Chapter 10 Flashcards
What previously used terms was used for Dicyemida?
- Mesozoa- middle animal between protists and Metazoa
- Rhombozoa- Dicyemida and Heterocyemida
What are the three families in Dicyemida?
- Conocyemidae
- Dicyemidae
- Kantharellidae
What do Dicyemida lack? (4)
- no body cavity or differentiated organ
- no symmetry
- lack layered extracellular matrix and basement membrane
- no clear evidence of germ-layer formation
What is the body plan of Dicyemida? (2)
- atypical spiral cleavage
- internal urn cavity, but not blastocoel
What does the morphology of Dicyemida tell?
no adequate method to recognize through morphology
What kind of body plan genes do Dicyemida have, and what does it suggest?
- DoxX gene and Hox expression suggest
- highly reduced and specialized symbionts in Spirilia
What is the lifestyle of Dicyemida? (3)
- obligate symbionts in renal sacs of cephalopod mollusks
- often in temperate seas
- most are in benthic octopus
How large is Dicyemida?
0.5 to 3 mm
How many cells do Dicyemida have?
9-41, depending on species
What type of cell-cell junctions do Dicyemida have? (3)
- septate
- adherens
- gap junctions
What are nematogens?
vermiform embryos asexually
How do nematogens eat?
consumes particulates and nutrients in urine through phagocytosis
What makes up the nematogen? (2)
outer sheath of 8-40 somatic cells
single long, interior axial cell
What makes up the somatic cells in nematogens? (4)
- 8-9 cells form polar cap on anterior end
- 2 parapolar cells under polar cap
- uropolar cells- two posterior cells
- trunk cells- cells between parapolar and uropolar cells
What makes up the axial cell in nematogens?
contains nucleus and axoblast (intracellular stem cells)
What are rhombogens, and what do they look like?
- infusoriform embryos from fertilized eggs
- enlarged with yolky material in somatic cells
How do young Dicyemida move?
using cilia to move in host urine
How do adult Dicyemida move?
attach to inner lining of nephridia using polar cap; cilia serves to bring nutrients to surface cells
What do DIcyemida do to hosts?
unconfirmed, but large number can negatively affect host
What do asexual vermiform embryo form? (5)
- asexually as axoblasts
- first division of an axoblast is produces a large axial cell and a small somatic cell
- somatic cell divides repeatedly to cover the axial cell
- axial cell divides unequally, with smaller one being engulfed
- smaller cell becomes the embryo, and eventually leaves
What does the vermiform stage consist of?
vermiform stage consists of an axial cell and 8-30 ceiliated peripheral cells
What does the embryo do in a new host?
cells grow into new worms in renal sac of host
How do infusoriform embryos develop? (5)
- internal fertilization and development
- produced around hermaphroditic gonads called infusorigens
- each has an outer layer of ova and an inner mass of sperm
- sperm fertilizes ova to form embryos
- embryo leaves body through urine
What do infusoriform embryos look like? (3)
- embryo has two large apical cells and other ciliated cells to sheath around a ring of capsule cells (37-39 total)
- capsule cells enclose four central cells
- number of infusorigens and embryos depends on size
How do Dicyemida shift between asexual and sexual forms?
- shifting between asexual and sexual reproduction may be due to high population density in renal sac
- infusoriforms escape sac to search for new host
How is life outside the host for Dicyemida?
- undetermined
- sinks to the bottom of ocean
- reproduces asexually
- may enter an intermediate host
What is the theory for Dicyemida in the bottom of the ocean?
- some parts of embryo enters another host to become a stem nematogen
- stem has 3 axial cells unlike vermiform
- reproduces asexually
