Mollusca Biology Study Guide PDF

**Mollusca** Why is the octopus kept in the phylum Mollusca? - Quora **Characteristic features:** 1\. they are triploblastic 2\. they don´t have body segmentation 3\. they have a soft body, many of them have a **shell** (sometimes the shell is reduce or lost -- cuttlefish 4\. the shell is sec...

**Mollusca** Why is the octopus kept in the phylum Mollusca? - Quora **Characteristic features:** 1\. they are triploblastic 2\. they don´t have body segmentation 3\. they have a soft body, many of them have a **shell** (sometimes the shell is reduce or lost -- cuttlefish 4\. the shell is secreted by a special epidermal tissue called the **mantle** (plášť) 5\. the body consists of: a **head**, **foot** and **visceral hump** 6\. they have a **coelom** (secondary body cavity) but only in embryonal stage, later it fuses with the primary body cavity called **enteron**. **Classification of Mollusca:** 1\. Class: Gastropoda (ulitníky) - snails (slimáky) slugs (slizniaky) 2\. Class: Bivalvia (lastúrniky) - cockles, mussels 3\. Class: Cephalopoda (hlavonožce) - octopus, squid, cuttlefish (without a shell) Introduction to Mollusca - video: [[https://youtu.be/r9gO-l1FVIQ]](https://youtu.be/r9gO-l1FVIQ) **Comparison of Pseudocoelom (Nematoda) and Coelom (Annelida) and Acoelomata (Platyhelminthes) - revision:**  **1. Class Gastropoda** **Characteristic features:** 1\. distinct head with eyes and sensory tentacles 2\. single coiled assymetrical shell (**conch**), sometimes not present (slugs) 3\. they have a **radula** - (broad tongue-like organ with rows od teeth) in mouth for mechanical digestion) Radula diagram The mouth with a radula Morphology:  Anatomy: Snail Gross Anatomy  **Digestive system:** mouth, **radula**, pharynx, salivary glands, **crop**, esophagus, **stomach**, **hepatopancreas**, intestines, anus can be herbivorous, carnivorous, omnivorous, parasitic. **Breathing system:** terrestrial - **lung sacs**, marine or fresh water - **gills,** the air is going in and out of the body via a **respiratory pore -** (pneumostome) **Circulatory system:** the heart is in **pericardium** (osrdcovník) - which is the rest of coelom (secondary body cavity) in adult stage, the circulatory system is **open**, they have a **hemolymph** (blood mixed with the tissue fluid), it is yellowish **Excretory system:** **th**ere are two **kidneys**, or [**nephridia**](https://www.britannica.com/science/nephridium), in primitive gastropods, such as the [archaeogastropods](https://www.britannica.com/animal/Diotocardia), while, in the advanced forms, one kidney is **small or** **lost**. In both - marine and freshwater species, ciliary water currents sweep the excreted matter out of the mantle cavity. **Nervous system:** they have series of **paired ganglia** (knot-like masses of [nerve cell](https://www.britannica.com/science/neuron) bodies that collectively function as the central nervous system), ganglia are connected by **nerve cords.** There are **three main nerve ganglia** -- in head, foot and in the central part of the body. **Sensory organs:** they have **chemoreceptors** in the skin to have information from the environment, **tentacles**, **palps** (hmatadlá). They have **eye spots** sensitive to light on the top of the tentacles on their head. A pair of **statocysts** are organs of balance, present in non-sessile taxa. **Reproductive system:** mostly hermaphrodites, only some have separate sexes, they have **ovaries** and **testes**, they can have **internal** or **external** fertilisation. **Locomotion:** they move with a **muscular foot**, which secretes **mucus** by the foot glands to adhere to the surface, it produces muscular **pedal waves** on ventral surface as it moves with the periods of **relaxations** of muscles (interwaves), the waves propagate from **tail to head** Figure 1 from Effects of serotonin, dopamine and ergometrine on \... **Habitat:** some are terrestrial (snail), many live in marine and fresh waters (limpets) The structure of Mollusca -- video: [[https://youtu.be/tbhQb5MjSwg]](https://youtu.be/tbhQb5MjSwg) Mating and love darts in snails: [https://youtu.be/QBrZ5iyz\_rg?si=HW3Snce9rIO3PQAU] Facts about snails video: [https://youtu.be/VTV23B5gBsQ?si=KEeoqtgIp7G-aux5] **Representatives of Gastropoda:**  1\. Helix pomatia (slimák záhradný) Helix pomatia 2\. Slug (slizniak)  3\. Limpets (marine gastropods) Limpet shells \| Limpet shell, Shells, Sea shells **2. Class Bivalvia** **Characteristic features of Bivalvia:** 1\. head is **reduced**, **no tentacles, no radula** 2\. the shell has **two parts** (valves) connected by a strong ligament 3\. they are usually **filter- feeders** Morphology:  Lunule - mesiačikovitá priehlbina lastúry - poznávací u znak jednotlivých druhov. Escutcheon -- štít Anatomy: 11 mollusca **Digestive system:** Bivalvia feed with phytoplankton, zooplankton, algae and other nutrients and particles in water. The trapped **food, (they are filter feeders) is** transported to the mouth, esophagus, stomach with **digestive glands**, intestines where it is digested and expelled as feces via anus. **Breathing system:** they have gills, the water comes in through **incurrent siphon**, oxygen is taken to gills form water and water leaves through **excurrent siphon.