Mollusks Honor

Nature Study

Requirements

1. What does the term "mollusk" mean?

   Answer: "Mollusk" comes from the Latin molluscus, meaning "soft". It refers to the characteristic soft body of these animals, usually protected by an external calcareous shell. They form the second-largest animal phylum (Mollusca), with about 85,000 species among slugs, snails, octopuses, squid, mussels, oysters and others. — The name was coined by Aristotle (Mollia) and kept by Linnaeus in the Systema Naturae in 1758; only arthropods surpass mollusks in number of species; the giant is the colossal squid (Mesonychoteuthis hamiltoni) at 14m in length, and the smallest is the snail Ammonicera rota with a shell only 0.5 mm in diameter.

2. Regarding the mollusks of the gastropod, cephalopod, and bivalve classes, answer:
   • Their main characteristics
   • At least one representative of each class

   Answer: 1) Main characteristics of each class — Gastropods: a body of bilateral symmetry with a muscular ventral foot for crawling, a well-defined head with tentacles and eyes; a generally single, spiraled shell (some without a shell, like slugs); they have a radula to scrape food. Cephalopods: a highly developed head with complex eyes, a mouth surrounded by tentacles/arms with suckers, locomotion by jet propulsion; a mantle with no visible external shell (an internal shell that is reduced or absent); they are the most active and intelligent mollusks. Bivalves: a soft body protected by two calcareous valves joined by a hinge, with no defined head and no radula; they are filter feeders that take food from the water by means of siphons. 2) At least one representative of each class — Gastropods: the garden snail (also slug, limpet). Cephalopods: the octopus (also squid, cuttlefish, nautilus). Bivalves: the oyster (also mussel, clam, scallop). — These are the three main classes of the phylum Mollusca; cephalopods have the most complex nervous system of all invertebrates, with intelligence comparable to that of birds according to Peter Godfrey-Smith in "Other Minds" (2017); oysters filter about 200 liters of water per day, being essential to the quality of coastal water in the global marine environment.

3. Which are the only terrestrial mollusks? To which class do they belong?

   Answer: The only truly terrestrial mollusks are snails and slugs (genera Helix, Achatina, Limax, among others). They belong to the class Gastropoda (subclass Pulmonata), with a lung adapted instead of gills for breathing in air — an evolutionary adaptation that allowed them to colonize dry environments far from water. — The Pulmonata developed a lung from the mantle 350 million years ago; Achatina fulica is an agricultural pest in Brazil (the African snail); Helix aspersa is the escargot of French cuisine — the only mollusk widely edible on dry land; cephalopods and bivalves live only in water, with no known terrestrial representatives.

4. Cite 3 characteristics of mollusks.

   Answer: Three characteristics: (1) a soft body, divided into head, foot and visceral mass, usually protected by an external calcareous shell; (2) the presence of a mantle, which secretes the shell and covers the internal organs; (3) a complete digestive system with a radula (a toothed strip used to scrape food), except in bivalves, which are filter feeders. — The radula has thousands of microscopic teeth and is a structure unique to mollusks, absent in bivalves; the mantle is the region of the body that produces nacre (mother-of-pearl, the basis of pearls); both are key taxonomic characters used for classification in the phylum Mollusca, according to zoology manuals of the Brazilian University of São Paulo currently in effect.

5. Identify and understand the following structures:
   • In bivalves
   • In gastropods

   Answer: 1) Structures in bivalves — Two calcareous valves joined by a hinge with teeth that fit them together; adductor muscles that close the valves; a mantle that lines the body and produces the shell; inhalant and exhalant siphons through which water enters and leaves for respiration and filtration of food; gills (which capture food and carry out gas exchange); and a muscular foot used to bury itself in the substrate. 2) Structures in gastropods — A single shell, generally spiraled (absent in some, like slugs); a muscular ventral foot used for locomotion by crawling; a well-defined head with one or two pairs of tentacles and eyes; a radula (a scraping ribbon with denticles) used in feeding; a mantle that produces the shell; and an operculum (a horny or calcareous lid that closes the shell opening) present in some gastropods. — The hinge of bivalves has interlocking teeth that keep the valves aligned; siphons filter thousands of liters per day; in gastropods, the operculum is the "lid" that closes the shell opening against predators and desiccation — absent in Pulmonata; the radula is a unique structure exclusive to the phylum Mollusca across all living classes.

6. Can all shells be found on beaches? Where can they be found? Which areas of the world provide the greatest variety of shells?

   Answer: No. Shells are found on beaches, but also in rivers, lakes, mangroves, reefs and even on land (terrestrial snails). The greatest variety is in warm tropical seas (the Indo-Pacific — the Philippines, Indonesia, Australia), where about 60% of the planet's marine mollusk species are concentrated in coastal waters. — The Coral Triangle (Indonesia, the Philippines, Papua New Guinea) is home to more than 600 species of coral and thousands of mollusks; warm water accelerates carbonate deposition and diversifies forms; the book "Compendium of Seashells" by Abbott and Dance lists 4,000 oceanic species — with the tropical Indo-Pacific being the world's richest region for marine shells, currently in effect.

7. Describe 3 different ways used by mollusks for their locomotion.

   Answer: Three ways: (1) crawling by a muscular foot (snails and slugs glide over lubricating mucus); (2) jet propulsion (octopuses and squid expel water through the siphon to move quickly); (3) opening and closing the valves (scallops swim by clapping the valves, expelling water in a jet to propel the body). — The snail's mucus reduces friction and protects against desiccation; cephalopods reach 40 km/h in a burst; the scallop (Pectinidae) is the only bivalve that actively swims, clapping the valves up to 30 times per second — this peculiar locomotion was first described by Aristotle in "History of Animals" in the 4th century BC.

