Draw straight lines from clue to clue to form a single loop that doesn’t cross or touch itself, and that passes every clue. The loop must turn at every clue, with an angle that is acute (< 90°) for triangles, right (=90°) for squares, and obtuse (>90°, <180°) at pentagons.
I first saw this type in the Toketa books.
Maybe Puzzles 
Is it the case that the loop may only turn at clues? I’m pretty sure this is correct, but I have to be certain.
Is it not implied? But yes, that’s correct.
It is implied, but not explicitly stated, so technically you would have multiple solutions for this particular puzzle.
Is this better? Replaced “Connect clue polygons by straight lines t form …” by “Draw straight lines from clue to clue to form …”. I’m meaning to express that the loop is built from straight segments that have clues at both ends.
The rules are not adequately stated yet. This puzzle is solvable if ‘either’ of the two angles made at each node satisfies the conditions. If the inner angle is considered, the puzzle has no solution.
The rules are just fine I think, since the angles are specified to be less than 180º.