0:00:03.364,0:00:04.461
University of Lille 1 - Faculty of biology

0:00:04.630,0:00:06.145
Animal Biology

0:00:33.640,0:00:38.339
Sea star dissection

0:00:39.613,0:00:41.698
Morphology

0:00:46.382,0:00:48.993
The Asteria rubens sea star

0:00:49.023,0:00:50.799
is an Echinoderm

0:00:50.799,0:00:52.821
belonging to the class of Asteroidea.

0:00:54.804,0:00:56.434
It lives on costs

0:00:56.487,0:00:58.406
we may find it in the intertidal zone

0:00:58.406,0:00:59.882
at low tide.

0:01:02.285,0:01:04.394
It feeds chiefly on mussels

0:01:04.397,0:01:06.482
fixed on rocks.

0:01:09.430,0:01:12.390
The sea star is part of the foreshore food web

0:01:12.409,0:01:15.277
and can fall prey to other animals.

0:01:20.837,0:01:22.837
The body of the sea star is flattened,

0:01:22.997,0:01:25.761
in a shape of a star with 5 arms.

0:01:27.484,0:01:29.797
The arms merge at their base

0:01:29.797,0:01:32.279
and are attached to the flat disk.

0:01:37.520,0:01:40.083
The arms are called radius

0:01:41.238,0:01:45.330
The zones between the arms are called interradius.

0:01:47.990,0:01:51.974
This organisation is representative of the pentaradial symmetry,

0:01:51.974,0:01:55.557
characteristic of the adult echinoderms.

0:01:58.529,0:02:01.096
The sea star has two faces:

0:02:01.515,0:02:03.345
the upper face,

0:02:03.345,0:02:04.797
or aboral surface,

0:02:04.797,0:02:07.660
is convex and pigmented.

0:02:08.105,0:02:09.774
The bottom side

0:02:09.774,0:02:10.827
or oral surface,

0:02:10.843,0:02:12.789
is flattened, and clearer,

0:02:12.789,0:02:15.197
in contact with the substrate.

0:02:18.060,0:02:19.979
This surface includes the mouth,

0:02:19.979,0:02:22.377
located in the middle of the flat disk.

0:02:25.504,0:02:27.211
On the aboral surface,

0:02:27.249,0:02:29.178
at the interradius level,

0:02:29.178,0:02:31.966
we can see a whitish limestone plate,

0:02:32.016,0:02:34.286
the madreporic plate.

0:02:36.658,0:02:40.143
There are bony spines convering the body,

0:02:40.214,0:02:43.136
organized in rows.

0:02:43.264,0:02:44.748
On the aboral surface,

0:02:44.748,0:02:49.565
there is a row in the middle of each arm

0:02:49.629,0:02:51.859
and two or three lateral rows.

0:02:55.946,0:02:57.730
By turning the sea star over,

0:02:57.783,0:03:00.688
we can see a supramarginal row

0:03:02.084,0:03:04.863
and an inframarginal row

0:03:08.413,0:03:10.655
Two rows of prikly adambulacra

0:03:10.665,0:03:12.688
delimit a central furrow,

0:03:12.742,0:03:14.726
the ambulacral groove,

0:03:19.827,0:03:23.693
Every ambulacral groove has 4 rows of fleshy and movable tubes

0:03:24.281,0:03:27.050
tube feet or podia,

0:03:27.779,0:03:30.177
ended by a sucker.

0:03:32.840,0:03:36.688
At tip of each arms we can see eyespots,

0:03:37.688,0:03:39.852
sensory organs red in coulour

0:03:39.967,0:03:42.373
sensitives to the light.

0:03:44.229,0:03:47.475
Integument

0:03:47.858,0:03:49.173
In the sea star,

0:03:49.173,0:03:51.194
the body and the spines are covered

0:03:51.210,0:03:52.933
by an ciliated epidermis

0:03:54.830,0:03:55.498
The dermis,

0:03:55.498,0:03:57.174
situated beneath the epidermis,

0:03:57.212,0:03:59.012
has calcareous plates,

0:03:59.044,0:04:00.820
or ossicles

0:04:00.820,0:04:03.114
in which the spines are articulated.

