Exam 3 Study Guide: Invertebrate Biology (Tardigrada, Mollusca, Arthropoda)

Comprehensive practice flashcards covering comparative anatomy, physiology, life histories, and taxonomy of Phylum Tardigrada, Phylum Mollusca (Polyplacophora, Bivalvia, Gastropoda, Cephalopoda), and Phylum Arthropoda (Trilobita, Chelicerata, Myriapoda, Crustacea, Hexapoda).

What superphylum, germ layer classification, body symmetry, and coelom type characterize Phylum Tardigrada?

Tardigrades belong to Superphylum Ecdysozoa, are triploblastic, have bilateral symmetry, and possess a eucoelomate body plan with a hemocoel.

What is cryptobiosis in Phylum Tardigrada?

A unique state of suspended animation/metabolism in which tardigrades survive extreme conditions by expelling almost all body water and forming a barrel-shaped tun.

How do tardigrades perform gas exchange and circulate nutrients?

They lack specialized respiratory and circulatory systems; oxygen and carbon dioxide diffuse directly across the epidermis, and fluid circulates freely within the hemocoel.

How is metabolic waste removed in Phylum Tardigrada?

Metabolic waste is concentrated by Malpighian tubules (or Malpighian glands) and transported directly into the digestive system to be eliminated through the anus.

Describe the locomotory structures and body organization of tardigrades.

They have a cylindrical body with simple cephalization (eye spots, sensory papillae, and bristles) and four pairs of clawed legs (the first three pairs for locomotion and the fourth pair for clinging).

How does reproduction occur in Phylum Tardigrada?

They are dioecious and reproduce sexually via external fertilization, which typically occurs during molting when eggs are deposited onto the shed cuticle.

What three universal anatomical features are shared by all members of Phylum Mollusca?

A muscular foot used for locomotion, a visceral mass containing internal organs, and a mantle that covers the visceral mass and secretes the calcium carbonate ($CaCO_3$) shell.

What is the radula in mollusks, and which class lacks this structure?

An abrasive, chitinous, toothed tongue used for scraping, grinding, or boring food; it is completely absent in Class Bivalvia.

What fundamental circulatory difference separates Class Cephalopoda from other molluscan classes?

Cephalopods have a closed circulatory system with systemic and branchial hearts, whereas other mollusks (polyplacophorans, bivalves, gastropods) possess an open circulatory system where hemolymph bathes tissues in a hemocoel.

What defining morphological feature characterizes Class Polyplacophora (chitons)?

A dorsal shell divided into $8$ overlapping articulated plates (valves) surrounded by a girdle.

Which larval stage is shown here, characteristic of Polyplacophora and marine gastropods/bivalves?

The trochophore larva, characterized by a spherical body encircled by bands of cilia (prototroch) and an apical tuft of cilia.

How do bivalves feed and exchange respiratory gases in the absence of a radula and head?

They are filter feeders; water is moved through siphons across enlarged, ciliated gills that both extract dissolved oxygen and trap food particles to transport them to the mouth.

What is embryonic torsion in Class Gastropoda?

A developmental rotation of the mantle and visceral mass by up to $180^\circ$ relative to the head and foot, shifting the anus and mantle cavity anteriorly above the head and swapping left- and right-sided organs.

How do terrestrial gastropods accomplish gas exchange without gills?

Through a vascularized network of thin blood vessels within the mantle lining, which functions as a modified "lung" exchanging gases with the atmosphere.

What cell types allow cephalopods to execute rapid camouflage and color/pattern change?

Chromatophores (containing black, brown, and yellow pigments), along with iridophores and leucophores that reflect ambient light to produce greens, blues, and whites.

How do the chambered Nautilus and cuttlefish regulate buoyancy?

By actively pumping sodium ($Na^+$) and chloride ($Cl^-$) ions into or out of shell chambers: water follows via osmosis, allowing gas to fill the chamber to decrease density, or water to enter to increase density.

What substances comprise cephalopod defensive ink, and how does each component affect predators?

Melanin protein creates an ink screen/cloud; mucus binds melanin into a pseudomorph or "blob" roughly the size of the animal; and dopamine disorients the attacker's sensory systems.

How do cephalopods transfer sperm during reproduction?

Males package sperm into spermatophores and transfer them into the female mantle cavity using a modified arm called a hectocotylus or a penis.

