Echinoderms and Chordates

Echinoderms

• Sea stars and most other echinoderms are slow-moving or sessile marine animals

• A thin epidermis covers an endoskeleton of hard calcareous plates

• Echinoderms have a unique water vascular system, a network of hydraulic canals branching into tube feet that function in locomotion, feeding, and gas exchange

• Males and females are usually separate, and sexual reproduction is external

Fig. 33-39

Anus Stomach

Spine

Gills

Madreporite

Radial nerve

Gonads

Ampulla

Podium

Tube feet

Radial canal

Ring canal

Central disk

Digestive glands

• Living echinoderms are divided into six classes:

– Asteroidia (sea stars)

– Ophiuroidea (brittle stars)

– Echinoidea (sea urchins and sand dollars)

– Crinoidea (sea lilies and feather stars)

– Holothuroidea (sea cucumbers)

– Concentricycloidea (sea daisies)

Fig. 33-40

(a) A sea star (class Asteroidea)

(c) A sea urchin (class Echinoidea)

(e) A sea cucumber (class Holothuroidea)

(b) A brittle star (class Ophiuroidea)

(d) A feather star (class Crinoidea)

(f) A sea daisy (class Concentricycloidea)

Sea Stars

• Sea stars, class Asteroidea, have multiple arms radiating from a central disk

• The undersurfaces of the arms bear tube feet, each of which can act like a suction disk

• Sea stars can regrow lost arms

Fig. 33-40a

(a) A sea star (class Asteroidea)

Chordates

• Phylum Chordata consists of two subphyla of invertebrates as well as hagfishes and vertebrates

• Chordates share many features of embryonic development with echinoderms, but have evolved separately for at least 500 million years

Chordates have a notochord and a

dorsal, hollow nerve cord

• Vertebrates are a subphylum within the phylum Chordata

• Chordates are bilaterian animals that belong to the clade of animals known as Deuterostomia

• Two groups of invertebrate deuterostomes, the urochordates and cephalochordates, are more closely related to vertebrates than to other invertebrates

Derived Characters of Chordates

• All chordates share a set of derived characters

• Some species have some of these traits only during embryonic development

• Four key characters of chordates:

– Notochord

– Dorsal, hollow nerve cord

– Pharyngeal slits or clefts

– Muscular, post-anal tail

Lancelets

• Lancelets (Cephalochordata) are named for their bladelike shape

• They are marine suspension feeders that retain characteristics of the chordate body plan as adults

Fig. 34-4

Dorsal, hollow nerve cord

Notochord

Tail

Cirri

Mouth

Pharyngeal slits

Digestive tract

Atrium

Atriopore

Segmental muscles

Anus

2 cm

Tunicates

• Tunicates (Urochordata) are more closely related to other chordates than are lancelets

• They are marine suspension feeders commonly called sea squirts

• As an adult, a tunicate draws in water through an incurrent siphon, filtering food particles

Fig. 34-5

Tunic

Water flow

Excurrent siphon

Atrium

An adult tunicate

Pharynx with slits Anus

Atrium

Excurrent siphon

Incurrent siphon to mouth

Dorsal, hollow nerve cord

Incurrent siphon

Excurrent siphon

Muscle segments

Notochord

Tail

Stomach

Intestine

Intestine

Esophagus

Stomach

Pharynx with slits

A tunicate larva

• Tunicates most resemble chordates during their larval stage, which may last only a few minutes

Derived Characters of Vertebrates

• Vertebrates have the following derived characters:

– Vertebrae enclosing a spinal cord

– An elaborate skull

– Pectoral and pelvic appendages

Jawless fish- Class Agnatha

• Lampreys represent the oldest living lineage of vertebrates

• They are jawless vertebrates inhabiting various marine and freshwater habitats

• They have cartilaginous segments surrounding the notochord and arching partly over the nerve cord

Fig. 34-10

Chondrichthyans (Sharks, Rays, and Their Relatives)

• Chondrichthyans (Chondrichthyes) have a skeleton composed primarily of cartilage

• The cartilaginous skeleton evolved secondarily from an ancestral mineralized skeleton

• The largest and most diverse group of chondrichthyans includes the sharks, rays, and skates

• Placoid dermal scales

• Lateral line sense vibrations

Fig. 34-15

Pelvic fins Pectoral fins

(c) Spotted ratfish (Hydrolagus colliei)

(a) Blacktip reef shark (Carcharhinus melanopterus)

(b) Southern stingray (Dasyatis americana)

• Nearly all living osteichthyans have a bony endoskeleton

• Aquatic osteichthyans are the vertebrates we informally call fishes

• Most fishes breathe by drawing water over gills protected by an operculum

• Fishes control their buoyancy with an air sac known as a swim bladder

Class Osteichthyes ---- Bony Fish

Fig. 34-16

Intestine

Adipose fin (characteristic of trout)

Cut edge of operculum

Swim bladder Caudal

fin

Lateral line

Urinary bladder Pelvic

fin

Anus

Dorsal fin

Spinal cord

Brain

Nostril

Gills

Kidney

Heart

Liver

Gonad

Anal fin

Stomach

Class Amphibia

• Amphibians (class Amphibia) are represented by about 6,150 species

• Amphibian means “both ways of life,” referring to the metamorphosis of an aquatic larva into a terrestrial adult

• Most amphibians have moist skin that complements the lungs in gas exchange

• Fertilization is external in most species, and the eggs require a moist environment

Fig. 34-22

(c) Mating adults

(a) Tadpole

(b) During metamorphosis

Class Reptilia

• The reptiles includes the tuataras, lizards, snakes, turtles, crocodilians, birds, and the extinct dinosaurs

• Reptiles have scales that create a waterproof barrier

• They lay shelled eggs on land: amniotic eggs

Fig. 34-27

(a) Tuatara (Sphenodon punctatus)

(c) Wagler’s pit viper (Tropidolaemus wagleri)

(b) Australian thorny devil lizard (Moloch horridus)

(e) American alligator (Alligator mississippiensis)

(d) Eastern box turtle (Terrapene carolina carolina)

• Most reptiles are ectothermic, absorbing external heat as the main source of body heat and poikilothermic

• Birds are endothermic, capable of keeping the body warm through metabolism and homeothermic

Birds: Class Aves

• Almost every feature of their reptilian anatomy has undergone modification in their adaptation to flight

• Many characters of birds are adaptations that facilitate flight

• The major adaptation is wings with keratin feathers

• Other adaptations include lack of a urinary bladder, females with only one ovary, small gonads, and loss of teeth

Derived Characters of Birds

Derived Characters of Class Mammalia

• Mammals have

– Mammary glands, which produce milk

– Hair

– A larger brain than other vertebrates of equivalent size

– Differentiated teeth

– Homeothermic endothermic

– Most have placenta

– Diaphragm separating abdominal and thoracic cavities

Monotremes

• Monotremes are a small group of egg-laying mammals consisting of echidnas and the platypus

Marsupials

• Marsupials include oppossums, kangaroos, and koalas

• The embryo develops within a placenta in the mother’s uterus

• A marsupial is born very early in its development

• It completes its embryonic development while nursing in a maternal pouch called a marsupium

Eutherians (Placental Mammals)

• Compared with marsupials, eutherians have a longer period of pregnancy

• Young eutherians complete their embryonic development within a uterus, joined to the mother by the placenta