Topic 2: Cnidaria Flashcards
מערכת הצורבים (57 cards)
1
Q
Radiata
A
Ancient invertebrates with radial symmetry. Phylum Cnidaria (צורבים) + Phylum Ctenophora (מסרקניות)
2
Q
Symmetry in Cnidaria
A
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)
3
Q
Ctenophora (מסרקניות)
A
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)
4
Q
Body layers
A
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)
5
Q
Invagination & Blastopore
A
- 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)
6
Q
Embrionic Development
A
- 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.
7
Q
- Importance of Epithelium/Epithelial cells
A
-separates body compartments of different chemical composition
-Once regulated independently, each body compartment could adopt one or more specialized functions
8
Q
Mezoglea
A
Intermediate layer in between the Endoderm and the Ectoderm, it has either no cells or very few of them.
9
Q
- Main Characteristics of Epithelium/Epithelial cells
A
- 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
10
Q
Internal and external Epithelia
A
External Epithelium: Epidermis, formed from the embrionic ectoderm
Internal Epithelium: Gastrodermis (מערכת עיכול), formed from the embrionic endoderm
11
Q
Importance of the gatro-vascular cavity
A
(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).
12
Q
Gastro-vascular cavity
A
Cavity surrounded by a layer of endoderm
13
Q
Classes inside Cnidaria
A
- Anthozoa + Medusozoa (
- Staurozoa,
- Scyphozoa,
- Cubozoa,
- Hydrozoa)
**there is some controversy about the phylogenetic classifications
14
Q
Characteristics of Cnidaria
A
(*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)
15
Q
Cnidocytes
A
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
16
Q
- Mechanism
A
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
17
Q
- Function of Cnidocytes
A
- paralysation and prey capture
- helps bringing the pray (depending on size) into the חלל העיכול
- defense from predators.
- Different types: Nematocyst, spirocysts & ptychocysts
18
Q
Characteristics of Class Hydrozoa
A
- 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
19
Q
Obelia life cycle
A
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.
20
Q
Hydroid Colony
A
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)
21
Q
Hydromedusa Body Structure
A
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
21
Q
Special hydrozoan orders (סידרה בהידרתיים)
A
- 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
22
Q
Summary of Hydrozoa (הידרתיים)
A
- there are two life forms: polyps or medusas or both (for example in the life cycle of Obelia the sexual stage is the medusa that releases the gametes)
- The mezoglea constitutes most of the volume of the organism. It doesn’t have cells.
- The cnidocytes are only in the epidermis
- The gametes develop only in the epidermis
- In order to create a colony the organism employs asexual reproduction
- There is polymorphism in the colony (gastrozooid for nutrition, gametozooid for reproduction and dactylozooid for defenses)
- The muscle system developed the best around the edges of the bell and is responsible for movement strokes
- The vellum increases the jet of water that comes out of the medusa and helps the movement
- They have some species that זוחלים בקרקע
- Nervous system a bit more developed than that of the polyp but still simple
- The edge of the bell contains a light-sensitive ocelli and a statocyst - (a small sensory organ of balance and orientation in some aquatic invertebrates, consisting of a sensory vesicle or cell)
- Special orders (סדרות): Syphonophora (למשל: ספינת קרב פורטוגזית) & Hydrocorals (אלמוגי אש)
24
Q
Symmetry in Cnidaria
A
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)
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Directional movement.
Jet propulsion in Scyphozoa
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Class Scyphozoa - Characteristics
| מדוזות הסוכך= canopy medusas
- There are about 200 species
- They range in size, from small to really big (they're bigger than the medusas in hydrozoa)
CHARACTERISTICS:
- The dominant life form/stage is the sexual one of the medusa. Most of the species that belong to this class have also a polyp phase but it is mostly very small and doesn't move)
1. Velum is absent
2. Manubrium (mouth) opens out into oral arms (it's not a tubular opening like in hydrozoans)
3. Thick mesoglea, contains ameboid cells originating from the epidermis (unlike the hydrozoans that don't have any cells in the mesoglea)
4. Gastric pouches (אונות קיבה) - the gastro-vascular cavity is divided into 4 sacs
5. The cnidocytes are in both in the epidermis and the gastrodermis- when they catch a prey the cnidocytes (תאים הצורבים) help her paralize it and get it closer to the mout...
