Topic 3: Worms (תולעים) Flashcards
(15 cards)
The three main Phylums in Worms (מערכות עקריות בתולעים)
- Phylum Platyhelminthes (תולעים שטוחות = flat)
- Phylum Nematoda (תולעים עגולות = round)
- Phylum Annelida (תולעים פרוקות = segmented)
Definition of worm
- *Is not a taxonomic definition, just refers to a body type:
- invertebrates
- crawls on the ground
- long and narrow
- soft bodies
- no limbs (חסר גפיים)
Increase in complexity (From Cnidaria to Worms)
- First organisms in evolution to move with intent and hunt
- The morphology complexity is superior to those in Phylum Cnidaria, their body morphology (triplobastic with bilateral symmetry) is the basis for other animals with higher complexity.
- Ability to move
- Directionality (directionality is created in the body because there is a certain directionality in which it begins to move relative to the environment.)
- Cephalization (sensory organs in the front)
**early in evolution there is a common feature of all systems except sponges and is the creation of a blastula. Then split into diploblasts - (two embryonic layers from which the entire body develops). Then another split into bilateral triploblasts - (3 embryonic layers with bilateral symmetry).
Triploblasts
- Body derived from three embryonic cell layers (ectoderm, mesoderm, and endoderm) (in all multicellular animals except sponges (ספוגים) and coelenterates (Cnidaria - צורבים).
- Blastula -> Gastrulation (invagination forms endoderm and ectoderm) -> embryonic development continues, cells from the endoderm move into the blastocell cavity and form a third cell layer, the mesoderm (meso = middle).
- *Brings an advantage because the mesoderm turns genitalia and other tissues - The creation of the new layer and the filling of the blastocoel (בלסטוצל) in the tissues, enabled abilities that did not exist before - improved mobility abilities and increased body complexity.
Bilateral Symmetry
Symmetry axis when the organism is cut in the middle -Right side of the body is a mirror image of the left side
**Sponges have no symmetry, Cnidaria has radial symmetry (makes sense because gametes and nutrients or preys come in the water from any direction so it’s convenient to be round).
Planaria
- model organism of flat worms (Platyhelminthes) - grows in fresh water, has a head and eyes, can move the head to the right and the left and can move the body forward
- *Lower part (צמוד למצע) (ciliated) is different from upper part (in contact with water), front part (with ocelli) different from posterior part, left side same as right side
Cephalization
Concentration of the sensory organs in the anterior portion of the body
Cell types that each layer contributes to in Triploblasts
Ectoderm - mainly outer part of the body - cover cells, sensory and nerve cells, cells that line the front and back of the digestive system.
Endoderm - cells that pad most of the digestive tract and glands and digestive organs.
Mesodermic (important), genitalia and other tissues.
Influence of the addition of the Mesoderm in development/evolution
- > Mesoderm -> Development of muscles
- > Movement -> Cephalization & -> Development of the Nervous System
- > Increase in body mass -> Development of Transport, Respiration and Excretion systems
organ systems in planaria
digestion, nerves, reproduction, filtration and secretion
**Flat worms have an increase in body complexity. Beyond tissues with specific functions, the body contains organs and organ systems that function together (digestion, nerves, reproduction, filtration and secretion) as a result of the development of movement and the appearance of the mesoderm.
structure of a planaria.
A-Reproduction and Osmoregulation systems.
B - Digestive tube and nervous system.
C - pharynx continuing from the ventral mouth (abdominal).
Body-structure types in Triploblastic Organisms
1- Acoelomate (אצלומטים) - (חסרי חלל צלום): Flat worms (תולעים שטוחות) - don’t have a secondary body cavity (other than the חלל המעי)
2- Pseudocoelomate (בעלי חלל צלום מדומה) - (פסאודוצלומטים: Nematodes (תולעים עגולות) - it has sort of a secondary cavity, it’s full of liquid but not surrounded by a membrane
3- Coelomate (צלומטים) - עם חלל צלום) - Annelida (תולעים פרוקות), Mollusks (רכיכות), Arthropods (פרקי רגליים), Echinoderms (קווצי עור) & Chordata (מתרנים) - There is a secondary body cavity, between the outside part of the body and gastric cavity
Coelom - צלום
the body cavity in metazoans (except sponges and cnidaria), located between the intestinal canal and the body wall.
*The original function of the coelom was movement but with evolution it added other functions
Protostomia vs. Deuterostomia
Protostomia:
- The mouth of the Protostomia (proto, “first”; stoma, “mouth”) develops from the first opening into the embryonic gut (blastopore). The coelom (body cavity) forms from a split in the embryonic mesoderm (middle tissue).
- annelid worms, arthropods and mollusks
Deuterostomia:
- The mouth of deuterostomes develops from an opening into the embryonic gut other than the blastopore, which develops into the anus. The coelom (a fluid-filled body cavity lined with mesoderm) develops from buds off the embryonic gut.
- Echinodermata, Chordata…?
Phylum Platyhelminthes (תולעים שטוחות) - Characteristics
- Mainly aquatic, very few species in mainland with humidity
- Some free (חופשיים), some parasites (פולטים)
- Gastrovascular cavity (extracellular digestion) with one single opening (פתח), the mouth.
- Breathing (taking O2 and releasing CO2) through diffusion.
New:
- Bilateral symmetry
- Triploblasts acoelamates
- Cephalization - defined head + central nervous system
- Organ systems (specially developed reproductive system)
- System of filtration and excretion (mainly osmoregulation)
Main Classes in the Phylum Platyhelminthes - מחלקות עקריות במערכת תולעים שטוחות
1 free & 3 parasitic (Neodermata)
- Turbellaria (תולעי ריסים) - free (חופשיות), planaria for example
- Trematoda (עלקות) - internal parasites of animals
- Monogenea (עלקות חד-פונדקאיות) - external parasites of animals
- Cestoda (שרשורים) - parasites of the digestive system of animals
