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Chapter 23 Chordata

Subphyla

Urochordata

Cephalochordata

Vertebrata

48000 spp

29 spp

1400 spp

Unicellular (acellular)

protozoan protists

Multicellular (metazoa)

Poorly defined

tissue layersDiploblastic Triploblastic

PoriferaPlacozoa

CnidariaCtenophora

Priapulida

Chaetognatha

Gastrotricha

Entoprocta

Loricifera

PlatyhelminthesRhynchocoela (Nemertea)

Mesozoa

Gnathostomulida

Rotifera

NematodaKinorhyncha

Acanthocephala

Nematomorpha

Annelida

Mollusca

ArthropodaOnychophora

Pentastomida

Pogonophora

Sipuncula

Echiura

EchinodermataHemichordata

Chordata

Brachiopoda

Phoronida

Bryozoa

Uncertain Acoelomate Coelomate Pseudocoelomate

Protostomes Uncertain (misfits) Deuterostomes

Chordate Characteristics

notochord

dorsal hollow nerve cord

pharyngeal pouches or gill slits

endostyle

postanal tail

recently recognized

secretes mucus in

invertebrate chordates/

lamprey larvae

becomes the thyroid glands in

adult lamprey/remaining vertebrates

bilateral symmetrical

deuterostome

distinctive characteristics

VertebrataCraniata

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Figure 23.01a

Subphylum: Urochordata (Gr: tail string)

Class: Ascidiacea

Class: Larvacea

Class: Thaliacea

1250 spp

70 spp

70 spp

Figure 23.06

Class: Ascidiacea (solitary tunicates)

larval stage

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Figure 23.04

Figure 23.05b

Figure 23.05a

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0144.jpg

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Class: Larvacea larvalike pelagic, walnut size

Paedomorphosis (Gr: child + form)

sexually mature animals retaining larval characteristics

build gelatinous houses every 4 hrs

1) neoteny-slow growth rate of body form

adult form never attained at maturity

2) progenesis-precocious maturation of gonads in larval form;

body stops growing never attains adult form

3) postdisplacement: onset of a developmental process delayed

relative to reproductive maturationadult form is not attained

food source for fish in pelagic open oceans

Walter Garstang 1928

1869 tunicate tadpole larva descendant of an ancient free-swimming chordate ancestor

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Figure 23.08

Class: Thaliacea

free-living, planktonic

achieve mobility through modification

of adult rather than larval form

buccal & atrial siphons at opposite ends

highly developed bands of circular muscles

nearly transparent

avoid detection by predators

avoid detection by prey

100-1000 of individuals/m3

pyrosomes

salps

doliolids

ciliary activitydrives food through large pharnygeal basket

provides locomotion

close buccal aperture

contract circular muscles5 mm individual travel 25 cm/sec

pharnygeal basket reduced to bar

cilia compact mucus net & food string

muscular contraction-feeding/locomotion

pharnygeal ciliafeeding currents

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Figure 23.07

colonial thaliacean

Cephalochordata

small <10 cm length

laterally flattened

notochord extends beyond the nerve cord to anterior end

notochord contractileV-shaped muscles called myomeres

Figure 23.09

Amphioxus (Gr: both ends sharp)

Branchiostoma (Gr: gill mouth)

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Figure 23.co

Figure 23.09b

Figure 23.10

Pikaia an early chordate (cephalochordate) from Burgess Shale

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Figure 23.11

Haikouella, a chordate from early Cambrian shales of Haikou, China

Chordate Larval Stage

Figure 23.12

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Figure 23.13larval stage of lamprey

resemble amphioxus except

well-developed brain

paired eyes

pronephric kidney

heart

Figure 23.15

Conodont vertebrate ancestor

Paleozoic fossils similar to amphioxus

Figure 23.01b

persists throughout life

In hagfish & lamprey

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Figure 23.485a

Figure 23.485b

Figure 23.485c

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Figure 23.491b

Figure 23.p482a

Figure 23.p482b

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Figure 23.p490

Figure 23.p491a

Figure 23.p491b

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Figure 23.02