Elasmobranchs Flashcards
Describe the unique structure of elasmobranch skin.
What type of scales do they have?
How does skin thickness vary with species?
What about rays? What about Chimaeras?
What defensive mchanisms do they have in the integumentary system?
What sensory organs do they have within their skin?
Integument
- Placoid scales (aka dermal denticles) - formed like teeth (calcified layer, dentin, enamel)
- Silk sharks - denticles minute (softer skin); Blue sharks - females have sig. thicker skin d/t mating trauma
- Many rays have few to no scales - tend to have sig. mucus layer
- Porcupine rays and some others - “armor” on dorsum
- Many batoids, some sharks - sharp spines; venomous spine or barb in most rays (except mantas, mobulas, porcupine rays); can have more than one barb
- Barbs covered by integument including cells for venom production
- Chimaeras - scaleless (except juveniles), very sensitive to skin trauma
- Visible, symmetrical epithelial pores
- Pit organs - free neuromasts; sensory hair cells detect water motion
- Ampullae of Lorenzini - gel-filled tubular structures, detect electric fields for navigation, prey/predator detection, mating
Describe the unique adaptations of the elasmobranch muculoskeletal system.
How does their skeleton differ from other vertebrates?
Describe the feeding mechanisms.
What sharks have red muscle? What is its function?
Musculoskeletal System
- Entire endoskeleton cartilaginous - made of hyaline cartilage-like core supported by mineralized tesserae
- Bone exists - teeth, denticles
- Calcification can occur in vertebrae, jaws; true bone not present
- Centrum of vertebral cartilage can be used for aging
- If cartilage fractures - does not heal fully, fibrous “bandage”
- Prey capture - biting, ram feeding and/or suction feeding
- Permanent jaw protrusion assoc. w/ spinal deformity in sand tiger sharks
- Muscle similar to teleosts (red, white) - most poikilothermic but regional endothermy in some lamniform sharks (mako, white, salmon, porbeagle, thresher sharks)
How do elasmobranchs regulate their buoyancy?
Buoyancy
- Buoyancy d/t cartilaginous skeleton, large lipid-dense liver, urea and methylamine oxides in blood
- No cartilaginous fish have swim (gas) bladders; sand tiger sharks swallow air for additional buoyancy
Describe the anatomy of the elasmobranch eye.
What species have mobile eyes?
Describe the ray iris?
How does the PLR differ across species?
How do sharks adjust their tapetum?
What makes enucleation more challenging in elasmobranchs than in teleosts?
What species have the pinneal eye?
Ocular Anatomy
- Diverse eye anatomy - typically fixed eyelids (mobile in some - nurse and catsharks) - is blink reflex
- 3rd eyelid in some (requiem sharks)
- Pupil type and shape characterizing features in some
- Rays - upper iris modified into operculum pupillare covers iris during light adaptation
- PLR highly variable - diurnal –> rapid constriction, nocturnal –> intermediate, batoids –> slowest
- Dilation can be achieved w/ topical acetylcholine
- Sclera - thick w/ cartilaginous layer; Cornea - same layers as other vertebrates
- Many sharks - partially or totally occlusible tapetum - melanophores can migrate (some have fixed tapetum - catsharks, deep-sea sharks)
- Avascular retina, no choroid gland
- Many can pull globe into socket w/ extraocular muscles
- Optic pedicle - cartilaginous structure - connects globe to cranium
- D/t scleral cartilage, optic pedicle and size of optic nerve/vessels/muscles - enucleation more challenging
- Pineal organ/eye (epiphysis) well-developed in most (except absent in electric rays)
- Photoreceptors superficial on dorsal chondrocranium
Describe the auditory anatomy of sharks?
Auditory Anatomy
- Ears similar to other vertebrates
- Located in cartilaginous otic capsules caudal to large optic capsules; only external indication of position is tiny paired endolymphatic pores on dorsal chondrocranium near medial line
- Each ear - inner ear labyrinth (utriculus, sacculus, lagena) - none of accessory organs seen in teleosts
- W/in endolymphatic duct - no otolith, instead otoconial paste of CaCO3 granules in gel functioning like otoliths in teleosts
- Patches of sensory epithelium (macula neglecta) - vibration detection
- Audiograms - freq. 50-1500 Hz, greatest sensitivity 400-600 Hz (may be sensitive to pump/filters noise)
Describe the olfactory and gustatory anatomy of elasmobranchs?
