Topic 2: Cnidaria Flashcards
מערכת הצורבים
Radiata
Ancient invertebrates with radial symmetry. Phylum Cnidaria (צורבים) + Phylum Ctenophora (מסרקניות)
Symmetry in Cnidaria
Is the first group in the phylogenetic tree that has symmetry (sponges didn’t have symmetry and all the groups ahead have some type of symmetry)
Ctenophora (מסרקניות)
Gelatin-like organisms that are generally in groups, they look like medusas. Small Phylum with about 200 species.
- They have 8 מסרקים (“comb”)
- Get fed by טריפה
- They’re sometimes placed in different places in the phylogenetic tree (for the course purposes we don’t need to know the phylogenetic location)
Body layers
Diploblastic: An animal possessing 2 major tissue layers. These include the outer layer (the ectoderm) and the inner layer (the endoderm). (like Cnidaria (צורבים))
Triploblastic: An animal possessing 3 major tissue layers. It has a middle layer (the mesoderm), between the endoderm and the ectoderm. (complex organisms from flatworms to men - check this)
Invagination & Blastopore
- Invagination: critical step during Gastrulation in which the outer layer in the Blastula goes in to form the 2 new layers.
- Blastopore: opening formed with the invagination, which is an ancient form of “intestines” (מעי הקדום)
Embrionic Development
- Blastula ( hollow sphere of cells, referred to as blastomeres, surrounding an inner fluid-filled cavity called the blastocoele formed during an early stage of embryonic development in animals- the layer of cells surrounding the blastocoel is called blastoderm.) Early stage in development, it forms after fertilization and a few cell divisions.
- Gastrulation: formation of the Gastrula. Early stage in the embryonic development in which cells are organized in layers (Endoderm & Ectoderm) from which later on tissues are formed, and allows for there to be body layers.
- During this process there is a critical step called invagination, in which the outer layer in the Blastula goes in to form the 2 new layers.
- Importance of Epithelium/Epithelial cells
-separates body compartments of different chemical composition
-Once regulated independently, each body compartment could adopt one or more specialized functions
Mezoglea
Intermediate layer in between the Endoderm and the Ectoderm, it has either no cells or very few of them.
- Main Characteristics of Epithelium/Epithelial cells
- Continuous sheet of cells
- Apical-basal polarity
- Basal lamina: Cells rest on a basal lamina (non cellular thin collagenous, fibrous sheet secreted by epithelial cells and on which they rest)
- Intracellular junctions: Cells are joined by intracellular junctions (gap junctions - communicating junctions between cells) - allows for different parts of the body to take different functions
Internal and external Epithelia
External Epithelium: Epidermis, formed from the embrionic ectoderm
Internal Epithelium: Gastrodermis (מערכת עיכול), formed from the embrionic endoderm
Importance of the gatro-vascular cavity
(it’s formed with Gastrulation)
- Permits the processing of a larger amount of food
- First time the digestion in not intracellular: release of enzymes into the gastro-vascular cavity (the enzymes can’t be released into open sea cause they’d be diluted and wouldn’t work, Cnidarians like פוליפ & שושנות ים can close themselves up and digest prays like shrimps).
Gastro-vascular cavity
Cavity surrounded by a layer of endoderm
Classes inside Cnidaria
- Anthozoa + Medusozoa (
- Staurozoa,
- Scyphozoa,
- Cubozoa,
- Hydrozoa)
**there is some controversy about the phylogenetic classifications
Characteristics of Cnidaria
(*polips are attached to the מצע and look like medusas turned upside-down)
- Aquatics
- Larva called Planula
- Have cnidocytes (main characteristic of Phylum Cnidaria)
- Radial symmetry
- Get fed through טריפה: the tentacles (זרועות צייד) surround the mouth opening, mainly feed from plankton which means they’re predators
- Have two types of life-forms: polyp and medusa (פוליפ (ישיב, בנטוני=צמוד למצע) ומדוזה פלגית=בגוף המים)
- The mouth is the only opening to the gastro-vascular cavity, and acts as entrance and exit.
