Related FAQs:  TWA Invertebrates, Fishes of the Tropical West Atlantic, Tropical West Atlantic 2,  Related Articles: Algae, Vascular Plants, Introduction to Fishwatcher's Guide Series Pieces/Sections, Lachnolaimus maxiumus/Hogfish, Hogfishes of the Genus Bodianus,  Invertebrates, Algae and Vascular Plants of The Tropical West Atlantic: Bahamas to Brazil, Part 10 To: Part 1, Part 2, Part 3, Part 4, Part 5, Part 6, Part 7, Part 8, Part 9, Part 10, Part 11, Part 12, Part 13, Part 14, Part 15,

Bob Fenner

Mollusks

The Class Gastropoda, the Snails: are divided into two Subclasses: Prosobranchia and Opisthobranchia, 

Subclass Prosobranchia: In turn divided into three living Orders: Archaeogastropoda, Mesogastropoda and Neogastropoda. Marine, freshwater and terrestrial. Name refers to the position of the internal organs and mantle cavity; anterior vs. the opisthobranchs where these are located posteriorly in the body. Aquatic species with one or two gills,  Most have a shell and operculum (closeable cover). Most are dioecious (separate sexes). 

Egg Cowries, Shuttle Shells, Family Ovulidae:

Cyphoma gibbosum (Linnaeus 1758), the Flamingo Tongue. Tropical West Atlantic. To about an inch in length. Found principally on the Gorgonians Gorgonia flabellum and G. ventalina. Bahamas photos.

Cyphoma macgintyi , the Spotted Cyphoma (an Allied or Egg Cowries, family Ovulidae, Subclass Prosobranchia, Class Gastropoda...). This delightful small snail discovered at a LFS in San Diego (Fountain's) on a branch of an imported Gorgonian (which they feed on)

Superfamily Strombacea: Predominantly large mollusks with heavy shells with flared lips, siphonal canals. 

Family Xenophoridae: Struthiolaria, Aporrhais, the Conchs: Lambis, Strombis. 

Strombus alatus, the Florida Fighting Conch. Here fighting after death so it seems with a Queen Conch. most 2 1/3 to 3 1/2 inches. To five inches maximum. Shells with large knobs as last whorl of spires. Opening reddish orange in life. Head mottled brown, with long whitish eye stalks, large white ended proboscis.

Strombus gigas, the Queen Conch. 6-9 inches typically, to 12 in. maximum. Have large shells bearing a short conical spire with blunt spikes. Shells orangish, often covered with algae. Opening rosy pink. Covered by a claw-like operculum. Head gray with long tentacled eyes.  Live in Seagrass beds, cultured for aquariums. Below, a two inch cultured individual, an adult shell occupied by a large hermit crab in Cozumel, and typical in-the-wild appearance in Belize.

Superfamily Tonnacea. Heavy marine snails. The Helmet Shells: Cassis, Cassidarius. Bonnets: Phalium. Tritons: Cymatium. Tuns: Tonna. 

Family Cassididae: Helmuts. Typically of globular shells with short spires and apex whorls, and a vertical groove which the animals siphon protrudes. Feed almost exclusively on urchins. 

Cassis cornuta (Linnaeus 1758), the Horned Helmut. One of four species found in Hawai'i. Common in shallow sandy environments. Found buried in sand with only whorls in evidence. Largest Hawai'ian Helmut (to 15"); used as a "blow horn" by natives in shows. Some authors believe specimens with fewer, higher horns are males, shorter, more numerous females. Kona pix.

Cassis flammea, the Flame Helmet. Helmet shaped shell, with thick outer lip banded in seven or eight dark stripes. Feed at night on sea urchins... overtaking and consuming them spines and all. Bahamas pic.

Order Neogastropoda: The Advanced Gastropods. Possess a single monopectinate gill, and a solitary auricle and nephridium. Triturating mechanism is a radula with three teeth to a transverse row (termed a rachiglossate condition) and osphradia with bipectinate folds. Entirely marine. 

Superfamily Buccinacea: Snails of many forms with long siphonal canals. Whelks (Buccinidae): Buccinum, Neptunea. Melongenidae: Busycon. Tulip Shells (Fasciolariidae): Fasciolaria, Mud Snails (Nassariidae): Nassarius, Ilyanassa.

Family Fasciolariidae: Tulip Snails

Fasciolaria tulipa, True Tulip. Shell spindle-shaped. Patterned in broken spirals of variable shape. Body dark colored, brown operculum. 3-6 inches usually, 10 maximum. Cozumel pic*.

Subclass Opisthobranchia, Sea Slugs, Largely are missing or have reduced shells. Have other (chemical, biological defenses), camouflage. Comprise five living Orders: Anaspidea (Sea Hares), Cephalaspidea (Bubble Shells and Headshield Slugs), Notospidea (Side-Gilled Slugs), Nudibranchia (Nudbranchs) and Sacoglossa (Sap-Sucking Slugs). Opisthobranch means "gills behind" where most of these gastropods have their gills and anus situated (as opposed to the prosobranch snails with their anus and gills up front). Opisthobranchs are hermaphroditic, both functional females and males in one body, though cross-fertilization is the rule. Laid eggs in clusters or bands hatch out to pelagic trochophore larvae which metamorphose into veligers, finally settling down as miniatures of their parents. There are some 2,000 species worldwide, and about 150 of these can be found in Hawaiian waters. 

