Chapter 5 - Chondrichthyes Flashcards Preview

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Flashcards in Chapter 5 - Chondrichthyes Deck (38):

Synapomorphies of Chondrichthyes

- Tesserate (or prismatic) endoskeleton mineralization - a condition in which the superficial layers of cartilage have deposits of crystalline calcium
- Pelvic appendage claspers - male intromittent (specialized to deliver sperm) structure used in reproduction


(Extinct Paleozoic Chondrichthyes: Cladoselache) - External Features

- Shark-like appearance and about 2m long
- Large Fins: two dorsal, two pectoral, two pelvic, and a forked caudal fin
- 5 separate gill openings on each side of the head
- Placoid scales - scales with cusps of dentine covered with an enamel-like substance


(Extinct Paleozoic Chondrichthyes: Cladoselache) - Skeletal Features

- Amphistylic - multiples sites of jaw suspension
- Body only supported by a notochord, but cartilaginous neural arches gave added protection to the spinal cord


(Extinct Paleozoic Chondrichthyes: Cladoselache) - Feeding

- Terminal mouth - mouth that opens with upper and lower jaws equal
- Gape (size of the mouth opening at full extension) was large, with the jaw extending well beyond the rest of the skull
- Three-prong teeth with teeth rapidly being replaced
- Pelagic predators (not a bottom dweller, found in the middle of the water column)


(Extinct Paleozoic Chondrichthyes: Cladoselache) - Reproduction

- Pelvic claspers, which suggest internal fertilization


(Extinct Paleozoic Chondrichthyes: Xenacanthus)

- Similar to Cladoselache in braincase, jaws, and jaw suspension
- Freshwater bottom-dwellers
- Robust fins
- Heavily calcified, cartilaginous skeleton


(Extinct Paleozoic Chondrichthyes: Hybodus) - Characters shared with Cladoselache

- Terminal mouth
- Amphistylic jaw suspension
- Unconstrictednotochords
- Multicuspid teeth
- Claspers for internal fertilization


(Extinct Paleozoic Chondrichthyes: Hybodus) - Derived Characters - External

- More mobile and flexible pectoral and pelvic fins that allow for movement at different angles
- Caudal fin shape was altered to a heterocercal fin arrangement
- Anal fin appeared
- Narrow, more-pointed dorsal fin spines


(Extinct Paleozoic Chondrichthyes: Hybodus) - Derived Characters - Skeletal

-Heterodont definition - different shaped teeth along the jaw
- Hemel arches - opposite the neural arches in relation to the notochord


Extant Groups - Holocephali - Ratfish or Rabbitfish

- Undivided appearance of the head
- One gill opening
- Long, flexible tail
- Fish-like body
- Head with big eyes and buck teeth


Neoselachii - Sharks, Skates, and Rays

- Multiple gill openings on each side of the head


Neoselachii - Galeomorpha

- Shark-like (cylindrical body form and 5-7 gill openings) with an anal fin


Neoselachii - Squalomorpha

- Shark-like without an anal fin


Neoselachii -Batoidea

- Skates and rays, which are flattened dorsal ventrally and have 5 gill openings on the ventral surface of the head


Sharks - Sensory System - Lateral Line System

Surface sensory system found in aquatic vertebrates that are made up of a series of canals of neuromast organs (became more advanced in gnathostomes)


Sharks - Sensory System - Neuromast Organs

Clusters of hair cells and support structures that detect the movement of water


Sharks - Sensory System - Ampullae of Lorenzini

Sensitive electroreceptors found in the head of sharks that are used to detect prey and in navigation


Sharks - Sensory System - Chemoreception

Detected from the olfactory sacs is very important in the first detection of wounded prey


Sharks - Sensory System - Vision

Rod-rich retina and cells with numerous plate-like crystals of guanine that are located right behind the retina make their vision well developed under low light intensities


Sharks - Feeding - Cranial Kinesis

Mobility within the head skeleton


Sharks - Feeding - Hyostylic

A type of jaw supsension in fishes in which the upper jaw is attached to the skull by the hyomanibula


