Chondrichthyes: Cartilaginous Fishes

Chondrichthyes: Cartilaginous Fishes Review Superclass Gnathostomata - Jawed fishes I.
Chondrichthian characteristics & groups •
Class Placodermi (plate-skinned) extinct •
Class Acanthodii (spiny sharks) extinct A. Evolution of elasmobranchs •
Class Chondrichthyes living B. Elasmobranch basic characteristics •
Class Sarcopterygii living C. Elasmobranch basic adaptive patterns •
Class Actinopterygii living II.
Holocephali III.
Elasmobranchii D. Taxonomy of elasmobranchs Classes: Jawed vertebrates Superclass Gnathostomata Placodermi {extinct} Chondrichthyes cartilaginous fishes Acanthodii {extinct} An alternative view of the phylogeny of fishes •
Chondrichthyes are not ancestral to bony fishes •
based on DNA instead of morphology Arnason et al. 2001 Sarcopterygii lobe-finned fishes, tetrapods Actinopterygii ray-finned fishes Class Chondrichthyes, two major groups: Subclass Elasmobranchii (sharks & rays,
strap gills)
930 living spp. Infraclass Cladoselachimorpha (1 extinct order) Infraclass Xenacanthimorpha (1 extinct order) Subclass Elasmobranchii (sharks & rays) Infraclass Euselachii (2 extinct orders; 13 living orders in 2 subdivisions) Subclass Holocephali (chimaeras) Subclass Holocephali (chimaeras,
whole heads)
35 living spp. Superorder Paraselachimorpha (6 extinct orders) Superorder Holocephalimorpha •
6 extinct orders •
Chimaeriformes (1 living order) 1 Characteristics of Chondrichthyes: •
cartilaginous skeleton (w/ endoskeletal calcification) •
male intromittent organs (
claspers) ceratotrichia •
placoid scales •
teeth not fused to jaws (only to connective tissue) •
lipid (squalene) filled livers •
fin rays soft and unsegmented (ceratotrichia) •
swim bladder and lung absent •
high concentrations of urea and trimethylamine oxide (TMAO) in blood (for osmoregualtion) Subclass Holocephali (
whole head) Superorder Holocephalimorpha Order Chimaeriformes - chimaeras (ratfishes) Order Chimaeriformes: 3 families,
35 spp. Characteristics that separate them from Elasmobranchs: •
upper jaws attached to braincase (autostylic suspension) •
single opercular opening, covering 4 gill openings •
all are oviparous •
separate anal and urogenital opening - no cloaca •
mostly scaleless Other cool things about chimaeras: 3 orders of Chimaeras: longnose Rhinochimaeridae •
first dorsal has venomous spine •
some males have a
tenaculum on forehead •
tend to live very deep and are rare ploughnose Callorhynchidae shortnose (ratfishes) Chimaeridae 2 Subclass Elasmobranchii (sharks & rays) 1st elasmobranch radiation: Infraclass Cladoselachimorpha (cladoselachid sharks) Evolution of Elasmobranchs •
arose in early Devonian (400 mya) Cladodont (
branched tooth): all had a three-cusped tooth •
modern forms in place by early Cretaceous (144 mya) •
three major radiations: (1) Infraclass: Cladoselachimorpha Infraclass : Euselachii (2) Hybodonts (3) modern elasmobranchs Characteristics: Cladoselache 1.
terminal mouth 2.
fins broad-based and stiff, long radial elements 3.
no anal fin 4.
homocercal caudal fin 5.
body supported by notochord only 6.
spines often in front of dorsal, pectoral, pelvics Stethacanthus Cladoselache •
pelagic predators of placoderms, acanthodians, and bony fishes •
fed by engulfing or slashing Symmorium 2nd elasmobranch radiation: Infraclass Euselachii: Hybodonts early Mesozoic (250 mya) Hybodus Hybodont =
humpback tooth 1.
terminal mouth (same as cladoselachids) 2.
fins flexible and mobile 3.
anal fin Front teeth grasping Back teeth crushing 4.