- They’re diploblasts: have two body layers (Endoderm and Ectoderm), divided by the Mezoglea (non-cellular layer, not considered a real body layer - in sponges the connecting layer was called mesohyl)
Cnidocytes
They're a type of cell, they're "stinging" (צורבים), they usually have a toxin, in some cases these toxins can kill within minutes. A cnidocyte (also known as a cnidoblast or nematocyte) is an explosive cell containing one giant secretory organelle or cnida (plural cnidae) that defines the phylum Cnidaria (corals, sea anemones, hydrae, jellyfish, etc.).
Types of dangerous species with powerful venoms: box jellyfish & sea wasp
- Mechanism
1- Cnydocyst - (defining organelle of Cnidaria, with shape of capsule inside the Cnidocyte) - is triggered after the Cnidocil - (sensory “hair-like” flagellum? (שוטון) that projects from the surface of the cnidocyte) - senses movement in the vecinity
** how: there is a change in osmolarity caused by an increase in Calcium ions in the cells, as a result water rushes in raising the hydrostatic pressure inside the capsule causing the stylus (צלצל=harpoon) to exit the capsule
2-Stylus emerges through operculum
3-stylus hits target (the prey (טרף))
4-stylus inverts?
5-capsule empties (the thread goes out and releases the venom)
**it’s possible to use this mechanism in medicine by engineering a cnydocyst who would release a drug instead of a toxin
- Function of Cnidocytes
- paralysation and prey capture
- helps bringing the pray (depending on size) into the חלל העיכול
- defense from predators.
- Different types: Nematocyst, spirocysts & ptychocysts
Characteristics of Class Hydrozoa
- Considered to be the most ancient of classes in Cnidaria
- About 3500 species
- Sweet water
- Two life forms, polyp and medusa
- mezoglea with no cells at all
- gastrodermis with no cnidocytes
- Their gonads are generally epidermic
- Model organism in regenerative studies
Obelia life cycle
The gonozooid releases medusas -> the medusas release sex cells (ovules or sperm cells depending on the זיווג?) -> the sperm cell and ovules meet (זרע וביצית) -> zygote is formed -> after that the blastula is formed through cell divisions -> gastrula -> larva called planula surrounded by ריסים -> the planula settles in the מצע and forms a new colony
Sexual Stage: the one responsible for the secretion of the sex cells (gametes), meaning, the medusa. There are male and female medusas, which release the gametes and allows for mixing of the genetic material.
Asexual stage: the polyp, in order to grow he buds (מנץ) in a asexual way, without involvement of other genetic material.
Hydroid Colony
Class Hydrozoa’s larva settles (מתיישבים) and begins to grow through asexual divisions, forming colonies - meaning same genetic material (definition of colony), asexual reproduction -
In the colonies there are polyps with specialized functions,
- gastrozooid - for nutrition, they have tentacles and are responsible for capturing the prey
- gonozooid - for reproduction, releases תוצרי רבייה ?
- dactylzooid - for protection, they’re full of cnidocytes (תאים צורבים) in addition to the ones in the other polyps
- Sexual and asexual phases
** all the polyps have special functions but they’re not considered as organ specialization or differentiation (התמיינות)
Hydromedusa Body Structure
The important thing to know here is that:
- medusas of the הידרטיים are small
- Vellum: allows movement. (*Velum: a membrane or membranous part resembling a veil or curtain: such as
an annular membrane projecting inward from the margin of the bell in some jellyfishes (such as the hydromedusae))
- they’re the sexual stage in the life cycle of the colony
Special hydrozoan orders (סידרה בהידרתיים)
- הידרתיים פלגיים: (**means the medusa form, in the water, = פלגי, while בנטוני meant attached to the מצע, = polyp)
there are some hydrozoans (הידרתיים) in which the מחזור פלגי is more dominant. These are יצורים מושבתיים that when there’s a central floating polyp (פוליפ הציפה) they are full of CO2, release gastrozooid and gonozooid. Floating/buoyancy (ציפה) is advantageous since it puts the polyp close to the prey. Since they lack the capacity to move, they get dragged to the shore by the waves.
Some examples are Propita & vellela vellela
-Class Syphonophora is one of the most lethal among cnidaria
-Hydrocorals (אלמוגי אש): They belong to the hydrocorals and not the אלמוגי אבן. When looked at with a microscope they have polyps