Order Anaspidea, Sea Hares: Named for their rabbit ear-like projections called rhinophores (used for taste, current detection), and two anterior-projecting oral tentacles. Some can swim in the water column. Herbivorous, eating Red, Green, Brown Algae and Seagrasses. Can be dangerous in captivity if disturbed to the point of releasing fish-repelling purple "ink"...

Family Aplysiidae: In old Hawai'i sea hares were called Kualakai and some were cooked in an imu wrapped in ti leaves... and consumed.

Aplysia dactylomela, the Spotted Sea Hare. 3-6 inches usually, 12 in. maximum. Shallow to 120 feet in depth. Tropical West Atlantic. Feed on algae. Discharge purple "ink" if disturbed... may be problematical in captive conditions. Two photographed at night off of Cozumel.

Order Sacoglossa: Sap-Sucking Slugs. Specialized feeders on algae, mainly seaweeds in shallow waters (Common name for having a radula of one row of piercing teeth for suctorial feeding on algae... whose chloroplasts they sometimes retain and use for solar-powered sources of sugars). Shelled and shell-less/slug-like. Elysia, Alderia, Berthelina. 

Elysia (Tridachia) crispata, the Lettuce Sea Slug (not a nudibranch), may be brown, green or yellow in general coloration. Needs live rock, algal growth for food. Take care to screen pump intakes as this animal is often sucked into them. To 1 1/2 inches in length. Aquarium and Bonaire photos.

Order Nudibranchia- Naked-gill sea slugs. Largest of the five Orders of Opisthobranch gastropods. Lack shells, are carnivorous (feed on sessile invertebrates like sponges, sea fans, hydroids, corals... some are predaceous on other nudibranchs.). Lack predators by and large themselves due to unpalatability, toxicity, venom... mainly from recycled molecules via their prey. 

Considering their small size, often bizarre body shapes and dazzling coloration, it's no wonder nudibranchs are often unidentified by divers, aquarists and tide-poolers for what they are; marine snails that lack shells, just like their lowly terrestrial cousins found sliming around under rotting wood and vegetation.

But most of us emote "oohs" and "aahhs" rather than "yecch" when we view these "butterflies of the sea". Unfortunately, few efforts at keeping them in captivity have been successful. Many failures, as you'll see, are aquarist-originated; chemical poisoning, unstable conditions, and most importantly, starvation.

Suborder Dendronotacea:

Family Chromodoridae:

Chromodoris nyalya Red-Line Blue Sea Goddess. Occasionally found in Florida, S. Bahamas. To 3/4 ". This one off Bimini.

Family Bornellidae:

Bornella calcarata Borch 1863. Tropical West Atlantic.

Bivalve Mollusks: Shellfish with two opposing shells that are hinged at one end with an elastic byssal material and brought together with attached muscles. May be attached to hard substrates, burrowed into same or wood, buried in sand, mud or free-living, able to jettison about with powerful discharges of water from their exhalant siphons. 

    Most bivalves are filter-feeders, sifting food through their gills, which also function as respiratory organs. Some notable aquarium species, the giant clams (family Tridacnidae) utilize endosymbiotic algae (zooxanthellae) to produce food through exposing their mantles to bright light.

Flame Scallops that are not. Pen Shells, family Limidae: A popular item, particularly Lima scabra out of the Caribbean. Most all of these die in short order from starvation. Need frequent "immersion type" feedings... daily.

Lima (Limaria) scabra (Born 1778), sold as "Flame Scallops" in the aquarium interest, this is aka the Rough Fileclam of the Penshell family Limidae. Can "swim away" if threatened. A beautiful animal that generally starves in captivity due to a lack of food. Aquarium images of not so healthy and healthier specimens, and a real good specimen... in the wild (St. Thomas, U.S.V.I.)

Thorny Oysters, Family Spondylidae: Have sturdy, ribbed shells, sometimes with continuing projections at their openings. Attached to rocks. When open have colorful mantles and small bluish eyes. Four Hawaiian species. 

Spondylus americanus Herman 1781, the Atlantic Thorny Oyster. Caribbean. To four inches across. Here off St. Lucia and the Bahamas in the Caribbean.

Family Pinnidae: Penshells

Pinna carnea, the Amber Penshell. Found singly in mud, sand, interspersed between rocks on reefs, fore-reefs. Look like their thin shells were stuck in the sand facing up, slightly agape. Tropical west Atlantic. Bonaire pic of a view from above.

Family Pteriidae: Wing Shells

Pteria colymbus, Atlantic Wing-Oyster. Tropical West Atlantic. 2-3 inches. Found attached to Gorgonians, mostly Sea Plumes. Often overgrown in turn by other organisms. Turks photo.

Cephalopods: "Head feet"... the brainy Mollusks. Masters of disguise, ambush, speed (well, for some).  

Octopus macropus, the White-Spotted Octopus. 12-20 inches. Here is a small individual off of Cozumel at night.

Octopus vulgaris Cuvier 1797, Common Octopus. Worldwide in tropical seas. Have a dark ring around each sucker.  Most commonly occurred octopus species out during the day. One in Cancun, Mexico, another in St. Thomas, U.S.V.I.

To: Part 1, Part 2, Part 3, Part 4, Part 5, Part 6, Part 7, Part 8, Part 9, Part 11, Part 12, Part 13, Part 14, Part 15,