Weird river spot with AK

[SEABEAST]

Villain is 21/16 and I've never seen him get out of line. I am 25/20 and quite aggro, but new to FT so not well known. Is this a snapcall hoping to split? It felt really weird at the time. If I feel there is a 0% chance he is purely bluffing, can I call?

Full Tilt Poker - No Limit Hold'em Cash Game - $2/$4 Blinds - 6 Players - (LegoPoker Hand History Converter)

SB: $1,499.50
BB: $690.95
UTG: $792.35
MP: $442.40
Hero (CO): $373.50
BTN: $400.00

Preflop: Hero is dealt K[img]/images/graemlins/spade.gif[/img] A[img]/images/graemlins/heart.gif[/img] (6 Players)
<font color="red">UTG raises to $14.00</font>, MP folds, Hero calls $14.00, BTN calls $14.00, 2 folds

Flop: ($48) 5[img]/images/graemlins/spade.gif[/img] 5[img]/images/graemlins/club.gif[/img] 4[img]/images/graemlins/heart.gif[/img] (3 Players)
UTG checks, Hero checks, BTN checks

Turn: ($48) A[img]/images/graemlins/diamond.gif[/img] (3 Players)
UTG checks, <font color="red">Hero bets $35.00</font>, BTN folds, UTG calls $35.00

River: ($118) K[img]/images/graemlins/diamond.gif[/img] (2 Players)
UTG checks, <font color="red">Hero bets $77.00</font>, <font color="red">UTG raises to $322.00</font>, Hero...