BIOL 3610U: Comparative Zoology (Lectures 1–9)

Vocabulary practice flashcards covering essential concepts, anatomical structures, taxonomic classifications, and physiological mechanisms across Comparative Zoology Modules 1 through 8.

Hypothesis

A tentative, testable explanation formulated to account for an observed natural phenomenon, serving as the basis for empirical experimentation or comparative testing.

Theory

A well-supported, overarching explanation of natural phenomena that accounts for a broad range of observations, supported by extensive, repeated empirical evidence.

Paradigm

An overarching conceptual framework or foundational model that guides scientific research, inquiry, and experimental methodology within a discipline.

Two Foundational Paradigms of Modern Zoology

Darwin's Theory of Evolution (explaining history, adaptation, and diversity) and the Chromosomal Theory of Inheritance (explaining transmission and expression of genetic information).

Proximate Causes

Biological mechanisms that explain the immediate physiological, cellular, biochemical, developmental, or anatomical factors underlying a trait or behavior, answering the question "How?".

Ultimate Causes

Biological factors that explain the evolutionary history, origins, and adaptive significance of a trait across generations, answering the question "Why?".

Methodologies for Investigating Biological Causation

Proximate causes are investigated using the experimental method, whereas ultimate causes are investigated using the comparative method.

Teleology

The mistaken notion that natural phenomena, including biological evolution, are directed by intent, predetermined goals, or an inherent drive toward an optimal or "perfect" design.

Transformational Theory of Evolution

Lamarck's model proposing that organisms acquire phenotypic modifications during their lifetime through use and disuse of parts and pass those acquired changes directly to offspring.

Variational Theory of Evolution

Darwin and Wallace's model proposing that evolutionary change results from natural selection operating on pre-existing, stochastic, heritable phenotypic variation within a population across generations.

Scala Naturae

Aristotle's static, hierarchical view of species classification ordering living organisms along a linear scale of perfection.

Buffon's Geological Contribution

Proposed that species undergo morphological changes over time and estimated Earth's age to be approximately $70{,}000\,\text{years}$, extending the temporal scale for evolutionary change.

Uniformitarianism

The geological principle formulated by Charles Lyell establishing that constant physical and geological processes operating today operated identically in the past.

Perpetual Change

The theory that the living world is non-static, with biological structures and populations continuously transforming over geological time.

Common Descent

The evolutionary theory stating that all living forms originate from a single ancestral lineage through continuous branching processes.

Speciation (Mayr's Theory)

The evolutionary theory stating that the multiplication of species occurs through the splitting and divergence of single ancestral lineages into distinct descendant species.

Gradualism

The theory that evolutionary transitions occur through the accumulation of small, continuous, incremental phenotypic changes across generations rather than sudden large leaps.

Natural Selection

The population-level accumulation of favorable heritable traits resulting from differential survival and reproductive success among varying individuals.

Malthusian Logical Framework: Inference 1

A struggle for existence occurs among organisms within a population, deduced from high potential fertility, population stability, and limited natural resources.

Malthusian Logical Framework: Inference 2

Varying organisms show differential survival and reproduction favoring advantageous traits, deduced from the struggle for existence and heritable individual variation.

Malthusian Logical Framework: Inference 3

Differential survival and reproduction acting over many generations gradually produces new adaptations and distinct species.

Law of Superposition

The geological principle establishing that in undisturbed sedimentary rock strata, older layers lie beneath younger layers.

Index Fossils

Fossils of widespread, abundant, and short-lived species used to identify, date, and correlate the relative ages of rock strata across geographically distant regions.

Species Persistence Baseline

The average geological duration that most animal species persist in the fossil record before extinction or speciation, lasting approximately $1\,\text{to}\,10 \times 10^6\,\text{years}$.

Biological Criteria for Defining a Species

Common descent from a shared ancestral population, reproductive compatibility among members paired with isolation from other groups, and phenotypic/genotypic trait continuity.

