Participants in the 18th Annual “No Pants Subway Ride” travel in the subway on January 13, 2019 in New York. The “No Pants Subway Ride” is an annual event started in 2002 by Improv Everywhere in New York, the goal of which is for riders on the subway train to dress in normal winter clothes without pants while keeping a straight face. (Photo by Johannes Eisele/AFP Photo)

With its huge eyes, comical name and diminutive size, Mark R. Smith’s image of a baby Hawaiian bobtail squid can’t help but raise a smile. A curiously endearing creature, the cephalopod is just 1.5cm across, its mantle cavity bearing more than a passing resemblance to a rather natty shower cap. But it is also a beautiful example of symbiosis – nature’s version of “I’ll scratch your back if you scratch mine” – for on the underside of the squid is a light organ which houses bioluminescent bacteria. The squid offers the bacteria protection and food, while the bacteria emit a glow – a handy trait that the squid uses to offset its silhouette, helping it to evade predators in the depths below. Mark R. Smith’s entry combines several images of a Hawaiian bobtail squid with different focus lengths to create a final picture with greater depth of field than normal. (Photo by Mark R. Smith/Wellcome Images/Macroscopic Solutions)

A boy flies his kite in a cemetery in the Vila Operaria Favela of Rio de Janeiro, Brazil, July 9, 2016. (Photo by Nacho Doce/Reuters)

“A Little Monkey on the Cliff”. “A cold front hit the Nagano prefecture. I saw a little monkey enduring the cold in Jigokudani Monkey Park. This little monkey is really cute”. (Photo by Hidetoshi Ogata/Smithsonian Photo Contest)

Cuban migrant Yamilen Arbelo, 40, walks down a hill as she crosses the border from Colombia through the jungle into La Miel, in the province of Guna Yala, Panama November 29, 2015. According to local authorities in La Miel, some 100 to 150 Cubans have been entering Panama from Colombia every day for the last three months. Scores of Cubans have come to Panama as they seek overland passage towards the United States fearing a recent detente between Washington and Havana could end their preferential treatment. (Photo by Carlos Jasso/Reuters)

A “super blood blue moon” is seen during an eclipse behind an elephant statue at a temple in Bangkok, Thailand, January 31, 2018. (Photo by Athit Perawongmetha/Reuters)

In this August 17, 2016, photo, from left to right, Chhering Chodom, 60, Tashi Yangzom, 50, Lobsang Chhering, 27, and Dorje Tandup, 58, drink milk tea on the side of the road. For centuries, the sleepy valley nestled in the Indian Himalayas remained a hidden Buddhist enclave forbidden to outsiders. Enduring the harsh year-round conditions of the high mountain desert, the people of Spiti Valley lived by a simple communal code – share the Earth's bounty, be hospitable to neighbors, and eschew greed and temptation at all turns. That's all starting to change, for better or worse. (Photo by Thomas Cytrynowicz/AP Photo)

High-flying photographer Jeffrey Milstein, renowned for his aerial photos of US cities, snaps landmarks through the open door of a helicopter. This month he hired a chopper in London and amazingly he had just an hour to cover all the buildings he wanted to capture including Buckingham Palace, the London Eye, the glass roof of the British Museum and the Gherkin and Walkie Talkie towers in the City. Here: Jeffrey Milstein captured these stunning images through the door of a helicopter hovering over central London. (Photo by Jeffrey Milstein/Rex Features/Shutterstock)