Q.Describe the general characters of class Arachnida.

Cockroaches see through compound eyes built of many ommatidia, and the combined partial images from each ommatidium form a mosaic picture of the surroundings.

A cockroach's compound eye is composed of a large number of tightly packed visual units called ommatidia, each with its own lens, crystalline cone, and set of light-sensitive (photoreceptor) cells. Each ommatidium samples light from a very narrow angle of the visual field and sends its own small, separate image fragment to the brain. The brain assembles all these tiny fragments together, much like tiles in a mosaic, into one composite picture of the surroundings. This type of vision is called mosaic vision. It is not especially sharp …

Arthropoda is the largest phylum of the Animal Kingdom, mainly because of the enormous diversity and number of insect species it contains.

Among the given options:

• Chordata includes animals with a notochord (fish to mammals) — a large but comparatively much smaller phylum.
• Arthropoda includes insects, crustaceans, arachnids and myriapods — jointed-legged animals with a chitinous exoskeleton.
• Annelida includes segmented worms like earthworm and leech.
• Echinodermata includes spiny-skinned marine animals like starfish and sea urchin. …

A cockroach can live for roughly a week without its head because it does not breathe through its head, and its nerve ganglia are distributed along its body rather than centralised solely in the head.

Unlike vertebrates, an insect such as a cockroach does not rely on its head for breathing — it takes in oxygen through small openings called spiracles located along the sides of its thorax and abdomen, connected to a network of tracheae that deliver oxygen directly to tissues, bypassing the need for lungs or a head-based respiratory centre. Its nervous system is also organised as a chain of ganglia (a 'ladder-like' nerve cord) running along the ventral side of the body, with each segment's ganglion able to control basic reflexes for that segment fairly independently of the brain.

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Arthropoda matches with Malpighian tubules, their excretory organ.

Phylum Arthropoda is the largest animal phylum, characterised by a chitinous exoskeleton, jointed appendages, and an open (haemocoelic) circulatory system. Excretion in most terrestrial arthropods (like insects) occurs through thin, finger-like structures called Malpighian tubules that open into the gut and …

Periplaneta (the cockroach) is classified under Phylum Arthropoda (jointed appendages, chitinous exoskeleton) and Class Insecta (three body regions, three pairs of legs, usually winged).

Periplaneta (the common cockroach) possesses a hard chitinous exoskeleton, a segmented body, and jointed appendages — the defining features of Phylum Arthropoda. Within this phylum, it belongs to Class Insecta, characterised by a body divisible into head, thorax and abd …

Phylum Arthropoda is characterised by a hard, chitinous exoskeleton (cuticle) covering the body, which is periodically shed and replaced as the animal grows.

Arthropoda (from Greek 'arthron' = jointed, 'podos' = foot/leg) is the largest phylum in the animal kingdom, including insects, crustaceans, arachnids, and myriapods. A defining feature of this phylum is a tough, non-living external covering — the exoskeleton or cuticle — secreted by the underlying epidermis. This cuticle is composed mainly of chitin, a nitrogen-containing polysaccharide, often hardened further by proteins and, in crustaceans, by calcium salts. Because this exoskeleton is rigid and cannot grow with the animal, arthropods must periodically shed it and form a new, larger one in a process called ecdysis or moulting. By contrast, Annelida (segmented worms like earthworms) have a soft, moist cuticle without chitin and no jointed appendages; Echinodermata (starfish, sea urchins) have an interna …

Mosaic vision arises from compound eyes, a hallmark of arthropods like the cockroach.

A compound eye is made of numerous ommatidia (visual units), each of which captures a small part of the visual field. The brain assembles these many partial images into one composite 'mosaic' image, which is especially good at detecting motion.

• (a) Cockroach — has compound eyes → mosaic vision. Correct. …

'Haemocoel' matches 'Cockroach' — arthropods like the cockroach have an open circulatory system in which blood fills a body cavity called the haemocoel.

In animals with a closed circulatory system (e.g., annelids, vertebrates), blood remains confined within blood vessels throughout the circuit. In contrast, arthropods such as the cockroach have an open circulatory system: blood (haemolymph) is pumped by a dorsal tubular heart into large, unenclosed body spaces called the haemocoel, where it directly bathes the internal organs and tissues before draining back toward the heart …

Arthropods (e.g. cockroach, other insects) excrete nitrogenous waste through Malpighian tubules, thread-like structures that empty into the alimentary canal.

Malpighian tubules are numerous fine, blind-ending, thread-like tubules that arise at the junction of the midgut and hindgut and lie free in the body cavity, bathed in haemolymph.

• They absorb nitrogenous wastes (mainly uric acid) and other solutes directly from the surrounding haemolymph.
• The wastes are converted into and concentrated as semi-solid uric acid, which is passed into the hindgut and eliminated along with faecal matter through the anus. …