Answer to Question #152660 in Zoology for maria

Question

what is the economical and medical importance of actinopterygii and sarcopterygii?

Answer 1

1. tail is usually *homocercal (symmetrical) for maximizing forward thrust (without driving the animal up or down)

+ diverse tail shapes depending on mode of swimming

2. skin with mucous glands and embedded dermal (skin) scales of *bony origin.

+ scales are formed of bone from the deeper skin, or dermal layer

+ the trend in dermal scales have been to reduce weight and increase flexibility by being light the thin

+ scales are absent in some to reduce drag and increase speed

+ 2 types of dermal scales:

i. Cycloid scales

ii. Ctenoid scales

+ are overlapping and partially embedded in the skin

+ lateral line system senses vibrations close to the fish and has modifie scales

3. fins are median and paired with supporting fin rays

+ the thin, segmented fin rays of actinopterygians are flexible and delicately artculated with the skeleton, thus allows for greater maneuvrability

4. usually a terminal mouth with many teeth (some toothless), jaw present

+ mouth may be terminal with protrusible 突出 jaws

+ in more derived actinopterygians, there is greater flexibility in the jaws with fewer attachments of the maxilla 上顎 and premaxilla切牙骨 to the skull (allows for greater jaw extension)

5. gills covered by a single *operculum (gill cover)

+ bony

+ also serves in respiration by pumping water through the gills

6. *swimbladder often present for buoyancy

+ provides positive buoyancy an acts as a *hydrostatic organ, but occupies only ~5% of the fish's body volume, as gas provides a lot of positive buoyancy (or lift)

7. most species are oviparous (produce eggs) with external fertilization.

+ Actinopterygii have a wide variety of reproductive strategies

+ oviparous forms (egg laying) are the common

+ indirect development within a larval stage

+ in viviparous species, fertilization is internal and development is direct, a few show parental care (e.g. seahorses)