Animals: Non-Vertebrate Deuterostomia Flashcards
Clade Deuterostomia
Clade Deuterostomia consists of three phyla: Hemichordata (acorn worms), Echinodermata (echinoderms, incl. starfish and sea urchins), and Chordata (chordates, incl. vertebrates).
Deuterostomia shares clade Bilateria developmental characteristics:
- Bilaterally symmetrical; triploblastic embryonic development.
Deuterostomes undergo deuterostome embryonic development:
- Radial, indeterminate cleavage; coelom forms when mesoderm folds from the wall of archenteron; formation of the anus from the blastopore.
- However, some non-Deuterostomia animals also share some deuterostome developmental characteristics, e.g. Brachiopoda and Ectoprocta.
Clade Deuterostomia is defined by molecular phylogeny
Phylum Echinodermata
Deuterostomia
Echinoderms (phylum Echinodermata) include starfish (or sea stars), brittle stars, sea urchins, sea lilies, and sea cucumbers.
- Greek: ekhinos = sea urchin, derma = skin
- ~7,000 extant species, all marine.
- Found throughout ocean depth, from intertidal to abyssal zone.
Echinoderms evolved during the Cambrian period, and their evolution is documented in extensive fossil records.
- ~13k fossil species.
- Calcareous endoskeleton suited to fossilization (endo = inside)
What are the 3 phyla in clade Deuterostomia
- Hemichordata (acorn worms)
- Echinodermata (echinoderms, incl. starfish and sea urchins)
- Chordata (chordates, incl. vertebrates).
Echinoderm characteristics
Name all 5
Remember this is the starfish group (also sand dollars and sea cucumbers)
- Most adult echinoderms have radial symmetry
- A thin epidermis covers an endoskeleton of ossicles
- Echinoderms have a unique water vascular system
- Diffuse nervous system with no centralized brain
- Echinoderms usually have separate sexes and are typically broadcast spawners.
radial symmetry
Echinoderm Characteristics
Most adult echinoderms have radial symmetry.
- Pentaradial symmetry (penta = 5) is most common, although other multiples (≠5) are also observed.
- The mouth is at the center of the disc and faces downward.
- Except for sea cucumbers, which are secondarily bilateral.
Echinoderms evolved from a bilateral ancestor (Cambrian period) and subsequently evolved radial symmetry.
- Extant echinoderm larvae exhibit bilateral symmetry.
A thin epidermis covers an endoskeleton of ossicles
Echinoderm characteristics
A thin epidermis covers an endoskeleton of ossicles.
- Ossicles are calcareous plates ± spines embedded in the dermal tissues of echinoderms.
- The echinoderm body wall may contain 10s to 1000s of ossicles.
Water Vascular System
Echinoderm characteristics
Echinoderms have a unique water vascular system.
Derived from the coelom and consists of a ring canal in the central disk and a network of hydraulic canals running down the length of each arm.
- The radial canals branch into hundreds of fluid-filled, muscular tube feet, that can be adapted for locomotion, feeding, respiration, mucus production, or sensory perception.
- Tube feet are controlled by water pressure acting on the ampulla and podium, and they attach to substrates through a combination of suction and adhesive mucus production
The water vascular system is connected to seawater via a porous ossicle, the madreporite.
- Madreporite allows water to flow in and out of the water vascular system.
Water vascular system also used for circulation and respiration.
- Gas exchange occurs through simple gills and diffusion through tube feet.
Nervous System
Echinoderm characteristics
Diffuse nervous system with no centralized brain.
- The central disk has a nerve ring and radial nerves extending into the arms
This is what allows them to regrow limbs
Echinoderm Reproduction
Echinoderms usually have separate sexes and are typically broadcast spawners.
- Gametes (sperm and eggs) are released into open water for external fertilization, and there is no subsequent parental care of planktonic larvae.
- Some species free spawn, where the male releases sperm but the female retains and broods fertilized eggs.
What are the five clades of Echinodermata
Extant echinoderms are divided into five clades that arose in the late Cambrian/early Ordovician:
- Crinoidea (sea lilies and feather stars)
- Asteroidea (starfish/sea stars and sea daisies)
- Ophiuroidea (brittle stars)
- Echinoidea (sea urchins and sand dollars)
- Holothuroidea (sea cucumbers)
Diversity of adult body forms across the five clades.
- Differences in the developmental regulation of a single Hox gene cluster
Italisized clades are discused in this class
Name example species, ecological role, and. important traits
Asteroidea
Echinoderms
Asteroidea includes the starfish/sea stars and sea daisies (aster = star).
- They have 5 or more arms radiating from the central disk.
- The undersurface of each arm bears tube feet, which grip the substrate with suction/adhesive chemicals.
Starfish are predators that can greatly impact intertidal community structure.
- They often feed on molluscs by prying them open with tube feet.
- Evert stomach onto prey to engulf and digest food.
Some starfish species reproduce asexually by fission of their central disc.
- Many species can regenerate lost arms to regrow an entire new limb over several months or years
Name example species, ecological role, and. important traits
Echinoidea
Echinoderms
Echinoidea includes the sea urchins and sand dollars.
- No arms but have five rows of tube feet.
Slow-moving.
- Use spines (jointed ossicles) for locomotion and protection.
Sea urchins are herbivorous.
- Use jaw-like plates around the mouth to grasp and grind algae
Overharvesting of sea urchin predators leads to sea urchin population explosions that decimate kelp forests.
Name example species, ecological role, and. important traits
Holothuroidea
Echinoderms
Holothuroidea (sea cucumbers) are tube-shaped detritivores.
- Deposit or filter feeders.
- Appear bilaterally symmetrical.
- Secondarily bilaterally symmetrical; elongated along the anterior-posterior axis.
