Locomotion and...?

Question

1) What is a common method of locomotion used for both land and aquatic animals? Name one aquatic and oone terrestrial animal that uses it. [[I was thinking swimming]]
2) Three methods of obtaining oxygen [[I already have 2, gills & lungs, would skin be one? In animals such as certain frogs and other amphibians]]

Thanks for your imput!

Answer 1

Legged locomotion, bipedal or quadrupedal, can be used terrestrially and for some aquatic travel but slithering is very common to both.

Slithering can be done by snails, snakes, or worms.
http://www.weichtiere.at/Mollusks/Schnecken/land/landschn.html
http://en.wikipedia.org/wiki/Ampullariidae
http://www.woodbridge.tased.edu.au/mdc/Species%20Register/sea_snails.htm

Rolling also exists.
Pangolins roll up for defense but are able to give little pushes to move still. Mantis Shrimp rolls and jumps back to deeper water
http://www.serengeti.org/nightlife_animals.html
http://animals.jrank.org/pages/1759/Mantis-Shrimps-Stomatopoda-NO-COMMON-NAME-Nannosquilla-decemspinosa-SPECIES-ACCOUNTS.html

Respiration or gas exchange can be across specialized membranes in lungs or gills or across amphibian skin in cutaneous respiration. Terrestrial Plethodontidae salamanders rely solely on cutaneous respiration as they lack lungs and gills.