ארכיון יומן של אוגוסט 2022

אוגוסט 16, 2022

Fiddler Crab Guide: Atlantic Coast of the USA


This is part 3 of a series of planned posts about identifying fiddler crabs. Previous entries include:
  1. How to Identify Fiddler Crabs from Photos (or in the field)
  2. Is It a Fiddler Crab?


Fiddler Crabs of the Atlantic Coast of the USA

This guide is designed for identification “in the field” where you might be looking at live crabs by eye or through binoculars or from photographs. I will generally try to avoid characters that will require you to physically catch the crab, although I may mention a few for secondary verification. It does not include the more strict taxonomist-style characters that may only be visible under a microscope or via dissection. It is also assumed that the individuals are living, as death (and even capture) can cause dramatic color change.


This is a guide to the fiddler crabs of the Atlantic coast of the United States north of Florida (from New Hampshire in the north through Georgia in the south). Three species of fiddler crab are found in this region:
In general, these three species can readily be told apart by color, although some individuals can be ambiguous, particularly the female fiddler crabs (those with two small claws, rather than one large and one small).


Leptuca pugilator / Atlantic Sand Fiddler Crab


Leptuca pugilator is generally found on ocean or near-ocean shorelines up and down the coast, particularly in sandier areas. It is the most variable colored of the three species, with a carapace (that is the “shell” covering its back) that can range from appearing almost a solid, very dark blue to almost pure white. More often than not it will be in between these extremes, often with a blotchy/marbled appearance. In some individuals, the outer edges of the carapace may be red or orange.
The key indicator, however, is that there is almost always a patch of purple coloration in the center of the upper half of the carapace. This patch tends to be shaped roughly like a V with the bottom of the letter pointing between the eyes, although the shape of the patch is less important than any evidence of purple. You can see it in every single one of the following photos, even in the ones that appear mostly blue, if you look carefully. This purple coloration is a key indicator; if it is present, then it is this species. Also, if the carapace is at all white it is almost certainly this species (ignoring the presence of dried mud which might make the carapace appear to be white).
The following photos were chosen to demonstrate the range of variation in carapace colors.
https://www.inaturalist.org/observations/112474878 https://www.inaturalist.org/observations/109172261
https://www.inaturalist.org/observations/111374875 https://www.inaturalist.org/observations/108237300
https://www.inaturalist.org/observations/84516743 https://www.inaturalist.org/observations/97400063
https://www.inaturalist.org/observations/57290165 https://www.inaturalist.org/observations/80726667
https://www.inaturalist.org/observations/79595789 https://www.inaturalist.org/observations/43940001
https://www.inaturalist.org/observations/81505656 https://www.inaturalist.org/observations/80677001
In contrast, the two Minuca species tend to have carapaces that are more uniform in color, without the wide variation found in Leptuca pugilator.
Like the carapace, both the large and small claws of Leptuca pugilator can vary quite a bit in color, from a dark purple/red to mostly white.


Minuca pugnax / Atlantic Mud Fiddler Crab

Like Leptuca pugilator, Minuca pugnax is generally found on ocean or near-ocean shorelines, but tends to be in muddier areas. Although they will often subdivide a shoreline based on the mud/sand component (i.e., you might find one species in the sandier areas and the other in the muddier areas), it is not uncommon for the two species to intermix and be found together. They are more-or-less the same size, with full-sized adults usually less than 20 mm (¾ inch) wide (that is the width of the carapace at the front of the crab, from corner to corner), so can only be readily distinguished by color (in the absence of capturing them).

