Chapter 8 Flashcards
What are bilatarians called?
Triplobastica
Three traits of Bilatarians
- adult tissue from three embryonic germ layers: endoderm, mesoderm, and ectoderm
- body axis is anteroposterior, with a left and right symmetry
- regional specialization through cephalization
What supports monophyly in Bilatarians? (2)
- modern phylogenetic analysis
- presence of three Hox genes: anterior, central, and posterior
- only anterior and posterior are found in nonbilatarians
What does the mesoderm do? (2)
- development of derivative tissues
- mesodermal muscles, blood, and some organs
- lead to the coelom- true body cavity
What is the blastocoelem?
primary embryonic body cavity
How do we know if the coelom is from the mesoderm (2)?
- lining is a true epithelium
- polarized cells interconnected by apical adherens junctions
What is Xenacoelomorpha?
sister group of Bilatarian
What is Nephrozoa and Eubilatarians?
non-Xenacoelomorpha bilatarians
What do nephrozoans need? (2)
- evolved large body sizes
- evolved need for complex organs for circulation, gas exchange, osmoregulation, excretion, muscular movement, structural support
What are three apomorphies of Nephrozoa?
- through gut (gut with an anus)
- Platyhelminthes has a reduced gut
- protonephridia/ metanephridium for waste removal
- Chaetoghnatha and Bryozoa relies on diffusion
- Hox3 genes
What are the three groups in Deuterostomia?
- Chordata, Hemichordata, and Echinodermata
What are Deuterostomia traits? (3)
- anal blastopore
- some anus don’t originate from the blastopore
- egg development with radial cleavage
- some nondeuterostomes have this
- eneterocoelic coelom formation
What is eneterocoelic coelom formation
coelom from outpouch of archenteron
What consists of Protostomia?
Spiralia (15) and Ecdysozoa (8)
How diverse is protostomia, and what are the largest and smalles phylas?
- 95% of earth’s known species diversity
- largest phyla is Arthropoda and Mollusca
- smallest is Micrognathozoa and Cycliophora
What is the ancestral traits (2) of Protostomia?
- central nervous system with a dorsal cerebral ganglion
- circumesophageal connectives to ventral nerve cords
What protostomes have deuterostome development, and how is the coelem formed in most protostomes?
- some have deuterostome development
- nematomorphs, some brachiopods, and some crustaceans
- schizocoelic coelom formation (occurs in some deuterostomes)
What is schizocoelic coelem formation?
coelom from splitting of mesodermal tissues
What is key in knowing the differentiation of the blastopore?
blastopore, mouth, and anus have a degree of developmental independence
How do some clades go against blastopore development? (2)
- mouth formation from oral ectoderm may be ancestral to Bilateria, not just Protostomia
- some Spiralia have have mouths not from the blastopore
What is the the anal blastopore regulated by
anal blastopore is regulated by the brachyury and caudal genes
What are Deuterostome morphological characters? (3)
- pharyngeal gill slits
- six ordered genes
- four transcription factors for development of pharyngeal gill slits and branchial apparatus
- eneterocoelic development and trimeric condition of coelomic cavities (protocoel, mesocoel, and metacoel)
- not found in Chordata
What are protostomia apomorphies? (3)
- tricky to be defined by morphological synapomorphies
- ventral nerve cord
- not distinct in soft-bodied platyhelminthes and nemerteans
- circumesophageal brain
- some have deviations
What makes up spiralia? (3)
forms Dicyemida, Gnathifera, and Platytrochozoa
