Phylum Mollusca (soft bodied)

Phylum Mollusca (soft bodied)

Most described species in the animal kingdom next to Phylum Arthropoda ~100,000 species... Marine, freshwater and terrestrial. 35,000 fossil species. Most diverse group of animals

Snails

Slugs

Scallops

Limpets

Nautili

Chitons

Octopods

Squids

Scallops (bivalves)- Clams & Mussels

Oysters (Highly calcified valves)-

Neopilina

Tusk-shells

Vary in size giant squid to minute snail Architeuthis (primitive squid) 18 m long

Trochophore larva Similar to the larva of marine annelids.

Develop to Veliger larva marine mollusks

Radula

Class Aplacophora no shell bearing (Solenogasters) They lack a shell and the foot. The head is reduced; cylindrical worm-like body Mantle (dorsal epidermis) secretes calcareous scales or spines providing the animal a shining appearance. No true gills. Anus empties into a posterior chamber(serve as mantle cavity) Marine; In deep sea - abyssal (6000m or more); free-living bottom feeders; feed on cnidarians 320 species

Solenogaster with radula Ventral Dorsal

Class Monoplacophora - single shell bearing (Monoplacophorans) Single conical shell; directed forward. Foot is broad and flat. Head bears a pair of post oral tentacles. Marine; deep sea- abyssal, bottom feeders Neopilina Living fossil - the only living genus 3 cm

They have- 5-6 pairs of gills and 3-8 pairs of shell retractor muscles. Metamerism? mouth Post oral tentacles shell Gills in mantle groove Foot anus Neopilina

Class Polyplacophora chitons (many (7-8) plates bearing ) Chitons are flattened & dorsally convex. Surface (shell) is composed of 8 overlapping plates. Marine; on rocky surfaces close to the shore.

Head - reduced & lacks tentacles and eyes. Mantle - forms a girdle around the edge of the plates. Mantle cavity- forms two lateral grooves. Radula is file like to scrape algae on rocks

Foot -Broad & elongate- to creep or clinging on hard uneven surfaces like rocks Chiton Dorsal Ventral

Class Scaphopoda Boat foot (tusk shells) Scaphopods have prominent shells. The shell is slightly curved & tubular; It opens at both ends. The mantle is also tubular & open at both ends. The head is reduced and lack eyes. Marine; live buried on sandy bottoms ~900 species. Dentalium

The radula is internal and not used directly for food capture. They feed on small organisms like Foraminifera which are captured using numerous threadlike tentacles (captacula), each with an adhesive knob at the tip. The tentacles extend into the sand to capture food, which is brought back to the mouth via tentacular cilia. The foot is cone shape and used in burrowing. There are no gills and gas exchange occurs across the mantle membrane.

Dentalium

Class Gastropoda stomach foot

About 75% of mollusks (40,000 living species) are gastropods and they occupy most diverse habitats. Marine, freshwater and terrestrial Gastropods include snails, slugs, sea butterflies and many more

Terrestrial snails

Aquatic snails

Slugs

Sea butterflies

Sea hares

Limpets

Cowrie

Whelks Sea snails; having a pointed, spiral shell,

Conchs medium to large-sized sea snails; that have a brightly colored spiral shells and edible flesh

Periwinkles (Small sea snails) marine gastropod mollusk that has gills and an operculum

Nudibranch Soft bodied marine gastropod

Shipworm Using the shell, the shipworm bores into wood

Characteristics of Gastropods 1. Gastropods undergo torsion in its veliger stage: This is a process that move mantle cavity to front of the body, twisting the visceral mass by 90 180 degree rotation. This process change the bilateral symmetrical body to asymmetrical one.

2 The head is well developed and bears various numbers of cephalic tentacles, each bearing an 'eye'.

3 Gastropods have a heavy single shell (univalve) that is normally external and coiled or uncoiled. The shell protects the body and prevents water loss; by withdrawing the body into the shell. Coiled shell is an adaptation for efficient packing of visceral mass.

4 The foot is typically large and used for locomotion-creeping or swimming-and adhering to the substratum.

3. There is a proteinaceous shield known as operculum on the foot. Operculum is to cover the aperture.

They are sluggish and sedentary. The typically file-like radula is well developed and can be used to scrape surfaces, bore holes or harpoon food.

Sub class Opisthobranchs (posterior gill due to detorsion) the gastropod shell is reduced or absent allowing some species to swim. These include the planktonic sea butterflies and sea angels. They have very thin shells and swim by flapping their enlarged bilobed foot.

Class Pelecypoda (Bivalvia) Two valves

~30,000 species. Marine and freshwater. Includes oysters, mussels, clams, scallops

Clams- bivalves that burrow in sediment

Oysters live in marine or brackish habitats attach themselves to the substrate. The valves are highly calcified.

Mussels - saltwater and freshwater clams whose shell outline is elongated and asymmetrical Attach themselves to the substrate

Scallops- brightly colored, fan-shaped shells, with radiating fluted pattern

Cockles live in sandy, sheltered beaches throughout the world- Burrowers,

Bivalve bodies are laterally compressed. They are encased in two calcareous-proteinaceous valves (left and right hinged together by a ligament.

Bivalves are normally filter feeders, drawing water into the shell through a siphon, food is then passed to the mouth by the well-developed ciliated gills (ctenidia).

The head is vestigial lacking eyes but bearing labial palps. Foot is present and may be used in locomotion or burrowing but is often reduced in sessile species. Sessile species attach to the hard substratum : by cementing the shell:oysters, by chitinous byssal threads mussels. Burrowers, such as cockles, bury themselves in soft sediments (some can bore into rock and wood) using an enlarged foot. Commonly only the inhalant and exhalant siphons will be visible above the sediment surface.

The internal features of a bivalve clam (left valve removed).

Pearl oyster

Class Cephalopoda Head foot cuttlefish, squid, octopus, nautilus ~800 species. Marine.

1. Cephalopod heads are very well developed with complex eyes and the large cerebral ganglia form a discrete brain. 2. The radula is tongue-like inside the beaked mouth. 3. Mouth encircles with tentacles (often with suckers) used for feeding, and secondarily for locomotion in some groups. 4. The mantle is tubular and elongate, and utilized for locomotion by pushing water through a tubular funnel (the modified foot), giving the animal jet propulsion. 5. Shell is reduced except in Nautilus

Common cephalopod (Loligo- squid).

Squids In the true squid, the shell has been reduced to a chitinous 'pen (uncalcified), to provide structural support to the mantle. (Loligo) Squids have eight arms and two tentacles surrounding the mouth Species of Loligo are extensively exploited by commercial fisheries All of these internal shell forms are used as a buoyancy device.

Cuttlefish (Sepia) -internal shell (cuttle bone). The body of the cuttlefish (the cuttle) is flattened and has fins that extend along the entire length of the mantle. Brown pigment releases from its siphon when it is alarmed

Octopus Four pairs of arms surround mouth; No tentacles They have no shell. Octopuses are among the most intelligent and behaviorally flexible of all invertebrates.

Cephalopods shell is reduced: The shell in the Nautilus is external, spiralled and internally chambered About 90 tentacles surround the mouth (without suckers) Pelagic marine