I have a list of $\{x,y,z\}$ pairs representing points in $R^3$. For every unique value of $z$ there are many $\{x,y\}$ pairs defining a polygon/contour in that particular $z$-plane. My dataset looks like this:

Input:= Take[ptv, 3]
Output= {{61.52, -217.26, -80}, {63.48, -217.64, -80}, {65.43, -217.64, -80}}

These are coordinates of points residing on the $z=-80$ plane. There are other pairs for $z=-75$, $z=-70$, etc. Therefore ptv is of the form:

ptv: {{$x_1$,$y_1$,-80}, {$x_2$,$y_2$,-80}, ..., {$x_k$,$y_k$,-80}, ..., {$x_1$,$y_1$,-75}, ..., {$x_k$,$y_k$,-75}, ...}

My goal is to create a 3D surface where:

1. the points in every $z$-plane are connected into a polygon/contour and
2. the points in every $z$-plane are connected with their neighbors in the immediately above and below plane.

I have achieved 1., via:

Graphics3D[Line[ptv], Point /@ ptv}]

The result looks like this:

If I, instead, use:

ListSurfacePlot3D[ptv, AxesLabel->{"x","y","z"}]

I get some ugly artifacts (edges at the boundaries of the volume) as shown here:

Whereas, I was expecting a more "smooth" surface without any "openings". Any hints on:

1. Whether ListSurfacePlot3D[] is the proper function to use (i.e. in the documentation it is mentioned that ListSurfacePlot3D[] may "fold" over; perhaps this is why I'm experiencing these ruffles?) or
2. What other alternatives are there to consider ?

EDIT 1: Minimally working example:

ClearAll["Global`*"];
ptv = Import["http://leaf.dragonflybsd.org/~beket/ag1", "Table"]
ListSurfacePlot3D[ptv, AxesLabel->{"x", "y", "z"}]

EDIT 2: Are my data broken in some subtle way? I'm wondering because I excluded random z-planes from the 3D volume and some very "awkward" images came up. Here is the code:

(* Identify the values of z-planes *)
planes = ({a, b, c} = #; c) & /@ ptv // Union;

(* Generate some random sequences with z-planes-to-be-excluded *)
excludedPlanes = Table[
    RandomSample[planes, RandomInteger@{1, 4}],
    {k, 1, 20}]] // Union // Reverse;

(* Filter data by discarding points residing on excluded planes *)
FilterData[p_] := Select[ptv,
    Function[v, And@@(Unequal[v, #]& /@ p)][Last[#]]&]

(* Generate the 3D surfaces *)
ListSurfacePlot3D[#, AxesLabel->{"x","y","z"}]& /@ FilterData/@ excludedPlanes

And here is a screenshot: