The Smaller Lophocotrozoan/Molluscan success

Lophotrocozoa

Multiple Choice

TRUE OR FALSE. A lophophore is a circular or U-shaped ring of hollow, ciliated tentacles around the mouth.

• TRUE

• FALSE

Multiple Choice

TRUE OR FALSE. A trocophore is a specialized, free-swimming larval stage.

• TRUE

• FALSE

Multiple Choice

It is a traditional grouping of lophotrocozoan phyla

• Playzoa

• Lophophore

• Trocophore

• Phyla

Platyzoa is a traditional grouping of phyla: Platyhelminthes, Gastrotricha, Micrognathozoa, Gnathostomulida, Rotifera, and Acanthocephala​

Multiple Choice

It consist of mostly free-living flatworms

• Trematoda

• Monogenea

• Turbellaria

• Cestoidea

​PHYLUM PLATYHELMINTHES

​The phylum is divided into four classes (table 10.1): (1) the Turbellaria consist of mostly free-living flatworms, whereas the (2) Monogenea, (3) Trematoda, and (4) Cestoidea contain solely parasitic species.

​PHYLUM PLATYHELMINTHES

​Some general characteristics of the phylum Platyhelminthes

include:

1. Usually flattened dorsoventrally, triploblastic, acoelomate, bilaterally symmetrical

2. Unsegmented worms (members of the class Cestoidea are strobilated)

3. Incomplete gut usually present (gut absent in Cestoidea)

4. Somewhat cephalized, with an anterior cerebral ganglion and usually longitudinal nerve cords

5. Protonephridia as excretory/osmoregulatory structures

6. Most forms monoecious; complex reproductive systems

7. Nervous system consists of a pair of anterior ganglia with longitudinal nerve cords connected by transverse nerves and located in the mesenchyme

​​Class Turbellaria

Members of the class Turbellaria are mostly free-living bottom dwellers in freshwater and marine environments, where they crawl on stones, sand, or vegetation. Turbellarians are named for the

turbulence that their beating cilia create in the water.

Multiple Choice

TRUE OR FALSE. The digestive tract of turbellarians is incomplete—it has a

mouth opening but lacks an anus.

• TRUE

• FALSE

​Class Turbellaria

Food digestion is partially extracellular. Pharyngeal glands secrete enzymes that help break down food into smaller units that can be taken into the pharynx. In the digestive cavity, phagocytic cells engulf small units of food, and digestion is completed in intracellular vesicles.​

Multiple Choice

TRUE OR FALSE. The turbellarians have respiratory organs.

• TRUE

• FALSE

​

​

Multiple Choice

The approximately 10,000 species of parasitic flatworms in

the class Trematoda are collectively called flukes, which describes

their _____

• narrow, flat shape

• wide, thick shape

• wide, flat shape

• narrow, thick shape

​Class Trematoda

​The approximately 10,000 species of parasitic flatworms in the class Trematoda are collectively called flukes, which describes their wide, flat shape. Almost all adult flukes are parasites of

vertebrates, whereas immature stages may be found in vertebrates or invertebrates, or encysted on plants. Many species are of great economic and medical importance.

Multiple Choice

It is a common parasite of humans in Asia, where more than 30 million people are infected.

• Korean liver fluke

• Japanese liver fluke

• Chinese liver fluke

​Some Important Trematode Parasites of Humans

The Chinese liver fluke Clonorchis sinensis is a common parasite of humans in Asia, where more than 30 million people are infected. The adult lives in the bile ducts of the liver, where it feeds on epithelial tissue and blood (figure 10.13a). The adults release embryonated eggs into the common bile duct. The eggs make their way to the intestine and are eliminated with feces (figure 10.13b).​ The miracidia are released when a snail ingests the eggs. Following the sporocyst and redial stages, cercariae emerge into the water. If a cercaria contacts a

fish (the second intermediate host), it penetrates the epidermis of the fish, loses its tail, and encysts. The metacercaria develops into an adult in a human who eats raw or poorly cooked fish, a delicacy in Asian countries and gaining in popularity in the Western world (e.g., sushi, sashimi, ceviche).

Multiple Choice

TRUE OR FALSE. Monogeneans are mostly external parasites (ectoparasites) of freshwater and marine fishes, where they attach to the gill filaments and feed on epithelial cells, mucus, or blood.

• TRUE

• FALSE

​Class Monogenea

​Monogenetic flukes are so named because they have only one generation in their life cycle; that is, one adult develops from one egg. Monogeneans are mostly external parasites (ectoparasites) of freshwater and marine fishes, where they attach to the gill filaments and feed on epithelial cells, mucus, or blood.

Multiple Choice

The most highly specialized class of flatworms are members

of the class _____.

• Trematoda

• Monogenea

• Turbellaria

• Cestoidea

​Class Cestoidea

​The most highly specialized class of flatworms are members

of the class Cestoidea commonly called either tapeworms or cestodes. All of the approximately 3,500 species are endoparasites that usually reside in the vertebrate digestive system. Because they lack pigment as adults, their color is often white with shades of yellow or gray. Adult tapeworms range from 1 mm to 25 m in length.

