Phylum Mollusca- Marine Invert Biology

digestive system

Due to torsion, the gastropod's once straight ________________ loops with anus above head

posterior, anterior

Due to torsion, the mantle cavity containing the ctenidia and anus shift from ____________ to _____________

larger, more

Having a circulatory system allows organisms to become (larger/smaller) and (less/more) active

tentacles, arms , funnel

In cephalopods, the foot takes the shape of what 3 structures?

hemolymph

In invertebrates with an open circulatory system, the body fluid that bathes tissues, is mixed with coelomic fluid

byssal threads

In mussels, the foot has evolved into ______________, tough, fibrous protein threads that attach the mussel to a substrate

back and forth

Instead of altering its shape like vertebrates, the lens in the complex eyes of cephalopods move_________________ to focus.

Rhinophores

Opisthobranch sensory tentacles

2

Step ___ of Molluscan Gas Exchange - Deoxygenated blood enters the ctenidium from the sinuses via afferent vessel

3

Step ___ of Molluscan Gas Exchange - Oxygenated blood leaves the gill via efferent vessel

1

Step ___ of Molluscan Gas Exchange - a pair of ctenidia hang down and drive water into the mantle cavity

Pelecypod ctenidia

The ______________ has a duel function for gas exchange and food collection

site fidelity

The instinctual tendency of an animal to remain at or near a particular location

prismatic layer

The middle layer of the mollusk shell, composed of calcium carbonate; calcium prism is at a right angle from periostracum

foot

The muscular organ that is used for molluscan locomotion

Hinge teeth

These interlock to help the bivalve with alignment

hypothetical ancestral mollusc (HAM)

This idea suggests that the diversity of molluscs came about modifications from a single ancestor. All molluscs the same body plan plus or minus a few characteristics but modified in diverse ways.

Benefit of Gastropod Torsion

Torsion brings the mantle cavity above the head, which provides the space necessary to retreat the head more efficiently.

True

True or false: The cephalopod's ganglia concentration exceeds any invert species. This makes it capable of learning and memory, as well as distinguishing shapes and colors

head (cephalized)

What feature of molluscs includes: - sensory structures - ganglia - radula

Figure 8

What kind of shape does the nervous system form due to gastropod torsion?

opposite directions

When water and blood flow in ______________, blood is always adjacent to water (which has a higher O2 content) so that diffusion between blood and water occurs along the entire ctenidia

Walter Garstang (1920)

Who proposed that torsion benefits the larval gastropod?

siphuncle

a central tube like tissue connecting the chambers of shelled cephalopds such as Chambered Nautilus; used to transport liquids from which gases diffuse for buoyancy

trochophore

a free-swimming, ciliated larva of many worms and some mollusks

columellar muscle

a muscle that has its origin on the columella of a gastropod mollusk shell and serves to retract the animal into the shell

odontophore

a projection in the mouth of most mollusks that supports the radula.

hemocyanin

a protein containing copper, responsible for transporting oxygen in the blood plasma of arthropods and mollusks.

Radula

a set of chitinous teeth that are stretched over a supporting belt, arranged in horizontal rows, pointed backwards

septa

a wall, dividing a cavity or structure into smaller ones

visceral mass

area beneath the mantle of a mollusk that contains the internal organs (i.e. gonads, digestive, circulatory, and excretory systems)

closed circulation

blood is confined to vessels, heart pumps blood into large vessels which supply it to organs

open circulation

body fluid (hemolymph) bathes the organs directly, One major blood vessel and a heart keep fluid circulating

3-chambered heart

consists of 2 auricles and 1 ventricle

Labial Palps

fleshy folds of skin located near the mouth that collect food particles from the gills and transport them to the mouth

Class Gastropoda

largest class (greater than 60,000 species) - most are benthic, with some pelagic and sessile -dorsal-ventrally elongated - uses a shell as a protective retreat and to prevent dessication

sinistral

left-handed shell, when the shell of a gastropod opens to the left

branchial hearts

located at base of ctenidia and pump blood through the ctenidia

Umbo

oldest part of the shell of a bivalve from which the shell grows; this part points up when determining which half is which

cerata

organ on an Opisthobranch's back that functions as a gill and as a defensive weapon with nematocysts from consumed prey (nudibranchs)

