that serve to close the shells of bivalve mollusks. ; large mantle cavity, with posterior edges of mantle sometimes fused to form siphons; 1 pair of ctenidia, very large in most species and used for filter-feeding; greatly reduced head, without eyes or radula; mouth with palps; foot laterally compressed, often greatly reduced, in some forming burrowing organ; sexes usually separate; fertilization external; larval stages aquatic, benthic, sedentary or sessile. The unionid clams with semi-parasitic larvae called glochidia (text with tooltip) Glochidia (glochidium, sing.) is the distinctive larval stage of freshwater unionid clams. The glochidium is parasitic on the gill rakers of fish. . ~8,000 extant species.

• Subclass Palaeotaxodonta:
  • Acila, Malletia, Nucula, Yoldia.

• Subclass Cryptodonta:
  • Solemya.

• Subclass Pteriomorphia:
  • Adula, Brachydontes, Lithophaga, Modiolus, Mytilus, Anadara, Arca, Barbatia, Glycymeris, Crassostrea, Ostrea, Pinctada, Pteria, Malleus, Atrina, Pinna, Lima, Chlamys, Lyropecten, Pecten, Spondylus, Anomia, Pododesmus.

• Subclass Palaeoheterodonta
  • Lampsilis, Anodonta, Ensis, Quadrula.

• Subclass Heterodonta
  • Clinocardium, Laevicardium, Trachycardium, Cardita, Tridacna, Mactra, Ensis, Solen, Florimetis, Macoma, Tellina, Leptomya, Semele, Donax, Chione, Dosinia, Pitar, Protothaca, Tivela, Corbicula, Cardium, Mercenaria, Unio
  • Barnea, Chaceia, Martesia, Pholas, Bankia, Toredo, Corbula, Mya.

• Subclass Anomalodesmata:
  • Cuspidaria, Poromya, Pandora.