Geographical Barriers vs. Reproductive Barriers

Geographical barriers are extrinsic physical obstacles separating populations spatially; reproductive barriers are intrinsic biological traits preventing interbreeding between sympatric populations.

Habitat Isolation

A prezygotic reproductive barrier where sympatric populations occupy distinct microhabitats within the same geographic area and rarely encounter one another.

Temporal Isolation

A prezygotic reproductive barrier where populations reach reproductive maturity or spawn at different times of the day, season, or year.

Behavioural Isolation

A prezygotic reproductive barrier where divergent courtship rituals, species-specific visual displays, or vocal/chemical mating signals prevent mate recognition.

Mechanical Isolation

A prezygotic reproductive barrier involving structural or anatomical incompatibilities in copulatory organs that physically prevent successful mating or fertilization.

Reduced Hybrid Viability

A postzygotic reproductive barrier where genetic incompatibilities arrest embryonic development or produce frail hybrid offspring that fail to reach maturity.

Reduced Hybrid Fertility

A postzygotic reproductive barrier where hybrid offspring reach adulthood but are sterile due to meiotic failure during gametogenesis (e.g., mules).

Hybrid Breakdown

A postzygotic reproductive barrier where first-generation ($F\_1$) hybrids are viable and fertile, but $F\_2$ or backcross generations exhibit high mortality or sterility.

Homology

Structural, developmental, or genetic similarity between different organisms resulting from shared ancestry.

Apomorphy

A derived character state that evolved relative to the ancestral state within a lineage.

Synapomorphy

A shared derived character state present in two or more taxa and inherited from their most recent common ancestor; used exclusively to define monophyletic groups.

Plesiomorphy

An ancestral character state present in a lineage.

Symplesiomorphy

A shared ancestral character state present across multiple taxa that cannot be used to define unique clade relationships.

Monophyletic Group

A taxonomic group containing a single most recent common ancestor and all of its descendant species (a true clade).

Paraphyletic Group

A taxonomic group containing a common ancestor and some, but not all, of its descendant species.

Polyphyletic Group

An artificial taxonomic group that lacks the most recent common ancestor of all constituent members, defined by convergent homoplasies.

Asconoid Body Plan

The simplest and smallest sponge body plan, characterized by a low surface-area-to-volume ratio and choanocytes that line only the central spongocoel.

Syconoid Body Plan

An intermediate sponge body plan where the body wall is folded into radial canals lined with choanocytes, increasing internal surface area and water filtering capacity.

Leuconoid Body Plan

The most complex sponge architecture, which lacks a central spongocoel and features choanocytes lining millions of flagellated chambers connected to excurrent canals.

Choanocytes

Flagellated collar cells lining internal sponge chambers whose flagellar beats drive water currents and whose microvillar collars filter and capture microscopic food particles.

Archaeocytes

Amoeboid, totipotent cells residing in the sponge mesohyl responsible for nutrient transport, intracellular digestion, gamete production, and structural element secretion.

Pinacocytes

Flattened epithelial-like cells forming the outer pinacoderm of sponges that regulate body surface area and water intake through ostia.

Sclerocytes

Specialized mesohyl cells in sponges that synthesize and deposit mineralized calcareous or siliceous spicules.

Class Calcarea

Sponge class possessing spicules composed entirely of calcium carbonate ($\text{CaCO}\_3$) with 1, 3, or 4 rays, containing asconoid, syconoid, and leuconoid forms.

Class Hexactinellida

Glass sponges characterized by six-rayed siliceous spicules arranged in intricate glass frameworks and living tissue composed of an extensive syncytial network.

Class Demospongiae

The dominant sponge class comprising roughly $90\%$ of all species, possessing siliceous spicules, spongin protein networks, or both, organized strictly in leuconoid architectures.

Class Homoscleromorpha

Encrusting sponges possessing a true basement membrane underlying their epithelial layer, with spicules either highly reduced or entirely absent.

Gemmules

Asexual survival pods produced by sponges during harsh conditions, composed of dormant archaeocytes encased in a dense protective coat of spicules.

