the detailed description of skeleton of sponges is given.

1. Shazia Naaz
M.SC (Previous)
Department of Zoology
Bareilly College Bareilly
SKELETON IN SPONGES

2. Almost all sponges are
provided with a skeleton
Embedded in
mesenchyme
May consistof separate
spicules or interlacing
spongin fibers
Supports & protects
soft body parts
Serves as basis of
classification
CONTENTS

4. 1. STRUCTURE & TYPES
Spicules are
crystalline structure
Composed of spines
or rays radiating
form a point
Secreted by
specialized
mesenchymal
amoebocytes
(scleroblasts)

5. All kinds of spicules have a
core of organic material around
which isdeposited either calcium
carbonate (calcite) or colloidal
silica (silicon)
Accordingly they are of 2-types
Calcareous (Calcarea)
Siliceous (Hexactinellida)

6. According to size, larger
spicules forming main skeleton
(megascleres)
Smaller spicules occurring
interstitially (microscleres)
May occur in several forms

7. May be simple rod-like, forks,
anchors, shovels, stars, plumes
etc.
Forms depend upon the number
of axes & rays present
Can be divided into mono, tri,
tetra or polyaxons

8. A. MONOAXON
Formed by growth
along one axis
May be straight
needle-like or
curved
Ends may be
pointed, knobbed
or hooked
2-kinds

9. B. TRIAXON
With 3-axes t
h
a
t
cross each other at
right angles to
produce 6-rays
Hexactinal
Characteristic of
glass sponges
(Hexactinellida) only
Euplectella,
Hyalonema

10. C. TETRAXON
With typically 4-
rays each pointing
in different
direction
Usually one of four
rays is elongated
giving appearance
of a crown of 3-
rays
Termed triaenes

11. When all rays are
equal (calthrops)
When all rays persist
(tetra or quadriradiate)
When one of fours
rays (elongated one) is
lost (triradiate
characteristic of
calcareous sponges)
Elongated ray with disc
at both ends
(amphidisc)

12. Amphidisc

13. Euplectella

14. Hyalonema

15. D. POLYAXON
Spicules with
several equal rays
radiating form a
central point
May be grouped
to give star-like
appearance
Common among
microscleres

16. 2. DEVELOPMENT OF SPICULES
Calcareous spicules are
secreted byspecial cells
(sclerocytes) derived
from mesenchymal
scleroblasts
Monoaxon spicule or
each ray of triradiate
spiculeis secreted by a
group of 2-sclerocytes

17. One acting as
thickener cell
Other as founder cell
Binucleate scleroblast
is believed to give
rise to these cells
Formation of spicule
begins as a deposition
of a particle of
CaCO3 between 2-
nuclei

18. Particle grows
drawing apart first
2-nuclei & then 2-
sclerocytes
Thickener cell lays
down additional layers
of CaCO3 adding
thickeness to spicule
When spicule is fully
formed, both cells
wander into
mesenchyme

19. Is an organic, elastic,
horny substance
resembling silk in
chemical composition
Like nails, hairs &
feathers it is a
scleroprotein
containing Sulphur
Chemically related to
collagen
Spongin fibre

20. Insoluble, chemically inert &
resistant to protein digesting
enzymes
Contains a large amount of
iodine
8-14% in certain tropical
species (Spongiidae &
Aplysinidae)
Old herb doctors used bath
sponge as a cure forcroup
(throat condition of children
due to inflammation & partial
obstruction of larynx)

21. Occurs in various
forms (Demospongiae)
May occur as cement
connecting together
siliceous spicules
(Monoaxonida: Cliona)
More usually it is
found in the form of
branchingor
anastomosing fibers in
which siliceous spicules
are embedded

22. Cliona

23. Euspongia