6. The gametes are in the gastrodermis as well (in hydrozoans the gametes are mainly epidermic)
7. Rhopalium (a club-shaped, marginal sensory organ) is located in the rim of the bell, the rim is not really round, it has a twist inwards (כניסות) and that's where the rhopalium is located. It contains ocelli (can differentiate between light and darkness) and statocyst (gives a sense of location in the sense of gravitation).
8. Strobilation (הנצה של מדוזות קטנות - אפירות) - Strobilation or transverse fission is a form of asexual reproduction consisting of the spontaneous transverse segmentation of the body.
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Life cycle of Aurelia (Class Scyphozoa)
The medusa is the dominant life form (שלב הדומיננתי).
- > The medusa releases the sex cells
- > a zygote is formed when the זרע & ביצית meet (develops in arms of female) into a ciliated larva (planula) (לארבה בעל ריסים)
- > the planula settles
- > the planula turns into a polyp (named scyphistoma)
- > the scyphistoma buds into medusas called early strobila
- > a strobila is formed, which is able to
- > release a lot of small medusas called Ephyra (strobilation) (בגוף המים)
- > Normal sized medusas
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Strobilation
Strobilation (הנצה של מדוזות קטנות - אפירות) - Strobilation or transverse fission is a form of asexual reproduction consisting of the spontaneous transverse segmentation of the body.
During this process, each segmentation ("צלחות") that gets formed gets released into the water, and from it a medusa is formed. They're able to form up to 10 medusas and some species are even able to form (יכולים להנץ) another strobila.
Impressibe יכולת רבייה א-מינית
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Why is it impossible to get rid of the Rhopilema nomadica - חוטית הנודדת
They're a problem because they get stuck in the filters of the power plants that use water for cooling and result in them not being able to produce electricity.
-The reason is the Scyphistoma stage in the life cycle, even if they were to fish all the medusas, the scyphistoma is anchored to the soil or to other animals?? and therefor will keep releasing more medusas...
30
Cassiopea Andromeda (Species inside class Scyphozoa, inside Phylum Cnidaria)
They live in symbiosis with algae (אצות שיתופיות שעושות סימביוזה). Usually brown (color because they have the algae inside the gastrodermis). Usually the Cassiopea swims upside down, the algae sits on the tentacles, next to the mouth, so the Cassiopea flips so the algae can get sunlight.
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Table of comparison between Hydrozoans and Scyphozoans (Hydromedusae מחלקת ההידרתיים & Scyphomedusae מחלקת מדוזות הסוכך)
Scyphomedusae Hydromedusae
כ-3500 מינים כ-200 מינים
2 צורות חיים- מדוזה ופוליפ. השלב הדומיננטי במחזור החיים הוא המדוזה. יש שלב של פוליפ למרבית המינים אך לרוב הוא קטן מאד
יש וולום אין וולום
מזוגליאה לא מכילה תאים אלא סיבים אלסטיים מזוגליאה מכילה תאים אמבואידים מהאפידרמיס
קנידוציטים נמצאים רק באפידרמיס (לא בגסטרודרמיס) קנידוציטים נמצאים באפידרמיס ובגסטרודרמיס
גמטות נמצאות באפידרמיס גמטות נמצאות בגסטרודרמיס
בע"ח מושבתיים- מושבה נוצרת בעזרת רבייה א-מינית ויש בה פולימורפיזם. השלב הדומיננטי הוא השלב המיני של המדוזה, אין מושבות
הפרייה מתבצעת בשלב המיני בגוף המים הפרייה מתבצעת בשלב המיני בגוף המים
הלארבה נקראת פלנולה והיא בעלת ריסים הלארבה נקראת פלנולה והיא בעלת ריסים
ו-statocyst בעלי עינית שמבדילה בין אור לחושך -statocyst בעלי עינית שמבדילה בין אור לחושך
מדוזות קטנות יותר מדוזות גדולות יותר
פה (מנובריום) בצורת צינור פה (מנובריום) מתפצל לזרועות פה oral arms
ללא אונות קיבה בעלי אונות קיבה
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Movement in medusas - Jet propulsion
**Medusas are considered as plankton (all organisms that cannot oppose to the water current)
Jet propulsion:
- How? Through release of water pressure in one direction, the medusa gets pushed in the opposite direction.
- Where to? There are nerve connections to the Rhopalum that syncronize the Rhopalum to the "jet propulsion" (it's not a nervous system)
- What for? They try to swim towards other medusas for reproductive purposes.
