Spineless Wonders Trivia Quiz

Answer: Gastropod

Molluscs are an enormously diverse phyla with up to 200,000 species within the group. One would not think that such diverse creatures as snails, giant clams and cuttlefish (as seen in the cover photo) could share a common ancestor but they do. It's what makes this spineless group of animals so wonderful. They vary in size from snails that measure 0.7 mm (just over a quarter of an inch) to giant squid which can attain lengths of 12-14 m (40-46 feet).

The main distinguishing feature of molluscs is a hard outer shell that covers the top of the body and encloses the internal organs. Most molluscs have a distinct head region and a muscular foot, used for locomotion. However, the foot has evolved into many different variations, species-dependent. Two other unusual features of the molluscs are the mantle and a radula. The mantle is a tissue layer arranged between the shell and the body. It secretes a compound called calcium carbonate to form the shell. The mantle forms forms a cavity, between it and the body and the body. This cavity pumps water for filter feeding. The radula is a feeding organ. It has teeth made of chitin and is located in the mouth in the head region. The radula can scrape algae off rock surfaces or drill holes in the shells of other animals depending if the mollusc is a herbivore or carnivore.

Molluscs have a complete digestive system, though it differs radically from the more well-known mammalian system. Terrestrial molluscs exchange gases with the surrounding air within the lining of the mantle cavity. Aquatic molluscs respire underwater with gill-like organs which are thin filaments that absorb and emit gases between the blood and surrounding water. Their circulatory system has one, two or three hearts. The hearts are muscular and pump blood through the circulatory system (which may be open or closed, depending on the species) when the heart muscles contract.

There are four major groups within the phylum Mollusca:

Class Gastropoda contains the true snails and slugs which is the biggest within phylum Mollusca with at least 60,000 species in marine, freshwater, and terrestrial habitats.
Class Bivalvia are molluscs with hinged two-part shells such as clams, oysters, mussels, and scallops.
Class Cephalopoda are molluscs with large heads with eyes, and tentacles and include octopus, squid, cuttlefish, and nautiloids
Class Polyplacophora consists of chitons, snail-like molluscs with eight-part overlapping scale shells. This latter group is less well-known and, relatively speaking, has much fewer species.

Cornu aspersum, known by the common name of garden snail, is a species of land snail and, out of all terrestrial molluscs, this species is the most widely known. Characteristic of snails, it has a hard shell 25-40 millimetres (1-1.6 in) in diameter high, with four or five whorls. The body is soft and slimy, and can fully retract into the shell, which occurs when the animal is inactive or threatened. Unusually for land snails, It has no operculum (trapdoor) so during dry or cold weather the snail seals the opening of the shell with a thin layer of dried mucus.

Answer: Gastropod

Gastropods have a well-developed head, tentacles and an open circulatory system (which is comprised of a series of blood sinuses and cavities, rather than closed vessels associated with vertebrates). They are the most diverse group of molluscs with at least 50,000 species described, with snails and slugs appearing to be archetypes of the group. Most gastropods have a hard shell protecting the soft-bodied internal tissues. Some gastropods, such as sea slugs and garden slugs, lack a shell or have a reduced shell hidden in the folds of their mantle.

Most gastropods move around on a single flattened foot with many secreting mucus (known incorrectly as "snail trails") to help facilitate movement. Some can swim using extended folds of their mantle as fin-like appendages. Most snails and terrestrial slugs are herbivorous and use their radula to scrape algae from inorganic surfaces. Some use their radula to pierce plants. Some gastropods are carnivores, capturing other snails, worms, and fish for food.

Marine and freshwater gastropods breathe using ctenidia or gills. which are protected within the mantle cavity. Terrestrial slugs and snails, by comparison, have a mantle cavity that connects to the circulatory system which is vascularised to function as a rudimentary lung.

Limax cinereoniger, the ash-black slug, is a large species of air-breathing land slug in the terrestrial pulmonate gastropod mollusc family Limacidae, the keelback slugs. This is the largest land slug species in the world and measure in at between 10cm and 20cm (4-5 inches) long. Slugs are snails without shells. Some of these molluscs do have a shell, but the shell is internalised and it is used to store minerals.

Answer: Bivalve

Bivalves feature two half shells that open and close with a hinge, which gives them their name. They have no formed head and no brain. The circulatory system is open. Foot size is variable. Clams have a rectangular foot for moving along or for burrowing in sand or mud while oysters and mussels both have a small single foot, as they attach themselves to harder objects very early in life and then do not move. The related scallops do not use their small foot to move around but use a primitive form of jet propulsion, snapping their shells together which forces water out of the shell rim.

