Animal Diversity Unit 3

Deuterostomy

•Refers to animals who develop anus first

•Develops from the blastopore

•Thought to be a defining characteristic of the group, however some protostomes have independently evolved this developmental plan

Deuterostome Groups

•Echinodermata

•Hemichordata

•Chordata

Deuterostome - Echinodermata

•Starfishes, sea urchins, sand dollars

•radial symmetry but evolved from bilaterally symmetrical ancestors

•Over 7500 species recognized today but were incredibly diverse back in the Cambrian

•Fossil record is well-known because the echinoderm endoskeleton is calcareous

• Echinodermata: evolve from bilaterial symmetric ancestor → radial symmetry but larvae are bilaterial

• •Have dermal endoskeletons made of calcite ossicles

  •Can reversibly vary the rigidity of their dermis

  •They can stiffen their connective tissue (“Catch tissue”) while feeding or to ward off predators

  •Are also capable of autotomizing limbs to escape predators

Deuterostome - Asteroidea

•Sea stars

•Star-shaped free-moving body

•Hollow arms or rays projecting from a central disc

•Benthic and occur worldwide

•Typical in coastal regions

form —————

•Pentamerous symmetry

•Most species have five arms although some species may have more than 40

•Mouth is located centrally on the underside of the disc where it is in contact with the substrate

•A wide furrow extends radially from the mouth to each arm containing tube feet

•Ambulacrum = grooves

•Anus is inconspicuous and located on the dorsal side of animal

•Body wall consists of ossicles embedded in a matrix of dermis

•Ossicles are present in many forms and can be controlled independently

• water vascular system: seawater taken via madreporite, circulation transports O2 throughout the body + powers the tube feet → circulation / fluid volume maintenance

• •Consists of cyclic movement of the feet consist extension-attachment, force generation, and detachment; each tube foot moves - suction

• •All stars have gills – papulae along the upper sides of the arms + second vascular sys

• •And five radial nerves that originate on the nerve ring + circumoral nerve ring

•Digestive system is also pentamerous

•Blind gut

•Mouth and stomach are located centrally

• can evert their stomach for large prey

• carnivores and scavengers

Ophiuroidea

•Brittle and basket stars

•Most diverse clade of echinoderms with 2000 species (just over the number of starfish)

•Common in benthic and marine habitats

•Can reach high population densities in favorable conditions

•Most have five segmented arms

•The arms are distinct from the central disc and never contain viscera

•No ambulacral groove or radial nerves

•Oral disc is covered by a series of shields that frame the mouth and form the jaws

•Nervous system is composed of a circumorbital nerve ring

•Hold their central disc off the substrate and move using a rowing motion with their arms

Echinoidea

•Sea urchins

•Highly mobile, armless echinoderms

•Known for grazing on hard substrates

•Valued for food where they occur

•Body is covered in movable spines for protection and overlapping ossicles form the test

•Possess a sspines

•Body is divided into oral and aboral hemispheres with parts arranged radially around the polar axis

•The oral pole bears the mouth and the aboral pole bears the anus

•Statocysts but no eye spots

•pherical body with long spines

•Body is divided into oral and aboral hemispheres with parts arranged radially around the polar axis

•The oral pole bears the mouth and the aboral pole bears the anus

•Statocysts but no eye spots

•arranged symmetrically in the ambulacral and interambulacral grooves

•longest at the equator and shortest at the poles

•Feed using a structure called Aristotle’s lantern

Crinoidea

•Sea lilies and feather stars

•600 species alive today but many more known from fossils

•Have the longest fossil record of any echinoderm dating back to early Cambrian

•Fossils are also very common

•All possess radial symmetry and feed via suspension feeding

•Touch sensation but nothing else

•Body consists of an attachment stalk that bears a pentamerous crown

•In feather stars this stalk is lost during development and adults are free moving

•The stalk is conspicuously jointed and contains skeletal ossicles

•Sea lily stalks can reach 1m in length

•However, fossil species could reach 20 m

•Stalk attaches via a flattened attachment plate or with root-like extensions called cirri

•Pentamerous crown resembles the body of other echinoderms

•Stalk attaches to the aboral surface of the crown and the body is drawn out into arms with a centralized mouth

•Some crinoid species still possess five arms however most species have arms that bifurcate into ten

•Arms are covered in pinnules that resemble feathers and trap food

Holothuroidea

•Sea cucumbers

•Similar to other echinoderms, have endoskeleton made of ossicles and thick dermis

•Have tube feet used for walking, on the dorsal surface tube feet are sensory – 5 ambulacra

•Also have the ‘catch’ collagen that can be thickened at will

Sea cucumbers

•More developed water vascular system than other echinoderms

•Includes vessels and sinuses

•Have hemoglobin in the coelomic fluid

•Gills lie inside the anus so respiration occurs via sucking water in through the anus