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Class Staurozoa (מחלקת סטרוזואה ) - Characteristics
- There are only about 50 species known (most likely because biologists have a hard time investigating them)
- The gastro-vascular cavity is a long tube
- The edge of the polyp spreads out to 8 mail זרועות that spread out themselves into many tiny זרועות (tentacles) that contain the cnidocytes (תאי צורבים)
- Planula larva with no ריסים (different from Hydrozoans and Scyphozoans - הידרתיים ומדוזות הסוכך)
- They don't have a medusa stage in their life cycle
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Class Staurozoa (מחלקת סטרוזואה ) - Life Cycle
- > The planula larva settles,
- > releases gametes into the גוף המים
- > The gametes meet up to form a zygote
- > a planula larva is formed
* **THERE IS NO MEDUSA STAGE!!
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מחלקת מדוזות קופסא Class Cubozoa
- Medusa stage is the dominant one
- Small and squared shape (מדוזות קטנות ריבועיות )
- Only about 40 species are known
- The life cycle is not really known (only from one species)
- They have tentacles in each one of the "corners" - 4 tentacles
- In the tentacles they have many cnidocytes - highly toxic, can cause death, found mainly in Australia and Thailand
- They have rhopalium and ocelli (differentiation between light and darkness)
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Summary of Cnidaria (part A)
- All the species in the Phylum (מערכת) have two layers (דו-שכבתיים) - endoderm and ectoderm
- They all feed from טריפה
- They have two life forms: polyp attached to the soil and medusa in the water
- Life cycle: asexual and sexual phases
- Cnidocytes
- Ecology: מינים פולשים - they have a very strong impact in the zooplankton: they prey upon other plankton and leave no food for the rest, including fish (ניזונים מזואופלנקטון). Since they eat fish they also affect humans. They are no predators that hunt them, and since there is no problem with obtaining the food, they thrive (משגשגות). When there is a predator or a disease they disappear.
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מחלקת אלמוגאים Class Anthozoa
It's divided into two sub-clases:
1. Hexacorallia (ששאים) - solitary polyps or in colonies (מושבתיים) with 6 or more tentacles (לרוב מחזורים של 12)?. The tentacles are rarely feathered (זרועות מנוצות)
2. Octocorallia (שמונאים) (אלמוגים רכים) - have 8 "feathered" tentacles. With 8 partitions (מחיצות). Polyps are joined together? with the help of the oenenchyma
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מחלקת אלמוגאים Class Anthozoa - examples of organisms
שושנות ים, אלמוגי אבן, אלמוגים רכים
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General Characteristics of Anthozoans
- They only have the polyp stage in the life cycle (no medusa life form)
- The body wall is around the mouth opening is מקופל inwards and creates a pharynx (צווארון פנימי, לוע) that leads into the חלל המעי
- The חלל המעי is divided into several pouches (מחולק ע"י מחיצות) - each order has a different amount of pouches.
- The mesoglea has cells that migrated to it from the epidermis or the gastrodermis
- They also have תאים צורבים in the gastrodermis
- The gonads have gastrodermal origin (contrary to the Hydrozoans whose gonads have epidermal origin)
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Sub-class Octocorallia - תת מחלקה שמונאים Octocorallia (אלמוגים רכים) - Characteristics
- They have exactly 8 "feathered" tentacles (זרועות מנוצות), they're soft corals (אלמוג רך)
- 8 internal partitions inside the polyp (מחיצות פנימיות בפוליפ)
- usually in colonies: each polyp in a colony it's not an organism by it self, more like a part, of the colony that is the whole, the colony is an organism, where all the polyps have the same genetic information (מטע גנטי)
- They're predators: if one polyp ate a prey and digested it, then the תוצרים go to the rest of the polyps in the colony, cause there is connectivity (קישוריות)
- צננכימה Coenenchyme
- Axial Rod
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צננכימה Coenenchyme (Sub-class Octocorallia in Class Anthozoan, Phylum Cnidaria)
- The connective tissue that connects the polyps is called צננכימה Coenenchyme - mass of mesoglea that contains the shared gastro-vascular cavity.
- It contains ameboid cells and also cells that secrete "skeleton needles" (מחטי שלד) - which gives structural stability to the colony and protects it from predators.
- The cells that secrete the מחטי שלד have ectodermal origin, and migrated from there into the צננכימה.
- When the organism dies and the organic material rots (נרקב), the needles remain. (The needles do not create a skeleton like in the אלמוגי אבן cause they're in a gelatinous medium)
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Axial Rod (Anthozoans)
Group of skeleton needles (צבר מחטי שלד) that give structural stability to the אלמוג רך.