0:04:05.300,0:04:06.958
The locations of ossicles

0:04:06.961,0:04:09.067
are visibles on the surface of the animal.

0:04:11.854,0:04:14.674
The integument has specialized structures,

0:04:14.706,0:04:16.382
pedicellariae,

0:04:19.097,0:04:21.913
put in the shape of a crown at the base of the spines.

0:04:24.528,0:04:25.889
In Asteroidae,

0:04:25.889,0:04:28.211
they have a form of a pincer with two jaws.

0:04:30.652,0:04:32.551
Pedicellariae are used

0:04:32.551,0:04:34.433
to clean the integument

0:04:34.433,0:04:36.469
and the defense of the animal

0:04:38.917,0:04:41.504
Organs used for the breathing,

0:04:41.700,0:04:43.894
gills or papules,

0:04:43.894,0:04:46.075
are associated with the integument.

0:04:49.162,0:04:52.269
they are between the ossicles of the skeleton.

0:04:55.141,0:04:56.877
The presence of an epithelium

0:04:56.892,0:04:59.547
ciliated on the inner side of the integument

0:04:59.570,0:05:01.700
enables the circulation of the liquid

0:05:01.746,0:05:04.349
inside the body cavity,

0:05:04.379,0:05:06.493
the coelom.

0:05:10.448,0:05:14.039
Echinoderms have a calcareous internal skeleton,

0:05:14.071,0:05:16.107
formed by ossicles.

0:05:21.053,0:05:23.739
the cross section of the arm enables us

0:05:23.739,0:05:26.986
to observe the organisation of the dermal plates.

0:05:38.059,0:05:39.510
We can see:

0:05:39.510,0:05:41.714
a dorsal ossicle

0:05:42.923,0:05:45.251
two supramarginal plates

0:05:46.100,0:05:49.767
and two inframarginal plates each having spines,

0:05:50.874,0:05:53.796
two adambulacra plates

0:05:53.796,0:05:56.227
and two ambulacral plates.

0:06:00.104,0:06:02.034
Between the ambulacral plates,

0:06:02.034,0:06:05.847
there are pores that allows the passage of the tube feet.

0:06:11.062,0:06:13.982
General anatomy

0:06:14.204,0:06:17.150
To observe the internal organisation of the sea star,

0:06:17.502,0:06:21.104
we have to cut the sea star with scissors.

0:06:22.837,0:06:24.552
Incise the integument

0:06:24.552,0:06:26.805
following the outline

0:06:26.805,0:06:29.144
to separate the upper half

0:06:29.239,0:06:32.208
from the lower half of the animal.

0:06:33.787,0:06:36.575
Identify the madreporic plate

0:06:39.139,0:06:42.994
and avoid it when you incise.

0:06:47.267,0:06:49.628
Lift the integument of the aboral surface

0:06:49.628,0:06:51.944
starting from the end of the arms

0:06:54.143,0:06:57.168
and cut carefully the underlying organs

0:06:59.500,0:07:02.133
ending by the flat disk.

0:07:05.885,0:07:09.927
The rest of the dissection will be done in the water.

0:07:12.711,0:07:15.646
In the coelom we can see gonads

0:07:15.747,0:07:18.871
and a part of the digestive system.

0:07:21.755,0:07:24.861
The digestive system

0:07:25.211,0:07:28.357
The digestive system includes the mouth,

0:07:29.541,0:07:32.871
the stomach divided in two superimposed chambers,

0:07:33.827,0:07:37.332
the pyloric ceca and the rectal ceca.

0:07:37.815,0:07:40.517
It ends by a microscopic anus,

0:07:40.517,0:07:43.339
located in the aboral surface.

0:07:45.281,0:07:47.370
The observation of the digestve system

0:07:47.383,0:07:50.782
will be done using the aboral portion.

0:07:52.376,0:07:54.422
In the central part of the disk,

0:07:54.442,0:07:57.484
we notice two rectal ceca.

0:08:01.124,0:08:04.747
Below we notice the upper chamber of the stomach,

0:08:04.776,0:08:08.918
the pyloric portion with a pentagonal shape.

