Answer: Tube within a tube of body plan is found in the phylum Nematoda. Explanation: Nematodes have a smooth, elongated and cylindrical body structure which is packed in a tough, elastic covering called cuticle.
Option (d) Porifera- they show aggregate plan i.e. they consist of clusters of cells. Aschelminthes are also called Nementhelminthes – means roundworms. Their body cavity is known as pseudocoelomate. A digestive canal is present in the body cavity for this reason it is known as tube-within-a-tube body plan.
Annelida includes metamerically segmented animals with true coelom. They may be aquatic (marine and fresh water) or terrestrial. They exhibits concentric 'tube within tube' type body plan.
The blind sac body plan is the body plan where the there is a single opening of the digestive system. The tube-like digestive system starts with a single opening through which the food is taken inside and the digested food is expelled through the same opening.
Sycon (Scypha) is a sponge and does not perform locomotion. It is a genus of calcareous sponges belonging to family- Scyettidae, Class-Calcaronea and phylum- Porifera.
Hint:The cell aggregate plan is a type of body plan in which the body has cluster or aggregation of cells which are not organized into tissues or organs. In the blind sac plan, the body has a single cavity which functions as digestive tract and coelom both.
Segmentation is the serial repetition of similar organs, tissues, cell types or body cavities along the anterior-posterior (A-P) axis of bilaterally symmetric animals (bilaterians). You, like other vertebrates, are segmented — consider the skeleton, musculature and nervous system of your trunk.
The body plan of the flatworm is bilateral, with a head that leads—a plan that continues in most animals living today. The structure of this bilateral plan is ideal for an active hunter. Flatworms are the first animals to transmit signals from sensory receptors along nerve cells to the brain.
The life cycle of a plant-parasitic nematode has six stages: egg, four juvenile stages and adult. Male and female nematodes occur in most species, but reproduction without males is common, and some species are hermaphroditic (Afemales@ produce both sperm and eggs). Egg production by the individual completes the cycle.
Roundworms do not breathe in the sense that vertebrates, such as humans and other mammals, do. Instead, roundworms (also known as nematodes) obtain the oxygen their bodies need through diffusion, a process of gas exchange commonly used among flatworms and earthworms as well.
Free- living nematodes are very important in maintaining the soil bio-dynamic system, especially in soil with low organic matter content, whereas PPNs feed on plants and reduce crop growth and yield efficiency.
CO2 levels increase inside the nematode's body before diffusing to lower CO2 concentration levels on the outside of the body. This process means that nematodes don't need blood vessels or lungs; they can allow natural concentration gradients to exchange gasses for them.
Excretory systemIn many marine nematodes, one or two unicellular 'renette glands' excrete salt through a pore on the underside of the animal, close to the pharynx. In most other nematodes, these specialized cells have been replaced by an organ consisting of two parallel ducts connected by a single transverse duct.
While the nervous system of these animals is less centralized, associative learning still occurs. Snails, flatworms, and nematodes are examples of organisms with a lesser degree of cephalization.
The epidermis (skin) of a nematode is highly unusual; it is not composed of cells like other animals, but instead is a mass of cellular material and nuclei without separate membranes. This epidermis secretes a thick outer cuticle which is both tough and flexible.
Furthermore, the nematodes, or roundworms, possess a pseudocoelom and consist of both free-living and parasitic forms.
The pseudocoelomates include the nematodes, rotifers, gastrotrichs, and introverts. Some members of some other phyla are also, strictly speaking, pseudocoelomate. These four phyla of tiny body size (many species no larger than the bigger protozoans) are placed together in part because they…
