Locomotory system in invertebrtes

This is a small presentation regarding locomotory organs in invertebrates.

1. T Name:-Umangi Thakkar Roll no:-062 Class:-M.Sc.part-2 Topic :-Locomotory system

2. What is locomotion? Locomotion is directional movement that enables someone or something to move from one location to another.The word derives from the Latin words  locō  (place) and  mōtiō  (to move). Animals move for a variety of reasons, such as to find food, a mate, a suitable microhabitat, or to escape predators. ... For many animals, the ability to move is essential for survival and, as a result, natural selection has shaped the locomotion methods and mechanisms used by moving organisms.

3. 1) Pseudopodia Pseudopods also known as pseudopodia (singular noun: pseudopodium ), pseudopods are temporary extensions of the cytoplasm (also referred to as false feet) used for locomotion and feeling They can be found in all sarcodines as well as a number of flagellate protozoa that either exist as  parasites  or as free living organism.   There are four types of pseudopods that include: 1) Lobopodia. 2)Axopodia 3) Filopodia. 4)Reticulopodia/Rhizopoda /

4. Lobopodia Lobopodia refer to the finger-shaped pseudopod and is the most common type observed in nature. They are characterized as short, blunt, and bulbous projections that contain both endoplasm and ectoplasm of the  organism . An example is the lobose amoebae, which is considered the largest of all pseudopodia.

5. Reticulopodia Reticulopodia are also referred to as rhizopodia (or extrathalamous cytoplasm) . reticulopodia are thread-like pseudopodia that branch and fuse to form a network that is extremely dynamic. They can be found in a number of organisms including Endomyxa amoebae and some foraminiferans (an ancient group of protists). In these organisms, reticulopodia are involved in feeding and locomotion .  reticulopodia are composed of microtubules and cytoplasm. microtubules that make up the pseudopods consist of a unique type of tubulin known as Type 2 beta-tubulin. This tubulin forms helical filaments (HFs) which is the basis for the microtubule found in foraminiferan reticulopodia. Reticulopodia play an important role in feeding and locomotion.

6. Filopodia Filopodia are slender actin-based structures that serve sensory and locomotory functions. filopodia are cellular protrusions and thus extend from the cell surface.   Some single-celled organisms such as members of the genus Dictyostelium use filopodia for feeding.  The formation of filopodia starts with the nucleation of actin filaments under the influence of nucleators (a group of proteins). Although two models have been proposed to explain filopodia initiation (induction), the process appears to be triggered by the binding of  GTPase Cdc42 to an essential regulator known as N-WASP .This results in the activation of N-WASP which in turn binds to Profilin and Arp2/3 to form a complex that nucleates the formation of a new pseudopod.

7. Axopodia Axopodia are long and thin protrusions from the cells. However, they are more rigid (and thus appear needle-like ) than filopodia which tends to be more flexible in nature. They can be found on the cell surface of various organisms (e.g. members of the phylum Antinopoda ) where they are involved in feeding and locomotion Some of the main characteristics of Axopodia. Rigid - As such, they are more resistant to bending compared to the other pseudopods Thin and elongated - Needle-like During unfavourable conditions, they can retract (rapid contraction) where the filaments are reabsorbed following the dispersion of fibrils in the axoplasm.

8. Cilia Cilia form a characteristic feature of ciliates but they are also found in the larval stages of Suctoria . In primitive forms (e.g., Opalina , Paramecium etc.) cilia cover the entire body, but in more specialized forms (e.g., Vorticella ) cilia are restricted to certain regions of body only. They are commonly arranged in longitudinal , diagonal or spiral rows. Cilia may be of equal length all over the body or may be longer at definite spots (e.g., cilia of caudal tuft of Paramecium are longer than other body cilia).

9. Functions of cilia Cilia are used for locomotion in isolated cells, such as certain protozoans (e.g.,  Paramecium ) . Motile cilia use their rhythmic undulation to sweep away substances, as in clearing dirt, dust, micro-organisms and mucus, to prevent disease.  Cilia play roles in the cell cycle as well as animal development, such as in the heart. Cilia selectively allow certain proteins to function properly. Cilia also play a role in cellular communication and molecular trafficking. Non-motile cilia serve as sensory apparatus for cells, detecting signals. They play crucial roles in sensory neurons. Non-motile cilia can be found in the kidneys to sense urine flow, as well as in the eyes of the photoreceptors of the retina. They also provide habitats or recruitment areas for symbiotic microbiomes in animals. 

10. Flagella Flagella are extremely fine fibres having a central axoneme made of two longitudinal fibrils, and an enveloping protoplasmic sheath having nine double longitudinal fibrils forming a ring. All 20 fibrils lie in a matrix of dense cytoplasm and they fuse at the base to join a basal granule or kinetosome. flagellum is a thread-like cylindrical or flattened, band-like structure typically consisting of a stiff, elastic axial filament or axoneme, surrounded by a protective contractile outer sheath. The axoneme may be straight or spirally coiled. It consists of nine longitudinal paired peripheral fibres, at equal distance from each other, forming a cylinder and two longitudinal central fibres enclosed by a membranous inner sheath.