- Have rows of tube feet along the body.
- In some species, tube feet around the mouth form feed tentacles.
- Sea cucumbers lack external spines, and the endoskeleton is reduced to scattered ossicles.
Chordates
Chordates (phylum Chordata) are bilaterian animals that belong to clade Deuterostomia.
- Chordates are bilaterally symmetrical coelomates with segmented bodies.
- Chordates share many features of embryonic development with echinoderms (i.e. deuterostomes) but have evolved separately for at least 500 million years.
The majority (>95%) of chordate species have vertibral columns (backbones): the vertebrates (subphylum Vertebrata).
− Chordates consist of all vertebrates and two groups of invertebrates, the urochordates and cephalochordates
Shared derived traits of chordates
- Notochord
- Dorsal, hollow nerve cord
- Pharyngeal slits or clefts
- Muscular, post-anal tail
Note: all these traits can be found in chordates, but they may not exist at all stages of life
- Human tails (present as embrios, absent for maturity)
Notochord
Chordate shared derived traits
The notochord is a longitudinal, flexible rod located dorsally between the digestive tract and the nerve cord.
- noto = back, chord = cord
- Glycoprotein core sheathed in collagen fibres.
The notochord provides flexible skeletal support throughout most of the length of invertebrate chordates
The notochord forms during embryogenesis when organ systems begin to develop from embryonic layers.
- The notochord develops from the dorsal mesoderm and is present in all chordate embryos and some adults.
- In vertebrates, a more complex, jointed skeleton (vertebral column) replaces the notochord before birth.
- Adult vertebrates retain only remnants of embryonic notochord as parts of the vertebral discs between vertebrae.
Dorsal, hollow nerve cord
Chordate shared derived traits
The nerve cord of chordate embryos develops from a plate of ectoderm that rolls inward forming the neural tube dorsal to the notochord.
- Signalling molecules secreted by the notochord and other mesodermal cells induce the neural plate to form from the ectoderm.
- The neural plate curves inward, forming the neural tube.
- The neural tube develops into the central nervous system (brain and spinal cord).
- A dorsal, hollow nerve cord is unique to chordates: other animal phyla have ventrally located solid nerve cords
Pharyngeal slits or clefts
Chordate shared derived traits
In most chordates, embryonic arches develop in the pharynx (the region just posterior to the mouth).
Pharyngeal grooves (or clefts) between the arches develop into slits that open to the outside of the body in most aquatic chordates.
- Allows water entering the mouth to exit through the pharyngeal slits, preventing it from passing into the digestive tract.
Functions of pharyngeal clefts/slits:
- Filter-feeding structures in invertebrate chordates.
- Gas exchange in aquatic vertebrates (excl. tetrapods): gills develop along the pharyngeal arches, which are ventilated when water is forced through the gill slits.
- Pharyngeal arches are only present during the embryonic development of tetrapods.
- They form precursors that develop into various skeletal and muscle elements of the head and neck in tetrapods
Muscular, post-anal tail
Chordate shared derived traits
Most adult chordates have a muscular tail posterior to the anus.
- The digestive tract of most non-chordates extends full body length.
The tail contains skeletal elements and muscles.
- It provides propulsive force in many aquatic chordates, i.e. fish.
- Tails function as rudders and provide balance, grip, etc.
In some chordates, the tail is greatly reduced during embryonic development.
Segmentation
| Chordate characteristics
Segmentation, e.g. vertebral column, muscle blocks.
Most chordates have segmented body plans, at least during embryonic development.
- The segments are often highly specialized into distinct body regions.
- Segmentation of chordates evolved independently from segmentation of other phyla, e.g. annelids and arthropods.
- Segmentation is considered a primitive character of clade Deuterostomia.
Segmentally arranged muscle blocks are present in all adult chordates except in the Urochordata.
- Muscle blocks develop from blocks of mesoderm (somites) that flank the notochord.
- Muscle blocks arranged in chevron (»>) patterns.
- Alternating contractions of the muscle blocks cause the notochord/vertebral column to flex side-to-side → swimming in marine chordates!
Name example species, ecological role, and. important traits
Cephalochordata
Chordates
Lancelets (subphylum Cephalochordata) are named for their blade-like body shape; ~25 species.
- Resemble bony fish, but they are invertebrate chordates.
Lancelets are marine sedentary suspension feeders that retain characteristics of the chordate body plan as adults.
- Wriggle backward into the sand.
- Water is drawn into the mouth by ciliary action and particles are extracted using mucus-covered pharyngeal slits.
- Water exits the body through the atriopore.
- Mucus net ingested (along with trapped food)
Name example species, ecological role, and. important traits
Urochordata
Chordates
Tunicates (subphylum Urochordata) are more closely related to vertebrates than they are to lancelets.
- Tunicates (~2,100 species) are suspension-feeding marine invertebrate chordates.
- Most adult tunicates are sessile, e.g. sea squirts/sea tulips that are permanently attached to rocks; other tunicates are pelagic.
- Tunicate larval stages most closely resemble the chordate body plan.
- The larval stage exhibits the four chordate shared derived traits.
Adults do not look like chordates
- “Tadpole”-like larvae have a brief free- swimming phase.
- Attach to the substrate by the head.
- Metamorphose to adult body plan (lose chordate traits).
- Become sessile suspension feeders.
Urochordata Structure and Reproduction
Chordates
Tunicates (subphylum Urochordata)
- Adult tunicates are covered by a tough polysaccharide “tunic”.
- They draw water in through an incurrent siphon, filtering it through the mucus- covered pharyngeal basket that collects food particles; filtered water exits out the excurrent siphon.
- Some tunicates reproduce asexually by budding, forming colonies
