Is Coenobita carnescens Dana, 1851, a valid species?
(My records for the last decade)
Coenobita carnescens Dana, 1851, is an accepted species from WoRMS (close marine only, on extant only).
According to Naksone (1988) < Land Hermit Crabs from the Ryukyus, Japan, with a Description of a New Species from the Philippines (Crustacea, Decapoda, Coenobitidae>, this species would be valid.
However, it is hard to find any detailed description of Coenobita carnescens, there is still not scientific research to investigate if C. carnescens is valid species.
2011.11 (First comment)
I wrote an article (In Chinese) with comments respond to Morphological and Molecular Evidence for a Stepwise Terrestrial Evolution and Species Delimitation on the Coenobita Phylogeny.
Below link Page 23-26:
From my comment in Chinese → English
I some found images on the web (⇓📷), those land hermit crabs had white body colour with transverse band in brown tone (hereinafter referred as specimens). I thought these specimens were Coenobita pseudorugosus.
According to Nakasone (1988) < Land Hermit Crabs from the Ryukyus, Japan, with a Description of a New Species from the Philippines (Crustacea, Decapoda, Coenobitidae>, walking legs of C. pseudorugosus with a dark brown band or stripe.
These specimens were always regarded as juvenile Coenobita perlatus.
I compared colour in life of juvenile C. perlatus in the wild, most of them with full of orange or red body colour, some of them with transverse band in orange tone, not that kind of brown bone.
Moreover, Asakura (2004) < Recent topics on taxonomy of hermit crabs rrom Japanese waters – Family Coenobitidae> (wrongly said Nakasone 1988 on my comment) named Japanese name of C. pseudorugosus as ‘アカツキオカヤドカリ’, ‘オカヤドカリ’ = land hermit crab, ‘アカツキ’ = something like sunburn, so I thought it might related to band or stripe on the specimens. These specimens I found on the web were C. pseudorugosus?
Original comment from Asakura (2004) in Japanese:
またその論文で，フイリッピンから新 種 Coenobita pseudorugosus Nakasone, 1988 (図1)も 記載された。なお原記載者の仲宗根幸男先生は，こ の時特に和名を与えていなかったので，本稿執筆時 に仲宗根先生にお尋ねしたところ，何か良い名前を 与えてほしいとのことであった。そこで，この種は 生きているときは背面が美しい紅色〜オレンジ色 をしている（図1)ので，その体色を日の出の朝焼け の空の色になぞらえて，和名をアカツキオカヤド力 リとすることにした。
** Later found that Fig.1 (=図1) in fact was juvenile C. perlatus
On the other hand, I found these specimens with same habitat as C. perlatus (⇓📷), so was it possible that they could be juvenile C. perlatus? Or they were new species? I thought we had to wait someone who was able to collect these specimens and had a DNA test.
2014 (Madagascar – Coenobita pseudorugosus?)
A Japanese blogger mentioned that he found C. pseudorugosus ‘アカツキオカヤドカリ’ in Madagascar (⇓📷), but I thought it was juvenile Coenobita violascens.
Juvenile C. violascens had been confused with juvenile C. perlatus due to their orange body colour.
Finally specimens from East Africa corresponded to C. violascens in 2018, see below link
2016 (Coenobita pseudorugosus?)
Barnes (2002) < Ecology of subtropical hermit crabs in SW Madagascar: Refuge-use and dynamic niche overlap > described C. pseudorugosus was very similar to Coneobita rugosus, the shape of left cheliped of them was different.
If so, I thought that body colour of C. pseudorugosus might also very similar to C. rugosus. That mean there was a higher possibility that the specimens had white body colour with transverse band in brown tone could be juvenile C. perlatus instead of C. pseudorugosus.
Page about Coenobita pseudorugosus, see below link
2016.06.09 (From my blog – juvenile of Coenobita perlatus?)
I found a movie from instagram from Tikehau, French Polynesia, please see the small crab next to adult C. perlatus at bottom left corner (⇓📷). That small crab had white colour with brown transverse band on the walking leg, was this small crab juvenile C. perlatus?
2016.06.23 (From my blog – juvenile of Coenobita perlatus? 2)
I found another movies from instagram, the small crab with dark brown transverse band on the walking leg, was this crab juvenile of Coenobita perlatus? (Sorry links are invalid now).
