Animal Diversity: EXAM 3: Tom Holder

Deuterostomes

• the 2nd opening becomes the mouth

• the blastopore becomes the anus

Protostomes

• 1st opening becomes the mouth

Phylum Chaetognatha

• arrow worms

• evolutionary position is still debated

• pelagic marine predators

• highly specialized for their planktonic existence

• horizontal fins bordering the trunk are used in flotation rather than in active swimming

Characteristics of the Phylum Echinodermata

• unique water-vascular system

• pentaradial symmetry

• endoskeleton with spines

• digestive system complete

• free-swimming bilateral larvae

• excretory organs absent

• no other group has such complex organ systems and have radial symmetry.

Phylum Echinodermata: evolution/history

• likely descended from bilateral ancestors since larvae are bilateral

• perhaps evolved radially as an adaptation to sessile existence

• found from marine intertidal to abyssal regions

• lots of diversity in this group

Phylum Echinodermata: Ecological importance

• due to spiny structure, they are not often preyed upon

• a few fish and sea otters are adapted to feed on sea urchins

• sea stars feed on mollusks, crustaceans and other invertebrates

• play important ecological role as top predator

sea stars

• key stone predator

• help maintain increase in species diversity

Phylum Echinodermata: Class Asteroidea

• sea stars (commonly known as starfish)

  • can regenerate lost parts by casting off injured arms and regenerating new ones

  • about 1,500 living species that range from 1cm to more than 1m across with variable colors and structural features

  • 2 common species: Asterias sp. and pisaster sp.

Phylum Echinodermata: Class Asteroidea: Asterias species

• common on the east coast of U.S and often used in school labs

Phylum Echinodermata: Class Asteroidea: pisaster species

• common on west coast

• keystone predator

Phylum Echinodermata: adaptive diversification

• have greatly diversified within the benthic habitat and range from:

  • creeping forms with filter feeding

  • scavenging

  • herbivorous

  • pelagic, predatory forms

  • predaceous intertidal

Phylum Hemichordata

• Acorn worms and tube worms

  • formerly considered a subphylum of chordates based on presence of gill slits and rudimentary notochord.

  • bottom dwellers, living in shallow waters with cosmopolitan distribution but are fragile and secretive

  • most are sedentary or sessile

Phylum Hemichordata: rudimentary notochord

• a buccal diverticulum called stomochord.

• NOT homologous to chordate notochord

Phylum Hemichordata: Class Enteropneusta

• Acorn worms

  • sluggish, wormlike creatures that live in burrows in the mud and sand

  • proboscis is the active part of this animal

    • it probes its surroundings and collects food in mucous strands.

Phylum Hemichordata: Class Pterobranchia

• Tube worms

  • basic plan of this class is similar to that of enteropneusta with modifications due to sedentary lifestyle

  • small animals, usually 1 to 7 mm in length

  • many individuals may live together in collagenous tubes

    • zooids are not connected but live independently in the tubes and extend their crown of tentacles out through the openings.

Phylum Hemichordata: adaptive diversification

• far from bein completely understood

• share characters with both echinoderms and chordates

Phylum Hemichordata: similarity with chordates

• both have:

  • pharyngeal slits

  • chordata is placed as a sister taxon to hemichordates

Phylum Hemichordata: similarity with echinoderms

• both:

  • diffuse epidermal nervous system but dorsal nerve cord in collar region of hemichordates is not diffused

  • the larva is identical to larva of asteroida

  • echinoderms are sister groups of hemichordates

Phylum Chordata: Structural plan

• name comes from the notochord

• all of these have 5 basic characteristics at some point in their life history.

Phylum Chordata: notochord

• supporting rod along dorsal axis

Phylum Chordata: 5 basic characteristics

1. dorsal hollow nerve cord

2. notochord

3. pharyngeal gill pouches and slits

4. an endostyle or thyroid gland

5. post-anal tail

Phylum Chordata: shared features with other invertebrates

• bilateral symmetry

• anteroposterior axis

• coelom

• tube-within-a-tube body plan

• metamerism (repetition of body parts)

• cephalization (head)

• chordates have more structural unity in body plan than many other phyla.