** **Circulatory system:** an **open** **circulatory system** that bathes the organs in **hemolymph**, the heart is in **pericardium** (the rest of coelom) **has** **three chambers**: two **auricles** ( atria) receiving blood from the gills, and a single **ventricle** which is muscular and pumps hemolymph into the **aorta**, and then to the rest of the body **Excretory system:** they have a pair of **nephridia** (kidneys). Each of these consists of a long, looped, glandular tube, which opens into the body cavity just beneath the **heart**, and a **bladder** to store urine. It has a **nephridiopore** to excrete the urine. **Nervous system:** they **have** a simple **nervous system** with usually three sets of **ganglia** connected by **nerve** fibers. Ganglia **are** clusters of **nerve** cells that **form** simple **nerve centers** distinct from the brain. **Bivalves do** **not have brains**. **Sensory organs:** Since they **do** not **have** a head region, their **tentacles and eyes** are often located along the **mantle edge**. These **sensory organs** range from simple light sensing tissues called **ocelli**, to more complex eyes that **have** lens. **Reproductive system:** they release eggs and sperm into the water, where **external fertili-** **sation** occurs. The fertilized eggs then float on the surface of water as plankton. Within 48 hours after fertilization, the embryo develops into a planktonic, **trochophore** larval stage. **Trochophore** changes into another type of larval stage called **veliger.** Parasitic species have a parasitic larva called **glochidium.**  **Locomotion of Bivalvia:** they move with the help of their muscular foot, they can bore themselves into sand A--G) Digging and burrowing process exhibited by juvenile geoducks \... **Habitat:** mostly marine species, but some are also found in fresh water (Korýtko rybničné) Digestive system of Bivalvia : [[https://youtu.be/YCq0HQsu4\_4]](https://youtu.be/YCq0HQsu4_4) Anatomy of Bivalvia: [[https://youtu.be/ipnv3nYeOwg]](https://youtu.be/ipnv3nYeOwg) **Representatives of Bivalvia:** 1\. Pearl oyster (perlorodka)  2\. cockles, mussels, clams, oysters (srdcovky, mušle, ustrice) Cockle Mussel Clam Bivalvia, Oyster PNG clipart \| free cliparts \... Clam dissection video: [[https://youtu.be/ADGkuX8IL9c]](https://youtu.be/ADGkuX8IL9c) **3. Class Cephalopoda** **Characteristic features of Cephalopoda:** 1\. they have a **conspicious head** with well **developed eyes** and tentacles 2\. they have a **beak** and **radula** used for feeding 3\. they are fast-moving, active, considered the **most intelligent invertebrates** 4\. they are mostly without a shell. (octopus, cuttlefish) Morphology:  Cuttlefish Body Plan Internal Organ Anatomy Diagram  **Basic anatomy of an octopus** **Digestive system:** they have a beak for crushing the food, mouth with a **radula**, salivary glands, **crop**, esophagus, stomach, digestive gland (similar to liver), intestines and anus **Breathing system:** breathing by **gills**, there are two **branchial hearts** (gill hearts) they move blood through the capillaries of the gills. They exchange O~2~ and CO~2~ in their gills~.~ **Circulatory system:** **Cephalopods** are the only mollusks with a **closed** circulatory system. They **have two or three hearts**. A single (one or two branchial hearts in gills) and a **systemic heart** that pumps the oxygenated blood through the rest of the body. They have a system of blood vessels in the body. Like most molluscs, cephalopods use [**hemocyanin**](https://en.wikipedia.org/wiki/Hemocyanin), a protein **containing** **cooper**, rather than [hemoglobin](https://en.wikipedia.org/wiki/Hemoglobin) (contains iron), to transport oxygen. As a result, their blood is **colorless**, deoxygenated and turns blue when exposed to air. **Excretory system:** Most cephalopods possess a single pair of **large [nephridia](https://en.wikipedia.org/wiki/Nephridium)**. Filtered [nitrogenous waste](https://en.wikipedia.org/wiki/Nitrogenous_waste) is produced in the **[pericardial](https://en.wikipedia.org/wiki/Pericardium) cavity of the [branchial](https://en.wikipedia.org/wiki/Branchial_heart)** **heart** each of which is connected to a nephridium by a narrow canal. They have a bladder like structure (**renal sac**) to store the excreted