Chapter 29 – Mollusks, Segmented Worms and Starfish ( Sea Stars) Snails, Earthworms and Starfish

What is a Mollusk? Clam,squid, snail…….octopus 1. Soft bodies …and a shell 2. Bilateral symmetry 3. A coelom ( a true body cavity) 4. A muscular foot, mantle and visceral Mass 5. Two body openings (mouth and anus) 6. Swimming, ciliated larva 7.) All but bi-valves have a radula (tongue-like organ) to take in food with

Three classes of Mollusks 2. Gastropoda- Those one shell (usually spiral) and slide on their foot. 3. Cephalopoda – no shell tentacles and well developed nervous systems. –1. Bivalves - two shells – a hatchet-like foot

Body systems of a Mollusk Have a true coelom which contains organs for digestion, like the radula, esophagus, stomach and intestines. Many mollusks use gills to extract oxygen from the environment (almost 50%), while others use moist skin. Excretion is done using a nephridia, which will also recover molecules needed to remain in the body (sugar, salt, water)

Body Systems continued Many mollusks have a three chambered heart that pump blood to an open circulatory system. Blood is sprayed over vital organs for diffusion of nutrients. Octopuses and squid are the exception with both having a closed system to allow for the speed and endurance both possess

Reproduction Hermaphrodites exist within the phylum but most are sexual reproducing organisms. Some oysters are able to change sex over and over.

Where do mollusks live?? Mollusks live in a wide variety of habitats They live in polar regions and tropical regions. Some are free swimming, others sessile, & some move across land.

A close look at Gastropods… 37,000 called the univalves…(one shell) The largest class…. snails, slugs, and sea slugs. Herbivorous, using the radula (a rasp-like tongue) to scrape surfaces for food. The body of the snail, called the visceral mass, is found within the shell. Crawls on belly - (foot) secretes mucus….

A close look at Gastropods… sometimes called univalves Open circulatory system allows blood to flow everywhere 2- pairs of antenna eyes on long ones - smell for short Most land univalves are hermaphrodites. The abalone and conches are examples of marine univalves.

Naked gastropods…the slugs No shell, just a thick layer of mucus coating their bodies. Some sea slugs called nudibranchs feed on jellyfish and incorporate the nematocysts into their own tissues! Some sea slugs secrete a poisonous mucus for protection.

A closer look at BIVALVES A large muscular foot for burrowing in the mud Bivalves are filter feeders. Gills are coated with mucus and cilia. They trap food in the mucus. The mantle secretes the shell… and any particle caught in between the shell and mantle is coated to stop irritation. (a pearl)

Bi-Valves continued Adductor muscles located on the opposite side of the opening halves cause great contractions and can even help scallops travel from place to place. Siphon tube, opposite the foot of a bi- valve is a hollow tube to draw in water and filter prey. ( No radula, so they filter feed)

Cephalopods- Squid, Octopus These are the most complex mollusks. Tentacles with suckers are used for moving and capturing prey. A sharp beak-like radula for ripping apart the prey. These species have a closed circulatory system (most efficient).

Phylum Annelida…... The giant earthworm of Australia can be 3m long! Fan worms trap food in the mucus of their fan-like gills. Leeches secrete chemicals that are used as anesthetics, anti-clotting agents, and to dilate blood vessels to increase blood flow.

Segmentation Repeating segments that move independent of each other. Helps in the advanced movements of organisms. Each segment has it’s own muscles attached to help control movements

The annelids….segmented (tiny rings) worms !! Earthworms,bristle worms and leeches These have a coelom and two body openings. Each segment has its own muscles! Each segments has a kidney and a nerve bundle.

The Body System of the Annelids The digestive system is complete with a pharynx, crop, gizzard, glands, intestines, and anus. The circulatory system is closed and has 5 aortic arches that pump blood

Body Systems Continued Excretion is performed by nephridia With the addition of segmentation comes specialization. Which means stimuli must be stored and controlled by a ganglion (Very simple brain) Septa are the segments and nutrients get to each by circulation and the impulses come from the nerve cord.

Setae “Anchor” Away Small hair like projections stick out of each septa to anchor and aide in motion. Movement is also controlled by muscle contractions.

Reproduction of Annelids Although they are hermaphrodites, annelids reproduce with a partner every time and they all get pregnant. Earthworms lock, pass sperm to each other, eggs get fertilized.

Echinoderms = Sea Stars ( The starfish) 5 to many arms around a central disk No blood!! Pump sea water thru body! Eyespots on end of arms External Digestion- stomach is thrown up out of body!! Eat Clams oysters and others!! Internal skeleton- spines

Echinoderm Types Sea Stars – starfish – 5 to 12 arms Brittle stars – wire-like arms move very fast Sea Urchin – many spine-like arms looks like a pin cushion

Deuterostomes In all other blastula organisms, the mouth was the first to develop, but now it is second. Chordates and echinoderms development in the same way during embryo development

Body Systems to perform life Water vascular system is used for gas exchange, eating, and movement. Tube feet also help in respiration, excretion and circulation ( no blood)

Other characteristics.. Tubed feet that acts as suckers Spiny external skeleton (ossicles) Madreporite – filters sea water before it enters animal! Regenerate lost arms! Sexual reproduction!

Importance of Mollusks and Echinoderms…. Serve as food for many people. Most eaten invertebrate type! Pearls and other jewelry… Snails destroy crops.. And serve as a carrier for disease- causing parasites! Starfish eats clams, oysters, and others. Sea cucumbers are eaten in China!