Micropyle

The specialized circular aperture in a gemmule's protective coat through which dormant archaeocytes escape to reconstitute a functional sponge body.

Gametogenesis Origins in Porifera

Sperm develop from transformed choanocytes, whereas eggs and oocytes originate from transformed choanocytes or archaeocytes.

Polyp vs. Medusa Body Forms

Polyps are cylindrical, sessile morphs with upward-directed mouths specialized for feeding and asexual budding; medusae are bell-shaped, motile morphs with downward-facing mouths specialized for sexual dispersal.

Nematocyst

A stinging capsule inside a cnidocyte that encloses a coiled, barbed thread which everts explosively under hydrostatic pressure to inject venom into prey.

Cnidocyte Discharge Mechanism

Stimulation of the cnidocil trigger increases cell membrane permeability, driving rapid water influx and hydrostatic pressure that explosively inverts the stinging barb.

Class Hydrozoa

Cnidarian class characterized by alternating polyp and medusa generations, where the medusa typically possesses an inward muscular shelf known as a velum.

Velum

An inward muscular shelf found on the margin of the umbrella in hydrozoan medusae that constricts the aperture to increase swimming jet propulsion efficiency.

Class Scyphozoa

True jellyfish where the medusa stage dominates and lacks a velum, exhibiting a gelatinous thick mesoglea and a reduced polyp stage (scyphistoma).

Class Cubozoa

Box jellyfish possessing square bells, tentacles suspended from blade-like pedalia, complex rhopalia eyes, and highly potent neurotoxic venom.

Class Anthozoa

Exclusively marine cnidarian class completely lacking a medusa stage, characterized by polyps whose gastrovascular cavities are partitioned by longitudinal septa or mesenteries.

Class Staurozoa

Goblet-shaped cnidarians (stalked jellyfish) lacking a free-swimming medusa, anchored to marine substrates via an adhesive basal stalk with eight tentacle clusters.

Triploblastic Acoelomate Architecture

A body plan featuring three embryonic germ layers (ectoderm, mesoderm, endoderm) and bilateral symmetry, but lacking a coelomic cavity between the body wall and gut.

Parenchyma

Mesodermal tissue that completely fills the internal body space between the outer body wall and the digestive tract in acoelomate flatworms.

Neodermis

A non-ciliated, syncytial outer tegument found in parasitic platyhelminths that protects against host digestive enzymes and evades immune responses.

Key Morphological Adaptations to Endoparasitism

Syncytial tegument, specialized adhesive organs (suckers/hooks), reduction or absence of digestive and sensory systems, and massive reproductive investment.

Class Turbellaria

Free-living, mostly aquatic flatworms motile via a ciliated ventral epidermis and mucus secretions, possessing an incomplete branched gut and sensory auricles/ocelli.

Class Trematoda

Endoparasitic flukes featuring oral and ventral suckers (acetabula), an incomplete digestive tract, and complex indirect life cycles requiring a mollusc intermediate and vertebrate definitive host.

Class Monogenea

Ectoparasitic flatworms primarily targeting fish gills and skin, completing a direct single-host life cycle and anchoring via a specialized posterior opisthaptor.

Opisthaptor

A specialized posterior attachment organ armed with hooks, suckers, or clamps found in ectoparasitic flukes of the class Monogenea.

Class Cestoda

Endoparasitic tapeworms living in host intestinal lumens, lacking a digestive tract, absorbing nutrients across microtriches, and anchoring via an anterior scolex.

Scolex

The specialized anterior attachment structure of tapeworms (Class Cestoda), equipped with hooks and/or suckers to anchor into the host intestinal lumen.

Microtriches

Specialized microvillar surface amplifications covering the tapeworm neodermis that maximize surface area for direct nutrient absorption.

Foot (Phylum Mollusca)

A muscular ventral structure adapted primarily for locomotion, substrate attachment, or burrowing, which is secondarily modified into a siphon and tentacles in cephalopods.