Minuca pugnax generally has a carapace that is a dark brown (often with paler speckles), with a very noticeable cobalt blue stripe across the front just behind the eyes. The width of this stripe can vary, but is usually (although not always) present; in rare cases the entire carapace will be blue. The eyestalks will often have some blue tint to them as well. Females are more likely to be solid or nearly solid brown, without the obvious blue tint.
https://www.inaturalist.org/observations/112330333 https://www.inaturalist.org/observations/105988247
https://www.inaturalist.org/observations/110164204 https://www.inaturalist.org/observations/96972001
https://www.inaturalist.org/observations/109337025 https://www.inaturalist.org/observations/93912141
https://www.inaturalist.org/observations/98540443 https://www.inaturalist.org/observations/61031876
The large claw of male Minuca pugnax tends to be a yellowish-cream color, with the “hand” of the claw often a bit darker brown. Occasionally the claw will be a bit paler, more gray than yellow, but the yellow-cream color is more typical. The small claw tends to be the same pale yellow. While Leptuca pugilator will often have pale large claws, they lack the yellow tint that is common in Minuca pugnax (compare the colors of the claws of the two species in the previous photos).


Minuca minax / Red-jointed Fiddler Crab

Unlike the other two species, Minuca minax tends to be found farther from the ocean shoreline, generally preferring slightly more brackish (fresh) water and is therefore more likely to be found farther up rivers, as well as farther from the water’s edge. In areas where all three species might coexist, if you consider the layout of the intertidal zone (the area between the water’s edges at high and low tides), Minuca minax will be found in the upper intertidal zone (closer to the high tide edge) while the other two species will be found in the lower intertidal zone (closer to the low tide edge). Although all three species can be found on the same shoreline, it is much less common to find Minuca minax intermingling with the other two. Minuca minax is also notably larger than the other two species, almost double the size on average, with full sized adults reaching 37 mm (1.5 inches). Until you have experience with all three species, however, size can be hard to judge in a vacuum.

Minuca minax has a carapace that tends to be a sort of olive-gray or brown, generally lighter toward the front of the crab and darker toward the back. This color is distinct from that of the other two species.
https://www.inaturalist.org/observations/98207108 https://www.inaturalist.org/observations/78085489
https://www.inaturalist.org/observations/90903317 https://www.inaturalist.org/observations/80096373
https://www.inaturalist.org/observations/87317267 https://www.inaturalist.org/observations/78790507
https://www.inaturalist.org/observations/10907753 https://www.inaturalist.org/observations/82034976
Beyond the carapace color, many (although not all) individuals will have one or more distinct red markings along the joints of the legs and the claw. You can see these in many of the previous photos, particularly along the edge of the major dactyl (the movable finger on the large claw) and the outside edge of where the large claw attaches to the male crab’s arm. These markings can appear on other joints as well, including the small claw and the walking legs.
Note that the red markings are essentially highlights on the joints, they are not red limb segments. Some Leptuca pugilator can have reddish limbs, particularly on the large claw; which are very different from the red markings along the joints of Minuca minax.
https://www.inaturalist.org/observations/106018263 The Leptuca pugilator in this photo has an unusual amount of red along the joints. This color appears to be part of the joint itself, which is quite different than the red markings in the earlier photos of Minuca minax where the red along the various joints are highlights on the fringe of the harder shell covering the limbs, rather than actually within the joints.
Not all Minuca minax will have these red marks along the joints; while the presence of these markings is essentially diagnostic, the absence cannot be used to automatically eliminate the species.
By and large, Minuca pugnax and Minuca minax tend to be less variable than Leptuca pugilator, so within this Atlantic coast region individuals that are not good matches for any of the three are more likely to be Leptuca pugilator than the other two.
הועלה ב-אוגוסט 16, 2022 06:42 אחה"צ על ידי msr msr | תגובה 1 | הוספת תגובה

אוגוסט 17, 2022

Fiddler Crab Guide: West Africa and Europe


This is part 4 of a series of planned posts about identifying fiddler crabs. Previous entries include:
  1. How to Identify Fiddler Crabs from Photos (or in the field)
  2. Is It a Fiddler Crab?
  3. Fiddler Crabs of the Atlantic Coast of the USA


Fiddler Crabs of West Africa and Europe

This guide is designed for identification “in the field” where you might be looking at live crabs by eye or through binoculars or from photographs. I will generally try to avoid characters that will require you to physically catch the crab, although I may mention a few for secondary verification. It does not include the more strict taxonomist-style characters that may only be visible under a microscope or via dissection. It is also assumed that the individuals are living, as death (and even capture) can cause dramatic color change.


