T. penetrans: morphological features include biting mouth parts used for attachment to animal tissue.
Image taken from: http://www.biosci.ohio-state.edu/~parasite/tunga.html.
original image from The Veterinary Parasitology Images Gallery, University of Sao Paolo

Tungiasis is a disease caused by an ectoparasite, the sand flea Tunga penetrans (also known as Sarcopsylla penetrans) and other related species. Other names for the parasite include: pigue, bicho de pie, chigoe flea, chigger, nigua, and pico. Pregnant female sand fleas imbed into the skin of their human host, usually under the toe nails or inbetween toes, and feed off human blood. The imbedded fleas can produce painful or itchy nodules, which can ulcerate. In the weeks following the initial infection, the female flea releases its eggs into the external environment and subsequently dies. If no secondary infections result, the dead female is sloughed off naturally without further complications. However, the risk of secondary infections is high and can be very severe. Gaseous gangrene, tetanus, and bacteremia can possibly result and cause death. Tungiasis is usually treated by surgical removal of the imbedded fleas and antibiotic treatment for secondary infections.