Hemichordates (graptolites) Flashcards
What is the age range for the Phylum Hemichordate?
Cambrian to recent
What is Phylum Hemichordate united by?
the presence stomochord (convergent with the notochord of chordates) for at
least half their life cycle
How does Hemichordate fall into the metazoans?
Bilaterian - deuterostome
What is the 3 relationship with hemichordates?
Hemichordates
Echinoderms
Chordates
(super phylum)
What can extant hemichordates be divided into?
Pterobranchs
Enteropneusts (acorn worm)
What is an example of a modern pterobranch?
Rhabdopleura
What are the characteristics of Rhabdopleura? (pterobranch)
Colonial organism
Mouth at base of arms
Individual zooids ciliated, tentacle bearing arms
What are the individual zooids like of Rhabdopleura? (pterobranch)
Cephalic shield - with glands secreting zooidal tubes
How do Pterobranchs reproduce?
Initially sexually produced zooid generates a stolon which in turn produces other zooids asexually
What are the different names for the pterobranchs of the recent and Cambrian?
Recent = Rhabdopleura compacta
Cambrian = Rhabdopleura obuti
What are cephalodiscus? (pterobranchs)
Individual zooids which crawl out of the colony and wander onto spines to feed away from low regime of the sea bed
What is the age range of Class Graptolithina?
Cambrian to mid-Carboniferous
What are the characteristics of class Graptolithinia?
Colonial
Rhabdosome
Periderm - scleroproteinaceous skeleton
Ribbon like cortical bandages
How are the cortical bandages produced? (graptolites)
Secreted by zooids
How is graptolithinia usually preserved?
Carbonaceous films
How are 3d graptolithina extracted from matrix?
Dissolved out of limestone as protein periderm is acid resistant
What is the structure of rhabdosome?
Sicula - point of origination
Nema - projection
If Nema buried in colony = Virgula
Zooids housed in Theca
Apertural spines
Stipes
What 2 parts can the Sicula be split into?
Protosicula - net like
Metasicula - bandage like
How is the colony of rhabdosome (graptolithina) connected?
Connected by a common canal (stolon in pterobranch) runs close to nema
What are stipes in rhabdosome?
Branches of thecae
How can graptolithina be divided?
Dendroidiea
Graptoloidea
What is the age range of Dendroidea?
Mid Cambrian to carboniferous
What is the age range of Graptoloidea?
Lower Ordovician to lower Devonian
What is the Rhabdosome morphology of Dendroidea?
Multibranched
Numerous stipes
Connecting dissepiments
What are the 3 type of thecae in Dendroidea?
Stolothecae - continuous chain
Autothecae - large (female?)
Bithecae - smaller and narrower (male?)
What is Wimans rules?
Triad budding of Thecae with chain of Stolothecae with branches of individual Auto and Bi
What are Graptoloidea like in comparison to Dendroidea?
Reduced stipe number
Single thecae type = auto
Hemaphrodite
What was the mode of life of dictyonema?
Thickened nema so thought epifaunal benthic
What habitat is dictyonema associated with?
common in shallow water siltstones, sandstones & limestones
What was the mode of life of Rhabdinopora?
Weak nema
Found in deep water sediments
Planktonic
What was the feeding method of dendroids?
Passive
Why are graptaloids so good for biostratigraphy?
Found in a range of sediments so not facie restricted
What evidence is there for automobility of dendroids?
Based on structures which promote/ enhance spinnign and thought that zooids used to “swim” back up the water column
What is the function of the thecal spines?
Increase water flow
What are the stipe orientations of biserial graptoloids?
scandent (ridges point out)
reclined
reflexed
horizontal
deflexed
declined
pendant (ridge pointing in- rotation of scandent)
What is an example of a scandent graptoloid?
Didymograptus bifidus
Where is Didymograptus bifidus locally common?
Abereiddy Bay in Pembrokeshire
