Date post: | 05-Jan-2016 |
Category: |
Documents |
Upload: | brittany-morton |
View: | 233 times |
Download: | 0 times |
Cephalochordates
Urochordates(Ascidians)
Vertebrates
Hemichordates
Echinoderms
Ambulacraria
Deuterostomia
PhylumChordata
Phylum HemichordataEnteropneusta (acorn worms)Pterobranchia (colonial)
Phylum Chordata SubPhylum Urochordata (the Tunicates)
Ascidiacea (Ascidians) Thaliacea (Salps) Appendicularia (Larvaceans)
SubPhylum Cephalochordata
SubPhylum Vertebrata
Class Enteropneusta (acorn worms, 75 spp.)
Class Pterobranchia (colonial; 25 spp.)
- wormlike body with proboscis (prosome), collar (mesosome), and trunk (metasome), each with a (coelomic compartment)
- pharyngeal gill slits and dorsal hollow nerve chord like in chordates; no notochord
- separate sexes; asexual reproduction common (in pterobranchs)
- mouth + anus form secondarily after blastopore closes
- unique excretory structure, the glomerulus
Phylum Hemichordata
Acornworm
Enteropneusts (acorn worms)
proboscis used for movement in burrows, and for deposit- feeding on organic matter on the surface outside the burrow
Enteropneusts (acorn worms)
- cilia draw water through mouth (where food particles may be captured), then water exits pharyngeal gill slits
water in
water out,thru slits
Class Pterobranchia Colonial filter-feeders with 0-1 gill slits
Bryozoan-like features: 1) tentacles move water in same way as a lophophore
2) mesocoel extends into ciliated tentacles used in filter-feeding
3) live in secreted hard tubes
4) U-shaped gut, anus opening outside the tentacles
water flow
food
Class Pterobranchia Colonial filter-feeders with 0-1 gill slits
Bryozoan-like features: 1) tentacles move water in same way as a lophophore
2) mesocoel extends into ciliated tentacles used in filter-feeding
3) live in secreted hard tubes
4) U-shaped gut, anus opening outside the tentacles
5) colony of zooids produced by asexual growth
immatureasexualbud
Cephalochordates
Urochordates(Ascidians)
Vertebrates
Hemichordates
Echinoderms
Ambulacraria
Deuterostomia
PhylumChordata
Phylum HemichordataEnteropneusta (acorn worms)Pterobranchia (colonial)
Phylum Chordata SubPhylum Urochordata (tunicates)
Ascidiacea (ascidians) Thaliacea (salps) Appendicularia (larvaceans)
SubPhylum Cephalochordata
SubPhylum Vertebrata
At some stage of development, all chordates possess:
- Pharyngeal gill slits
- Dorsal, hollow nerve chord
- Dorsal notochord (hollow flexible tube)
- Post-anal tail, tadpole stage at some point in lifecycle
- Gland in pharynx that processes iodine:- endostyle
(Urochordata, Cephalochordata)
- thyroid gland (Vertebrata)
Phylum Chordata
pharyngeal gill slits: Out-pockets in the pharynx Become gill chambers and gills in aquatic chordates Become jaws, inner ear, and tonsils in terrestrial chordates notochord: a firm, flexible rod derived from mesoderm cells; becomes the endoskeleton in vertebrates
dorsal nerve cord: a hollow tube above the notochord; becomes the spinal cord and brain in vertebrates
The combination of these characters is a synapomorphy for Chordata, but all 3 traits rarely show up in the adult stage
- numerous gill slits on pharynx used in suspension feeding
- oral + atrial siphons
- notochord and nerve chord present in tadpole larvae
- no coelom or bony tissue
- adult body covered in secreted tunic, a polysaccharide coating
SubPhylum Urochordata 3,000 spp.