Phylum Chordata: 5 basic characteristics: Dorsal hollow nerve cord

• invertebrate → nerve cord → ventral to canal and solid

• chordates → single cord → dorsal to canal → tubular

Phylum Chordata: 5 basic characteristics: notochord

• extends the length of the body and lies between the gut tract and nervous system

• stiffens the body, providing skeletal scaffolding for attachment of swimming muscles

Phylum Chordata: 5 basic characteristics: notochord: in protochordates/jawless vertebrates

• the notochord persists throughout life.

Phylum Chordata: 5 basic characteristics: notochord: in vertebrates

• the notochord is entirely displaced by vertebrae but persists as intervertebral discs.

Phylum Chordata: 5 basic characteristics: notochord: in vertebrates: intervertebral discs

• vertebral column for support

Phylum Chordata: 5 basic characteristics: pharyngeal gill pouches and slits

• pharyngeal slits lead from the pharyngeal cavity to the outside

• in tetrapods, the pharyngeal pouches give rise to a variety of structures, including the Eustachian tube, middle ear cavity and tonsils.

• the perforated pharynx functions as a filter-feeding apparatus in protochordates

Phylum Chordata: 5 basic characteristics: endostyle or thyroid gland

• recently, the endostyle was recognized as a shared chordate character

• found in ALL chordates. ONLY

• metabolic gland

Phylum Chordata: 5 basic characteristics: post-anal tail

• provides motility for larval tunicates and amphioxus to swim.

• musculature → invertebrate groups

• this was increased in fishes but became smaller or vestigial in later lineages

• ex: human: coccyx

Phylum Chordata: Ancestry and Evolution

• the deuterostomes (2 openings) are a natural grouping that has a common origin in Precambrian seas

• arose about 570 MYA

• from a lineage related to echinoderms and hemichordates

• molecular data suggest that a clade containing both echinoderms and hemichordates is the sister group of chordates

Phylum Chordata: Subphylum Urochordata

• invertebrates

• tail chordates but commonly known as tunicates

  • about 1,600 species of tunicates.

  • all salt water/marine

  • most are sessile as adults

  • Tunic

    • a tough, non living tissue containing cellulose that surrounds tunicates

  • only the larval form bears all the cordate hallmarks but adults retain the notochord only in the tail region

Phylum Chordata: Subphylum Urochordata: Class Ascidiacea

• sea squirts

• have hearts that drives blood first in 1 direction for a few beats and then reverses direction

Phylum Chordata: Subphylum Cephalochordata

• lancelets

Phylum Chordata: Subphylum Vertebrata: adaptations and evolution

• vertebrates

• has series of vertebral elements making up the vertebral column

• earliest vertebrates were substantially larger than protochordates and considerably more active

• modification of skeletal structures and muscles increased speed and mobility.

• higher activity level and size of vertebrates required structures specialized in the location, capture, and digestion to support a high metabolic rate

• predation: increased mouth size/ JAWS

Phylum Chordata: Subphylum Vertebrata: structure

• musculoskeletal modification occurred in most vertebrates that passes both an exoskeleton and endoskeleton made of cartilage or bone

• *endoskeleton permits almost unlimited body size.

• vertebrates have disc-like centra that replaced the notochord and neural spines provide more area for attachment of segmented muscles.

• segmented body muscles (myomeres) changed from v-shaped muscles of ancestral chordates to w-shaped muscles of vertebrates which allowed for powerful control over body

Phylum Chordata: Subphylum Vertebrata: endoskeleton

• composed initially of cartilage and later of bone

• cartilage grows faster and is more flexible than bone which is an ideal first framework

• endoskeleton of living hagfishes, lampreys, sharks, and their kin, and even some “bony” fishes, like sturgeons, composed of cartilage.

• *bone formation may have been adaptive for early vertebrates.

• structural strength of bone is SUPERIOR to cartilage

  • this makes bone more ideal for muscle attachment in areas in high mechanical stress.

Phylum Chordata: Subphylum Vertebrata: modifications

• bone may have also evolved as (30)