liquid which is released into the mantle cavity through a **nephridiopore**. **Nervous system:** they are regarded as **the most intelligent** of the [[invertebrates]](https://en.wikipedia.org/wiki/Invertebrate), and **have** **well developed senses** and **large brain** (larger than other [[gastropods]](https://en.wikipedia.org/wiki/Gastropod)) connected to other nervous ganglia by **nerve cords**. Many cephalopods are social creatures. **Senses: they** have **advanced vision**, can detect gravity with [**[statocysts]**](https://en.wikipedia.org/wiki/Statocyst), and have a variety of **chemical sense organs**. Octopuses use their arms to explore their environment and can use them for depth perception. They have very big complex **chamber eyes**. https://upload.wikimedia.org/wikipedia/commons/thumb/9/9c/Nautilus\_pompilius\_%28head%29.jpg/250px-Nautilus\_pompilius\_%28head%29.jpg  An eye of Nautilus A cuttlefish with W-shaped **pupils** which may help them distinguish colors. **Hearing:** Some squids have been shown to detect sound using their [**[statocysts]**](https://en.wikipedia.org/wiki/Statocyst). **Changing the colour, camouflage :** https://upload.wikimedia.org/wikipedia/commons/thumb/1/1c/Cuttlefish\_color.jpg/220px-Cuttlefish\_color.jpg This [broadclub cuttlefish](https://en.wikipedia.org/wiki/Broadclub_cuttlefish) (*Sepia latimanus*) can change from camouflage tans and browns (top) to yellow with dark highlights (bottom) in **less than a second**. **Coloration:** Cephalopods can change their colors and patterns in **milliseconds**, whether for [signalling](https://en.wikipedia.org/wiki/Signalling_theory) (both [within the species](https://en.wikipedia.org/wiki/Sexual_selection) and for [warning](https://en.wikipedia.org/wiki/Aposematism)) or [active camouflage](https://en.wikipedia.org/wiki/Active_camouflage), as their chromatophores are expanded or contracted. **Ink:** all known cephalopods (except Nautilus) have an **ink sac**, which can be used to **expel a** **cloud of dark ink** to confuse [predators](https://en.wikipedia.org/wiki/Predator). This sac is a muscular bag , it lies beneath the gut and opens into the anus, into which its contents -- almost pure [**melanin**](https://en.wikipedia.org/wiki/Melanin) -- can be expelled. The ejected cloud of melanin is usually **mixed with [mucus](https://en.wikipedia.org/wiki/Mucus)** and it forms a thick cloud, resulting in visual (and possibly chemosensory) impairment of the predator. **Reproductive system:** they are **dioecious**, have separate sexes, mostly external fertilisation, **internal fertilization** is seen only in octopodes. The initiation of copulation in octopuses begins when the male catches a female and wraps his arm around her, either in a \"male to female neck\" position or mouth to mouth position, depending on the species. The male inserts its copulatory arm (hectocotylus) in the siphon of a female and deliver sperms. The female stores sperms until the eggs are mature and fertilise them afterwards. Females **lay eggs in clutches**; each egg is composed of a protective coat to ensure the safety of the developing embryo when released into the water column Once the eggs are released and attached to sheltered substrate, the females then die. They have **sexual dimorphism**, usually females are bigger than males. **Often females eat males after** **copulation.**  https://upload.wikimedia.org/wikipedia/commons/thumb/3/33/SquidEggCases-MontereryAquarium-April2-07.png/220px-SquidEggCases-MontereryAquarium-April2-07.png Copulation of octopuses Egg cases laid by a female Squid  Mostly females eat males after copulation, Large Pacific Striped Octopus is an exception. **Locomotion:** most cephalopods can move by **[jet](https://en.wikipedia.org/wiki/Jet_(gas)) propulsion** through the siphon, this is a very **energy-consuming way** to travel compared to the tail propulsion used by fish. The efficiency of a [propellor](https://en.wikipedia.org/wiki/Propellor)- driven [waterjet](https://en.wikipedia.org/wiki/Jet_(fluid)) is greater than a [rocket](https://en.wikipedia.org/wiki/Rocket). **Habitat:** they live in all seas and oceans, in marine waters Cephalopoda video: [**[https://youtu.be/h2M-6jvCLZM]**](https://youtu.be/h2M-6jvCLZM) **Representatives of Cephalopoda**:  1\. Octopus (chobotnica) Farming octopuses is a really bad idea 2\. Cuttlefish (sépia) 3. Squid (kalmár)  Squid Egg Laying Egg And Babies Squid Hatching Process In The \... 4\. A giant squid  4\. Nautilus (lodenka) One of nature\'s most perfect forms \-- the nautilus shell  Cephalopoda video: [[https://youtu.be/NuIFazO7tXM]](https://youtu.be/NuIFazO7tXM) Octopus mating video: [[https://youtu.be/4fkQZrfeYXQ]](https://youtu.be/4fkQZrfeYXQ) Reproduction of octopuses video: [ https://youtu.be/C69uqPCz1ac]