caudal fin heterocercal 3 3rd elasmobranch radiation: coming of the modern sharks mid-Mesozoic (200 mya) spines on D fin notochord with neural arches Hybodus •
Jaws: subterminal mouth with protrusible upper jaw •
Dentition: tooth replacement system terminal mouth multiple basal elements with cartilage supports •
Fins: ceratotrichia supporting the fin calcified vertebral centra •
Vertebrae: calcified vertebrae instead of notochord Squalus
improved feeding and locomotion (parallel changes were occurring in bony fishes) ventral mouth protrusible jaw Teeth replaced differently in modern sharks Modern sharks: rows of replacement teeth 3 fused basal elements - radials flexible, horny rays - ceratotrichia Spiral tooth replacement Helicoprion (
spiral saw) Extinct sharks (e.g. Helicoprion): spiral replacement of teeth Hexanchiformes Living Elasmobranchs (
strap gills) 2 subdivisions: •
Selachii (sharks) Selachii + Echinorhiniformes Sixgill sharks 2 families, 5 spp 9 orders 32 families > 400 spp Bramble sharks 1 families, 2 spp Squaliformes Dogfish sharks 6 families, > 97 spp Pristiophoriformes 2 superorders Saw sharks 1 family, 9 spp - Galeomorphi (4 orders) (
shark form) Squatiniformes Angel sharks 1 family, 15 spp - Squalomorphi (5 orders) (
dogfish form) Heterodontiformes Bullhead sharks 1 family, 9 spp •
Batoidea (skates & rays) (4 orders) Orectolobiformes Carpet sharks 7 families, 32 spp > 75% of species in 2 orders Lamniformes Mackerel sharks 7 families, 15 spp Carcharhiniformes Ground sharks 8 families, >224 spp 4 Batoidea 4 orders 725
17 families > 530 spp. Rajiformes dae
Skates & Guitarfishes 285 spp Pristiformes Sawfishes, 7 spp Torpediniformes Electric rays, 59 spp Myliobatiformes dae
Stingrays, 183 spp Rhinobatidae Guitarfishes, 42 spp Characteristics of living Elasmobranchs: 1.
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cartilaginous skeleton gill slits (usually 5-7) not covered by an operculum paired ventral nostrils subterminal mouth (usually) protrusible upper jaw (usually) (hyostylic suspension) fin rays are unsegmented, soft, epidermal = ceratotrichia placoid scales enlarged liver for buoyancy spiral valve intestine electrical field receptors: Ampullae of Lorenzini cloaca (shared urogenital and anal opening) internal fertilization (males have claspers) now placed in Rajiformes (Nelson 2006) Hyostylic suspension – allows protrusion of the upper jaw Resting position Snout lifted, lower jaw depressed Palatoquadrate rotated forward and down, lower jaw forward and upward normal position Snout dropped down, palatoquadrate retracted Placoid scales Sand tiger shark with palatoquadrate rotated forward and downward 5 large, lipid-filled liver intromittent organs: claspers ampullae of Lorenzini spiral valve intestine female Biological Attributes: 1. distribution: mostly marine 2. generally adapted for movement at low energy costs: - heterocercal tails - placoid scales - cartilaginous skeletons - static buoyancy mechanism - enlarged liver with squalene 3. feeding: most are predators, carnivorous, and tend to be large male Biological Attributes: 4. Reproduction: a) in general: - mature late (6 - 35 yrs) - produce few relatively large young - internal fertilization (male claspers) b) Modes: 1. Oviparous: lay eggs externally 2. Viviparous: live-bearing 6 Biological Attributes: 5. Sensory physiology: non-visual senses are extremely acute 6. Vital statistics: - low fecundity - slow growing - long-lived … thus very susceptible to overfishing Threats to sharks: finning Biological Attributes: 7. Tend to be highly mobile •
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Living Orders of Elasmobranchs: Subdivsion Selachii Galeomorphi 1.
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Heterodontiformes (8 species) Orectolobiformes (32 species) Lamniformes (15 species) Carcharhiniformes (224 species) Squalomorphi 5.
Hexanchiforrmes (5 species) 6.
Echinorhiniformes (2 species) 7.
Squaliformes (97 species) 8.
Squatiniformes (15 species) 9.
Pristiophoriformes (5 species) Subdivision Batoidea 1.
Torpediniformes (59 species) 2.
Pristiformes (7 species) 3.
Rajiformes (285 species) 4.
