Start by opening an image of deep sea surface.



Insert a cutout of a finger.



Duplicate, resize and rotate. Place as shown below.



Select eraser tool with soft brush settings and erase the hard overlapping edges of fingers.



Similarly add more fingers to complete a starfish shape.

Select and merge all the finger layers. Double click the layer to open layer style window. Apply settings as shown.







Duplicate the layer. Remove drop shadow from the layer style. Change the layer mode to "Color Dodge".





Here is the fruits of your hard work.