0:08:12.067,0:08:14.880
5 canals start from this chamber

0:08:14.903,0:08:18.048
that extend themselves in the arms of the star.

0:08:19.612,0:08:22.953
Each pyloric canal is connected to two pyloric ceca

0:08:22.953,0:08:25.869
that take up a large part of the arms.

0:08:28.602,0:08:30.455
The pyloric ceca,

0:08:30.455,0:08:33.651
composed by dozens of diverticula on dead end

0:08:33.669,0:08:35.604
play a digestive key role

0:08:35.604,0:08:39.585
and are used to the storage of nutrients.

0:08:40.604,0:08:43.649
To observe the rest of the digestive system

0:08:43.836,0:08:46.774
we have to remove the rectal ceca,

0:08:49.304,0:08:51.134
pyloric ceca

0:09:03.599,0:09:05.566
and the pyloric stomach.

0:09:10.243,0:09:13.655
The ventral chamber or cardiac stomach,

0:09:13.676,0:09:17.251
has a shape of five lobes rose.

0:09:19.536,0:09:21.010
For the ingestion of preys,

0:09:21.010,0:09:25.124
this part of the stomach is everted.

0:09:26.520,0:09:28.614
After the external digestion,

0:09:28.978,0:09:32.194
the stomach gets back to its position

0:09:32.194,0:09:36.128
thanks to the contraction of five pairs of retractor muscles

0:09:36.159,0:09:40.118
put in the ambulacral plates.

0:09:41.225,0:09:43.505
To see the mouth,

0:09:43.558,0:09:46.598
we have to detach the retractor muscles

0:09:50.873,0:09:54.696
and remove the portion of cardiac stomach.

0:09:56.472,0:09:57.748
The mouth,

0:09:57.839,0:10:00.319
located in the middle of the flat disk,

0:10:00.814,0:10:02.961
surrounded by a membrane,

0:10:02.963,0:10:04.716
the peristomium.

0:10:08.305,0:10:10.179
Reproductive system

0:10:12.337,0:10:13.698
In Asteroidea

0:10:13.698,0:10:15.274
the sexes are separated

0:10:15.274,0:10:17.907
but there is not a sexual dimorphism.

0:10:19.826,0:10:22.841
Gonads are located in the coelom.

0:10:26.194,0:10:27.932
To observe the gonads

0:10:28.094,0:10:30.621
we have to remove the pyloric ceca,

0:10:32.656,0:10:35.024
and the upper chamber of the stomach.

0:10:38.793,0:10:39.831
Every gonad,

0:10:39.831,0:10:41.500
with a granular apsect,

0:10:41.500,0:10:43.569
is divided in deux lobes

0:10:43.569,0:10:48.476
that all extend in two adjacent arms.

0:10:50.590,0:10:52.989
The size of gonads is variable,

0:10:53.225,0:10:57.345
it depends on the state of sexual maturation of the animal.

0:10:58.973,0:11:02.051
Females and males produce gametes

0:11:02.065,0:11:05.725
through genital pores located in the interradius

0:11:05.738,0:11:09.045
at the junction with the flat disk.

0:11:11.513,0:11:14.379
The fecondation is extern.

0:11:17.204,0:11:20.203
Aquifer system

0:11:20.787,0:11:23.678
One of the characteristic of Echinoderms

0:11:23.678,0:11:25.762
is the existence of an aquifer system.

0:11:26.801,0:11:31.308
It is involve in the locomotion and the food intake.

0:11:32.697,0:11:35.908
This system have a network of conduits

0:11:35.908,0:11:37.360
filled with a liquid

0:11:37.360,0:11:40.627
whose composition is close to the sea water

0:11:42.186,0:11:46.605
The aquifer system have a madreporic plate,

0:11:48.002,0:11:49.679
the stone canal,

0:11:50.766,0:11:53.084
the ambulacral ring,

0:11:53.813,0:11:55.934
five radial canals,

0:11:56.924,0:12:00.388
and many tube feet or podia.

0:12:01.643,0:12:04.988
To observe the different parts of the aquifer system

0:12:05.254,0:12:07.115
we have to open the sea star

0:12:08.772,0:12:11.288
and remove the digestive

0:12:13.304,0:12:14.519
and reproductive system.