What portion of the brain is well developed in elasmobranchs for these senses.
Elasmobranchs use olfaction for hunting at what range?
What leads sharks to predation when they are otherwise well fed in aquaria?
Olfactory and Gustatory Anatomy
- Olfactory bulbs w/in rostrum, part of forebrain (telencephalon) - well-developed
- Bulbs detect amino acids, bile salts, pheromones
- Nares (endolymphatic pores) possible entry route for development of meningitis
- Taste buds in oropharyngeal cavity
- Olfaction - used for feeding w/in 3-15 m, vision more important at closer range (<3 m)
- One study showed sharks become conditioned to the odors from normal, healthy fish
- Fish have different odors when frightened, stressed, or excited - can stimulate predation
Describe the dentition of elasmobranchs.
How are their teeth replaced?
How are their teeth attaches?
How often are they replaced?
What is the function of the denticles in the back of some species pharynx.
Oral/Pharyngeal Cavity
- Teeth or dental plates dictated by feeding strategy
- Teeth/plates erupt, roll out continuously w/ Cd.-most gradually replacing front (polyphyodont dentition)
- Lyodont teeth - embedded in oral mucosa, not ankylosed to jaw); have dentine and enameloid
- Tooth replacement rate varies by spp., 8-10 days per row up to 5 weeks per row
- If they typically eat hard-bodied prey (i.e. crustaceans, etc) - overgrowth of plates can occur
- Gingival hyperplasia and neoplasia described in sand tigers
- Denticles - pharynx of most sharks (except carpet sharks) and some others (guitarfish)
- May decrease drag for ram ventilators, prevent trauma, improve predation success
Describe the GI anatomy of elasmobranchs.
What is the function of the spiral valve?
What species have pyloric cecae?
What is the function of the rectal gland?
What are the cloacal pores used for?
Gastrointestinal System
- GI tract short, simple - slightly S- or J-shaped tube
- Ileum includes spiral or valvular intestine - sig. increases surface area (colloquially spiral colon - not technically colonic though)
- 4 variations - spiral winding around central column, cones directed Cd. or Cr., and scroll-shaped
- Empties into short tube (colon/rectum)
- A few have pyloric cecum or ceca (deepwater dogfish)
- Rectal gland - unique intestinal appendage - Cd. to valvular intestine @ colon/rectum
- Osmoregulatory function, secretes Na/Cl rich fluid (~2x plasma concentration) in contrast to urine (not concentrated)
- Sig. reduced in FW elasmobranchs
- Bilateral coelomic (abdominal) pores in cloaca - suspect excretory function (also catheter access point)
Describe the liver of elasmobranchs.
What does a healthy versus an unhealthy liver look like?
What is the hepatosomatic index?
Liver and Gallbladder
- Liver - 1º lipid storage organ, helps maintain neutral buoyancy
- Large volume of lipid must be stored, size and density critical in maintaining position in water column
- Major indicator of general health/caloric intake; size can fluctuate w/ age and repro cycle
- Hepatosomatic index (HIS) - ratio of liver wt to body wt ID’d for many species
- Grossly should be tan, fill a large portion of coelom and float in formalin
- Gallbladder - dynamic in appearance
Describe the respiratory anatomy of elasmobranchs.
How many gill arches do they typically have?
What is the spiracle? What species is it well developed in?
What are the two modes of respiration for sharks?
Respiratory System
- Usually 5 gill arches, may be up to 7 - hemibranch cranially (one filament row) and holobranchs for remaining (2 filament rows)
- Interbranchial septum extends to form gill slits on external surface
- Cranial most gill slit modified to spiracle in some spp.; well developed in skates, rays, slow-moving sharks and absent in pelagic sharks
- Damage to gills affects gas exchange and other physiology; in SW spp. gills have important role in acid-base balance and in FW spp. important salt regulation
- Critical for urea retention, esp. some species (spiny dogfish)
- Oral cavity - orobranchial and parabranchial cavities
- If buccopharyngeal pumping - double pumping action delivering oxygenated water through mouth or spiracles to gills
- In ram-ventilating species - mandibular muscles control opening of mouth
Describe the cardiovascular system of elasmobranchs.
