Dark, bigheaded, skinny bodies? 1/4"= long, congratulations papa! They sound like baby Giant dianos to me, I have had that happen a couple times to my tanks. Try to get a good look at one in a teaspoon with a magnifying glass. You might not be able to see the fins but at that size you should see it looking back at you. If so and you have a spare 5-10g tank around put em in their and feed them filter gunk until you can get some liquid fry food, throw some elodea in there too!