Mollusks and Annelids

What group are terrestrial mollusks?

Gastropods

What is the modified part of mollusks?

The body wall to a mantle with gills,

What type of Lophotrochozoans are mollusks?

Coelomate Lophotrochozoans

Where are the organs found?

Within a visceral mass

Mollusks express a distinct head-region, what is this trait called?

Cephalization

How is the mollusk shell grown?

Incrementally

What is their specialized feeding appendage?

Radula, a tongue-like organ with backwards facing teeth

What are the layers of the shell, in order?

Periostracum, then Prismatic, then Nacreous

What is the respiratory organ found in aquatic mollusks?

Ctenidia

Do some mollusks have lungs?

Yes

Do mollusks have asexual reproduction?

No

Mollusks sexual reproduction

Species can be either dioecious or hermaphrodites

What type of cleavage do mollusks undergo?

Spiral Cleavage

What type of larva do mollusks have?

A modified lochophore larva, veliger larva

How is gas exchange performed in mollusks?

Gills, lungs, mantle, or body surface.

What mollusks have a well-developed eye

Cephalopoda

What are the defining characteristics of the class Monoplacophora?

Univalve shell, Limpet-like, serially repeated organs

What are the defining characteristics of the class Polyplacophora?

Common name chitons, lack the 3 layers of the shell and have 7-8 layers instead. Dorsoventrally flattened Dorsal surface convex with plates/valves. Girdle formed by mantle.

What are the defining characteristics of the class Scaphopoda

Tusk shells, tube-shaped mantle wrapped around the visceral mass. Respiration occurs via the mantle only as they have no gills. Detritus-feeding (decaying organic matter); food captured by captacula.

What are the defining characteristics of the class Gatropoda

Contains snails, slugs, . The stomach and foot are fused, hence the name. They have a unipiece shell (one piece). Dextral (right) or Sinistral (left) coiling of the shell and body. Torsion brings the once polar mouth and anus towards the same side.

What are the subclasses within Gastropoda?

Prosobranchs, Opisthobrancha, and Pulmonates

Characteristics of Prosobranchs

Only one pair of tentacles and are dioecious

Characteristics of Opisthobranchs

Detorsion (oral and anal regions are at opposite ends. Chemosensory receptors known as rhinophores. Shells are either greatly reduced or absent

Characteristics of Pulmonates

Lung-like vascularized mantle wall. Detorsion in some groups (slugs as they lack shells so no torsion). Terrestrial species with 2 pairs of tentacles. Posterior pair is eye bearing

What is torsion

It is the twisting of the gastropod body as the shell grows and can be either ontogenetic (during development) or evolutionary torsion (occurs in evolution)

What part of the body is modified in Cone snails (Conus)

The radula is modified to be harpoon-like to inject potent venom

Characteristics of Bivalvia (clams, oysters, and allies)

Two shells (valves) that are connected by ligament. Concentric lines of growth from the umbo (characteristic as a very dark and dense spot). Adductor muscles open and close valves. No head, no radula, prominent foot for locomotion or burrowing. The shell is created through the incremental deposition of calcium carbonate

How are pearls formed?

A foreign body enters the shell, and in response the layer of nacre surronds the foreign body to form a pearl.

Characteristics of Cephalopoda

Marine mobile predators, using chitinous beak for prey capture.

Bilaterally symmetrical. Foot is fused with head, modified into form for jet propolsion. Chromatophores for coloration changes. Dioecious, males with modified arm for sperm transfer (Hectocotylus) into the body cavity of the female. No free-swimming larval stages as they develop in eggs as fertilization is internal. Developed eyes.

Characteristics of Nautiloidea. Nautliluses

80-90 tentacles surronding mouth. Chambered shell, that aid in bouyancy by adding or removing air. Deep water extant species.

Characteristics of Coleoidea and Differences between the groups

Exclusively marine: Squids, Octopuses, Cuttlefish. Shelless, in Cuttlefish possess the cuttlebone, Squids have a gladius/pen that is a calcified structure. 8-10 tentacles or arm with suckers. Chitinous beak and triangular fin for Squids. Long and broad fin and cuttlebone in Cuttlefish. 8 arms, no shell, pen, or cuttlebone, Bulbous body and a beak in Octopuses, which walk but can jet propulse if needed.

What is the class Ammonoidea (Ammonoids)

Extinct group but was abundant in the ancient seas. All that we know of them is through their numerous shells

What are the characteristics of Annelida

Name from annelus meaning ring as they are roundworms and bilaterally symmetrical. Body is arranged into segments (metameres) as they possess true metamarism. Segmented external apprance and each segment is compartalized but have an undivided digestive system. Have 3 regions the Head, Body, and Tail (Pygidium) that has an anus. The Head is has two main regions the prostomal and peristomium. Chitinous covering (cuticle). Schizocoelous. Regeneration from segments in some groups. Can be dioecious or monoecious. Respiration through gills, lungs, and/or paraspodia (a modified foot)

How many species of Annelida

15000+

What makes them have true metamerism

Structure and organ systems are segmented except for the digestive system

What makes them have a true coelomate

They possess a cavity that is filled with coelomic fluid that functions as a hydrostatic skeleton.

How is movement performed in Annelids

Locomotion through Peristalsis, the longitudinal and circular muscles propel annelids

Characteristics of Errantia, Errant worm, may also be called Brisle worms

Molite marine worms, some in brackish water. Live under rocks, coral crevicues, or abandoned shells, but some are planktonic. Well-dffiereniated head, no clitellium. Many setae, whisker like structures, that are arranged in bundles in parapodia. Palps on the prostomium to help sense. Unique traits include that they are dioecious but have no permanent sex organs as they have a unique method of external fertilization.

What is the process of Epitoky in Errantia

These animals spend most of the year as immature atokes. Portion of the body, posterium, enlargens and elongates with gametes forming the epitokus. Epistokes swim/float to the release to release the gametes. Remaining antokes regenerate new proterior segments. This is used to prevent being predated on while spawning or reproducing.

What are the three types of Errantia worms

Scale worms - covered in scales

Sandstriker worm - Otherwise known as the bobbit worm

Claim worm

Characteristics of Sedenataria

Borrowing or tube-forming organisms. Body buried beneath sediment, except the tentacles. Pinnules have cilia to sieve out food.

Characteristics of Clitellata

Oligochaeta (Oligochaeta) and class Hirudinida (Leeches). Monoeciousl free-living or parasitic. Clitellum as a thick band or secretory cell used for reproduction, secretes music to adhere two individuals. Sperm exchange and then eggs are released and are fertilized.

Characteristics of Class Hirudinida

True leeches (Hirudinea), Acanthebdelida, and Branchibdellida. True leeches have 34 segments, anterior and posterior suckers. Movement via the suckers and saliva contains anti-bloodcloting properties that were used in medival research