Molluscan Foot Modifications across Classes

Modified into a broad flat sole for rocky adhesion in Polyplacophora, a creeping sole in Gastropoda, a wedge-shaped burrowing organ in Bivalvia, and a funnel/siphon with tentacles in Cephalopoda.

Head-Foot Region

The anterior, motile body division of molluscs containing the mouth, feeding apparatus (such as the radula), and major sensory structures.

Visceral Mass

The internal body region situated dorsal to the foot containing digestive, circulatory, reproductive, and excretory organ systems.

Mantle (Phylum Mollusca)

An epidermally derived fold of body wall tissue covering the visceral mass that encloses the mantle cavity and secretes the calcareous shell.

Mantle Cavity

The internal structural space enclosed between the mantle fold and visceral mass housing respiratory gills, excretory nephridiopores, and reproductive outlets.

Ctenidia

Paired, comb-like gills housed within the mantle cavity of molluscs, utilized for respiratory gas exchange and, in bivalves, ciliary filter feeding.

Radula

A specialized, ribbon-like rasping organ in molluscs lined with transverse rows of chitinous teeth used to scrape, tear, or bore food items.

Periostracum

The outer organic layer of the molluscan shell, composed of the protein conchiolin and secreted by a fold at the mantle margin to protect inner calcium layers from chemical erosion.

Prismatic Layer

The thick middle layer of the molluscan shell, composed of densely packed calcite or aragonite crystals embedded in an organic matrix and secreted by the mantle edge.

Nacreous Layer

The smooth, iridescent inner layer of the molluscan shell ("mother-of-pearl"), composed of thin parallel calcium carbonate sheets secreted continuously by the entire epithelial surface of the mantle.

Torsion

A developmental process in gastropod veliger larvae involving a $180^{\circ}$ counterclockwise rotation of the visceral mass, mantle, and mantle cavity relative to the head-foot.

Advantages of Gastropod Torsion

Enables the vulnerable larval and adult head to retract into the protective mantle cavity first before the foot, and directs sensory organs and clean water intakes forward.

Gastropod Fouling Solutions

Evolutionary workarounds preventing waste from contaminating gills after torsion, including unidirectional water flow, dorsal shell slits/apertures, or secondary detorsion.

Countercurrent Gas Exchange

A physiological mechanism in molluscan ctenidia where blood flows opposite to the flow of water across gill filaments, maintaining a concentration gradient for oxygen along the entire capillary bed.

Class Polyplacophora

Molluscs possessing a shell composed of eight overlapping dorsal calcareous plates, a broad creeping foot, and multiple ctenidia within the pallial groove.

Class Bivalvia

Molluscs enclosed in two hinged lateral valves joined by an elastic ligament, lacking a radula, and using enlarged ctenidia for filter feeding and respiration.

Class Cephalopoda

Active marine predators characterized by a modified foot forming a funnel/siphon and grasping arms/tentacles, closed circulatory systems, and a reduced or absent shell (except Nautilus).

Subclass Prosobranchia

Gastropods displaying full torsion with anteriorly placed mantle cavities, ctenidia situated in front of the heart, and separate sexes (predominantly marine snails).

Subclass Opisthobranchia

Marine gastropods exhibiting partial or complete detorsion, leading to lateral or posterior placement of gills and frequent shell reduction or loss (e.g., sea slugs).

Subclass Pulmonata

Terrestrial and freshwater gastropods that have lost ctenidia, utilizing a highly vascularized mantle cavity converted into an air-breathing lung.

Metamerism

True body segmentation characterized by the serial repetition of internal and external body sub-units (metameres) along the anterior-posterior axis.

Annelid Peristaltic Locomotion

Movement produced by alternating waves of localized circular and longitudinal muscle contractions acting against compartmentalized hydrostatic coelomic units separated by septa.

Clade Errantia

Active, motile marine annelids possessing a well-developed head with sensory prostomium appendages and prominent lateral parapodia bearing numerous chitinous setae.

Clade Sedentaria

Sessile, burrowing, or tube-dwelling annelids whose parapodia and setae are reduced, absent, or specialized into ciliated tentacular crowns.