Chapter 15 – Gnathiferans and Smaller Lophotrochozoans

Forty question-and-answer flashcards summarizing key facts about gnathiferan and lophotrochozoan phyla, their anatomy, life cycles, and taxonomy.

Where do members of Phylum Gnathostomulida typically live?

In fine coastal sediments, though some inhabit deep-water sediments.

What type of body cavity do gnathostomulids possess?

They are acoelomate (lack a body cavity).

What is distinctive about the epidermal cells of gnathostomulids?

Each epidermal cell bears a single cilium (monociliated).

What kind of gut do gnathostomulids have?

A simple, blind gut with jaws leading to it (no anus).

What is the sole described species in Phylum Micrognathozoa?

Limnognathia maerski.

How many pairs of jaws are found in Limnognathia maerski?

Three pairs of jaws.

In what year was Limnognathia maerski formally described?

The species was described in 2000 (discovered in 1994).

What adhesive structure helps micrognathozoans move and attach to the substrate?

A unique ventral ciliary pad that secretes glue.

What is the characteristic wheel-like organ on a rotifer called?

The corona (wheel organ).

What remarkable survival ability is exhibited by some rotifers?

They can desiccate into a dormant state and revive years later.

How do rotifers usually move from place to place?

By creeping with their foot, swimming with coronal cilia, or both.

What is the function of the mastax in a rotifer?

It is a muscular pharynx with hard jaws (trophi) that grinds food.

What type of body cavity is present in rotifers?

A large, fluid-filled pseudocoel.

Which rotifer class entirely lacks males?

Class Bdelloidea.

How do mictic eggs differ from amictic eggs in rotifers?

Mictic eggs must be fertilized to form diploid embryos, whereas amictic eggs are already diploid and develop parthenogenetically.

Which rotifer class produces amictic, mictic, and dormant eggs?

Class Monogonata.

What attachment organ characterizes acanthocephalans?

An invaginable proboscis armed with rows of spines.

Do acanthocephalans possess a digestive tract?

No, they completely lack a digestive tract.

What is the first larval stage of acanthocephalans called?

The acanthor.

In what type of host does the cystacanth stage of acanthocephalans develop?

Inside an intermediate arthropod host, commonly an insect or crustacean.

Where are members of Phylum Cycliophora found?

Attached to the mouthparts of living decapod crustaceans.

What free-swimming larval form is produced by Cycliophora during sexual reproduction?

A chordoid larva.

How would you describe the body shape of a gastrotrich?

Small (<3 mm), dorsoventrally flattened and covered with spines or bristles.

Which excretory cells replace flame cells in gastrotrichs?

Solenocytes.

What is the principal reproductive strategy of gastrotrichs?

Parthenogenesis; they function as parthenogenetic females.

Where is the anus located in entoprocts relative to their tentacle crown?

Inside the ring of ciliated tentacles, alongside the mouth.

Do entoprocts have a circulatory system?

No, they lack both circulatory and respiratory systems.

What name is given to an individual animal within an ectoproct colony?

A zooid.

What is the rigid external case produced by an ectoproct colony called?

A zoecium.

What term describes the first zooid that founds an ectoproct colony?

The ancestrula.

How do brachiopod shell valves differ from those of bivalve molluscs?

Brachiopods have dorsal and ventral valves, whereas bivalves have left and right lateral valves.

What stalk-like structure anchors many brachiopods to the substrate?

The pedicel.

Do brachiopods have an open or closed circulatory system?

An open circulatory system with a contractile heart.

What is the free-swimming larval form of Phoronida called?

An actinotroch larva.

What overall gut shape is shared by all lophophorate phyla?

A U-shaped gut with the anus outside the lophophore ring.

By what mechanism do lophophorates obtain food?

Ciliary feeding using the lophophore’s tentacles to filter particles from water.

What is controversial about the phylogenetic placement of lophophorates?

It is unclear whether they belong among protostomes, deuterostomes, or represent an intermediate condition.

What network in acanthocephalans increases body-wall surface area for nutrient absorption?

The lacunar system (series of epidermal trenches).

What is the common name for Phylum Ectoprocta, formerly called Bryozoa?

The moss animals.

Which rotifer class is primarily marine, elongate, and has a vestigial corona?

Class Seisonidea.