8. How do mollusks protect themselves?

   Answer: Mollusks protect themselves mainly by the external calcareous shell (snails, oysters, mussels); by camouflage and color change (octopuses, squid with chromatophores); by releasing dark ink (cephalopods); by an operculum (a lid that closes the shell opening) and by burying themselves in the sand or muddy substrate. — Octopuses have millions of chromatophores under the skin that change color in milliseconds, mimicking textures; the ink jet of squid contains melanin and stuns the predator; studies from the University of California (Roger Hanlon) prove that cephalopods have "dynamic camouflage" — an evolutionary adaptation unique in the global animal kingdom today.

9. How are shells produced by most mollusks? What are they made of?

   Answer: Shells are produced by the mantle, a thin tissue that envelops the mollusk's body and secretes calcium carbonate (CaCO₃) in layers. They are made of calcite or aragonite combined with the protein conchiolin, forming a resistant structure. The innermost layer (nacre or mother-of-pearl) is responsible for the luster of pearls and some shells. — The carbonate comes from seawater (rich in dissolved calcium); the mantle deposits concentric layers that enlarge the shell as the animal grows; studies from the University of Cambridge show that this calcareous structure is five times more resistant than common cement, inspiring modern biomaterials engineering currently in effect.

10. Cite 5 uses of shells and mollusks for humankind.

    Answer: Five uses: (1) food (oysters, clams, octopuses, squid — a source of protein); (2) jewelry (pearls and mother-of-pearl); (3) crafts and adornments (necklaces, sculptures); (4) limestone in construction and agricultural fertilizer (lime from ground oysters); (5) musical instruments and historical currency (the cowrie in some traditional, ancient African cultures). — In some regions of Africa and the Pacific islands, cowries (Cypraea moneta) were used as currency for centuries; natural pearls are worth millions — the Hope Pearl is 12.5 cm and is estimated at US$8 million; lime from ground oysters has been used in construction since the colonization of Brazil, in pre-colonial indigenous shell mounds (sambaquis).

11. Make a collection of 20 different shells. These must be identified with the date of collection or acquisition and place of origin.

    Answer: You gather 20 varied shells — collected on beaches, rivers, mangroves, or bought in stores. Clean each one with fresh water and neutral soap, let it dry well and identify it with a label containing the scientific or common name, the date and the place. Present them in an organizer box with each piece numbered for the instructor. — Scientific collections require rigorous identification to be useful for study; the catalog "Seashells of the Brazilian Beaches" by Eliezer Rios (Oceanographic Museum of Rio Grande, 1994) has 1,500 registered species; labels must contain the collector, date, place and code — the standard used by the MNRJ collection in Rio de Janeiro, Brazil, currently in effect.

12. Where do pearls come from? What amazing lesson does the pearl teach us? (Read Christ's Object Lessons, pp. 115-118)

    Answer: Pearls come from bivalve mollusks, mainly from oysters (and some freshwater mussels and clams). When a foreign body (a grain of sand, a parasite or a fragment) penetrates between the mantle and the shell, the animal envelops it with successive concentric layers of nacre (mother-of-pearl), the same material as the inner part of the shell, to protect itself from the irritation. Over time these layers form the pearl. The lesson the pearl teaches (according to Christ's Object Lessons, pp. 115-118) is that something precious and beautiful can be born from suffering and difficulty: just as the oyster transforms an irritation into a jewel, Christ is the Pearl of great price (Matthew 13:45-46) and the Christian, in seeking Him, finds the treasure worth more than anything. Difficulties faced with faith and patience produce character and eternal value. — Ellen White comments on the parable of the Pearl of Great Price (Matthew 13:45-46) in "Christ's Object Lessons" (pp. 115-118), comparing Christ's suffering to the formation of the pearl — "His glory shines forth more brightly through afflictions"; natural pearls take 5 to 10 years to form, according to data from the world industry's Pearl Source currently in effect.

13. Which of the Bible texts below tell us that:
    • The aquatic creatures were created on the fifth day.
    • The number of aquatic creatures is innumerable.
    • Water creatures perish out of the water.
    • Job considered corals to be of great value.
    • Solomon had knowledge about marine life.
    • Jesus used a product made from shells twice to teach a spiritual lesson.
    • A businesswoman sold the famous purple-colored dyes, extracted from murex shells of the Mediterranean Sea.
    • Paul condemned the use of pearls.
    • Mollusks are not appropriate to eat.
    • The 12 gates of the Holy City are 12 pearls.

    Answer: 1) Aquatic creatures were created on the fifth day — Genesis 1:20-23. 2) The quantity of aquatic creatures is innumerable — Psalm 104:25. 3) The creatures of the waters perish out of the water — Isaiah 50:2. 4) Job considered corals to be of great value — Job 28:18. 5) Solomon had knowledge about marine life — 1 Kings 4:33. 6) Jesus used a product of shells (the pearl) twice to teach a spiritual lesson — Matthew 7:6 and Matthew 13:45-46. 7) A businesswoman sold the famous purple-colored dyes, taken from the murex shells of the Mediterranean Sea — Acts 16:14 (Lydia, a seller of purple). 8) Paul gave guidance about the use of pearls — 1 Timothy 2:9. 9) Mollusks without fins and scales are not appropriate to eat (unclean) — Leviticus 11:10. 10) The 12 gates of the Holy City are 12 pearls — Revelation 21:21. — Tyrian purple came from the murex (Murex trunculus) and was extracted from the snail's gland in small quantities; purple was a symbol of royalty in the Roman Empire; the 12 gates of pearls in Revelation 21:21 symbolize the New Jerusalem — the Adventist theological basis for hope in the second advent of Christ, currently in effect.