(2)E fish live in water, breathe with gills and swim with fins. The caudal fin can control the forward direction, and the swing of the trunk and caudal fin can generate the forward power.

(3)A snail belongs to mollusk, D butterfly belongs to arthropod, belongs to invertebrate, and has no spine.

B Birds have feathers on their bodies, and their hearts have two atria and two ventricles. They have the structure of generating heat and dissipating heat, and belong to warm-blooded animals.

(4) Hair on the body surface, differentiation of teeth, diaphragm in body cavity, four cavities in heart, breathing with lungs, developed brain, constant body temperature, viviparous and breastfeeding. Bats have hair on their bodies, not feathers; Without wings, it glides by the skin membrane between the forelimbs and hind limbs; The most prominent feature of bat growth and development is viviparous lactation;

(5) Butterflies belong to insects. Their bodies are divided into three parts: head, chest and abdomen. They have three pairs of feet, usually two pairs of wings and an exoskeleton.

(6) Please arrange the animals in A ~ E in descending order: A, D, E, C, B. 。

So the answer is: (1) software; Mantle;

(2) caudal fin; Swing of tail and trunk;

(3)D； b；

(4) viviparous breastfeeding;

(5) chest; Third;

(6)A、D、E、C、b。