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Superphylum

 

Panarthropoda

• Includes Onychophora, Tardigrada,

Arthropoda• All have paired segmental appendages

• Are segmented• Secreted exoskeleton that must be

molted for growth• Terrestrial

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Phylum Onychophora

• 110 described species

• Tropics and temperate in SouthernHemisphere

•Nocturnal

• Need humid microenvironment

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Phylum Onychophora

• Wormlike (called velvet worms)

• 5 – 

15 cm long

• Segmented body –

 

repetition of 

 – Appendages – Ostia

 –

Nephridia – Ganglia

• Segmentation not actually visible

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• Tagmosis

 

weak

• 13 - 

43 paired segmental trunk appendages – Similar, uniramous, fleshy

 – Called lobopods

 – Terminate with pair sclerotized

 

claws

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• Head appendages – Annulated, sensory antennae

 – Mandibles

 – Oral papillae

 – Slime glands –

 

used to capture prey, can eject slime 15 cmfrom body

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• Thin exoskeleton

 –Resembles arthropod –

 

α-chitin, protein – Thin epicuticle

 

and procuticle

• Highly permeable (why habitat choice)

• Molt frequently (every 2 wk over 6 yrlife span

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• Musculature

• Hemal 

system

• Saccate

 

nephridia

• Trachea

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Onychophoran

 

Phylogeny

• Similarities with Annelids

• Body-walled muscles in continuoussheets

•Thin cuticle, lacking sclerotized

 

plates• Weak tagmosis

•

Simple brain• Wormlike body

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Onychophoran

 

Phylogeny

• Similarities with

Arthropods

• Ecdysis

• Α-chitin and

noncollagen

 

protein

• Coelom

 

reduced to

nephridia

 

and gonads

•

Open hemal 

system• Appendages

(mandibles) for feeding

•

Trachea• Superficial cleavage

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Onychophoran

 

Phylogeny

• Similarities with Both

• Segmented body

• Paired segmental appendages

• Paired segmental nephridia• Double ventral nerve with multiple

ganglia

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Onychophoran

 

Phylogeny

• May be an intermediate between

annelids and arthropods• Other lines of evidence, including

molecular, needed• If relationship not confirmed,

similarities would be convergence

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Phylum Tardigrada

• Water bears

•Most 0.3 –

 

0.5 mm,some reach 1.2 mm

• ~600 species

(always growing)

• Aquatic –

 

a few

freshwater andmarine; most in film

• Cuticle

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Tardigrade 

Mating

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Tardigrada

 

Phylogeny

• Morphological similarities with

Arthropoda 

and Cycloneuralia• Also molecular links between both

groups• Why it is often grouped with “enigmatic

phyla”