What is the relationship between the percardium and the coelom?
What are the the four parts of the elasmobranch heart?
What is the function of the second vascular system?
Cardiovascular System
- Heart in rigid pericardial chamber w/ large volume pericardial fluid
- Pericardial lumen communicates w/ coelomic cavity via pericardiocoelomic canal (usually closed unless pericardal pressure exceeds coelomic cavity)
- Pericardial cavity fluid reported to be different from plasma, coelomic fluid
- Heart - sinus venosus, atrium, ventricle, conus arteriosus (similar to bulbus arteriosus)
- Sinus venosus - thin walled, very compliant
- Atrium - flaccid, larger volume than ventricle
- Ventricle - thickest myocardial tissue
- Conus arteriosus - tubular and thick w/ prominent valvular structures
- Often synchrony b/w respiratory and cardiac beat - inconsistent, no obvious clinical consequence
- ECG similar to other vertebrates except V-wave (depolarization of sinus venosus) prior to PQRS
- Secondary vascular system (SVS) w/ different blood values than 1º system
What are the lymphoid tissues of sharks?
Where are they located?
Hematopoietic and Immunologic System
- Tissues include epigonal organ, Leydig organ, thymus, meninges of brain, eye orbit, spleen, gut-associated lymphoid tissue (GALT)
- Epigonal organ - physically associated w/ gonads; in some spp. enclosed w/in epigonal organ (common guitarfish, dogfish) or may be attached (stingrays)
- Generally if prominent epigonal organ 🡪 Leydig organ is unapparent or absent
- Leydig organ - in some spp., (not Leydig organ involved in sperm maturation) - sometimes ID by lighter-colored area w/in dorsal (occasionally ventral) submucosa of esophagus (may be raised)
- Spp. - skates, some rays, guitarfish, some shark species (velvet belly lanternshark)
- All have bilateral thymus - dorsal near gills
- Some species (catsharks, nurse sharks) - involution with age
- Others (bullhead sharks, some rays) - remains visible/small through life
- Spleen - dark red, strap-like to oval; lacks marginal zones and germinal centers (like in mammals) - likely b/c no true lymphatic system
- Melanomacrophages in spleen, liver - do not aggregate like in teleosts
Describe the endocrine anatomy of elasmobranchs.
What is the function of the interrenal gland? Where is it located?
Where is the thyroid location?
What is the function of the ultimobranchial bodies? Where are they located?
Endocrine System
- Complex, but organs, stimuli and targets of action similar to other vertebrates
- Pituitary similar to teleosts, slight anatomical variations
- Hypothalamus (w/in diencephalon) well-developed, important for feeding, reproduction, aggression, likely migration
- Interrenal gland (equiv. of adrenal cortex) - grossly visible 🡪 section of yellow b/w each kidney (long thin strip in sharks, smaller oval in skates/rays)
- Chromaffin cells of suprarenal bodies separate, located on dorsal kidneys near dorsal aorta
- Hypothalamo-pituitary-interrenal axis considered endocrine stress axis - not fully characterized
- Single thyroid gland - encapsulated, varies in size/shape
- Batoids - usually ventral to pharynx, near bifurcation of ventral aorta
- Sharks - under commissure of mandible
- Ultimobranchial bodies - produce calcitonin (similar to mammal parathyroid system) - actions of calcitonin in cartilaginous fish less well-understood
- Batoids - paired, found in caudal wall pericardial cavity
- Sharks - only L side of body on dorsal wall of pericardial cavity
- Pancreas (bilobed) and GI tract - produce expected hormone; detail on function and activity limited
- Heart and kidney also produce several natriuretic peptides - have renin-angiotensin system (regulates renal and cardiovascular systems)
- Pineal organ and gonads also have endocrine function
Describe the renal anatomy of elasmobranchs.
Where are the kidneys located?
Describe the flow of urine from the kidney to the urogenital pore?
How can you collect a urine sample?