Class Ascidiacea (Ascidians)- benthic; solitary or colonial
Class Thaliacea (Salps)- pelagic, colonial
Class Appendicularia (Larvaceans) - pelagic, solitary- adults retain larval characteristics
Class Ascidiacea – the ascidians, or tunicates- sessile, benthic adults; large, short-lived tadpole larvae- solitary forms, or colonial (may be social or compound)- colonies form by asexual reproduction- hermaphrodites- often colorful + chemically defended- tropical species contain a photosynthetic symbiont, the cyanobacterium Prochloron
- sheets of iodinated mucus produced by ciliated tract called the endostyle
- mucus sheets move over the gills slits in the pharynx, through which water is pumped, trapping food particles
Filter-feeding in ascidians
Solitary Ascidians
Styela montereyensis
Colonial ascidians 1: In social species, individuals are clones from asexual reproduction, but do not share a common tunic (covering)
PHOTO B: colonial species in which each individual animal retains its own inhalent and exhalent siphons
PHOTO C: colony in which individuals are packed in a ring and share a centrally placed, common exhalent siphon (yellow arrow).
Colonial ascidians 2: In compound species, individuals are clones that share a common tunic, and
may even share siphons
Tadpole larvae show the chordate features that are not seen in the adult ascidian
- all ascidian larvae are lecithotrophic (non-feeding) and most are very short lived, swimming for a few minutes to find a suitable site for attachment and metamorphosis
Ascidian Metamorphosis
Class Thaliacea, the salps
- pelagic animals living in open water- gelatinous + transparent
- atrial siphon is shifted to posterior end- contraction of circular muscles compresses the tunic, forcing water out of atrial siphon & causing jet-propulsion forwards
colonial salp
Salps can be solitary or colonial. Colonial forms make long chains, which easily break apart.
Class Appendicularia, the larvaceans- pelagic, live in a secreted mucous house- pharynx reduced, bears only 2 slits- complex mucus nets spun for filter feeding- neoteny: larval form develops gonads for reproduction, adult stage is gradually lost from the life cycle - postanal tail beats to produce water currents
- notochord + reduced dorsal nerve chord present in tail
larvacean out of its house
larvaceans live inside a 2-layer gelatinous (jelly-like) house:
(1) pre-filter web, 1 meter across, traps large particles
(2) inner mucus filter traps small particles (2-20 m) which are eaten
As webs and house become clogged with debris, they are castoff (15 times per day)
- animal spins a new house just before leaving old one, quickly inflates it
- old houses sink to deep sea
larvacean out of its house
larvaceans live inside a 2-layer gelatinous (jelly-like) house
An outstanding mystery in marine science: what supplies all necessary food to sustain animals of the deep sea?
- 30% of the carbon needed to keep the deep sea alive could not be accounted for in sediment traps
Answer: sinking larvacean webs supply the missing nutrients to feed the ocean floor (Robison et al., Science 2005, 308:1609-1611)
Also remove up to 50% of particulate material that rivers dump into the upper 5 meters of the sea
- important to keep water clear enough for light to penetrate for photosynthetic organisms
Thus, larvaceans are critical living filters that sustain communities living in near-surface waters and the deep-sea!
- Amphioxus, fishlike animals also called lancelets
- Ciliary mucus suspension feeders, much like ascidians- water moved through pharyngeal gill slits by cilia- iodinated mucous produced by endostyle traps food
- Closed circulatory system similar to that of fishes, but no heart
- Segmented muscle bands called myotomes
- notochord lasts through adult life, but never becomes vertebral column and no brain develops (i.e., definitely not a vertebrate)
SubPhylum Cephalochordata25 spp.
Expression patterns ofdevelopmental genes arealso being used to study theevolution of vertebrates
- whole nervous system of lancelet-like ancestor was essentially compressed into the vertebrate brain
SubPhylum Vertebrata: the vertebrates
vertebral column houses dorsal nerve cord
there’s a lot of interest in studying the other chordates to understand how our lineage evolved – who’s our nearest relative among the invertebrates?
Analysis of the highly conserved 18S gene suggested that the nearest relatives of vertebrates were the cephalochordates
vertebrates
New analyses of hundreds of protein-coding genes consistently support Ascidiacea as the sister group of the vertebrates, not the cephalochordates
AscidiaceaCephalochordata
Vertebrata