The ornamental design for a marineinfantseat, as shown and described.
FIG. 1 is a perspective view of the marine infant seat showing my new design;
FIG. 2 is another perspective view of the marine infant seat;
FIG. 3 is another perspective view of the marine infant seat;
FIG. 4 is a perspective view of the marine infant seat with the tray removed for ease of illustration, wherein other views of FIG. 4 being similar to the views of the marine infant seat shown in FIG. 2;
FIG. 5 is a side view of FIG. 1;
FIG. 6 is the opposite side view of FIG. 1;
FIG. 7 is a front view of FIG. 1;
FIG. 8 is a top view of FIG. 1;
FIG. 9 is a rear view of FIG. 1;
FIG. 10 is a bottom view of FIG. 1; and,
FIG. 11 is another bottom view of FIG. 1.
The broken lines shown in the drawings are for illustrative purposes only and form no part of the claimed design.