Bivalves are encompassed more by their shells than other types of molluscs. Water enters and exits a bivalve via two tubes called siphons. One siphon draws in water while the other drives out water and waste. Oxygen and food particles are suspended in the intake water. Examples of filter feeders include sponges, corals, and bivalve molluscs. Intake water flows across the gills. Oxygen and carbon dioxide are exchanged between the circulatory system and the water on the gill's surface which also contains mucus. This traps microscopic food particles, and then cilia hairs move the food-containing mucus toward the mouth.

Bivalves do not have a radula as they do not need it. The food is suspended in mucus to move through the digestive organs, where it is metabolised and absorbed. Some bivalves, (eg oysters), have mantles that secrete nacre, a shiny substance that coats any foreign particles (irritants) that lodge in the space between the mantle and the shell A pearl forms when layers of nacre coat the foreign particle.

The Pacific razor clam, Siliqua patula, is a species of large marine bivalve mollusc and is found along the Pacific West Coast of North America from Alaska to California. Its favoured habitat is in sandy beaches in the intertidal zone with water depths up to 9 m (30 ft). It has an oval narrow shell, from 8 to 15 cm (3 to 6 in). It is similar to the smaller Atlantic razor clam, Siliqua costata, which is found on the East Coast of the United States. It is well known because of its value as a foodstuff.

Answer: Cephalopod

The class Cephalopoda comprises approximately 800 living species and includes squid, octopi, cuttlefish, and nautili. They have highly developed nervous systems with complex brains that are capable of learning and remembering information and also have eyes that are able to form images. These two features alone make cephalopods the most intelligent invertebrates. They are the only molluscs with a closed circulatory system. A few are capable of very rapid movement including jet propulsion, a novel locomotive function. The shell is generally reduced in cephalopods, with the nautili species being an exception. Species of squid and cuttlefish have a much reduced internal shell that acts only as a scaffold, while octopi have lost the shell entirely. Octopus, squid, and cuttlefish species are able to change colour to camouflage themselves against their surroundings or to communicate with each other. These species have specialised pigment cells called chromatophores that induce these colour changes.

The common cuttlefish has two tentacles and eight arms. These are used for hunting prey such as small fish and crustaceans. When such a creature is within range, the cuttlefish shoots out its tentacles to seize the prey. This movement is so fast that it is hard to see with the naked eye.

Answer: Gastropod

Limpets are aquatic snails with conical shells ( "patelliform" - dish-shaped) that encompass the entire organism except for a very prominent foot on the underside of the shell. They resemble barnacles, which are not molluscs but arthropods, and mussels, which are bivalve molluscs that attach themselves to a fixed surface for their whole adult lives. However, limpets are capable of movement instead of being permanently attached in a single position.

Their circulatory system is open and is based on a single triangular three-chambered heart including an atrium, a ventricle, and an aorta bulb. The latter pumps the blood (haemocel) into the body cavity. Blood returns to the atrium via the circumpallial vein after being oxygenated by the circular set of gills located around the edge of the shell. The nervous system is quite well developed for an invertebrate.

Answer: Cephalopod

The colossal squid (Mesonychoteuthis hamiltoni) is, by far, the largest member of its family, Cranchiidae. It is sometimes called the Antarctic cranch squid or giant squid. There is also a giant squid in genus Architeuthis. It is believed to be the largest squid species in terms of mass and can reach at least 500 kilograms (1,100 lb), Its total length has been estimated between 10 metres (33 ft) and 14 metres (46 ft) .

The colossal squid has features common to all squids: a mantle for locomotion (jet propulsion), one pair of gills, a beak or tooth, and certain external characteristics like eight arms and two tentacles, a head, and two fins. With an estimated diameter of 27-30 cm (11-12 in), the colossal squid has the largest eyes of any known creature that has ever existed.

The colossal squid is found in the Southern Ocean north of Antarctica, north to South Africa, Australia and South America. It preys on large fish and smaller squid. Its predators are sperm whales and sleeper sharks.

Answer: Bivalve

The Pacific oyster, Magallana gigas, is also known as the Japanese oyster, or Miyagi oyster. It is native to the Pacific coast of Asia and, because of its role as a human food, is an introduced species in North America, Australia, Europe, and New Zealand.

The thin mantle produces a large robust shell - the two valves are slightly different in size and shape, with the right valve being somewhat concave. Like most bivalves, oysters have no head and the foot is primitive, allowing limited side to side locomotion and being used to bury itself in seabed sand or attach to artefacts in oyster aquaculture. There are gills for respiration but oysters lack a nervous system. Unlike other classes of mollusc they lack feeding structures and are filter feeders obtaining food in the same way they receive oxygen.