I also found a image (⇓📷) from French Polynesia, Fakarava from instagram, when these specimens grew larger, would they look like this?
2017.03.15 (Drawing, a break through)
That year my project was to update the pages about species of Coenobita, I found more additional information and images (got credit from owner) for every species, I checked CRUSTA again to see if there was any updated data and photos.
I overlooked a data (⇓📷) → According to the drawings provided by Dana, Coenobita carnescens could be in fact the juvenile form of C. perlatus (cf. Poupin, 1994a: 12, pl. 1d-f)
Drawing? I contacted with Joseph Poupin to see if he had the information of that drawing.
Thank you Joseph Poupin, sent me the link of the drawing!! The drawing showed very clear that the specimens with transverse band on walking legs (⇓📷).
Unfortunately, the drawing was black and white colour, we did not know the body colour.
C. perlatus was identified by H. Milne Edwards in early 1837, but the drawing from Dana, James Dwight was in 1852. If the specimens were juvenile C. perlatus, why Dana did not regard them as C. perlatus but a new name C. carnescens?
I also checked the Latin ‘carnescens’, it meant ‘to become gray or white’, ‘grayish-white’ etc. Was it alluding to live colour of the transverse band on walking legs and both chelipeds?
Although I described colour of transverse band was dark brown or brown tone, Dana might thought that colour was gray? But I did not find any information at that moment.
2017.03.15 (Specimens in Tahuata)
At the same time, I asked Joseph Poupin about the specimens he found in Tahuata in 2012. Joseph Poupin regarded them as C. perlatus. No DNA test applied.
2017.04.04 (Updated my website – Species related to Coenobita carnescens)
I re-checked the images I found before. Actually there were some specimens with brown transverse band, some with transverse band in gray tone. I do thought that drawing and name of ‘carnescens’ matched the images of those specimens (with gray-brown transverse band) I found on the web.
I changed colour of transverse band from ‘brown’ to ‘gray or brown’, which might better descript the colour of ‘carnescens’ in Latin
At that time, I speculated that these specimens were not juvenile C. perlatus. Juvenile C. perlatus always with brownish-red or orange colour transverse band on both chelipeds and walking legs, most of them with brownish-red or orange marks on surface of shield (like ⇓📷 from Cocos (Keeling) Islands, from a Japanese article, from alamy.com and from iNaturalist).
Juvenile C. perlatus along with adult on Cocos (Keeling) Islands
Image from < Altitudinal distribution of large terrestrial isopod and decapod crustaceans on
Minami-Iwo-To Island >
An image (⇓📷) I found in 2011 from Cook Islands that I thought it was representative of these specimens. Image show the appearance and colouration of juvenile crab on left hand side and adult crab on right hand side were same, with gray or brown transverse band on both chelipeds and walking legs.
That meant there was no different between juvenile and adult during the growth. Although some individuals of juvenile C. perlatus, the colouration varied from almost white, pale orange, light orange, when they grew larger the red orange colour would gradually appear.
Colouration might not a significant standard in Taxonomy, I believed that the specimens were different from C. perlatus. It was because I found a distribution information I missed from WorMS (⇓📷).
WorMS showed C. carnescens distributed in French Polynesian Exclusive Economic Zone. This matched the images I found, they distributed on Islands between Pacific Ocean and North Pacific Ocean (including French Polynesia).
I updated my website, opened a new page – Species related to Coenobita carnescens Dana, 1851.
I kept updating data, images and movie for my website during this period.
2019.01.15 (One’s habitat Blog)
A researcher from Japan (One’s habitat Blog) insisted that C. carnescens was heterotypic synonym of C. perlatus and speculated that C. carnescens was a colour variation of juvenile C. perlatus.
2019.01.17 (Coenbita carnescens vs Colour variation of Coenobita perlatus)
From my blog in Chinese → English
I found an interesting image from Tepuka Island, Funafuti Atoll, Tuvalu, upper part of the crab like C. perlatus with orange colour, while lower part with gray or brown tone transverse band like C. carnescens. Was this crab colour variation of C. perlatus?
2019.04.12 (My blog – images on Henderson Island)
I found some images on Henderson Island, specimens related to C. carnescens and C. perlatus both could be found on this Island.