Urinary System
- Manages osmotic and ionic regulation
- Marine elasmobranchs - maintain high plasma osmolality d/t high Na, Cl, urea, methylamine oxides
- Slightly hyperosmotic 🡪 uptake of water to balance fluid lost in urine
- Drinking negligible (unlike marine teleosts)
- Gills, kidney, rectal gland important for maintaining homeostasis
- Kidney primary urea regulator
- FW elasmobranchs - urea, electrolytes, osmolality much lower
- Kidneys microscopically similar
- Rectal gland significantly reduced
- Kidneys - paired, firmly attached to dorsal wall
- Sharks - midway in coelomic cavity, widen caudally
- Skates, rays - more caudal in coelomic cavity, more lobulated
- Males - ureters leave kidneys medially 🡪 midline 🡪 seminal vesicles 🡪 sperm sacs 🡪 exit through single (sometimes double) urogenital pore/papilla
- Small urine sample - catheter past repro tract; large volume not possible d/t low production
- Semen sample can be collected more distally
- In SW - unable to produce concentrated urine - ionic conc. cannot be higher than that of plasma
- GFRs 0.2-4.0 mL/kg/h - higher than SW teleosts but similar to FW teleosts
- In dilute enviro 🡪 increased urine flow 🡪 decreased urea absorption
- FW stingray have GFR of 8-10 mL/kg/h
Describe the reproductive anatomy of elasmobranchs.
Where does sperm storage occur in males and females?
Describe the flow of sperm in males.
Describe the sections of the oviduct.
Describe the uterine anatomy and function.
Reproductive System
- Diverse anatomy and biology - mode generally split by oviparity or viviparity and fetal nutrition
- Synchrony (seasonal aggregation) important in some species
- Gestation 4.5 months to 2 years (up to 3.5 yr if egg cases included)
- Embryonic diapause confirmed in 3 species (Australian sharpnose sharks, common stingrays, bluntnose stingrays) but may be more common
- Parthenogenesis in many species; polyandry (multiple paternity) also occurs
- Sperm storage in males (ampullae of distal epididymis; weeks to months) and females (oviductal gland; weeks to over a year)
- Fertilization internal in all elasmobranchs; all males have external claspers (part of pelvic fins)
- Tend to increase in size and internally calcify; able to rotate
- Internal paired organs - testes (diametric, radial, compound); genital ducts; Leydig glands (produce sperm maturation substances); alkaline glands (Marshall’s glands - in skates - seminal fluid)
- Genital ducts (efferent ductules, epididymis, ductus deferens, seminal vesicle) - embedded in dorsal abdominal wall
- Epigonal organs can embed testis, incorporate caudal end, or be separate
-
Copulation - sperm ejaculate 🡪 urogenital papilla(e) 🡪dorsal groove of clasper
- Batoids - clasper glands w/ many proposed functions
- Sharks - subdermal siphon sacs - either for sperm propulsion or to wash rival sperm out (can be prominent on ultrasound)
- Surgical amputation of claspers when necessary - may not impact repro capacity
- Ovaries - typically paired, may be single (left is dominant in batoids, right in viviparous sharks)
- Developing follicles of various sizes, follicles undergoing atresia, corpora lutea-like tissue
- Can be within or separate from epigonal organ
- Oviduct - differentiated into an ostium (receives the ovum), oviducal (nidamental or shell) gland, isthmus (some spp.), leads to uterus, cervix, common urogenital sinus
-
Uterus - single (typ. L side) or paired
- In oviparous - uterus hardens egg capsules and hold until oviposition
- Yolk-sac viviparous - uterus creates intrauterine milieu - supplying O2, water, nutrient to embryo and regulates wastes
- Uterine wall vascular, folded
- Stingrays - secretory cells w/in uterine trophonemata (large villous projections) - produce histotroph
- All placental species have limited histotrophic stage after absorption of yok sac before placental implantation where uterus provides nutrients (complex subject)
Elasmobranchs have many reproductive strategies.
Describe the various strategies and give some example species of each.

Describe the neuroanatomy of elasmobranchs.
What are the parts of their brain?
What is unique about the cerebellum of several species?
How does their blood brain barrier differ from other vertebrates?
