The Slender-legged Fiddler Crab, Uca tenuipedis (Fiddler Crab of the Week)

The Slender-legged Fiddler Crab (Uca tenuipedis), is a very small species from the eastern Pacific Ocean, ranging from about El Salvador to northern Peru. It is similar in size to some of its sympatric associates, such as Uca batuenta, Uca intermedia, and Uca saltitanta, but is readily distinguishable from the first of these by the somewhat triangular shape of the pollex and manus, and the latter two by its color: a fairly cryptic-colored brown and gray body, with a white pollex and pinkish-salmon dactyl and top part of the major claw.

Photos by M. Rosenberg, Panama, 1997.

The waving display of this species involves bringing both the large and small claws straight out to the side, pausing for a moment, then bringing them up and forward in a circle back to the starting open-wide position. The whole body rocks backwards slightly with this motion and sometimes the first few legs may come off the ground as well.

Unlike some of the other local species, this one seems to stay closer to the shoreline, found among the muddy stream banks or the fringes of mangroves rather than out on the open mudflat.

Introducing the Fiddler Crab Paper of the Month

This endeavor will be similar to my Fiddler Crab of the Week series, except less often and without the random component. The goal will be to try to highlight one fiddler crab research study every month. Around the start of each month I will look at all of the papers about fiddlers published in the previous month (more or less…I’ll also include older papers I happened to only discover in the previous month) and choose one to discuss. The basic rules about choosing a paper will be:

  1. One or more fiddler crab species have to play a prominent role in the paper, preferably as the focus, but optionally as a major component of the study.
  2. Any sort of publication is eligible: journal articles, books, book chapters, dissertations, theses, etc.
  3. I need to be able to get a hold of a copy of the publication to discuss it.
  4. My own publications are ineligible (since I’ll likely discuss and/or highlight them on the blog anyway).

If nothing meets the criteria from those published and/or discovered in the previous month, I may just choose an older publication that I find interesting. I will also tentatively try to avoid repeating papers by the same author(s) if they happen to be particularly productive (over a reasonable time span), and will also try to choose papers on a wide variety of topics rather than sticking to one particular subarea of research.

Nothing precludes me from highlighting multiple papers in a single month if the mood (and time) strikes me, but the goal will be to get to at least one. The precise publication schedule is not fixed, but my aim will be to post within the first week of the month. Keep an eye out for the first of these in the next week or so.

The Pygmy Fiddler Crab, Uca pygmaea (Fiddler Crab of the Week)

The Pygmy Fiddler Crab (Uca pygmaea) is an obscure, very small fiddler found on the Pacific coast of the Americas, from southern Costa Rica through northwestern Colombia. It’s name refers to it’s tiny size. Almost nothing is known about this species; there appear to be no observational studies of it in nature beyond its original collection along the muddy bank of a stream in Costa Rica.

The large claw of this species is interesting in that the hand is very thick and the fingers are relatively short and stubby. Many species have juveniles with claws that are thick and stubby; as they get older the proportions shift into those that we tend to associate with most fiddler crab claws today. This change in shape with size is known as allometry. It has been proposed that the Pygmy fiddlers’ claws stop developing at a more “juvenile” shape, a pattern known by the technical term paedomorphosis. It is certainly not a requirement that a species this size have a claw of this shape; while thicker, stubbier claws are not uncommon among some of the other very small species (e.g., U. saltitanta and U. inaequalis), one of the very smallest, Uca batuenta, has a perfectly “normally” proportioned claw.