- It's a very common element in אלמוגים רכים, characteristic pricipally of (גורגוניות (מניפות ים - they're in places with very strong water current, so the stability that the skeleton needles provide is what helps them in such conditions...
- In גורגוניות the Axial Rod is made of an organic material called Gorgonin, a type of collagen, usually ספוג in Calcium Carbonate.
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Examples of Soft Corals (אלמוגים רכים)
- גורגוניות: from the Caribbean
- נוצות ים (sea pen): looks like a feather, yellow, it's a Octocorallia, the 8 feathered tentacles can only be seen with augmentation. It can generate physical lights in the darkness.
- אוגבית אדומה Tubipora musica: it's out of the ordinary, when it dies it leaves a hard skeleton (גירני - chalk) even though it's not an אלמוג אבן, it has a particular color, redish,
- Heliopora: also out of the ordinary, also leaves a hard skeleton after dying, from chalk, blue color.
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Sub-Class Hexacorallia - תת מחלקה ששאים
| Order Actinaria - סדרת שושנות ים
- There is only polypoid life form, no medusoid stage
- No skeleton
- Asexual and sexual reproduction
- Solitary - doesn't form colonies
- They have a pharynx ((פארינקס (לוע) that goes to the חלל המעי.
- Pedal disk (the part that attaches to the soil)
- Acontia - organ exclusive to the שושנות ים that helps with digestion (looks like חוטים)
- Siphonoglyph - groove that allows for water flow
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Siphonoglyph
מין שושנות ים
תת מחלקה ששאים - Hexacorallia
מחלקת אלמוגים - Anthozoa
מערכת הצורבים - Cnidaria
- It's a small groove (hendidura, ranura) that extends into the pharynx and is used to create currents of water into the pharynx.
- Importance: These water currents are important for respiration and maintenance of internal pressure. Even when the שושנות ים is closed allows for water to go into and out of the חלל המעי, and also is important for opening back up, the skeleton is hydrostatic (מבוסס נוזל) so if it contracted very hard to take the water out, now it need water to opening back up.
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Acontium
מין שושנות ים
תת מחלקה ששאים - Hexacorallia
מחלקת אלמוגים - Anthozoa
מערכת הצורבים - Cnidaria
- Thread that stretches inside the חלל המעי
- Full of תאים צורבים
- Helps with digestion and paralysation of the prey (שיתוק הטרף)
- It originates from one of the partitions of the main pouch in the חלל המעי and extends from there
- When the שושנת ים feels a threat (איום) it contracts and closes up and the Acontia threads go out
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Reproduction in שושנות ים
מין שושנות ים
תת מחלקה ששאים - Hexacorallia
מחלקת אלמוגים - Anthozoa
מערכת הצורבים - Cnidaria
The שושנות ים can reproduce asexually:
- Pedal laceration: they can leave a piece behind and from it a new שושונת ים will grow (this is indicative of a very simple organism)
- Fission (ביקוע): It can grow a lot and divide into two pieces.
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Movement in שושנות ים
מין שושנות ים
תת מחלקה ששאים - Hexacorallia
מחלקת אלמוגים - Anthozoa
מערכת הצורבים - Cnidaria
These are organisms that are attached to the soil (צמודי מצע), where the planula larva settles, that's where they stay for the rest of their lives, but nonetheless they have יכולת תנוע: if they feel a כוכב ים (predator - טורף) getting close, they can escape
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Characteristics
Sub-Class Hexacorallia - תת מחלקה ששאים
Order Scleractinia - סדרת אלמוגי אבן
- Only polypoid life form, no medusoid stage
- Can reproduce sexually and asexually
- They can form colonies or live in solitary form (one lone אלמוג אבן that can get to be very big)
- Life cycle: they release the gametes and a planula is formed from the zygote, it settles and a polyp grows from it.
- The outer skeleton is secreted from the Ectoderm (they don't have an internal skeleton) - the live tissue (the polyp) נמצאת על גבי השלד החיצוני??