Chromatophores

pigment cells that change the color of an organism, allowing it to camouflage; expansion and contraction is controlled by muscle elements in the skin

Pen

remains of a shell; helps support the squid

dextral

right handed shell, when the shell of a gastropod opens to the right

Mollusca

second largest phylum with 100,000 species of invertebrates including snails, cephalopods, bivalves

cuttlebone

shell (endoskeleton) of a cuttlefish

Ctenidia

specialized gills in mollusks

Hawaiian Bobtail Squid

symbiotic light-emitting bacteria, Aliivibrio fischeri, living in a special organ. This bacteria is acquired through horizontal transmission from the environment. The light emitted by the bacteria is caused by quorum sensing due to high density in the light organ of the squid.

captacula

tentacle-like projection that is present in tusks shells to catch prey

homing behavior

the ability of an animal to find its home area

Gastropod Torsion

the anti-clockwise twisting of the visceral mass to 180 degrees during early development

countercurrent exchange

the opposite flow of adjacent fluids that maximizes transfer rates; for example, blood in the gills flows in the opposite direction in which water passes over the gills, maximizing oxygen uptake and carbon dioxide loss.

Periostracum

the outermost layer of a molluscan shell produced by the mantle's edge

mantle

thin layer of tissue that covers the mollusc's visceral mass and secretes the shell

nacreous layer

thin, innermost calcareous layer of mollusc shells, produced by all parts of the mantle

siphon

tubelike structure through which water enters and leaves a mollusk's body

Class Scaphopoda

"tusk shells" - ~400 species - curved-tube shell, opening at each end - burrows in sediment with narrow end above substrate - posses a captacula

Class Aplacophora

- "without plates" - deep water - vermiform (wormlike) - most burrow or live on cnidarians

cephalopod circulatory system

- 2 branchial hearts and one 3-chambered systemic heart - lacks countercurrent exchange

Class Cephalopoda

- 600 living species, 10,000 fossil species - among the largest inverts general characteristics: - closed circulation - foot modified into arms, tentacles, and funnel - high concentration of ganglia (nerve cells) - chromatophores, ink sac

Class Monoplacophora

- Deep-sea (175 m or more) - single-cap shaped shell (similar to limpets) - 31 described species (few specimens have been studied alive

Class Polyplacophora

- includes chitons - commonly found on hard substrates - dorsally-ventrally flat - broad and powerful foot adapted for clinging and living in wave-washed intertidal zone - shells consist of 8 overlapping articulating plates surrounded by a girdle

Molluscan Gas Exchange

- mainly by gills called ctenidia in the mantle cavity - many, thin gill filaments increases surface area for gas exchange

Class Ophistobranchia

- ~5,000 species - includes sea hares, sea slugs (nudibranchs), bubble shells - has a reduced or lost shell and operculum - limited torsion or detorsion (~90 degrees) - has a cerata instead of ctenidia

Closed circulation pathway

1. Heart ventricle 2. aorta 3. smaller arteries 4. capillaries 5. vessels to ctenidia 6. ctenidia 7. heart auricle (repeat)

open circulation pathway

1. Heart ventricle 2. aorta 3. smaller arteries 4. sinuses (hemocoel) 5. vessels to ctenidia 6. Ctenidia 7. heart auricles (repeat)

Pelecypod feeding

1.) cilia drive water flow 2.) trapped food particles moved toward food grooves entrained in mucus 3.) mucus string moves toward labial palps, which sorts and transports food toward the mouth

Class Pelecypoda (Bivalvia)

2nd largest mollusc class, 9,000 species - hinged 2-piece shell with left and right sides - lateral compression of body and foot - lack of cephalization - spacious mantle cavity - has a siphon instead of a radula

posterioly

According to Garstang's theory, the head was more vulnerable to predation because the untorted shell opened________________, so the head would be drawn in last.

food grooves

Ciliated tracts along the dorsal and ventral margins of the gills of bivalves; transport food filtered by the gills toward the mouth

active

Closed circulation is very efficient O2 transport in _______________ molluscs such as Cephalopods

posterior adductor muscle

Connected to the back half of a mollusk. Major muscle for closing the valves.