This is a guide to the fiddler crabs of West Africa and Europe. There is only one species, so identification is guaranteed.


Afruca tangeri is the only fiddler crab found in the eastern Atlantic Ocean, including the West coast of Africa, from Angola in the south to Morocco and the Strait of Gibraltar in the north, major islands such as Cape Verde and the Canary Islands, and southwestern Europe, including the southwestern coast of Spain and the southern and southwestern coasts of Portugal. It is not found past the Strait of Gibraltar into the Mediterranean.
הועלה ב-אוגוסט 17, 2022 02:53 לפנה"צ על ידי msr msr | 0 תגובות | הוספת תגובה

Fiddler Crab Guide: Southern California, USA

Fiddler Crabs of Southern California, USA

This guide is designed for identification “in the field” where you might be looking at live crabs by eye or through binoculars or from photographs. I will generally try to avoid characters that will require you to physically catch the crab, although I may mention a few for secondary verification. It does not include the more strict taxonomist-style characters that may only be visible under a microscope or via dissection. It is also assumed that the individuals are living, as death (and even capture) can cause dramatic color change.
This is a guide to the fiddler crabs of southern California in the United States. Prior to 2018, only a single species of fiddler crab was found in California. Now there are two known species:
These two species are extremely easy to tell apart and within California they should always be readily identifiable.
The two primary features you should focus on are size and how close the eyestalks are to each other. Uca princeps is substantially larger than Leptuca crenulata, as shown in the following photos:
https://www.inaturalist.org/observations/32684153 https://www.inaturalist.org/observations/13824586
The larger crab in both photos is Uca princeps, while the smaller surrounding crabs are Leptuca crenulata. Leptuca crenulata generally only grows between about 10-15 mm (approx ½ inch) in width (that is the width of the carapace at the front of the crab, from corner to corner), while Uca princeps can reach 35-50 mm (approx. 1 ½ to 2 inches).
Beyond size, another key difference is the relative distance between the eyestalks. Uca princeps is what is known as a “narrow front” fiddler crab, meaning the bases of the eyestalks are close together with only a tiny bit of carapace squeezed between them. In contrast, Leptuca crenulata is what is known as a “broad front” fiddler crab, meaning the bases of the eyestalks are farther apart and there is substantial carapace between them. This difference is very striking as shown in the examples below.


https://www.inaturalist.org/observations/60849706
Uca princeps
“Narrow front” / eyestalks are close together


https://www.inaturalist.org/observations/55469339
Leptuca crenulata
“Broad front” / eyestalks are separated

While there are other features that can be used to distinguish the two species (e.g., notice the differences in claw shape in the above photos), both size and eyestalk configuration are individually adequate to identify these two species within California in the USA.

Leptuca crenulata is the more common of the two species in California and ranges as far north as Santa Barbara. Uca princeps was only first discovered in southern California in 2018, and while it has been found there every year since, it is substantially rarer and as of now has only been found as far north as Huntington Beach.
הועלה ב-אוגוסט 17, 2022 03:08 לפנה"צ על ידי msr msr | 0 תגובות | הוספת תגובה

אוגוסט 19, 2022

Fiddler Crab Guide: East Africa

Fiddler Crabs of East Africa

This guide is designed for identification “in the field” where you might be looking at live crabs by eye or through binoculars or from photographs. I will generally try to avoid characters that will require you to physically catch the crab, although I may mention a few for secondary verification. It does not include the more strict taxonomist-style characters that may only be visible under a microscope or via dissection. It is also assumed that the individuals are living, as death (and even capture) can cause dramatic color change.


