First Few Live Coloration photos of Crab Platychirarma buettikoferi

I was scrolling through iNaturalist observations of Land, shore marsh grapsoid crabs of West Africa this past Monday when I came across an observation of a small crab with weird laterally-compressed chelae. In my mind, I had identified it to the family Sesarmidae. It was so unique - I had never seen anything like that in any sesarmidae species, much less the whole subfamily of Grapsoidea. It didn't seem to fit morphologically any of the known genera from this area that were already recored on iNaturalist: Guinearma, Metagrapsus curvatus Armases elegans ... though it did look relatively similar to our American genus Sesarma. Many grapsoidea like Pachygrapsus gracilis and genus Goniopsis occur in both the Eastern side of south america and Western africa due to continental drift. I wasn't sure, though that Sesarma occurdd in Africa as it is a New-World genus.

Because many beaches in West Africa are private, a wide diversity of crab species-including numerous sesarmids and many still-unknown species-remain largely under observed. However because crab species were documented by colonists and scientists in the late 19th and 20th centuries, there still remains many papers out there about the species in the area. The challenge is that, due to the lack of photography at the time, we must rely on written descriptions by scientists to attempt to identify unknown crab species.

I started the identification process by looking at a kind-of-old paper that collected data from older papers. It was dated 1984 and had clear descriptions of the brachyura in the photo. I scrolled down to sesarmidae and read the description.

Sesarma buettikoferi (Rathbun, 1921)

The specimens from Lagune Ebrie carried a note stating that in life the chelae are purplish blue with red tips. Additional color notes were provided by Rossignol (1957:91).BIOLOGY.—This species inhabits littoral estuarine areas, particularly mangroves and adjoining inland regions (see Rathbun, 1921:449, 450).