The Lophotrochozoans Study

lophotrochozoan clade

includes 18 animal phyla that are grouped together based primarily on molecular similarities.

What is the symmetry of all lophotrochozoans?

Bilateral

Most lophotrochozoans have 1 of 2 features…

Lophophore or Trochophore larva

what are lophotrochozoans names after, even though some lack these structures?

The lophophore and a trochophore

salinity

the dissolved water content of the water

brackish

water systems where salinities can change from almost fresh to almost marine in a matter of hours as tides move in and out.

osmoconformer

passively allows osmosis to occur until the animal’s internal ion concentration conforms or matches the outside salinity; the organism will gain or lose water

osmoregulator

actively adds or removes ions or water from their cells and bodies in an attempt to maintain a constant internal ion concentration no matter the salinity around them.

lophophore

feeding structure that bears tentacles, found in a few lophotrochozoan phyla

trochophore

a type of ciliated larvae found in some marine & aquatic lophotrochozoan

cephalization

development of a head with sensory organs

endoparasites

parasites found in digestive, respiratory, urinary and reproductive tracts of vertebrates

ectoparasites

parasites found on skin and gills

scolex

in tapeworms, attaches worm to host

proglottids

in tapeworms, segments filled with reproductive organs

setae

hair-like bristles

corona

ciliated wheels found on a rotifer's head, used for feeding and locomotion

mastax

muscular pharynx of a rotifer that grinds up ingested food. Moves rhythmically and looks like a beating heart.

parapodia

leg-like, paired appendages used by errantians for movement.

clitellum

thick external band of a sedentarian (earthworm) used for copulation.hirudin: in leeches, anesthetic and anticoagulant in saliva

radula

rasping teeth of molluscs

aperture

opening of a gastropod shell

operculum

plate on the back of foot in gastropod, closes aperture

venomous

organism that injects toxin

poisonous

organism that is toxic by ingestion

pen

internal chitinous reduced shell of squid

Pen Function

Provide structural support, aids in jet propulsion, enhance movement efficiency, protects internal organs, and contributes to buoyancy control

What happens in brackish environments?

animals can encounter rapid changes in salinity due to tidal movements, tidal inundation, and an influx of freshwater from flooding.

Osmoconformers examples

If the ocean salinity is 32, the animal’s internal ion concentration is 32.

How do osmoconformers make sure their internal ion concentration matches the environment?

By passively gain or lose water (and therefore mass) via osmosis

What animals are osmoconformers?

sponges, cnidarians, ctenophores, and some echinoderms

Where are osmoconformers usually found?

environments where salinity is relatively stable.

Osmoregulator Example

If the animal’s internal ion concentration is 25, but the environmental salinity changes to 18, the animal’s internal ion concentration will remain at 25.

How do osmoregulators maintain a constant internal ion concentration?

By actively add or remove ions from their cells in order to maintain their internal ion concentration

Where are osmoregulators usually found?

where salinity fluctuates, or in areas where salinity is stable.

What do osmoregulators have that osmoconformers don’t?

specialized organs that are used to maintain their internal ion concentration and do not gain or lose water (or mass) when the environmental salinity changes.

What animals are osmoregulators?

annelids, arthropods, and vertebrates

1st Osmoconformers Advantage

Don’t need specialized structures/organs for osmoregulation

2nd Osmoconformers Advantage

Don’t spend energy actively pumping ions/H₂O

1st Osmoconformers Disadvantage

Very sensitive to salinity changes, can’t survive for too long

2nd Osmoconformers Disadvantage

Gain and lose H₂O could damage cells

3rd Osmoconformers Disadvantage

Need a stable environment

1st Osmoregulators Disadvantage

Need specialized structures/organs for osmoregulation

2nd Osmoregulators Disadvantage

Requires more energy to actively maintain stable internal osmotic balance

1st Osmoregulators Advantage

Can survive in many habitats (broader range of salinities) including habitats with rapid fluctuations in salinity

2nd Osmoregulators Advantage