Myliobatiformes (183 species) Nicole, 12.5 ft female great white shark tagged off S. Africa showed up 99 days later off W. Australia, 11,000 km away. 6 months later, she was back in S. Africa! Class Chondrichthyes Subclass Elasmobranchii Subdivision Euselachii Order Heterodontiformes - 1 family, 8 species - examples: bullhead shark, horn shark 7 Order Heterodontiformes Sleeping Horn shark •
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2 dorsal fins, each with a spine anal fin 5 gill slits large pectorals two types of teeth

grasping

crushing •
benthic, smallish (max. size 165 cm) Horn shark egg Order Orectolobiformes
carpet sharks - 7 families, 32 spp. - examples: whale shark, nurse shark, wobbegong Epaulette shark Order Orectolobiformes •
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2 dorsal fins, no spines anal fin 5 gill slits small teeth, terminal mouths mouth usually with barbels tropical shelf fishes Wobbegong 8 Whale shark: the largest living fish Order Lamniformes (mackerel sharks) nurse shark Order Lamniformes - 7 families, 15 spp. - examples: •
sand tiger •
thresher •
megamouth •
basking •
great white •
mako •
salmon •
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2 dorsal fins w/o spines anal fin 5 gill slits no nictitating membrane mouth extends well beyond eyes epipelagic, often coastal generally large, active sharks Carcharodon megalodon, extinct lamniform, estimated to 16 m in length White shark 9 Basking shark mako sharks Order Carcharhiniformes (ground sharks or requiem sharks) •
7 families, 224 spp. examples: tiger, bull, hammerhead, blue, leopard, smoothhound Megamouth shark sand tiger Order Carcharhiniformes •
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2 dorsal fins w/o spines anal fin 5 gill slits nictitating membrane dominant in tropics (90% of all sharks there) pelagic and coastal 10 Hammerhead Blue shark Leopard shark Order Hexanchiformes 2 families, 5 spp. examples: frilled, sixgill, & sevengill sharks Order Hexanchiformes •
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single dorsal fin, far back, without spine anal fin six or seven gill slits cone-like teeth (eat sharks, rays, bony fishes) patchy distribution, wide ranging deepwater or cold areas (usually) Order Echinorhiniformes (bramble sharks) 1 family, 2 spp. examples: bramble shark, prickly shark 11 Order Echinorhiniformes •
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1 family, 97 spp. examples: dogfish, sleepers, cookie cutter 2 dorsal fins without spines anal fin 5 gill slits denticles few and large (brambles or prickles) deepwater (usually) large (3-4 m) Order Squaliformes •
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Order Squaliformes cookie cutter shark 2 dorsal fins w/ or w/o spines no anal fin 5 gill openings nictating lower eyelid absent mostly deep sea wounds on dolphins Order Pristiophoriformes Order Pristiophoriformes 1 family, 5 spp. saw sharks •
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2 dorsal fins no anal fin 5-6 gill openings (lateral) rostral barbels (taste sensors) toothed, elongated rostrum (saw) 12 Squatiniformes (angel sharks) 1 family, 15 spp. example: Pacific angel shark Subdivision Batoidea •
Torpediniformes •
Pristiformes •
Rajiformes •
Myliobatiformes Order Squatiniformes •
intermediate between sharks and rays in appearance - dorso-ventrally compressed (= depressed) •
2 dorsal fins w/o spines •
no anal fin •
5 gill openings, lateral •
pectorals not attached to head •
large spiracles on top of head •
lie-in-wait predator Batoids •
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ventral gill openings enlarged pectorals, attached to side of head no anal fin eyes and spiracles on top of head pavement-like teeth bottom feeders (except torpedo rays, mantas) Torpediniformes electric rays Order Torpediniformes 2 families, 59 spp. •
two dorsal fins example: Pacific torpedo ray •
caudal fin well developed •
thick disc •
electric organs 13 Pristiformes (sawfishes) one family, 7 spp. Pristiformes •
toothed, elongated rostrum (saw) •
barbels absent •
two dorsal fins and strong caudal fin •
gill slits ventral •
big: to > 6 m! Bigtooth and smalltooth sawfish are endangered, due to bycatch Rajiformes (skates, guitarfishes, etc.) 4 families, 285 spp. examples: shovelnose guitarfish, big skate •
two dorsal fins •
no strong electric organs •
egg layers Rajiformes: Rajidae Rajiformes: Rajidae 14 Myliobatiformes stingrays, mantas, etc. 10 families, 183 spp. examples: southern stingray, round stingray, manta ray, bat ray bat ray Myliobatiformes •
spine near tail •
small or no caudal fin •
1 or no dorsal fin •
viviparous Myliobatiformes: Dasyatidae freshwater stingray in Cambodia: 2 m across Manta •
plankton feeder •
up to 20 feet and 2,000 pounds! 15