Mollusks - Advanced Honor

Nature Study

Requirements

1. Have the Mollusks honor

   Answer: The prerequisite is to complete the basic Mollusks Honor (EN-031). Without the basic level you cannot begin the advanced one, according to the rules of the Pathfinder Honors Manual. — Advanced Honors require completing the basic one first. Basic Mollusks covers the 5 classes and general identification; the advanced one delves deeper into comparative anatomy, reproduction, and ecology. A standard of the South American Division and the General Conference.

2. Know 5 classes of mollusks and be able to distinguish the main characteristics of each one. Know at least 2 representatives of each class.

   Answer: Gastropoda (snail, slug), Bivalvia (mussel, oyster), Cephalopoda (octopus, squid), Polyplacophora (chiton, cryptochiton), and Scaphopoda (dentalium, cadulus). The 5 main classes of the phylum Mollusca. — The phylum Mollusca has about 85,000 living species, being the second largest phylum in the animal kingdom. Gastropoda leads with 70%; Bivalvia has two valves; Cephalopoda is the most cephalized; Polyplacophora has 8 plates; Scaphopoda is tubular.

3. Distinguish between univalve and bivalve mollusks, considering the following:
   • Shell
   • Body of the mollusk
   • Reproduction
   • Movements
   • Search for food
   • Self-preservation

   Answer: 1) Shell: univalves (gastropods) have a single shell, usually spiraled (spiral-shaped); bivalves have two shells (valves) joined by a hinge, which open and close. 2) Body of the mollusk: in the univalve the body has a defined head, with eyes, tentacles, and a radula (scraping tongue) and a muscular foot; in the bivalve there is no head or radula, the body stays protected between the two valves, with siphons for water intake and outflow. 3) Reproduction: univalves are often hermaphrodites or use internal fertilization; most bivalves have separate sexes and use external fertilization, releasing eggs and sperm into the water. 4) Movement: the univalve moves by gliding on its muscular foot; the bivalve is barely mobile, either fixed to the substrate or moving slowly by burrowing with its foot (some swim by opening and closing the valves). 5) Search for food: the univalve actively seeks food using the radula to scrape algae or capture prey; the bivalve is a filter feeder, retaining particles and plankton from the water that passes through its siphons and gills. 6) Self-preservation: the univalve protects itself by retracting the body into the shell, closing it with the operculum; the bivalve protects itself by tightly closing the two valves with the adductor muscles. — Univalves use the radula to scrape food (herbivores/carnivores) and move actively; bivalves have neither head nor radula, are filter feeders via the gills, fixed or burrowing, with generally separate sexes and veliger or glochidium larvae.

4. Identify, from the shells or from drawings, and know the following conchological terms:
   • Valve
   • Apex
   • Aperture
   • Byssus
   • Foot
   • Mantle
   • Operculum
   • Mother-of-pearl
   • Lips
   • Epidermis
   • Rib
   • Teeth
   • Concentric lines
   • Canal
   • Spines
   • Whorls

   Answer: 1) Valve: each of the halves (shells) that form the shell of a bivalve mollusk. 2) Apex: the initial and oldest tip of the shell, from which growth begins (in gastropods it is the top of the spiral). 3) Aperture: the opening or mouth of the shell through which the mollusk's body emerges and retracts. 4) Byssus: a set of strong filaments that some bivalves produce to attach to rocks and other substrates. 5) Foot: the mollusk's muscular organ used for locomotion or to anchor/burrow into the substrate. 6) Mantle: the body membrane that lines the mollusk and secretes the material that forms the shell. 7) Operculum: a horny or calcareous piece attached to the foot of many gastropods, which closes the aperture like a lid when the animal retracts. 8) Mother-of-pearl: the nacre, the lustrous, iridescent inner layer of the shell, formed of mother-of-pearl. 9) Lips: the edges that border the aperture of the shell (outer and inner lip). 10) Periostracum: the thin outer layer, usually horny, that covers and protects the surface of the shell. 11) Rib: the raised ridges or crests that run across the surface of the shell. 12) Teeth: the projections of the hinge that interlock the valves of bivalves, or the denticles of the aperture of some gastropods. 13) Concentric lines: the growth lines that follow the contour of the shell, forming rings parallel to the edge. 14) Siphonal canal: the groove or extension on the aperture of many gastropods that houses and protects the siphon. 15) Spines: pointed projections that form on the surface of some shells, serving as defense. 16) Whorls: each of the turns the shell makes around the central axis, forming the spiral of gastropods. — Conchology is the study of shells. The terms come from Latin (epidermis = periostracum, the outer organic layer). Concentric lines mark growth; ribs are radial protrusions; teeth are the hinge gears in bivalves that articulate the valves.