Sharks - Feeding - Behaviors

Differ based on the species of shark and the species of prey


Sharks - Reproduction

- Males have claspers, females have cloaca
- Internal fertilization is accomplished by sperm being ejaculated from the genital tract into the dorsal groove of the pelvic claspers


Sharks - Reproduction - 3 Ways of Copulation

- In Copula - males secure themselves by wrapping themselves around the female
- Swim side by side with their bodies touching
- In a sedentary position, with their head on substrate and their bodies angled upward


Sharks - Development - Oviparous vs. Viviparous

- Oviparous - offspring hatches from an egg that is outside the body of the mother (all oviparous are lecithotrophic)
- Viviparous - a fully developed offspring is born (lecithotrophic or matrotrophic)


Sharks - Development - Lecithotrophy

Embryo is nourished mostly from the yolk


Sharks - Development - Matrotrophy

Embryo is nourished from the reproductive tract of the mother

- Placentotrophic matrotrophy - embryo obtains nourishment from the maternal uterine bloodstream via a highly vascular yolk sac
- Embryos feed on a their siblings and eggs that may continue to be ovulated
- Embryo feed on a milky nutritive substance that is secrete from extensions of the oviduct


Sharks - Social Behavior

- Although it was once thought that sharks were solitary animals, new evidence has suggested that they do forms schools. These schools are thought
to be related to reproduction or feeding behavior.
- There are some peculiar characteristics of some these schools:
- In hammerheads, females form first and the most dominant female is in the center of the school. Then males arrive and immediately go to the center of the school and mate with the largest females.


Sharks - Life History

- Mature late in life
- Small litter size (as opposed to other aquatic vertebrates)
- Mate relatively few times
- Reproductive success relies on high success rate of offspring survival


Sharks - Conservation

- Human disturbance of shallow inshore areas have negatively affected shark nursery grounds
- Overfishing of sharks for sport and food consumption has caused some species to decline significantly in population number or biomass


Skates & Rays: External Features

- Flattened dorsoventrally
- Pectoral fins are laterally extended
- Gills on ventral side
- Spiracles (remnants of gill slits) on dorsal side are very large
- Large areas of the body are missing the placoid scales
- Bucklers - enlarged denticles along the dorsal midline


Skates & Rays: Feeding

- Mouth is located on ventral side
- Teeth are all flat-crowned plates
- Feed on benthic (bottom dwellers) and small fish; although a few species consume plankton via filter feeding
- Many lie buried in the sand and ambush their prey
- Wing-flapping - use their pectoral fins to stir up the bottom sediment


Skates & Rays: Reproduction

- Internal fertilization
- Skates are oviparous
- Rays are viviparous
- Benthic ray dentition is sexually dimorphic
(Sexually dimorphism is not due to differences in prey items. May be because males will sometimes hold or stimulate the female with his teeth before copulation)


Difference Between Skates and Rays

- Tail morphology
- Skates: elongated, thick tail stalk that supports two dorsal fins and a caudal fin
- Rays: whip-like tail stalk with fins replaced by one or more enlarged, serrated, and venomous dorsal barbs


Holocephali: External Features

- Relatively small
- Elaborate rostral extensions
- Large mobile pectoral fins


Holocephali: Feeding

- Autostylic - type of jaw suspension in which the palatoquadrate (dorsal component of the mandibular arch) fused to the cranium
- Solidly fused tooth plates are used for nipping and crushing and continue to grow throughout their life


Holocephali: Reproduction

- Internal fertilization
- Spine-encrusted cephalic claspers are used to pin the female's pectoral fin against his forehead
- Pelvic claspers used for insemination
- Reproductive strategy is based on high survival of offspring


Holocephali: Specialized Armaments

- Poison gland associated with the stout dorsal spine
- Mace-like cephalic claspers
- Feed on shrimp, gastropods, and sea urchins