Bio 101 Exam #2 Mollusk, Segmented Worm, and Ecdysozoan

Do "worms" (Platyhelminthes, Annelida, and Nematoda) form a monophyletic group? Why or why not?

Animals that often are called "worms" do not form a monophyletic group, which is an ancestor and all of its descendents. Annelids and platyhelminths are more closely related to mollusks than they are to nematodes, and nematodes are more closely related to arthropods than they are to either annelids or platyhelminths. (FYI, the most recent common ancestor of Platyhelminthes, Annelida, and Nematoda is at Protostomia, but not all protostomes would be considered "worms".)

Bivalve molluks have lost their radula. How do they eat?

Bivalve mollusks eat through suspension feeding. They draw water with food particulates into their viscaeral masses through incurrent siphons, which directs the water over the gills. Food is trapped in the gills and moved to the mouth, and water is expelled through excurrent siphons.

What feature(s) make a clam a protostome bilaterian animal?

Clams, which are mollusks, are protostomes in that they exhibit spiral cleavage, the blastopore (first opening) develops into the mouth, and the nerve cord is positioned ventrally (along the belly side of the animal). Clams are bilaterians in that they are bilaterally symmetrical (divided into right and left halve), are cephalized (have a distinct head with a centralized nervous system), and triploblastic tissues (three tissue layers). Clams are animals in that they are multicellular eukaryotic organisms, heterotrophic, obtain nutrients through ingestion, and have collagen.

What is cryptobiosis, and how has it led to the success of tardigrades?

Cryptobiosis is a state of suspended animation observed in tardigrades, and it is characterized by a nearly complete drying of the body and a stop of metabolism. Cryptobiosis allows tardigrades to survive if the film of water in which they live dries, and it also allows them to survive extremely low temperatures, and even the vacuum of space!

What feature(s) make an earthworm an ecdysozoan protostome bilaterian animal?

Earthworms, which are annelids, are ecdysozoans in that they exhibit ecdysis (shedding of out cuticle layer). Earthworms are protostomes in that they exhibit spiral cleavage, the blastopore (first opening) develops into the mouth, and the nerve cord is positioned ventrally (along the belly side of the animal). Earthworms are bilaterian in that they are bilaterally symmetrical (divided into right and left halve), are cephalized (have a distinct head with a centralized nervous system), and triploblastic tissues (three tissue layers). Earthworms are animals in that they are multicellular eukaryotic organisms, heterotrophic, obtain nutrients through ingestion, and have collagen.

Which major clade of mollusk is the most diverse in terms of the greatest number of species?

Gastropoda.

Annelids have metameric segmentation. What does that mean?

Metameric segmentation is division of the body into serial parts divided by septa.

Briefly discuss the lifestyle(s) of nematodes. Are they free-living, symbiotic, or parasitic?

Nematodes can be free-living (such as the model organism C. elegans), mutualistic (such as species that live in the intestines of iguanas to help digest plant material), OR parasitic (such as round worms, hook worms, and pin worms)

What feature does members of Onycophora share with members of Tardigrada, but not with Nematoda?

Onycophora (velvet worms) and Tardigrada (water bears) possess unjointed appendages, but appendages are absent in Nematoda. In addition, the exoskeletons of onycophorans and tardigrades are composed of chitin, but the exoskeleton of nematodes is composed of collagen. (Arthropoda also has appendages and a chitinous exoskeleton suggesting that arthropods are more closely related to onycophorans and tardigrades than nematodes.)

List the major synapomorphies of Annelida.

Synapomorphies of Annelida include metameric segmentation and setae.

List the major synapomorphies of Mollusca.

Synapomorphies of Mollusca include the mantle, calcareous shell, muscular "foot", chambered heart, radula, and posterior gills.

List the major synapomorphy of Ecdysozoa

The major synapomorphy of Ecdysozoa is ecdysis

setae

chitinous bristles in annelids that anchor the body and aid in movement

Tardigrada

chitinous exoskeleton, four pairs of unjointed legs with claws, completely lack circulatory and respiratory systems, feed using stylets, undergo cryptobiosis; ("water bears")

Onycophora

chitinous exoskeleton, numerous pairs of unjointed appendages with claws, papillae that secrete slime from slime glands; ("velevet worms")

Nematoda

collagenous (non-chitinous) exoskeleton, no legs, unsegmented, longitudinal muscles only, free-living or mutualistic or parasitic; ("round worms")

Polyplacophora

flat shells with eight valves, foot adheres body securely to rocks, graze on algae; ("chitins"

Cephalopoda

foot is fused to head and forms a funnel to expel water from mantle cavity, tentacles for food capture surround beak-like radula, complex eye and sophisticated brain, may have external shell or internal guards (pens); ("squid")

chitin

hard carbohydrate that forms the exoskeleton and cuticle of several bilaterian clades

radula

hard mouthparts of mollusks that often are developed as a rasping tongue

adductor muscle

muscle found in bivalve mollusks that pulls the two valves together (closes shell

foot (in terms of mollusks)

muscular organ in mollusks that is used for movemen

There is only one clade of mollusk that includes fully terrestrial (land dwelling) species. Which clade is it?

only some members of Gastropoda are fully terrestrial.

Lumbricidae

segmented bodies without appendages, seatae but no parapodia, obvious clitellum; ("earthworms")

Hirudinidae

segmented bodies without appendages, setae are absent, clitellum is hidden (internal), anterior and posterior ends have "suckers" for attachment, a strong pharynx for sucking fluids; ("leeches")

"polychaetes"

segmented bodies without appendages, setae grow from parapodia, well differentiated heads, include suspension feeders (that live in tubes) and voracious predators; ("marine annelids")

ecdysis

shedding (molting) of outer, non-cellular cuticle layer; characteristic of Ecdysozoa

Gastropoda

single valve that often is coiled, muscular foot used for crawling (motile), well-developed heads and radulae, predatory and herbivorous; ("snails")

mantle

soft extension of the body wall in mollusks that secretes the shell

clitellum

thickened region of certain segments in many earthworms and leeches that secretes mucus during reproduction

Bivalvia

two valves, valves closed by adductor muscles and opened by hinge ligament, sedentary suspension feeders, no radula, hatchet-shaped foot, breath and feed using siphons; ("clams")