Hemichordates

•Essentially more worm guys

•Protosome - anterior pre-oral lobe

•Mesosome - mouth- bearing middle region

•Metasome -trunk region bearing gonads

•Coelomate – each region has a coelom or coelom pair

Acorn worms

•~200 described species

•Anterior proboscis – ciliated feeding organ

•Mouth located between proboscis and ‘collar’

•Live in burrows

•Solitary

•Trunk contains the pharyngeal slits or gill slits – these come up again

•Ventral and dorsal nerve cords

•Dorsal nerve cord hollow – precursor to chordate neural tube

Pterobranchia

•Colonial, live in tubes in the benthos

•Filter feed via tentacles

• 30 described species

Chordata

•An ancient lineage, appearing in the Cambrian

•Includes Tunicates and Cephalochordates (lancelets)

•The most species-rich clade of deuterostomes > 80,000 species

•United by key characteristics •Notochord

•Hollow dorsal nerve cord

•Pharyngeal gill slits

•Post-anal tail

•Endostyle

Notochord

•Flexible but incompressible longitudinal rod

•Causes body to bend rather than shorten with contraction of body wall musculature

•Notochord is cartilaginous and present in all embryonic chordates

•Is replaced by vertebral column in vertebrates

•Thought to provide directional signaling for cells in developing embryo

Dorsal Hollow Nerve Cord

•Dorsal Hollow Nerve Cord

•NOT THE NOTOCHORD

•Instead develops directly above it

•Forms the central nervous system

•Develops during a process called neurulation

Pharyngeal slits

•Characteristic of early branching chordates

•Repeated slits along the outside of the pharynx

•Used to draw water into the pharynx for respiration… sometimes!

•Post-anal tail

Endostyle

•Specialized filter-feeding structure located in the pharynx of urochordates and invertebrate cephalochordates

•Used to create mucus net to trap debris in the pharynx

•Present in larval lampreys but metamorphoses into the thyroid

•Thought that the thyroid in vertebrates is derived from the endostyle

Chordate Characteristics

•Smaller chordates were thought to use gill slits not for gas exchange but ion exchange

•Important for maintenance of homeostasis and potentially nutrient uptake

•Gills became important for larger chordate species as they led more active lifestyles

•Pharyngeal slits still used for filter feeding in lancelets

Early chordate evolution

•Fossils very similar in form to extant lancelets

•Swam with lateral undulations of the trunk

•Filter fed with pharynx

•Musculature really characteristic and frequently fossilizes

Cephalochordata

•Roughly 30 species

•Commonly referred to as lancelets or amphioxus

•Posses the archetypal chordate form

•Occur in tropical oceans worldwide

•Primarily burrow in sediment in shallow subtidal habitats

•Rarely emerge

•Instead they stick their mouths out of their burrows to filter feed

•4-8 cm in length

•Laterally compressed with head tapered to a point - rostrum

•Internal organs are usually visible through the skin

•Mouth is located ventral to the rostrum and is surrounded by oral cirri

•Endostyle produces mucus, cilia move food particles towards pharynx to trap them in mucus for ingestion

•Anus is located ventrally anterior to the tail fin

•Monolayered epidermis

•Pharyngeal slits used for feeding (not resp.)

•Gas exchange occurs across surface of animal

nervous system

•Consists of rudimentary brain, dorsal hollow nerve cord

•nerves exit the cord dorsally and innervate several structures

•Anterior to the brain are pigmented ocelli that sense light

•Many cephalochordates are negatively phototaxic

•Swimming muscles are arranged longitudinally as v-shaped myomeres

•We see the same thing in fishes

•Myomeres are divided by myosepta

•Allow for lateral undulatory swimming

•No fins!

Urochordata

•Sea squirts, tunicates and salps

•Do not resemble chordates as adults

•Some species are sessile and live attached to substrate

•Others are planktonic and colonial

•All have lost notochord, dorsal hollow nerve cord and post anal tail as adults

•But the tadpole larval stage posses the characteristic chordate traits

Urochordata - Ascidians

•Sea squirts

•Sessile

•Can be solitary or colonial

•Colonies are made up of zooids

•Typically found in shallow water attached to rocks

•Has buccal and atrial siphons used in filter feeding

•Body surrounded by ‘tunic’ hence the name – essentially an exoskeleton

•Body wall sits inside and has two openings, buccal and atrial siphons

•Water flows in through buccal siphon, filtration happens in the pharyngeal basket

