Zoology: Phylum Mollusca and Related Lophotrochozoans

These flashcards cover the characteristics, classification, and biological systems of Phylum Mollusca, as well as several minor lophotrochozoan phyla including Gastrotricha, Rotifera, Bryozoa, Brachiopoda, Nemertea, and Platyhelminthes based on the lecture transcript.

To which group are mollusks most closely related on the phylogenetic tree?

Annelids

How many species of mollusks have been identified?

$90,000$ species

What is the most notable characteristic of the phylum Mollusca?

The dorsal mantle layer

Where are most of the organs located in a mollusk?

In the visceral mass

What are the primary functions of the mantle cavity in mollusks?

It is a multifunctional chamber for respiration (where gills are located), waste excretion, gamete release, and contains the nephridia.

What are the common functions of the muscular foot in mollusks?

Locomotion (swimming or other movement), anchoring, and sometimes food capturing.

What are the hard structures located on the tongue in the head region used for scraping food?

Radula (on the ondontophore)

What is the prismatic layer of a mollusk shell made of?

Calcium carbonate ($CaCO_3$)

How is a pearl formed within a mollusk?

The mantle secretes a layer over an irritant to protect the internal organs.

What type of circulatory system and heart do most mollusks possess?

An open circulatory system and a $3$ chambered heart.

What is the respiratory pigment found in mollusks?

Hemocyanin

What are the three larval stages common in mollusks?

Trochophore larva, veliger larva, and late stage veliger larva.

Which mollusk class is characterized by a shell-less, worm-like body, burrowing habits, and one pair of gills?

Class Caudofoveata

What are the characteristics of Class Solenogastres?

They have no shell, possess calcium carbonate spicules, lack gills, are monoecious, and feed mainly on the eggs of cnidarians.

Which class is known as chitins and typically features $8$ plates?

Class Polyplacophora

What process in the veliger larva of Gastropoda causes the visceral mass to become asymmetrical and the anus to rotate $180$ degrees?

Torsion

How many species belong to the class Gastropoda?

$70,000$ species

What is the benefit of coiling and asymmetry in snails?

It creates unidirectional flow, allowing water and $O_2$ in while moving $CO_2$ and waste out, preventing things from getting stuck.

What is the pneumostome in terrestrial snails and slugs?

An opening to the body used for respiration (leading to the mantle cavity lung) and reproduction.

What are the identification keys for left-handed and right-handed snails?

Sinistral is left-handed; Dextral is right-handed.

What group of freshwater snails are air-breathing and lack an operculum?

Pulmonates (examples include Lymnaeidae, Planorbidae, and Physidae)

What are the distinguishing features of Class Bivalvia?

They have no head or radula, possess two shells (valves), are suspension feeders, and the intestine runs through the heart.

What is the larval stage of freshwater bivalves called?

Glochidia

According to the notes, how many of the $300$ freshwater clam species in the US are extinct?

At least $24$ species

How many hearts do cephalopods possess and what are their functions?

They have $3$ hearts: $2$ brachial hearts that pump blood through the gills and $1$ systemic heart that pumps blood through the rest of the body.

What structure allows cephalopods to change color rapidly for camouflage and mating?

Chromatophores

What are the characteristics of the subclass Nautiloidea?

They have an external shell for buoyancy and defense, $2$ pairs of gills, lack ink, and have many tentacles ($60$ pairs) without suckers.

What is the reduced chitinous shell found in squids called?

A pen

What defines the body cavity of a pseudocoelomate?

The mesoderm does not fully line the gut cavity.

What are the defining structures of Phylum Rotifera?

The corona (ciliated feeding structure) and the Mastax (muscular pharynx with jaws).

Which phylum consists of vertebrate endoparasites with an eversible spiny proboscis and no digestive system?

Phylum Acanthocephala

What is a lophophore?

A crown of ciliated tentacles (hollow tubes) used for suspension feeding and gas exchange.

What are statoblasts in Phylum Bryozoa?

Dormant structures in freshwater species that allow them to survive unfavorable conditions like winter.

How do Brachiopoda shells differ from Bivalvia shells?

Brachiopoda have dorsal and ventral shells, whereas Bivalvia have left and right shells.

Which phylum is known as ribbon worms and features an eversible proboscis housed in a rhynchocoel?

Phylum Nemertea

What are the three muscular layers that give flatworms (Platyhelminthes) control over their movement?

Circular, longitudinal, and parenchymal (dorsoventral) layers.