Diversity in Living Organisms

Polychaetes are generally dioecious (separate sexes), whereas leeches, flatworms, and earthworms are typically hermaphroditic.

Lumbricus is a genus of earthworm, which belongs to the class Oligochaeta, not Polychaeta. Polychaetes are typically marine worms.

Pontobdella is segmented worm under the phylum Annelida. It is a marine leech which is ectoparasite on elasmobranchs and is commonly called as 'skate sucker'.
Therefore, the correct answer is option B.

Nephridia is an organ involved in the excretory system. It is the characteristic feature of leech. Their bodies are much more solid as the spaces in their coelom are dense with connective tissues. In leeches, the botryoidal tissue is composed of two different cell types. The granular botryoidal cells and flattened endothelial-like cells which contains a brown pigment and may serve an excretory function. Leeches use a combination of mucus and suction to stay attached and secrete an anticoagulant enzyme known as hirudin into the host's blood streams. 

Chaetopterus, commonly known as paddle worm from class Polychaeta. It is worldwide in distribution. It feeds on small organisms, true filter feeders. The body is divided into an anterior region, middle region and a posterior region. Parapodia have modified accordingly to their function. They are modified into pumping fans, sucking discs and food ball organs and asexual reproduction by transverse fission. So, the correct answer is option B.

Acanthobdella forms a connecting link between Oligochaeta and Hirudinea. It is mostly parasitic on fins of salmon fishes. Body comprises of thirty segments only. Its body cavity is spacious and completely divided by septa, vascular system is composed of dorsal and ventral vessel. Hence, option B is correct.

Hirudinaria is an Indian cattle leech. This is the fresh water species. It is cosmopolitan. It feeds on the blood of frog, animals and men. 

The tube-within-a-tube body plan refers to an organism having a digestive tract with two openings (mouth and anus), which is characteristic of annelids like earthworms.

Trochophore, also called trochosphere, small, translucent, free-swimming larva characteristic of marine annelids and most groups of mollusks. Trochophores are spherical or pear-shaped and are girdled by a ring of cilia (minute hairlike structures), the prototroch, that enables them to swim.  Each segment bears a pair of paddle-like and highly vascularized parapodia, which are used for movement and, in many species, act as the worm's primary respiratory surfaces. Bundles of bristles, called setae, the project from the parapodia.

When birds flap their wings the density of the air decreases nearby since the air particles move apart. This less dense air rises and helps the bird to keep flying. The denser air replaces this space. This movement is known as convection current of air. 

A-  Coacervate can be defined as an aggregate of macromolecules such as proteins, lipids, nucleic acid often surrounded by the cell membranes and forms a stable colloid with properties that resemble living matter. According to Russian biochemist Aleksandr Oparin in the hot primitive seas, organic molecules would gather in small drops, similar to the actual cells. These small drops bunddled up in water molecules are called “coacervates”. 

Panspermia is the theory that life exists throughout the Universe, distributed by space dust, meteoroids, asteroids, or comets, often referred to as 'life spores'.

Mitochondria and Chloroplasts are the only cell organelles other than nucleus coated with double membrane. They have their own DNA and protein synthesizing machinery as well. One explanation for a cell organelle to have its own DNA is that these organelles were separate organisms. The chloroplast was an autotrophic cyanobacteria and the mitochondria was a separate heterotrophic organism which later on became lodged into a eukaryotic cell as endosymbionts.