Neurologic System
- Cranium encloses brain, olfactory bulbs, optic and otic organs
- Telencephalon (forebrain), diencephalon (epithalamus, thalamus, hypothalamus), mesencephalon (cerebellar body and auricles, medulla)
- Brains vary widely in shape and size; some have obvious asymmetry w/in cerebellum (rays, requiem sharks, hammerhead sharks)
- Notable on gross examination, not think pathologic on necropsy
- Cranial nerves similar
- Choroid plexus forms cerebrospinal fluid (CSF) - large space rostral to brain where can collect
- Electrolyte composition of CSF and plasma differs, independent regulation
- Blood-brain barrier differs from other verts - endothelium permeable but tight junctions b/w glial cells
Describe the generation of electricity in electric (torpedo) rays and skates.
Electric Organs
- Electric (torpedo) rays - large electric organs (electroplaques) on either side of gill arches - derived from branchial musculature - moderate electric discharges
- Skates - weak electric discharges from small bilateral electric organs in tail
- Both can have intermittent and focused discharges; coordination of discharge originates in medulla
- Relatively low amplitude 20-40 mV in skates vs. 30-60 V from electric rays
What is the order of Chimaeras?
What fish are in this group?
Describe their unique anatomy.
What is a concern with their eyes in managed care?
Chimaeriformes (Chimaeras, Ratfish, Ghost sharks)
- Cartilaginous skeleton but upper jaw has grinding tooth plates fused to cranium
- One gill opening, lack spiracle except as embryos; eyes cannot regulate light going onto retina - exposure to bright lights a concernà “bloody eye”, handling induced damage to pseudobranchial artery
- Scaleless except for denticles over pelvic claspers and tenaculum; dorsal spine venomous
- Lack stomach, ribs, epigonal organ, Leydig organ; there is spiral intestine and rectal gland
- Separate anal and urogenital openings; male have claspers and fertilization is internal
What order are the ground sharks in?
What groups are in this order?
What are the defining anatomic features?
Carcharhiniformes (Ground Sharks)
- Largest order of sharks, 2 dorsal fins in most, anal fin, 5 gill slits, 3rd eyelid, mouth extends behind eyes
- Oviparous, ovoviviparous, or viviparous
- Includes requiem, catsharks, hound, hammerhead and bonnethead sharks
- Requiem sharks look like “typical” sharks - internal nictitans and spiracles absent; scroll intestine valve
- Catsharks have rudimentary nictitans, small spiracles, spiral valve
- Hound sharks - spiracles, spiral valve
- Hammerhead/bonnetheads - lateral extension to head (cephalofoil) w/ eyes on lateral aspects; spiracles absent, have spiral valve
What order are mackerel sharks, white sharks, and sand tigers in?
What are the defining anatomic features of this group?
Lamniformes (Mackerel sharks, White sharks, Sand Tigers)
- 2 dorsal fins and an anal fin; 5 gill slits - broad and extend beyond base of pectoral fin
- Sand tiger sharks differ - gills in front of pectoral fin
- Spiracles present behind eyes but are small; eyes lack a nictitating membrane
- Mouth extends behind eyes; ring-type spiral intestine
- Practice of oophagy or adelphotrophy (uterine cannibalism); some practice endothermy
What order are dogfish adn gulper sharks in?
What are the defining anatomic features of this group?
Squaliformes (Dogfish, Gulper sharks)
- Two dorsal fins, may have spines; anal fins absent; 5 gill slits and spiracles present
- Small nictitating membrane in lower lid
What order are carpet sharks, bamboo sharks, and nurse sharks in?
What is the largest shark of this group?
What are teh defining anatomic features of this group?
Orectolobiformes (Carpet sharks, Wobbegongs, Bamboo sharks, Nurse sharks)
- 2 dorsal fins and an anal fin, 5 gill slits w/ spiracles close to eyes; no nictitating membrane, eyes dorsolateral; most have prominent nasoral grooves w/ barbels
- Wobbegong - dorsoventrally flattened head/body, rostral mouths, fang-like teeth
- Also includes whale sharks
What order are skates in?
What are the defining anatomic features of this group?
- Rajiformes (Skates)*
- Skates - dorsoventrally compressed w/ enlarged pectoral fins continuous with their heads; caudal fin and no anal fins; some have dorsal fins; tail has no barbs, oviparous; skin freq. has thorns and some have weak electric organs
























