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Hemichordates and Chordates
Description
Vertebrate Zoology (Hemichordates & Chordates) Mind Map on Hemichordates and Chordates, created by Litty Carter on 22/04/2013.
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hemichordates & chordates
vertebrate zoology
vertebrate zoology
hemichordates & chordates
Mind Map by
Litty Carter
, updated more than 1 year ago
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Litty Carter
over 11 years ago
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Resource summary
Hemichordates and Chordates
Hemichordates
e.g. Acorn worms & Pterobranchs
Marine and intertidal. Mostly dioecious (seperate sexes
Fragile and live in burrows/tubes
Previously subphylum of chordates
Physiology
Gill pores & dorsal nerve chord
Notochord (not homologous)
Buccal diverticulum
Open circulatory system
Glomerulus (unique)
Class 1: Enteropneusta
Deposit/suspension feeders
Asexual and sexual reproduction
Some TORNIA larval stage
Eggs hatch into swimming larvae which later metamorphose into acorn worms
Class 2: Pterobranchia
Small and colonial
Lophophore like feeding structure
Asexual reproduction in most species
Chordates and their Origin
Defining Characteristics:
1. Notochord (stiff rod)
2. Dorsal hollow nerve chord (runs along length of body)
3. Post anal tail (muscular, skeletal elements. Propulsion in aquatic forms)
4. Pharyngeal gill slits (allow water entering mouth to exit through body)
Other (some shared) Characteristics
Cephalisation (brain)
Segmented & regionally differentiated
Bilateral symmetry
Ventral heart (closed circulation)
Blood from heart to anterior, ventrally
Generally active
Possible ancestors
1. ANNELID WORMS?
FOR
Bilateral symmetry
Segmented
Active
Cephalisation
Longitudinal nerve chord
AGAINST
Flip over - Relocation of mouth and anus unlikely
Solid ventral nerve chord (opposed to dorsal)
Segmentation complete
No notochord and no gill slits
REJECT
2. ECHINODERMS?
FOR
Although echinoderms are sessile, larval forms are motile. Chordates evolved through paedomorphosis
Larval forms became sexually mature
Marine
AGAINST
Paedomorphosis doubted
Gutmann's (1981) "Chordates into Echinoderms" theory
Recent molecular evidence: only a subset of genes persist from tunicate larvae to adult (head without trunk
REJECT
3. HEMICHORDATES?
FOR
Bilateral symmetry
Motile
Progressive alteration of adult
AGAINST
Forms such as Branchiostoma close to main lineage, but Tunicates are distant
ORIGIN
Major unsolved problem
Evolved from ancestral deuterosome
CHORDATES: PHYLUM
Sub-phylum: Urochordata
Tunicates (Sea Squirts)
Ascidiaceans
All oceans, all depths
Solitary, social, compound
Larvaceans
Solitary, luminescent, planktonic
Retain larval features, paedomorphosis
Thaliaceans
Include free floating salps
Tropical/subtropical waters
No free swimming larval stage
Mostly sessile and colonial. Larval stage bears chordate characteristics
Settles, releases adhesive, radical metamorphosis. Tail and notochord reabsorbed. Sheds outer layer of cuticle, nervous system degenerates.
Sub-phylum: Cephalochordata
Lancelets - Branchiostoma
~29 species (all marine
up to 5cm long
Larval stages have chordate characteristics
Seperate sexes (dioeceous)
Live buried in sand
Ciliary mucus suspension feeders
Buccal cirri: prevent sediments and other large particles
Hatschek pit: mucus secretion structure near mouth
Dorsal and ventral fin like structures
Sub-phylum: Vertebrata
Vertebrates!
See vertebrates mind map
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