- Some are hermaphrodites (both sexes); some are נפרדי זיווג and some are dioecious (they switch their sex depending on environmental conditions) - very flexible
- The tentacles and also the partitions are 6 or multiples of 6 in accordance to the sub-Class Hexacorallia ( הזרועות וגם המחיצות הן 6 או כפולות של 6)
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Reproduction in אלמוגי אבן
סדרת אלמוגי אבן - Scleractinia
תת מחלקה ששאים - Hexacorallia
מחלקת אלמוגים - Anthozoa
מערכת הצורבים - Cnidaria
The אלמוג אבן divides into 2:
Brooding - Corals with internal fertilization: the male gametes released into the water reach a female colony, there's internal fertilization, they incubate the embryo inside, release a planula larva
Spawning - Corals with external fertilization: both male and female gametes are released into the water, where the planula grows. There are ways in which these organisms try and increase the efficiency of the fertilization process given that open sea is very big and they need to increase the chances of the gametes finding each other: Scheduled reproduction (רבייה מתוזמנת) if all the corals do it together the chance of success increases. Also, each species has a timing of their own.
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Life Cycle in אלמוגי אבן
סדרת אלמוגי אבן - Scleractinia
תת מחלקה ששאים - Hexacorallia
מחלקת אלמוגים - Anthozoa
מערכת הצורבים - Cnidaria
- > male and female gametes are released into the water
- > fertilization occurs
- > Development of the planula
- > The planula settles and turns into a polyp
- > The polyp reproduces asexually to form other polyps that form colonies
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Some out of the ordinary examples of אלמוגי אבן
- Corallimorpharia- אלמוגים שרוכשים לאקווריומים בגלל יופיים והצבעים הפלורסנטיים שלהם. זוהי סדרה שקרובה מאד לשושנות ים.
- Cerianthus- דמוי שושנת ים, חי קבור בסלע ויש לו נרתיק מחול.
- Zoanthids- פוליפים מושביים כמו שושנות אך הם לא משקיעים שלד גירני.
- אלמוגים שחורים
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Symbiosis between corals (אלמוגים רכים, אלמוגי אבן, שושנות ים) and algae (אצות)
Corals are predatory organisms that have symbiotic unicellular algae (זואוקסנטלות) inside their gastrodermis.
Zooxanthellae (זואוקסנטלות) - symbiotic algae that provide photosynthetic byproducts like sugars and amino acids to the corals in exchange for a place to live and some nutrients (phosphorous and nitrogen - זרחן וחנקן)
* *Usually coral reefs are in places with low concentration of phosphorous and nitrogen (שוניות האלמוגים נמצאות במקומות מאד דלים בזרחן וחנקן)
* *(generally in shallow water (במים רדודים ) for getting the sun, also the tissue of the coral is kind of transparent and allows the penetration of the sun rays)
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Coral Bleaching (הלבנה)
Phenomenon in which the symbiotic algae leave the corals, and therefore they don't get the sugars anymore, causing them to lose coloration (hence the name of bleaching)
- Reduction in lipid and protein contents
- Slow regeneration and growth
- Unable to reproduce
- They can even die if the situation persists for too long
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Conditions for the formation and existence of Coral Reefs (שונות אלמוגים)
There are corals in all parts and climates of the world but they only form Coral reefs if they have the right conditions:
- Sun light
- Water not too deep and transparent for the sun rays to reach the algae in the חלל המעי
- Warm temperature (more than 18 degrees)
- מליחות between 32-40
**תנאים אלה מגבילים את טווח שוניות האלמוגים בין קווי הרוחב 30- ו30
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Danger of extinction of Coral Reefs
- Bleaching
- Diseases of corals (black band, cancerous tumors...)
- Destruction by tourism
- Use of corals for building (because they're made of chalk (גיר)
- Eutrophication: excessive richness of nutrients in a body of water, frequently due to runoff from the land, which causes a dense growth of plant life (non-symbiotic algae) and death of animal life from lack of oxygen - causes a burst of predators, or lack of nutrients and the symbiotic algae leave the corals
- Acidification of the ocean: ongoing decrease in the pH of the Earth's oceans, caused by the uptake of carbon dioxide (CO2) from the atmosphere. Seawater is slightly basic (meaning pH > 7), and the process in question is a shift towards pH-neutral conditions rather than a transition to acidic conditions (pH < 7). (In this conditions the corals and other organisms have problems creating the skeleton, which is essential for growth and survival)
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Summary of Class Anthozoa - מחלקת האלמוגים
- All the members of Class Anthozoa have only polypoid life form, no medusoid stage
- They are more specialized than Hydrozoans (they can secrete more complex compounds, their breeding ability is more successful; Hydrozoans are considered to be more ancient)
- Most of the corals are מושבתיים with some exceptions like שושנות ים & אלמוגי אבן, where they're one big polyp.
- Larva planula