​

Multiple Choice

Taeniarhynchus saginatus means

• chicken tapeworm

• fish tapeworm

• beef tapeworm

• pork tapeworm

​Some Important Tapeworm Parasites of Humans

​One medically important tapeworm of humans is the beef tapeworm Taeniarhynchus saginatus. Adults live in the small intestine and may reach lengths of 25 m. About 80,000 eggs per proglottid are released as proglottids break free of the adult worm. As an egg develops, it forms a six-hooked (hexacanth) larva called the oncosphere. As cattle (the intermediate host) graze in pastures contaminated with human feces, they ingest oncospheres (or proglottids). When a human eats infected meat (termed “measly beef”) that is raw or improperly cooked, the cysticercus is released from the meat, the scolex attaches to the human intestinal wall, and the tapeworm matures.

Multiple Choice

TRUE OR FALSE. The gastrotrichs are members of a small phylum of about 500 free-living marine and freshwater species that inhabit interstitial spaces

(the space between ocean floor or lake bottom substrate particles).

• TRUE

• FALSE

​Phylum Gastrotricha

​The gastrotrichs are members of a small phylum of about 500 free-living marine and freshwater species that inhabit interstitial spaces (the space between ocean floor or lake bottom substrate particles). They range from 0.01 to 4 mm in length. Gastrotrichs use cilia on their ventral surface to move over the substrate. The phylum contains a single class divided into two orders. The nervous system includes a brain and a pair of lateral nerve trunks. The digestive system is a straight tube with a mouth, a muscular pharynx, a stomach-intestine, and an anus. The action of the pumping pharynx allows the ingestion of microorganisms and organic detritus from the bottom sediment and water. Digestion is mostly extracellular.

Multiple Choice

It is the most recently discovered (1994) and described

(2000) group of animals.

• Gastrotricha

• Micrognathozoa

• Gnathostomulida

• Rotifera

​Phylum Micrognathozoa

​Micrognathozoa is the most recently discovered (1994) and described (2000) group of animals. Limnognathia maerski lives interstitial in cold, homeothermic (constant temperature) springs on Disko Island, Greenland. With an average length of one-tenth of a millimeter, they are one of the smallest animals.

Multiple Choice

TRUE OR FALSE. The phylum Gnathostomulida is composed of over 1000 species

in 18 genera.

• TRUE

• FALSE

​Phylum Gnathostomulida

​The phylum Gnathostomulida is composed of over 100 species in 18 genera. Gnathostomulids are minute (less than 2 mm long), slender to thread-like, animals (figure 10.21). They are commonly called “jaw worms” because of their unique jawed

pharyngeal apparatus. Gnathostomulids are found interstitial in marine sands, often occurring in high densities in anoxic (low oxygen), sulfide-rich conditions. They occupy depths from the intertidal zone to more than 100 m. They have been found worldwide.

Multiple Choice

The rotifers derive their name from the characteristic ciliated organ, the _____, around lobes on the heads of these animals.

• mastax

• cilia

• corana

• trunk

​Phylum Rotifera

​The rotifers derive their name from the characteristic ciliated organ, the corona, around lobes on the heads of these animals. The corona functions in locomotion and food gathering. The cilia of the corona do not beat in synchrony; instead, each cilium is at a slightly earlier stage in the beat cycle than the next cilium in the sequence.

Multiple Choice

TRUE OR FALSE. Adult acanthocephalans are endoparasites in the

intestinal tract of vertebrates (especially fishes).

• TRUE

• FALSE

​Phylum Acanthocephala

​Adult acanthocephalans are endoparasites in the intestinal tract of vertebrates (especially fishes). Two hosts are required to complete the life cycle. The juveniles are parasites

of crustaceans and insects. Acanthocephalans are generally small (less than 40 mm long), although one important species, Macracanthorhynchus hirudinaceus, which occurs in pigs, can be up to 80 cm long.

Phylum Nemertea (Rhynchocoela)​

Characteristics of the phylum Nemertea include:

1. Triploblastic, acoelomate, bilaterally symmetrical, unsegmented

worms possessing a ciliated epidermis containing mucous glands

2. Complete digestive tract with an anus

3. Protonephridia

4. Cerebral ganglion, longitudinal nerve cords, and transverse

commissures

5. Closed circulatory system

6. Body musculature organized into two or three layers​

​Phylum Cycliophora

​Along with Micrognathoza, Cycliophora is one of the most recently described phyla. Cycliophorans live on the mouthparts of claw lobsters on both sides of the North Atlantic. These are very tiny animals, only 0.35 mm long and 0.10 mm wide. They were named Symbion pandora, the first members of this new phylum. They attach to the mouthparts with an adhesive disc on the end of an acellular stalk

​Phylum Ectoprocta (Bryozoa)

​Characteristics of the phylum Ectoprocta (Bryozoa)

include:

1. Coelomate, colonial lophotrochozoans

2. Lophophore circular or U-shaped

3. Gut U-shaped; anus opens outside base of lophophore tentacles

4. Circulatory and excretory structures absent

5. Colonies produced by asexual budding; zooid often polymorphic

6. Gas exchange occurs through the body surface

7. Sessile in marine and freshwater habitats

​Phylum Brachiopoda

​Characteristics of the phylum Brachiopoda include:

1. Triploblastic, coelomate, bilaterally symmetrical

2. U-shaped gut with or without an anus

​3. Body enclosed in dorsal and ventral valves

4. Nervous system with a ganglionated circumesophageal ring

5. Open circulatory system with one or more hearts

6. No gas exchange organs

7. Horse-shoe-shaped lophophore in anterior mantle cavity

Multiple Choice

Brachiopods possess a ____, which secretes a shell

comprised of dorsal and ventral valves.

• coelomate

• mantle

• gut

• valve