Larval and Rudiment Development in S' purpuratus

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Larval and Rudiment Development in S. purpuratus
Lisa A. Urry Mills College
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Pluteus
Juvenile
Stages I through VI
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Stages of Larval Development
III Vestibular invagination
I Four Arm
II Eight Arm
III Rudiment initiation
V Pentagonal Disc
VI Advanced Rudiment
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lpo
lpo
rpo
la
ra
la
A
A
R
An
Ab
L
P
Stage I Four Arm

• The anterolateral (la and ra) and postoral (lpo
  and rpo) arms partially extend.
• The coeloms partially extend along the gut.
• Feeding begins.
• The hydropore has already formed.

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left coelom
rpo
lpo
la
ra
right coelom
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Stage II Eight Arm
rpo
lpo
lpo
rpo
la
ra
lpd
rpd
oh
lpd
rpd
oh
ac
da

• The triradiate primordia of the spicules of the
  posterodorsal (lpd and rpd) arms and dorsal arch
  (da) appear.
• The tissues of the oral hood (oh) and anal cup
  (ac) become more elaborate.
• The left coelom differentiates into the axocoel,
  stone canal, hydrocoel, and somatocoel.
• The right coelom differentiates into the axocoel,
  hydrocoel and somatocoel.

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ra
rpd
rh
lax
sc
lh
ls

• Left coelom axocoel (lax), stone canal (sc),
  hydrocoel (lh), and somatocoel (ls).

• Right coelom axocoel (rax), hydrocoel (rh),
  and somatocoel (rs).

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Stage III Vestibular Invagination
rpo
lpo
la
ra
rpr
lpr
rpd
lpd
aep
vi
da
aep
pep
pep
ptr

• Left oral ectoderm invaginates (vi) to form the
  vestibule.
• The left and right somatocoels extend posteriorly
  and laterally around the stomach.
• The triradiate of the posterior transverse rod
  (ptr)appears.
• Preoral (lpr,rpr) arms lengthen, supported by the
  dorsal arch.
• Anterior and posterior epaulettes (aep,pep) begin
  to form.
• The indentation between the posterodorsal arms
  and the postoral arms lengthens.

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rs
aep
vi
pep
vi
lh
lh
ls
Abanal view
Anal view
III. Vestibular Invagination Stage
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Stage IV Rudiment Initiation
lpo
rpo
vf
lh
lh
rs
vf
ap
ls

• Vestibule and left hydrocoel become apposed.
• The vestibular floor (vf) thickens.
• The anterior portion of the left somatocoel
  becomes juxtaposed between the stomach and the
  hydrocoel.
• The left and right somatocoels meet at the
  posterior end of the stomach.
• Adult plates (ap) begin to form on the posterior
  ends of the posterodorsal spicules and on the
  body rods.

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lh
vw
vf
ls
ls
ls
A

• The vestibular floor (vf) is thicker than the
  wall (vw).
• The anterior portion of the left somatocoel
  becomes juxtaposed between the stomach and the
  hydrocoel.

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ra
la
rpd
lpd
aep
aep
vf
lh
rs
pep
pep
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Stage V Pentagonal Disc
la
ra
rpo
lpo
lpr
vi
tf
lpd
rpd
vf
tf
lh
tf
ap

• The five tube feet (tf) originate as projections
  of the hydrocoel against the vestibular floor
  which grow outward and upward.
• The left somatocoel projects against the
  vestibular floor between the tube foot extensions
  to form the dental sacs (ds).
• The anterior and posterior epaulettes reach their
  fullest extension.

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ra
la
lpo
rpo
vf
vc
tf
tf
tf
ls
Abanal view
Stage V Pentagonal Disc (early)

• Tube feet are forming
• Vestibular opening remains narrow

tf
Anal view
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vp
vc
View from left
Stage V Pentagonal Disc (late)

• Tube feet elongate as bilayered canals.
• Vestibule remains open to outside via a narrow
  vestibular canal (vc)and pore (vp).

Abanal view
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Stage VI Advanced Rudiment
tfs
sp
ep
tfs
js
Serial section through mid-rudiment
js

• The vestibular floor appears multi-layered (ep).
• Adult plates begin to form in the rudiment.
• Adult spines (sp) are present in the rudiment.
• Adult plates form at the dorsal arch and on the
  right anterolateral spicule.
• Structures with calcareous rings (tfs)are seen at
  the distal ends of the tube-feet.
• Five juvenile spines (js)form two at the
  posterior apex and three on the right side of the
  larva.
• Pigment cells cluster around the rudiment,
  posterior apex and near adult spines.

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tf
ds
sp
tfs
sp
sp
ap
tf
Serial section from left larval side
Stage VI Advanced Rudiment

• Adult plates (ap)begin to form in the rudiment.
• Adult spines (sp) are present in the rudiment.
• Structures with calcareous rings (tfs)are seen
  at the distal ends of the tube-feet.
• A dental sac (ds) flanked by two spines is
  present between each two tube-feet.

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tf
Stage VI Advanced Rudiment

• A dental sac (ds) flanked by two spines is
  present between each two tube-feet.
• The bilayered tube-feet have extended outward,
  forming primary radial canals.
• An opening exists in the center of the hydrocoel,
  defining the center of the ring canal.

ds
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Stage VI Advanced Rudiment (late)

• The rudiment (rud) occupies most of the
  blastocoelar space.
• Tube feet may protrude through the vestibular
  opening.
• Larval arms appear shorter and may bend away
  from the larval body.
• Metamorphosis may occur.

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Andy Cameron (Caltech)
Meighan Smith Luisa Smith (Mills College)
Brian Rowning (Lawrence Berkeley National Lab)
Simona Carini Lisa Labrecque
Fred Wilt Pat Hamilton (U.C.Berkeley)
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