The use of Pacific oysters as a commercial foodstuff has facilitated selective breeding techniques resulting in oysters being farmed that are sometimes much larger than the oysters found in the wild.

Answer: Bivalve

The Pacific geoduck (Panopea generosa) is a species of very large saltwater clam in the family Hiatellidae. It is native to the coastal waters of the eastern side of the North Pacific Ocean from Alaska south to Baja California. The shell of the clam ranges from 15 cms to over 20 cms (6-8 in) in length but, with its very long siphons, this feature can make the geoduck almost 1 metre (3 ft 3 in) in length. The geoduck is the largest burrowing clam.

The shell has three layers - the periostracum, prismatic, and nacreous layers. The periostracum, a spiny organic material acellular material, covers the whole surface of the geoduck. The foot aperture, a slit through the muscular mantle, is located medially in the anterior surface of the mantle and is a passageway for the foot. This aperture is the only opening from the mantle cavity to the outside except for the siphon. The very long siphon, or "neck" has two openings at the end - one for ingesting oxygen and phytoplankton for food. The other siphon is used for releasing excess water.

Answer: Cephalopod

Most people will be very familiar with the Spirula species as its spiral shell often washes up on beaches all over the world. However, many people mistake the shell as an external device with the mollusc residing inside. This is not the case as the shell is internal to the animal and it used as a buoyancy aid with gas or liquid pumped into the shell to make the mollusc rise or fall with its watery habitat. The animal itself is between 35-45 mm (under two inches) in length and resembles other cephalopods in appearance. However the 'entire' animal is rarely seen as it is a deep water inhabitant. The first time it was seen in its natural habitat was when a remote underwater vehicle photographed a specimen. By day, Spirula lives in the deep oceans, hovering at depths of around 1,000 m (over 3,000 feet). At night, it rises to 100-300 m (300 to just under 1,000 feet), as its preferred temperature is around 10 °C.

Spirula spirula is the only extant member of the genus Spirula, the family Spirulidae, and the order Spirulida. Because of the shape of its shell, it is also known as the ram's horn squid or the little post horn squid. It has has a light-emitting organ, so it is sometimes known as the tail-light squid.

Answer: Gastropod

The blacklip abalone, Haliotis rubra, is one of approximately 110 species of abalone. Blacklips are distributed around the south east and southern coast of Australia and Tasmania.

Abalone in general are also known as ear shells, sea ears in parts of Australia, ormer in the UK, perlemoen in South Africa, and paua in New Zealand. Because of their prominent shells, abalone are often categorised erroneously as bivalves when they are actually a gastropod. The shell is round to oval in shape and can grow up to 220mm (8 inches).The mantle is a cleft in the shell. Within the mantle, there is a row of holes, characteristic of the genus. These holes are respiratory apertures for expelling water from the gills and for releasing sperm and eggs into the water. They have a very large muscular foot for locomotion and which is also used to cling to rocky surfaces.

Answer: Cephalopod

Blue-ringed octopi consist of four species within the genus Hapalochlaena which are found in rock pools and coral reefs in the Indian Ocean and Pacific Rim. They have yellowish skin with characteristic blue/black rings. These can change color dramatically when the animal is threatened. Its most remarkable feature is a powerful neurotoxin which can, and has been, lethal to humans.

However, the venom is not primarily for defence but feeding. With a diet of mainly crustaceans, the octopus jumps on its prey, seizes it with its arms and pushes it near its mouth where its horny beak pierces through the tough crustacean exoskeleton, releasing its venom. The venom paralyzes the muscles used for movement, which kills the prey.

Answer: Bivalve

Placopecten magellanicusonce, referred to as the "giant scallop", is more commonly known as the Atlantic sea scallop. It is a bivalve mollusc native to the northwest Atlantic Ocean and is a commercially important animal. It is found from the Gulf of St. Lawrence south to southern North Carolina. The shell is smooth, unlike the more classic Pecten maximus (common name the "great scallop" ) which has flutes and scalloped edges. The shell is around 75 - 80mm (3 inches) across its width.

Scallops have a single large adductor muscle for forcefully closing the valves - this is the part that is eaten as a scallop. Scallops are usually found in sand in mainly clear water. They eat microscopic plants and animals. Scallops have gill cilia and secrete mucus which helps in the collection and movement of food particles toward the mouth, although they are not filter feeders.

Scallops have no foot as it is redundant . They are unusual in bivalves as they have the ability to swim, which occurs by spasmodic clapping movements of the valves. The water, ejected by jet propulsion, pushes the animal forward. Most scallops have a byssal gland which is is used to attach the animal firmly to a solid surface. Some scallops remain attached throughout their lifespan. Others break free and become spasmodic swimmers.