The Bilateria and Bilaterian Phylogeny

Question 1

Taxonomy

Answer 1

• the art of classification
• creating division sets for entities to exist in, and naming each set
• applied to almost anything
• often relies upon phylogeny

Question 2

phylogeny

Answer 2

• designed to elucidate the evolutionary relationships between one clade and another
• can only be reconstructed if the phylogenetic element has evolved
• aka evolutionary tree

Question 3

Give some examples of evolved entities

Answer 3

• a living organism
• a virus
• language

Question 4

Sometimes, morphological and genetic data are taken in tandem as

Answer 4

‘total evidence’.

Question 5

Morphological classification generally relies upon

Answer 5

a series of phenetic characteristics.

Question 6

Give some frequently employed morphological characteristics factored into taxonomy

Answer 6

• symmetry (radial, bilateral, or absent)
• germ layers (endoderm, mesoderm or exoderm)
• body cavities
• segmentation
• embryo cleavage (radial, or spiral).

Question 7

What is a body cavity?

Answer 7

fluid filled spaced found in the body often lined by a waterproof barrier of epithelial cells

Question 8

Describe radial embryonic cleave

Answer 8

with a vertical mitotic spindle

Question 9

Describe spiral embryonic cleave

Answer 9

with a diagonal mitotic spindle

Question 10

Give some disadvantages to Phenetic classification

Answer 10

• secondary loss
• convergent evolution
• character number (especially character loss)

Question 11

secondary loss

Answer 11

aka reversion

Question 12

When the first invertebrate phylogenetic tree was being reconstructed, the … was used.

Answer 12

18 Small Subunit ribosomal ribonucleic acid (S rRNA)

Question 13

What are the ‘three great clades’ of Bilateria

Answer 13

• Lophotrochozoa
• Ecdysozoa
• Deuterostomia

Question 14

Why was 18S rRNA used?

Answer 14

• common functionality
• small length
• useful and easy in experiments

Question 15

Give some examples of the Lophotrochozoans

Answer 15

• Annelids
• Bryozoans
• Molluscs
• Nemerteans (ribbon worms)
• Platyhelminths (flatworms)

Question 16

Describe the naming of the Lophotrochozoa

Answer 16

• some exhibit lophophore, and some trochophore larva
• they are animals.

Question 17

Describe the Bryozoans

Answer 17

• filter feeders
• lophophores

Question 18

Give examples of the Ecdysozoa

Answer 18

• Arthropoda
• Nematoda (round worms)

Question 19

Describe the naming of the Ecdysozoa

Answer 19

• undergo edysis (moulting)
• are animals.

Question 20

Give examples of the Deuterostomia

Answer 20

• Echinoderms
• Chordates

Question 21

Describe the naming of the Deuterostomia

Answer 21

• mouth forms second, after their anus
• after radial cleavage of the embryo, the blastophore is transformed into the anus first, and then the mouth is formed
• opposite to the Protostomia.

Question 22

Describe the general characteristics of the Bilateria

Answer 22

• bilateral symmetry
• anterior-posterior axis
• anterior brain and sensory organs
• centralised co-ordiating nerve cord
• muscle blocks on each side
• through-gut with both a mouth and anus found separately

Question 23

Describe the innovation of the Bilateral

Answer 23

• directionality allows three dimensional active environmental exploration through burrowing
• consequent bioturbulent sediment mixing and nutrient moving at the base of the Cambrian
• transformation of the two dimensional ‘biomat’ into the three dimensional world
• the bilaterians innovated depth.