Thank you Johnny R Briggs for credit ©
I compared the size of the crabs with human’s hand, could I said that C. carnescens was juvenile crab while C. perlatus was adult crab? If yes, might be just like comment from One’s habitat Blog, C.carnescens was just a colour variation of juvenile C. perlatus?
But I found many images, I only found one image from Tepuka Island, Funafuti Atoll, Tuvalu, half of body colour like C. carnescens, half like C. perlatus. It was hard to say C. carnescens would grow red or orange like adult of C. perlatus.
Might be C. carnescens was just a small size species? They would not grow to a very large size. So, they were not a colour variation of juvenile C. perlatus.
2020.04.05 (Article about Henderson Island)
One of the image (⇓📷) from article < Entrapment in plastic debris endangers hermit crabs > matched the specimens related to C. carnescens.
Fig. 3. (A) a strawberry hermit crab navigates through natural and anthropogenic debris on East Beach, Henderson Island.
I joined iNaturalist, it was very good for everyone to ID species and I could find many images of different species of Coenobita, included C. carnescens.
2020.05.19 (Article about Moorea, French Polynesia)
I found an interview about land hermit crabs in Moorea, French Polynesia.
Image (⇓📷) from interview showed some small crabs in bottom right corner had white colour with gray or brown tone transverse band, matched the specimens related to C. carnescens.
After that, I found that interview related to an article, Lindsay D Waldrop (2014) < Scaling of olfactory antennae of the terrestrial hermit crabs Coenobita rugosus and Coenobita perlatus during ontogeny > which was talking about C. perlatus.
I just wondered why everyone thought these specimens are C. perlatus. However, I was only able to find images on the web, it was hard to proof that if they were different from C. perlatus.
I thought if someone could help me to collect the specimens and check the shape of male coxae of 5th legs, it was easy to confirm if they were C. perlatus or not.
I started to send emails to some organization that could help.
2020.05.22 (Email, Cook Islands National Environment Service)
I found some images (⇓📷) from Cook Islands Biodiversity & Ethnobiology Database that matched the specimens related to C. carnescens.
That data descripted the young of this crab (C. perlatus) is creamy-white with red bands on wrists of the chelae and walking-legs.
I contacted with Gerald McCormack from Cook Islands Natural Heritage Trust to ask their comment.
According to their research so far, they had many adult of C. perlatus images but no juveniles with reddish bands.
Thank you Gerald McCormack, he provided an very useful information, he pointed out that Holthuis (1953) sorted juveniles from an atoll on the Marshall Islands determining that 174 were perlatus and ONE was carnescens(⇓📷). So obviously Holthuis recognized a basic difference.
Later I found that article, Holthuis (1953) < Enumeration of Decapod and Stomatopod Crustacea from Pacific Coral island > P37-P39, showed over 100 pcs of C. perlatus on Marshall Islands and 1 pc of C. carnescens. But my question was how Holthuis could identify between C. carnescens and C. perlatus? Unfortunately, there was no any drawing or description from that article.
I used ‘Holthuis 1953’ for searching and found two C. carnescens preserved specimens from GBIF. But it was hard to see very clearly appearance of the preserved specimens.
2020.09.18 (Updated my website from Species related to Coenobita carnescens to Coenobita carnescens)
2021.03.04 (Email, Moorea, French Polynesia)
I contacted with David Liittschwager who had did some survey at Moorea , French Polynesia to see if he could help me to check land hermit crabs in French Polynesia.
He introduced me Christopher Meyer at Smithsonian National Museum of Natural History who knew specimens from Moorea.
Thank you Christopher Meyer, I got a reply that they have sequenced Coenobita perlatus from Moorea. All four of these specimens (⇓📷) came out together in one clade with minimal genetic variation.
But they did not have information about the shape of male coxae of 5th legs from these specimens.
2021.11.10 (iNaturalist, Cook Islands)
I did not find any organization to collect the specimens so far I thought I had to give up …… And COVID-19 also affected everyone to do research outside.
But at that very moment, I found some amazing images (⇓📷) from Cook Islands from iNaturalist. I contacted with that user and knew the images was took in 2019, he was not there now.
Thank you Nuno Veríssimo P. for credit © , his research inspired me. It seemed that Cook Islands was more easily to find these specimens?
I started searching again if any organization on Cook Islands was able to find out the specimens and helped to check the shape of male coxae of 5th legs.