This is a guide to the fiddler crabs of East Africa, from South Africa in the south through southern Somalia in the north, including Madagascar, the Seychelles, Comoros, Mayotte, Mauritius, and Réunion. Six species are found within this region:
A number of features can be used to distinguish among these species, but a good place to start is to look at the distance between the base of the eyestalks. Fiddler crabs tend to split into two groups, those with the eyestalks very close together (“narrow front”) and those with the eyestalks separated a bit more (“broad front”). Three of these species (Austruca occidentalis, Cranuca inversa, and Paraleptuca chlorophthalmus) are broad front species, while the other three (the two Gelasimus and Tubuca urvillei) are narrow front species. The eyestalks of Paraleptuca chlorophthalmus are fairly close together and barely qualify as “broad front”.


https://www.inaturalist.org/observations/56720520
“Narrow front” / eyestalks are close together


https://www.inaturalist.org/observations/38981491
“Broad front” / eyestalks are separated

Broad front species


Cranuca inversa / Inversed Fiddler Crab

Male Cranuca inversa should be the easiest of any of the species to identify so long as one can get a good look at the large claw. In this species, the tip of the dactyl (the upper finger) on the large claw has a forked shape which is completely unique to this species. Compare the tip of the upper finger of the claw in the “broad front” photo above to those in the four photos below. While the colors of the crabs are very similar, the shape of the tip of the dactyl is distinctly different.

https://www.inaturalist.org/observations/73491591 https://www.inaturalist.org/observations/18730511
https://www.inaturalist.org/observations/18258981 https://www.inaturalist.org/observations/49297008
Beyond the shape of the dactyl tip, the “hand” and arm of the large claw tend to be pale pink, while the fingers are usually white. The carapace is generally a mix of black and white, usually although not always with more black than white. Unfortunately, this color scheme is very similar to the next species, so without a good view of the claw, it can be very hard to distinguish between them in the field. To my knowledge, there is no reliable way to tell females of the two species apart in the field.


Austruca occidentalis / East African Fiddler Crab

Austruca occidentalis looks a lot like Cranuca inversa. The carapace is predominantly black and white, with more black than white and the claw is often pink. The key feature is that the tip of the dactyl in Austruca occidentalis comes to a more “normal” point rather than the unique fork found in Cranuca inversa. Austruca occidentalis appears to have more color variation, however. In some males the claw is more red or orange rather than pink and the dactyl may be less white and closer to the same color as the rest of the claw. The color pattern of the carapace is subtly different between the two species as well: Austruca occidentalis tends to have smaller, more spotted markings while Cranuca inversa tends to have elongated, more stripe-like markings; I wouldn’t feel comfortable making identification solely on this pattern, however.

https://www.inaturalist.org/observations/38981491 https://www.inaturalist.org/observations/9262381
https://www.inaturalist.org/observations/578653 https://www.inaturalist.org/observations/9431179


Paraleptuca chlorophthalmus / Green-eyed Fiddler Crab

Paraleptuca chlorophthalmus should be readily distinguishable from the other two broad front species because its carapace is predominantly blue with black markings, although sometimes it will be nearly solid one or the other color. Its legs are frequently bright red (although occasionally darkening to almost black), and the large arm and claw tend to be bright red, with only partial whitening on the fingers. The eyestalks are usually yellow-green.

Compared to the previous two species, the large claw tends to appear a bit thicker and heavier, particularly with regard to the shape of the fingers.
For a broad front species, Paraleptuca chlorophthalmus has a relatively narrow front, so much so that the species it is most likely to be confused with is one of the narrow front species, Gelasimus tetragonon, described next.
https://www.inaturalist.org/observations/105022204 https://www.inaturalist.org/observations/58819159
https://www.inaturalist.org/observations/58819157 https://www.inaturalist.org/observations/67095501
https://www.inaturalist.org/observations/18258684 https://www.inaturalist.org/observations/106091778

Narrow front species


Gelasimus tetragonon (Tetragonal Fiddler Crab)


https://www.inaturalist.org/observations/64160983
Narrow front Gelasimus tetragonon


https://www.inaturalist.org/observations/18258684
Broad front Paraleptuca chlorophthalmus