•Water flows out through atrial siphon after nutrients absorbed in stomach

•colonial body form

Vertebrate Characteristics

•Well-defined heads with cartilaginous (at least) skulls

•Vertebral column

•3-part brain

•Neural crest cells

•Multi-chambered heart

•Muscularized pharynx

Early Vertebrates

•Fishes were the first vertebrates

•Many key vertebrate characteristics were early innovations during fish evolution:

•Bony endoskeletons

•Complex bones - dermal and endochondral bone

•Braincases

•Teeth

•Jaws

•Neural crest cells

stage 1

•Fishes were the first vertebrates

•Many key vertebrate characteristics were early innovations during fish evolution:

•Bony endoskeletons

•Complex bones - dermal and endochondral bone

•Braincases

•Teeth

•Jaws

•Neural crest cells

early

•Clearly recognizable fish fossils appeared 470 mya

•Exhibited true bone

•Muscular feeding pump for filter feeding

•Were frequently heavily armored

•For protection against giant marine invert predators

Earliest fishes lacked jaws

•We still have jawless fishes with us today!

•Hagfishes and Lampreys

•Thought to have evolved from armored ancestors

•Make their living in bizarre ways

Hagfishes

•Known from the upper Carboniferous (330 mya) (Myxinikela)

•Naked eel-like creatures

•Primarily scavengers in the deep ocean

•Feed using rasping tongue

•No vertebrae!

•Cartilaginous skulls

••Usually distinguished by tooth plate, gill slit, and slime pore morphology

• Slime mech , knots

• 
  

Lamprey

•Can be found and fresh and marine habitats

•18 out of 38 species are carnivorous and take chunks out of other animals

•All nonparasitic species are freshwater and don’t feed as adults

•Jawless

•Boneless

•All endoskeletal elements are cartilaginous including braincase

•Oral disc instead made of keratin

•Important model for developmental biology

Single spawning event and then die

•Burrow into sediment and expose only head for feeding

•before metamorphosis into adults → transformation in summer ; ammocoetes are parasite

hagfishes vs lampreys

•Lamprey have circumferential teeth on the oral disk

•Separate olfactory and respiratory pathways

•Lamprey attach to prey via mucus secretion from oral disk

•Muscles in the mouth expel water and create a negative pressure in the mouth

•Lamprey have functional eyes – hagfish have eyespots

•Lampreys have a dorsal fin – hagfish have no fins; 1 heart while hagfish has 4

Gnathostomata – jawed vertebrates

•Paired fins show up in the fossil record slightly before jaws but proliferate afterwards

•Other traits:

•Endochondral bone

•Three semi-circular canals

•Dentine-based teeth - perhaps the greatest of all vertebrate innovations

Paired fins

•Believed to have started off as immobile extensions of the body cavity

•passively generated lift initially

•Enhance maneuverability in water

•evolved alongside jaws

Endochondral vs dermal bone

•Dermal bone is laid down within a tissue membrane (direct from mesoderm)

•Very old

•Dermal bone forms many elements of the skull and jaws. Primarily dermal roofing bones

•Endochondral bone is comparatively young and ossifies from hyaline cartilage

•Forms parts of the skull and gill basket

Placoderms – early Devonian

•Name means “plate-skinned”

•Bony plates covered anterior portion of body

•Occurred in marine habitats and moved into freshwater

•Sharks eventually replaced them ecologically

•Many possessed a joint between the braincase and the cervical vertebrae allowing for increased gape size

•Dunkleosteus was a major placoderm predator

•Bladed jaws, strongest bite of fossil vertebrates

Chondrichthyes

•Sharks, rays, chimerae

•Economically and ecologically important

•Occupy every major marine habitat

•Critically important for the health of oceans

•Fun fact: sharks are older than trees evolutionarily

•Older even than Saturn's rings

•First appear in Early Devonian

•Cartilaginous endoskeleton

•Often calcified (never ossified)

•Neurocranium (chondrocranium) lacks sutures

•Swimbladder and lung absent

•Pelvic claspers

•Placoid scales

•Teeth replaced serially and not fused to jaw

•Single cloaca

Electroreception - ampullae of lorenzini

• Serially replaced teeth

spiral valve intestine: •Thought to increase surface area for digestion •Feature of all elasmobranchs Has evolved convergently in other fish groups

The legend of Helicoprion

•Genus of extinct shark-like holocephalid

•Basically a massive chimera

•Famous for its buzz-saw shaped tooth whorl

•as the individual grew, the older, smaller teeth were moved into the center of the whorl by larger, newer teeth appearing

•For nearly a century, no one knew the position of the tooth whorl

•In 2013 jaw cartilage was found with the fossil so now we know

Holocephali – modern chimaeras

•~33 species

•All marine are and  found at depths of 80-2600m (so mostly deep)

