Sergio Hanquet / Common octopus (Octopus vulgaris) female, close up of suckers on tentacles. Tenerife, Canary Islands.

Sergio Hanquet / Common octopus (Octopus vulgaris) female, close-up of suction cups on tentacles. Tenerife, Canary Islands.

Shane Gross / Loggerhead sea turtle (Caretta caretta) with two Remora fish (Echeneididae) above sea floor. Bahamas.

Shane Gross / Black grouper (Mycteroperca bonaci) with Remora fish (Remora sp). Caribbean Sea off Gardens of the Queen National Park, Cuba.

Magnus Lundgren / Wild Wonders of China / Big blue octopus (Octopus cyanea) , Xiaoliuqiu Island, Taiwan

Nigel Cattlin / Apple sucker (Cacopsylla mali) nymph, an orchard pest, on Apple (Malus domestica) leaf. Photomicrograph.

Nigel Cattlin / Apple sucker (Cacopsylla mali) nymph, an orchard pest, on Apple (Malus domestica) leaf. Photomicrograph.

Pascal Kobeh / Close-up of the head of a White tip shark (Triaenodon obesus) laying on the bottom with a Remora (Echeneis naucrates) on its head, Sulu sea, Philippines

Doug Perrine / Dugong or Sea cow (Dugong dugon) with a Remora (Echeneis naucrates) attached to its underside, Calauit Island, off Busuanga, Calamian Islands, Palawan, Philippines.

Marie Read / Red-breasted sapsucker (Sphyrapicus ruber) adult feeding on tree sap from shallow wells it has drilled in bark of Curl-leaf Mountain-mahogany (Cercocarpus ledifoius), Lee Vining Canyon, California, US...

Pascal Kobeh / Sicklefin devil ray / Chilean devil ray (Mobula tarapacana) with two shark suckers (Remora remora) Azores, Atlantic Ocean.

Pascal Kobeh / Close-up of Horn-nosed / Largenose boxfish (Ostracion rhinorhynchos) with a striped remora (Echeneis naucrates) on its head at night, Sulu Sea, Philippines