Gelasimus tetragonon is a wide-spread species that can be confused with Paraleptuca chlorophthalmus, despite the latter being a broad front species and the former being a narrow front species, as Paraleptuca chlorophthalmus is a relatively narrow fronted broad front species. Both species have predominantly blue and black carapace and tend to have bright red legs (which occasionally may be darker). Gelasimus tetragonon tends to have gray eyestalks, as opposed to the more yellow-green of Paraleptuca chlorophthalmus.
For males, the large claws of these species tend to be different. While the large claw of Paraleptuca chlorophthalmus tends to be dominated by red, that of Gelasimus tetragonon is more likely to be orange, with a noticeably darker red spot near the base of the pollex. The dactyl of Gelasimus tetragonon is more likely to be mostly white, while in Paraleptuca chlorophthalmus it tends to be more red. Gelasimus tetragonon frequently has brown spots on the top part of the hand of the claw; these spots are never present in Paraleptuca chlorophthalmus.

Gelasimus tetragonon has a lot of additional variability that does not overlap with other local species. In some places the carapace can lighten so that there is almost no blue, just a cream or pale orange with black markings. The pattern of the colors on the carapace can vary from stripes or blotches to tiny spots.
https://www.inaturalist.org/observations/64160983\ https://www.inaturalist.org/observations/66985053\
https://www.inaturalist.org/observations/67192392 https://www.inaturalist.org/observations/19029852
https://www.inaturalist.org/observations/40014105 https://www.inaturalist.org/observations/97981509
https://www.inaturalist.org/observations/67599172 https://www.inaturalist.org/observations/65173309
https://www.inaturalist.org/observations/108475731


Tubuca urvillei (d’Urville’s Fiddler Crab)

Superficially, Tubuca urvillei may seem similar to the previous two species as it is also a narrow front species with a predominantly dark blue carapace with black markings and a large claw with orange-red and white colors. This superficial description fails to convey some rather striking differences that usually make it easy to pick out from the previous two.

While the carapace of Tubuca urvillei is blue and black, it tends to have less complex patterning and more solid colors relative to the previous two species; in some cases it may appear almost solid dark blue. The shade of blue of Tubuca urvillei tends to be darker, with the other two a bit brighter or aqua, although this is not universal. Tubuca urvillei tends to have black or blue legs, and even if pale, they are never red.
https://www.inaturalist.org/observations/11109457 https://www.inaturalist.org/observations/5073575
https://www.inaturalist.org/observations/5073575 https://www.inaturalist.org/observations/25370185
https://www.inaturalist.org/observations/35123891 https://www.inaturalist.org/observations/22895957
https://www.inaturalist.org/observations/111128228 https://www.inaturalist.org/observations/106091776
Color-wise the claw of Tubuca urvillei is similar to that of Gelasimus tetragonon with an orange or brown-orange hand, frequently with a darker orange-red patch at the base of the pollex, with the entire dactyl and the latter half of the pollex predominantly white. However, it is structurally somewhat different. Tubuca urvillei has a more robust appearing claw, with clear, large tubercles (bumps) covering most of the outer part of the hand. The fingers are noticeably thicker and tend to be less pointed than the previous species, often having a noticeable flat edge along the lower tip of the dactyl. It may be hard to see through binoculars in the field, but Tubuca urvillei also has a clear deep groove running along much of the length of the pollex. You can see this in the photos in the first column above (particularly, the first three).


Gelasimus hesperiae (Western Calling Fiddler Crab)

Gelasimus hesperiae is a narrow front species with a white or pale greenish-brown carapace and a distinctively shaped large claw. It never has any blue and should be readily distinguishable from all of the other species. The dactyl on the large claw is usually white or pink, while the rest of the claw usually ranges from orange to pale yellow. The dactyl is relatively thick and straight for about half its length before clearly curving to a thick point. The pollex will frequently have two very clear large teeth, one about midway along the length and one near the tip, although one or both can be absent. Like Tubuca urvillei, it has large bumps (tubercles) on the hand of the claw and will often have a noticeable groove along the base of the pollex.

https://www.inaturalist.org/observations/67192391 https://www.inaturalist.org/observations/47636654
https://www.inaturalist.org/observations/9890177 https://www.inaturalist.org/observations/56720520
הועלה ב-אוגוסט 19, 2022 09:37 אחה"צ על ידי msr msr | 0 תגובות | הוספת תגובה