Ichthyology Exam Review: Diversity, Phylogeny, Anatomy, and Physiology

Vocabulary review flashcards covering fish taxonomy, phylogenetic diagnostic characters, anatomical features, scale morphotypes, digestive physiology, osmoregulation, and acoustic communication.

Gnathostomata

Jawed vertebrates defined by the presence of $3$ semicircular canals in the inner ear structure.

Chondrichthyes (Elasmobranchiomorpha)

Cartilaginous fishes defined by placoid scales and characterized by a heterocercal tail.

Teleostomi / Osteichthyes

Bony fishes defined by non-placoid scales and characterized by an ossified operculum.

Sarcopterygii

Lobe-finned fishes defined by true enamel on teeth, characterized by a $3$-lobed caudal fin and internal choanae (nares opening inside the mouth).

Actinopterygii

Ray-finned fishes defined by a single dorsal fin supported by internal rays, lepidotrichia (fin rays), and the absence of fulcra-like specialized scales at the fin base.

Neopterygii

Derived ray-finned fishes defined by a $1:1$ ratio of lepidotrichia to rays (support elements to rays) and characterized by a mobile maxilla.

Teleostei

Major bony fish radiation defined by a homocercal tail and characterized by a mobile premaxilla, $4$ pharyngobranchials, and $3$ hypobranchials.

Euteleostei

Clade of teleosts defined by nuptial tubercles on the head and body and characterized by a dorsal adipose fin.

Neoteleostei

Clade defined by the presence of a paired retractor dorsalis (RD) muscle and characterized by an internally symmetrical caudal fin.

Acanthopterygii

Spiny-rayed teleosts defined by the retractor dorsalis inserting specifically on the $3\text{rd}$ pharyngobranchial, featuring a mobile upper jaw and a low crest on the $2\text{nd}$ preural spine.

Percomorpha

Highly derived teleost clade defined by the pelvic girdle attaching directly to the pectoral girdle, typically with pelvic fins bearing $1$ spine and $5$ soft rays.

Osteoglossomorpha

The most primitive teleost subgroup, defined by a tongue-parasphenoid bite, eye-bisecting septum, fused hypurals, and the absence of a retractor dorsalis.

Elopomorpha

Teleost lineage (including eels and tarpons) defined by specialized, transparent, ribbon-like leptocephalus larvae.

Clupeomorpha

Teleost group including herrings and anchovies, defined by an auditory bulla that establishes an ear-to-swim-bladder connection.

Ostariophysi

Dominant freshwater fish clade defined by the Weberian apparatus, fright alarm substance in the skin, and absence of a retractor dorsalis.

Weberian Apparatus

A chain of modified vertebral ossicles linking the swim bladder to the inner ear, enhancing sound reception by up to $30\,\text{dB}$.

Protacanthopterygii

Teleost group including salmon, trout, and pikes, defined by specialized toothplates associated with the pharyngeal branchials.

Paracanthopterygii

Clade including cods, toadfishes, and anglerfishes, defined by a maxilla controlled by a muscle originating on the palatoquadrate and inserting on the premaxilla.

Atherinomorpha

Clade including silversides, needlefishes, and killifishes, defined by jaw protrusion lacking a ball-and-socket joint between the palatine and maxilla.

Heterocercal Tail

Ancestral caudal fin morphology where the vertebral column extends upward into the upper caudal lobe, characteristic of sharks and primitive ray-finned fishes.

Homocercal Tail

Derived caudal fin morphology that is externally symmetrical with the vertebral column ending at the hypural plate; diagnostic feature of Teleostei.

Paleoniscoid Stage

Primitive stage of jaw evolution characterized by a bite-only feeding mechanism where the premaxilla and maxilla are rigidly fused to the cranium without suction.

Holostean Stage

Intermediate stage of jaw evolution where the maxilla is freed, the premaxilla enters the gape, and suction feeding begins.