0:12:16.452,0:12:19.338
The madreporic plate, or madreporite,

0:12:19.787,0:12:23.299
is visible on the aboral surface of the animal.

0:12:24.546,0:12:27.002
This calcareous plate is riddle with holes

0:12:27.055,0:12:28.616
"aquifer pores"

0:12:29.739,0:12:32.573
that permit the sea water to enter in the system.

0:12:36.201,0:12:40.209
The madreporite is in connection with the madreporic canal

0:12:40.209,0:12:42.023
or stone canal.

0:12:43.120,0:12:44.573
This canal

0:12:44.573,0:12:47.597
sostained by superimposed calcareous rings,

0:12:47.597,0:12:50.791
go down toward the oral surface of the animal.

0:12:53.219,0:12:54.518
The stone canal

0:12:54.518,0:12:57.641
rejoin the ambulacral ring surrounding the mouth.

0:12:58.810,0:13:00.017
This ring is hidden

0:13:00.017,0:13:02.066
with calcareous plates of the skeleton.

0:13:04.115,0:13:06.640
On the circumference of the ambulacral ring of the star

0:13:06.832,0:13:08.870
in the interradial position,

0:13:09.055,0:13:12.747
we notice 9 vesicles with an immune function:

0:13:12.829,0:13:14.871
Tiedemann bodies.

0:13:19.212,0:13:21.810
From the aquifer ring goes in each arm

0:13:21.810,0:13:24.974
an ambulacral canal or radial canal,

0:13:25.850,0:13:29.499
located between the epidermis and the ambulacral plate.

0:13:32.448,0:13:36.690
From the radial canal goes many lateral canals.

0:13:40.371,0:13:44.472
Those are connected to the tube feet or podia.

0:13:48.188,0:13:51.768
The injection of a dye into ambulacral canal of an arm

0:13:51.768,0:13:53.582
enables us to hightlight

0:13:53.582,0:13:56.689
a large part of the aquifer system.

0:14:01.230,0:14:04.261
Podia have three parts:

0:14:04.792,0:14:07.798
ampulla or bulbous ampulla

0:14:10.483,0:14:13.096
a muscular and elongated foot

0:14:13.506,0:14:15.670
and a sucker at the end.

0:14:20.573,0:14:23.890
The podia go through the skeleton at pores level

0:14:23.890,0:14:27.261
located between the two adjacent ambucral plates.

0:14:30.026,0:14:31.541
To observe those pores

0:14:31.541,0:14:33.843
we have to scratch the polian vesicules

0:14:33.843,0:14:36.350
on a part of the arm.

0:14:37.529,0:14:39.809
The contraction of the polian vesicles

0:14:39.948,0:14:43.250
allows the turgescence of the tube feet

0:14:43.392,0:14:47.353
and the the monitoring of the sucker [br]for the locomotion of the animal

0:14:50.551,0:14:53.634
The podia within the ambulacral groove

0:14:53.634,0:14:57.538
are protected by rows of movable ambulacral spines

0:14:57.538,0:15:00.880
and by many pedicellariae.

0:15:03.722,0:15:05.275
Radial canals

0:15:05.282,0:15:07.783
end with sensory tentacles

0:15:07.901,0:15:11.096
close to the eyespot.

0:15:15.545,0:15:17.781
Pedagogical design: Pierre-Eric Sautière Jacopo Viziolo

0:15:19.862,0:15:24.408
Technical production: Bernard Mikolajczyk

0:15:24.695,0:15:29.203
Designs: Jacopo Vizioli

0:15:29.460,0:15:33.863
Computer graphics: 3D MEDICUS

0:15:39.190,0:15:41.911
Voice over: Alain Nempont

0:15:43.709,0:15:47.494
Music; Ambient slamming bass jam, Jay Berlinsky

0:15:48.813,0:15:53.495
Gratitude: Sébastien Lefebvre, Michel Priem

0:15:53.670,0:15:58.311
Gratitude: Patrick Flammang, Michel Jangoux

0:15:58.535,0:16:02.813
SEEM; Education Service and Multimedia