5. How long do mollusks live?

   Answer: It varies greatly: octopuses live 1-5 years, oysters 20-30, mussels 10-50, and abyssal bivalves like Arctica islandica reach 500 years (the one named 'Ming' was 507 years old when collected in 2006). — Longevity depends on the class: cephalopods have a short life and die after reproduction; cold-water burrowing bivalves (Arctica islandica) hold the record for the longest-lived non-colonial animal, at 507 years. Land snails live 5-15 years.

6. Present some facts about the life of a Strombus pugilis (fighting conch) and explain why this shell has that name.

   Answer: Strombus pugilis (fighting conch) is a marine gastropod of the family Strombidae, from the tropical Western Atlantic (the Caribbean, the Antilles, and northeastern Brazil), living on sandy bottoms and marine seagrass beds in shallow waters. Facts: it feeds on algae and detritus, has well-developed stalked eyes, and moves in 'leaps' rather than gliding. The name 'pugilis' (from the Latin pugil = boxer/fighter) and the nickname 'fighting conch' come from the sharp, hook/sickle-shaped horny operculum, which the animal uses as a lever to push off and 'leap,' and also as defense, striking predators as if throwing punches. — Strombus pugilis has a sickle-shaped horny operculum. When threatened, it violently contracts its muscular foot and uses the operculum as a defensive weapon, appearing to throw 'punches' — hence pugilis (boxer, fighter). It lives on sandy bottoms.

7. Identify and explain the activities of the Teredo.

   Answer: Teredo navalis is a marine bivalve with an elongated worm-like body, whose reduced valves function as drills. It bores into submerged wood (ship hulls, pilings) and digests the cellulose with symbiotic bacteria in its gut. — Known as the shipworm, Teredo has caused billions in historical damage — it destroyed the ships of Columbus and of the Dutch in the 17th century, leading to the sheathing of hulls with copper. It lives up to 2 years and bores galleries up to 1 meter long.

8. Give the name of 2 mollusks that do not have a shell.

   Answer: Octopus (Octopus vulgaris) and slug (Limax maximus). Other examples: colorful nudibranchs, squid (a reduced internal shell = the pen), aplysia. They lost their external shell through evolution, gaining agility. — Cephalopods (octopus, squid, cuttlefish) lost their external shell ~500 million years ago, except the Nautilus. Slugs and nudibranchs are gastropods that reduced their shell. The absence allows more agile locomotion but requires other defenses (ink, camouflage).

9. Find answers to the following intriguing questions:
   • How do bivalve and univalve animals attach themselves to their shells?
   • How is the color of a shell controlled?
   • Which mollusk has 4 gills?
   • From which marine animal was ink made in India?
   • Which mollusk leaves a shiny trail?
   • Which shells were used as money by ancient tribes?
   • Which shell is considered sacred by Tibetans?
   • The purple dye of ancient times was extracted from the secretion of which mollusk?

   Answer: 1) How do mollusks attach themselves? Bivalves attach by the byssus (protein threads); univalves use the foot/columellar muscle and the suction of the foot. 2) Where does the color of shells come from? From pigments secreted by the mantle during growth. 3) Which mollusk has 4 gills? The Nautilus (the only cephalopod with four gills). 4) From which mollusk is India ink extracted? From the ink sac of squid and cuttlefish (sepia). 5) Which mollusk leaves a trail of mucus? The slug and the land snail. 6) Which shell was once used as money? The cowrie Cypraea moneta. 7) Which shell is a sacred instrument in Tibet/India? The Turbinella pyrum (Sankha/sacred conch). 8) From which mollusk was royal purple extracted? From gastropods of the genus Murex. — Classic curiosities: Tyrian purple dye was worth more than gold in antiquity — extracted from the hypobranchial gland of Murex brandaris, it required 12,000 mollusks per gram of dye. Cypraea moneta circulated as currency in Africa until the 19th century.

10. Cite 6 commercial uses of shells.

    Answer: Jewelry (necklaces, earrings), mother-of-pearl buttons, lime production, agricultural fertilizer, poultry feed (calcium), decoration, and crafts. Paving of coastal roads and musical instruments (conch shells) as well. — The shell industry moves millions of dollars: mother-of-pearl from Pinctada is worth, per kilo, the equivalent of silver; calcitic lime (95% CaCO3) is an input for cement and paints; poultry supplementation uses shell meal as a source of digestible calcium.

11. Make a collection of 40 different shells. Identify them with the date of collection, location, the habitat of the mollusk that owned it, and the name of the class it belongs to. If you received it as a gift, indicate the name of the person who gave it to you, the date, the class it belongs to and, if possible, what the habitat of the mollusk that owned this shell was.

    Answer: Collect on the beach/mangrove, label each shell with a number, species, class (gastropod/bivalve, etc.), date, location, and habitat (intertidal/mangrove/reef). Shells received as gifts list the donor, date, and available taxonomic data. — A scientific collection requires methodology: never collect a live mollusk (only empty shells on the beach), respect environmental legislation (IBAMA prohibits threatened species), clean with fresh water, and dry. Label with India ink in a discreet spot.