Teleost Stage

Advanced jaw stage featuring a protrusible premaxilla and an expanding buccal cavity to generate rapid suction feeding.

Branchiostegal Rays

Skeletal elements that maintain a flexible opercular seal against the body during buccal cavity expansion, enabling suction feeding and water pumping across the gills.

Levator Externus 4 (LE4)

A gill arch muscle whose evolutionary reinsertion onto the lower pharyngeal jaw enables specialized grinding and crushing in cichlids, labrids, and scarids.

Placoid Scales

Tooth-like dermal denticles with an enameloid layer that define elasmobranchs (sharks and rays).

Cosmoid Scales

Ancestral scale type found in fossil groups and early sarcopterygians.

Ganoid Scales

Heavy, rhomboid, interlocking bony scales found in pre-teleost ray-finned fishes like gars and bichirs.

Cycloid Scales

Thin, overlapping teleost scales with a smooth, unnotched posterior margin, typical of soft-rayed fishes like salmon.

Ctenoid Scales

Thin, overlapping teleost scales bearing tiny, comb-like spiny teeth on their posterior exposed margins, typical of spiny-rayed teleosts like bass.

Standard Length (SL)

Morphometric measurement taken from the tip of the snout to the posterior edge of the hypural plate (the caudal flexion crease).

Fork Length (FL)

Morphometric measurement taken from the tip of the snout to the innermost fork of the caudal fin.

Total Length (TL)

Morphometric measurement taken from the anterior-most tip of the snout to the furthest reaching tip of the caudal fin lobes.

Pterygiophores

Internal skeletal bones located within the musculature that support the dorsal and anal fin rays.

Pyloric Caeca

Blind finger-like pouches near the stomach junction that secrete enzymes and serve as primary sites for pancreatic enzymatic digestion.

Gizzard Stomach

A thick, muscular stomach specialization found in mullets and shads adapted for the physical grinding of ingested material.

Type I Gut

Herbivorous alimentary tract characterized by a thin-walled, highly acidic stomach and a long intestine; exemplified by the browsing surgeonfish Acanthurus nigrofuscus.

Type II Gut

Herbivorous alimentary tract featuring a thick-walled, gizzard-like stomach and a long intestine; exemplified by the grazing mullet Mugil cephalus.

Type III Gut

Herbivorous alimentary tract with a pharyngeal mill, no true stomach, and a moderately long intestine; exemplified by the grazing parrotfish Scarus rubroviolaceus.

Type IV Gut

Herbivorous alimentary tract featuring a hindgut fermentation caecum and a long intestine; exemplified by the browsing sea chub Kyphosus sydneyanus.

Hyposmotic Regulation

Osmotic state of marine bony fishes where internal fluids are more dilute than surrounding seawater, requiring continuous water drinking and the excretion of minimal, concentrated urine.

Hyperosmotic Regulation

Osmotic state of freshwater bony fishes where internal fluids are more concentrated than ambient water, causing continuous osmotic water influx, avoided drinking, and large volumes of dilute urine.

Primary Freshwater Fishes

Strictly freshwater fishes making up $33.1\%$ of all known fish species (~$6,650$ species), heavily dominated by Ostariophysi (~$6,200$ species).

Secondary Freshwater Fishes

Freshwater fishes with secondary tolerance to saltwater (including cichlids, poeciliids, and cyprinodontids) comprising $8.1\%$ of living fish species (~$1,625$ species).

Pheromones

Chemical secretions released into the environment to communicate with and alert conspecifics (members of the same species).

Allomones

Chemical secretions released into the water column to communicate with, deter, or alert members of other species.

Stridulation Sounds

Acoustic signals produced mechanically through the friction and rubbing together of hard skeletal parts, such as fin spines, pharyngeal teeth, or skull bones.

Hydrodynamic Sounds

Acoustical signals generated by water turbulence created through swimming movements and rapid fin displacements.