I underrepresent my hand, now do i have to call down?

[SilentNoise]

Poker Stars - No Limit Hold'em Cash Game - $1/$2 Blinds - 4 Players - (LegoPoker Hand History Converter)

SB: $201.50
BB: $192.45
UTG: $149.30
Hero (BTN): $214.00

Reads: <font color="blue">readless. i assume hes fishy because he hasn't got the max infront of him.</font>

Preflop: Hero is dealt J[img]/images/graemlins/heart.gif[/img] J[img]/images/graemlins/diamond.gif[/img] (4 Players)
<font color="red">UTG raises to $6.00</font>, <font color="red">Hero raises to $18.00</font>, 2 folds, UTG calls $12.00

Flop: ($39) K[img]/images/graemlins/diamond.gif[/img] 6[img]/images/graemlins/heart.gif[/img] 2[img]/images/graemlins/heart.gif[/img] (2 Players)
UTG checks, Hero checks

Turn: ($39) T[img]/images/graemlins/spade.gif[/img] (2 Players)
<font color="red">UTG bets $16.00</font>, Hero calls $16.00

River: ($71) K[img]/images/graemlins/heart.gif[/img] (2 Players)
<font color="red">UTG bets $42.00</font> hero??

I normally call down in these spots all the time. But it must be pretty obvious to him that i have a hand like what i have. He must also know that the K pairing on the river is a bad bluffing card. So what hand could he betting here? What does he think im calling the turn with? Why would he think im calling the turn with JJ/QQ but folding the river? So why would he ever bluff here?