Histology of aurelia - epidermis gastrodermis and mesogloea and Nematocysts cell and their type , longitudinal & circular muscle & locomotion in aurelia. Notes-
Table of Contents (part- 2)
Histology of Aurelia (Jellyfish)
a. Epidermis
b. Gastrodermis
c. Mesogloea
Nematocysts-
a.Atrichous isorhizas.
b. Holotrichous isorhizas.
c. Heterotrichous microbasic euryteles
Musculature and locomotion of Aurelia (Jellyfish)
Aurelia (A Jellyfish)
Histology of Aurelia (Jellyfish)
The basic histological plan of Aurelia medusa is more or less the same as
that of the Obelia medusa. It is diploblastic and derived from two
embryonic layers, ectoderm and endoderm.
a. Epidermis
All the exposed parts of an umbrella, that is, exumbrellar surface, velarium,
tentacles, subumbrellar surface including subgenital pits, oral arms, and
manubrium, are covered by epidermis.
The gullet is formed by the evagination of the epidermis.
It consists of epithelial cells (on the exumbrellar surface), epithelio-muscle
cells (confined to subumbrellar surface) beside sensory cells, nerve cells,
gland cells, and cnidoblasts. Sensory cells form a sensory epithelium
between epithelial cells.
b. Gastrodermis
Gastrodermis has columnar ciliated epithelial cells, they have no muscle
processes; all the parts of the gastrovascular canal system, except the gullet,
are lined by the gastrodermis.
The gastric filaments are formed by the thin core of the mesogloea and a
double layer of gastrodermis.
Gonads are also gastrodermal structures.
The cavities of tentaculocysts and marginal tentacles, being an extension of
the gastrovascular canal system, are also lined by the gastrodermis.
Gastrodermis mainly consists of flagellated columnar endothelial cells.
The gland cells are present but nerve cells and muscle processes are
wanting. Cindoblasts are confined to gastric filaments.
In the interspace between gastrovascular canals, the gastrodermis of ex-and
sub-umbrellar surface fuse to form a thin sheet, of the gastrovascular
lamella.
c. Mesogloea
It constitutes the main bulk of the body, forming a thick gelatinous
layer between the epidermis and gastrodermis.
The mesoglea of Aurelia is not structureless, contains numerous
branching elastic fibers and wandering amoeboid cells derived
from the epidermis.
This type of mesogloea is more or less like connective tissue snd
is known as collenchyma.
It is ectodermal in an origin and endo-mesodermal as in higher
metazoans.
The mesogloeal fluid resembles seawater except that it has more
potassium and less sulfate.
Nematocysts
They occur on oral arms, ex- and subumbrellar surface, marginal tentacles,
as well as gastric filaments. They are of 3 types:
1. Atrichous isorhizas: Capsule is elongated. The thread tube is open at
the tip and is without a butt and spines.
2. Holotrichous isorhizas: Capsule is oval and butt is narrow. The thread
tube is long, open at the tip, and armed with a spiral row of small spines.
3. Heterotrichous microbasic euryteles: Capsule is small. The thread
tube is open at the tip and covered by minute spines. The butt is short nad
its distal dilated portion bears unequal spines.
Musculature and locomotion of Aurelia (Jellyfish)
a. Musculature
Aurelia has a well-developed musculature mainly confined to the
subumbrellar surface.
The musculature is formed by muscle processes of epithelio-muscle cells
of the epidermis.
A broad, circular, and peripheral muscle band, known as coronal muscle,
extends along the periphery of the sub-umbrella.
The conspicuous longitudinal muscle are present in the tentacles,
manubrium, and oral arms.
The radial muscle extends from manubrium to coronal muscle along the
main radii of the umbrella.
Coronal and longitudinal muscles of tentacles are striated, while others are
unstriated
b. Locomotion
The highly developed musculature brings about swimming movements of
Aurelia, during which the ex-umbrellar surface is kept upwards.
Rhythmic contractions of circular muscles force water out from the sub-
umbrellar cavity, like a jet. As a result, the body is propelled forward or
upward. This type of jet-propulsion is known as hydropropulsion.
When the contractions stop, the body gradually sinks to the bottom.
Horizontal movements depend on wave action and help in buoyance
because of their low density.
If the body is tilted, equilibrium is maintained with the help of 8
tentaculocysts.
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Aurelia playlist:-
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