2021.11 (Email, Cook Islands National Environment Service)
Oh !!! I got a reply from Cook Islands National Environment Service on early December!!
Thank you Joseph Brider for credit ©, he helped me to collected a specimen and sent me images (⇓📷).
The most important thing is that the shape of male coxae of 5th legs of that specimen is short and definitely no curved. It is different to C. perlatus!! I have compared shape of coxae with other species of Coenobita, none of them were same.
Many Many Thanks Joseph Brider
Male coxae of 5th legs of Coenobita perlatus
Both me and Joseph Brider have same question, where are the juvenile C. perlatus then?
On Cook Islands, is there any small crabs will full of orange or red colour as adult crabs？ If not, I have a crazy thinking that maybe coxae of adult C. perlatus on Cook Islands is also short and no curved, which is different with normal C. perlatus? Or short coxae will change to long coxae when they become adult?
2021.12.19 (Biology of the land crabs)
Now specimens had white body colour with gray or brown transverse band from Cook Islands, shape of male coxae of 5th legs had been confirmed different with C. perlatus, but how I could identify them as C. carnescens?
I re-checked an old book < Biology of the Land Crabs > and found C. carnescens with a key word ‘Eastern Polynesia (Alcock, 1905)’, I missed it all the time.
Article name of Alcock (1905) → < Catalogue of the Indian decapod Crustacea in the collection of the Indian Museum Part 2. >
2021.12.20 (Biodiversity Heritage Library)
From Alcock (1905) page 193, I found new information (⇓📷) that was from Dana!! →Dana, Proc. Ac. nat. Sci. Philad., 1851 (1852)
2021.12.20 (Detail description from Dana & James Dwight)
Finally I found detail description (⇓📷) of C. carnescens from < Crustacea VOL.13 (1852)(Dana, James Dwight, 1813-1895) > from Biodiversity Heritage Library, that was very important. I was very surprised that it had been already published on 1852 !!
Here was my comment about the description.
→ Tony: Matched what I said C. carnescens might be small species.
Paumotu Archipelago → Tony: In French Polynesia
Honden Island → Tony: Honden Eiland (Atoll Pukapuka) in French Polynesia
Raraka → Tony: In French Polynesia
Vincennes → Vincennes Island in French Polynesia
Carlshoff → Tony: In French Polynesia
Waterland Islands → Tony: Manihi, atoll in the Tuamotu Archipelago, part of French Polynesia
→ Tony: Matched the images I found in French Polynesia
→ Tony: What was the colour of flesh-tint? Flesh-tint is something like light brown. So flesh tint, white, whitish, brown spotted with white, colouration matched specimens in white body colour with gray or brown transverse band.
→ Tony: I think it meant series of ridges (////) on upper outer surface of palm of left cheliped was not so obvious as C. rugosus.
→ Tony: Matched image from Joseph Brider in Cook Islands and did not mentioned any description like ‘long curved’ as C. perlatus.
I thought the specimens had white body colour with gray or brown transverse band I found since 2011 almost 100% matched above description from Dana (1852). All records of the specimens in the past had been misidentified as C. perlatus.
2021.12.25 (Youtube video)
Thank you my cousin, sent me a youtube video (in Chinese) about crab in the wild from Hong Kong.
In that video, Chandler (Guest) pointed out a case about species delimitation of fiddler crabs (see below) that I thought might apply on C. carnescens and C. perlatus.
Gelasimus vocans (呼喚丑招潮蟹) and Gelasimus borealis (北方丑招潮蟹) have the same appearance. It is difficult to identify these two species by the external morphology although their sexual tubes are different. However, based on the high similarity of their DNA sequences (Molecular Markers), they might belong to a single taxonomy unit (i.e., species).
Since the gene used for species delimitation is different from the gene that affects the morphology of their sexual tubes, this contradictory observation should be possible.
** Special thanks to Li-Yuan Hung, who helped me to translate Chinese comment into English
Did it mean even we did DNA test for C. carnescens, they might belong to C. perlatus, although sexual tube of C. carnescens was different?
At the moment, I am working with Joseph Brider and a professor (Thank you Professor Shih) to see if we can further test the specimens found on Cook Islands.
Published on 1 January 2022
My analysis of the relationship between distribution and body colour of Coenobita perlatus and Coenobita carnescens.