Biol168_10F_Lecture 13_22Oct2010

Biol168_10F_Lecture 13_22Oct2010 - Dr. Morris Maduro, UC...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Dr. Morris Maduro, UC Riverside Biology 168 – 10F – Lecture 13, page 1 Lecture #13: Early development of sea urchins Textbook: 2nd Ed.: pp. 201-9; pp. 265-9. 3rd Ed.: pp. 202-208; pp. 269-273. Some figures in these notes are redrawn from Wolpert et al. (2nd edition). Sea Urchins are grouped with hemichordates and chordates Sea urchins are echinoderms , a group that also includes starfish. Although they lack a notochord, they are grouped with hemichordates and chordates because they are deuterostomes . In deuterostomes (“mouth second”), the oral opening is formed after the anal opening. As well, most deuterostomes form their body cavities from mesodermal pouches extending from the gut ( enterocoely ). In protostomes (“mouth first”), the oral opening is formed first, and body cavities are formed by hollowing out a solid block of mesoderm ( schizocoely ). schizocoely, as seen in protosomes enterocoely, as seen in deuterostomes Most echinoderms are indirect developers and go through a larval stage, but direct developing sea urchins are known. Driesch’s experiments showed that the early sea urchin embryo is regulative at the 2- cell and 4-cell stages. Fig. 6.12 from textbook
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Dr. Morris Maduro, UC Riverside Biology 168 – 10F – Lecture 13, page 2 Summary of sea urchin development. The egg has a polarity: The animal pole of the egg is opposite the vegetal pole. The vegetal side of the egg is where gastrulation will occur later; the animal-vegetal axis is set before fertilization. The sea urchin egg divides by radial cleavage (see figure above) three times symmetrically. The third cleavage occurs perpendicular to the animal-vegetal axis. The fourth division is asymmetric in the vegetal blastomeres, producing four small micromeres and four larger macromeres. After more divisions, the embryos is a hollow
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 4

Biol168_10F_Lecture 13_22Oct2010 - Dr. Morris Maduro, UC...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online