•Mysterious

••Four gill openings covered by an operculum

•Fused platelike teeth

•Persistent notochord

•Dorsal venom gland

•Separate genital and anal openings – i.e., no cloaca

•Pelvic and head claspers present

Elasmobranch Reproductive Biology

•Viviparity = live birth

•Sometimes developing embryo is retained in the uterus and nourished with a yolk sac

•In other cases, embryos exhaust yolk sac and feed directly on other eggs (e.g. great whites) oophagy

•Yolk is consumed and the empty yolk sac attaches to uterine wall

•Forms a yolk sac placenta

•Stalk of yolk sac which is attached to embryo  forms umbilical cord

•Transports nutrients and oxygen to embryo and transports metabolic waste

Oviparity

•Egg laying

•40% of living elasmobranchs lay eggs

•All skates lay eggs

•Clutch sizes are much larger than viviparous species (60 eggs a year)

•Eggs usually in the form of “mermaid purses”

•Egg is protected by tough keratinous shell that attaches to seaweed

•Some sharks retain egg cases in the oviduct and eggs hatch inside mother -  ovoviviparity

Endothermy in sharks

Primarily in lamniform sharks like great whites

Convergent evolution of endothermy

Deep red muscle generates heat

Heat retained via countercurrent exchange – vascular anatomy

Why bother being warm?

• upper jaw not connected to cranium, allows jaw mobility in sharks

What is a spiracle?

•Essentially breathing openings

•Can be found in insects, and cartilaginous fishes

•Allow organism to draw oxygenated water to the gills without operating gill slits

•Common amongst ray species

•Why might this be important?

Osteichtyes: Bony Fishes

•Three otoliths

•Homocercal tail

•Replaceable dentition

•Swim bladder that developed as an outpocket of the esophagus

•Fins supported by bony dermal rays

•Skull and pectoral girdles composed of dermal bone

•Eye is supported by sclerotic ring

•Operculum covers the gills

•No placoid scales

•Two extant classes

•otoliths - balancing organ in the inner ear

• sclerotic ring: bone that supports the eye

• Operculum: bone that covers the gills

Scale Types

•Placoid - Found in elasmobranchs

•Basically modified teeth covered in dentine

•Ctenoid - Found in “modern” fishes, do not have enamel covering. Have bony protrusions on the posterior margin of the scale (ctenii)

•Ganoid - Found in extinct holosteans and modern gar, sturgeon, bowfins, paddlefish and bichirs. Have a dentine covering and a layer of ganoine

•Cycloid - Also found in modern fishes, lack dentine layer and lack ctenii, usually have smooth surface

Actinopterygii

•Characterized by having fins with webs of skin supported by bony spines

•Fin rays attach directly to radials which are support structures coming off the pectoral and pelvic girdles

•Most dominant class of vertebrates

•420 million years old

•99% of “fishes”

•size variation , all habitats

Radials

•Tetrapods are nested within sarcopterygian fishes which we will discuss next

•But there is homology among actinopt, sarcopt fins and tetrapod limbs

Actinopterygii -Polypteriformes

•One family (Polypteridae)

•Commonly referred to as “bichirs” and “ropefishes”

•All freshwater, distributed in African rivers and flood plains

•Common in pet trade

•Species are typically elongate

•Unique set of 7-18 dorsal finlets

•Body is covered in ganoid scales

•Fleshy pectoral fins

•Immobile maxillary bones

•Also have spiracles

•Bichirs have lungs!

•Lungs are connected to the esophagus via the glottis

•Species are facultative air breathers, can breathe air in oxygen poor environments

•Can give useful insights on tetrapod evolution bec they can walk

Chondrostei

•Paddlefishes and sturgeons

•Heterocercal tail

•Cartilaginous skeleton

•Retained notochord

•Ossified head

•Spiral valve intestine

•Spiracle

paddle for electric sensing

Holostei

•Two orders

•Amiiformes (bowfin)

•Lepisosteiformes (gar)

•Ossified notochord

•Appeared 200 million years ago

•Used to inhabit marine and freshwater environments

•Relationship between two orders is in flux

Class: Teleostei

•Means “perfect bone”

•Appeared in the Triassic 215 mya

•Diversified extensively in the Cretaceous

•Outnumber all other living fish groups ~30,000 species

•More species than all other vert clades combined!

•Incredibly morphologically diverse

•Presence of uroneurals – supports caudal fin

•Unpaired basibranchial tooth plates

•Mobile maxilla = protrusible jaws

•Homocercal caudal fin = tail fin lobes about equal but backbone ends at base of fin

•Most of these guys suction feed

•

Pharyngeal jaws

•A second set of jaws!

•“oral jaws” are the more familiar jaws

•Likely evolved from gill arches similar to oral jaws

•Allow for both external and internal processing of food