Identify the three structural layers of the arthropod cuticle from superficial to deep.

1. Epicuticle (outermost, hard, contains wax lipids, proteins, and chitin; shed at molting); 2. Exocuticle (middle, hard, chitin and sclerotized proteins; shed at molting); 3. Endocuticle (innermost, soft, chitin and soft protein; reabsorbed prior to molting).

What endocrine mechanism triggers ecdysis (molting) in arthropods?

A brain neurosecretory structure releases a neurohormone into the blood, stimulating epidermal cells to produce ecdysone, which induces epidermal cell division and cuticle synthesis.

What anatomical structures anchor striated appendage muscles to the inside of the arthropod exoskeleton?

Apodemes (internal ingrowths/ridges of the cuticular exoskeleton).

What extinct arthropod subphylum, prevalent around $500\text{ million years}$ ago, is pictured here?

Subphylum Trilobita, a diverse group of extinct marine arthropods closely related to Chelicerata.

What tagmata and cephalic appendage characteristics define Subphylum Chelicerata?

A body divided into a prosoma (cephalothorax) and opisthosoma (abdomen), lack of antennae, and a first pair of appendages modified as feeding mouthparts called chelicerae.

What respiratory and excretory organs are found in terrestrial vs. aquatic chelicerates?

Terrestrial chelicerates use book lungs for respiration and Malpighian tubules for excretion; aquatic chelicerates use book gills and excrete ammonia via simple diffusion across the gill books.

What are the primary distinguishing features between centipedes and millipedes in Subphylum Myriapoda?

Centipedes have dorsoventrally flattened bodies, $1$ pair of legs per segment projected laterally, and venomous forcipules (carnivores); millipedes have rounded bodies, $2$ pairs of legs per segment directed ventrally, and no venom (detritivores/herbivores).

Identify the two appendage structural types depicted below and indicate which subphylum is defined by the branched form.

Biramous leg (two-branched, defining of Subphylum Crustacea) and uniramous leg (single-branched, seen in hexapods and myriapods).

What excretory organ is unique to Subphylum Crustacea?

The green gland (antennal gland), which concentrates metabolic wastes and releases them through an excretory pore near the base of the antennae over the gills.

Identify the two distinct crustacean larval stages shown below.

Left: Nauplius larva (characteristic of crabs and lobsters); Right: Zoea larva (characteristic of shrimp).

Describe the body tagmata and appendage arrangement of Subphylum Hexapoda.

Body is divided into head (mouthparts, $1$ pair of antennae, compound eyes), thorax ($3$ segments bearing $3$ pairs of walking legs and often $2$ pairs of wings), and an abdomen ($11$ subsegments with external reproductive structures).

What is the difference between complete and incomplete metamorphosis in hexapods?

Complete metamorphosis includes distinct developmental stages (egg, larva, pupa, adult) where larvae differ morphologically and ecologically from adults; incomplete metamorphosis features nymphs (instars) that resemble small, wingless versions of the adult.

How do Malpighian tubules in Hexapoda prevent desiccation while eliminating nitrogenous waste?

They extract metabolic waste as insoluble uric acid and excrete it into the rectum, where water, ions, and nutrients are actively reabsorbed before dry fecal pellets are expelled.

What are the primary defense and toxicity characteristics of the Bullet Ant (Paraponera clavata)?

It produces a stridulating hiss as a warning and delivers a neurotoxin rated $10/10$ on the pain scale that induces throbbing muscle spasms and intense pain lasting over $24\text{ hours}$.

What selective pressure produced the massive horns of the male Hercules Beetle (Dynastes hercules)?

Intrasexual selection (male-male combat for mating opportunities).

Compare the gas exchange mechanisms among the four covered classes of Mollusca.

Polyplacophora: mantle groove gills; Bivalvia: ciliated filter-feeding gills; Gastropoda: mantle cavity gills (aquatic) or vascularized mantle "lungs" (terrestrial); Cephalopoda: paired, highly folded branchial gills supported by branchial hearts.

Compare the nitrogenous waste excretion organs across the extant subphyla of Arthropoda.

Chelicerata: book gill diffusion (aquatic) or Malpighian tubules (terrestrial); Myriapoda: Malpighian tubules; Crustacea: paired green glands (antennal glands); Hexapoda: Malpighian tubules excreting uric acid into the hindgut.