— most ▁not ably ▁the ▁two ▁ph y la ▁consisting ▁of ▁sp ong es ▁and ▁pla co zo ans — anim als ▁have ▁bodies ▁that ▁are ▁differenti ated ▁into ▁t issues . ▁These ▁include ▁mus cles , ▁which ▁are ▁able ▁to ▁contract ▁and ▁control ▁lo com otion , ▁and ▁a ▁nerv ous ▁system , ▁which ▁sends ▁and ▁processes ▁signals . ▁There ▁is ▁also ▁typically ▁an ▁internal ▁dig est ive ▁chamber . ▁The ▁e uk ary otic ▁cells ▁possessed ▁by ▁all ▁animals ▁are ▁surrounded ▁by ▁a ▁characteristic ▁ext rac ell ular ▁matrix ▁composed ▁of ▁col lagen ▁and ▁el astic ▁g ly cop rote ins . ▁This ▁may ▁be ▁calc ified ▁to ▁form ▁structures ▁like ▁shell s , ▁b ones , ▁and ▁sp ic ules , ▁a ▁framework ▁upon ▁which ▁cells ▁can ▁move ▁about ▁and ▁be ▁re organ ized ▁during ▁development ▁and ▁m atur ation , ▁and ▁which ▁supports ▁the ▁complex ▁an atom y ▁required ▁for ▁mob ility . ▁ ▁Human ▁inter rel ations hip ▁ ▁Although ▁humans ▁compr ise ▁only ▁a ▁min usc ule ▁proportion ▁of ▁the ▁total ▁living ▁bi om ass ▁on ▁Earth , ▁the ▁human ▁effect ▁on ▁nature ▁is ▁dis pro port ion ately ▁large . ▁Because ▁of ▁the ▁extent ▁of ▁human ▁influence , ▁the ▁boundaries ▁between ▁what ▁humans ▁regard ▁as ▁nature ▁and ▁" made ▁environments " ▁is ▁not ▁clear ▁cut ▁except ▁at ▁the ▁extrem es . ▁Even ▁at ▁the ▁extrem es , ▁the ▁amount ▁of ▁natural ▁environment ▁that ▁is ▁free ▁of ▁disc ern ible ▁human ▁influence ▁is ▁dimin ishing ▁at ▁an