Question

3. Discuss the morphological diversity (= disparity) of mollusks. How is their basic body plan modified for different ways of life? 4. What adaptations for feeding, movement, and reproduction do the segmented worms and roundworms have? 5. Explain and contrast hypotheses for the enormous diversity of insects. Recent findings suggest insects are declining all over the world. Why is this a problem? 6. Explain ancestral and derived symmetry in Echinodermata, and how that relates to larval vs. adult symmetry in this phylum. 7. Why are the echinoderms exclusively marine? In other words, what anatomical feature precludes (prevents) them from adapting to freshwater or land? Explain. (Ctrl)

Answer 1

Answer:

3)

About 85000 species of mollusks are discovered.Mollusks are largest marine phylum. Numerous mollusks live in freshwater and terrestrial habitats.

They differ highly in size, habitat, behavior and anatomical structure. Cephalopod mollusks like squid, octopus are most neurologically advanced invertebrates. Giant squid is largest invertebrate. Gastropods( snails and slugs) are most numerous mollusks.

Mollusk has got a tissue that covers the animal called mantle? Involved in shell secretion and respiration. Presence of radula and structure of the nervous system, as 2 or 3 pair of nerve cordsand brain encircling esophagus.

The main body cavity is a hemocoel through which blood circulates. They have eyes and sensors to detect chemicals, vibration and touch.

They have kidney like organs for excretion and external reproduction. All produce eggs.

4)

Segmented worms-

They push pharynx out of its mouth to grasp hold to its food. Then pull food back into its mouth to wet it with saliva.

Each segment has got a circular muscle and longitudinal muscle through out length of body. This two help in movements of segmented worms.

They can reproduce sexually and asexually. Sexual reproduction with other worms and asexual by breaking into pieces.

Round Worms-

Pharynx is muscular which facilitate feeding by sucking action. Digestive tract is simple without storage facility as there is constant supply of food. Ingested food is predigested so not much digestive glands.

Its devoid of locomotory organs as parasite lives in intestine where protection from enemies and constant supply of food is ensured.

Well developed reproduction. Produce many eggs and show sexual dimorphism. Reproduce sexually. Male has got a pineal setae. Testis for males and ovary for females are present.

5)

The main point we can attribute to enormous diversity of insects is its age of origin. That is insects are age old products in evolution. The are formed much before other organisms on earth. With the passage of time evolution of speceis is possible. This can be by mutation or adaptive to environment.

The reason for decline in insect population is identified as due to habitat destruction by urbanization, farming, industrialization. Also widespread use of insecticides and herbicides is another cause. Climate change is also attributable.

6)

Echinodermata is evolved from animals with bilateral symmetry.

They exibit secondary radial symmetry in some parts of their body, at some stage of life.

They are evolved from bilateralia and exibit bilateral symmetry in their larval stage.

As an adaptation to their sessile life, they exibit radial symmetry later in life.

7)

The sessile nature of echinodermata is a reason for exclusive marine nature along with radial symmetry in adult life. Also they have very high regenerative power, so that no need for adaptations in barrier environments.

Echinodermata have mesodermal skeleton composed of calcareous plates. They are well preserved in chalk beds or lime stone. This feature also make them fit exclusively for marine life. Also they possess water vascular system, which is adaptive only to marine salinity.