Coenobita carnescens(EN)

Image©Antje SK

Available Information

Is Coenobita carnescens a valid species? Or it is juvenile form of Coenobita perlatus? 

① According to information from Worms Database, Coenobita carnescens was accepted and may be found in French Polynesia.

② Data from CRUSTA: Database of Crustacea, Joseph Poupin’s comment is that Coenobita carnescens could be in fact the juvenile form of C. perlatus according to the drawings provided by Dana in 1855.

③ Thank you Joseph Poupin providing information for the drawing. We can see the drawings (1855) with transverse band on walking legs. Unfortunately, this drawing is black and white, we do not know the colour of transverse band.

My Opinion

GBIF recorded two preserved specimen, but cannot see clearly the body colour.

⇒ https://www.gbif.org/occurrence/2434444670

⇒ https://www.gbif.org/occurrence/2434445337

Specific name (Latin specific epithet) carnescens mean covered in white; hoary, present participle of canescere‎(to become gray or white), is it refer to the white body colour with transverse band in gray or brown on both cheliped and walking legs? 

In 2011, I wrote an article (In Chinese) (Comment respond to Morphological and Molecular Evidence for a Stepwise Terrestrial Evolution and Species Delimitation on the Coenobita Phylogeny) and analyzed that they may be Coenobita pseudorugosus(Page 23-26)

⇒ https://www.tonycoenobita.com/commentonspeciesdelimitationbytony_trad.pdf

However, it is most likely that Coenobita pseudorugosus is merely a heterotypic synonym or a variety of Coenobita rugosus. And according to the meaning of specific name (Latin specific epithet), I think it is possible that this specimens is Coenobita carnescens in 2017, please see below some points.

1. Firstly, we can found many images from website that the specimens is in white body colour with transverse band in gray or brown tone on both cheliped and walking legs, matching the meaning of specific name (Latin specific epithet). The slightly different between Coenobita carnescens and Coenobita perlatus may be the colour of transverse band.

Juvenile form of Coenobita perlatus always with brownish-red or orange colour transverse band on both cheliped and walking legs, most of them with brownish-red marks on shield.

Specimens in white body colour with transverse band in gray or brown tone on both cheliped and walking legs

Juvenile form of Coenobita perlatus

2. This specimens can be found in many Islands. From the images, we can see not only individual, but also in group, so I guess they are well represented and the population had been established within these areas.

Samoa

Other images from Samoa:

Cook Islands

Cook Islands Biodiversity & Ethnobiology Database show they are juvenile form of Coenobita perlatus.

Other images from Cook Islands:

 

French Polynesia

Other images from French Polynesia:

Vuvalu – Fuadatu Island & Tepuka Island

Tonga

Other images from Tonga:

Kiritimati (Christmas Island)

Other images from Kiritimati (Christmas Island):

3. According to the information of < Poupin J., 1996. Crustacea Decapoda of French Polynesia (Astacidea, Palinuridea, Anomura, Brachyura) >, the distribution of this species is Tuamotu. Tuamotu Islands is a chain of islands and atolls in French Polynesia.

Tuamotu

Other images from Tuamotu:

⇒   

Tikehau

Tikehau is a coral atoll in the Palliser Islands group, part of the Tuamotu Islands in French Polynesia. So I put images here.

Other images from Tikehau:

 

4. I checked with Joseph Poupin, the specimens collected in Tahuata did not do any DNA test to confirm if they are actually Coenobita perlatus. Also they did not checked if male coxae of 5th legs is same as Coenobita perlatus.

Tahuata

5. Below image from Cook Islands show that the appearance of juvenile on left hand side and adult on right hand side are same, with gray or brown transverse band on both cheliped and walking legs. That means there is no different between juvenile and adult during the growth. Although some individuals of juvenile form of Coenobita perlatus are almost white or pale orange, when they grow larger the red orange colour will gradually appear.

6. Article in 1953 < Enumeration of the Decapod and Stomatopod Crustacea from Pacific Coral islands > P37-P39, Holthuis found over 100 pcs of Coenobita perlatus in Marshall Islands and 1 pc of Coenobita carnescens. Although there is not image, this founding show that Holthuis can identify between Coenobita carnescens and Coenobita perlatus?

Kwajalein Underwater Home show they are Coenobita rugosus.

Other images from Marshall Islands:

aitutaki-vacation.com/photo-gallery

Hermit crab, Honeymoon Island, Aitutaki, Cook Islands, South Pacific 

Status

Only found one article < The effect of isolation on the behavioral interaction of juvenile land hermit crab (Coenobitidae) from the Motus of Mo’orea French, Polynesia > with image  reported that this speices as juveniles Coenobita perlatus.

This specimens are widely distributed on Islands between Pacific Ocean and North Pacific Ocean. I think the population had been welly established, they are not Coenobita perlatus. Although coloration may not a significant standard in Taxonomy, shape of male coxae of 5th legs can show if they are Coenobita perlatus. Beside, DHA also can show if they are heterotypic synonym or a variety of Coenobita perlatus.

A researcher from Japan think they are heterotypic synonym of Coenobita perlatus, here is his comment.

***UPDATED NEWS – 2022.01.01***

Is Coenobita carnescens Dana, 1851, a valid species?

⇒ https://tonycoenobita.com/coenobita_carnescens_validspecies.htm

Reference links

  • http://crustiesfroverseas.free.fr/
  • http://travel2unlimited.com

Reference articles

  • Dana J. D., 1855. Atlas. Crustacea. United States Exploring Expedition during the years 1838, 1839, 1840, 1841, 1842 under the command of Charles Wilkes, U.S.N.
  • Holthuis, L.B., 1953. Enumeration of the Decapod and Stomatopod Crustacea from Pacific Coral islands
  • Poupin J., 1996. Crustacea Decapoda of French Polynesia (Astacidea, Palinuridea, Anomura, Brachyura)
  • Van Zerr, Vanessa E., 2008. The effect of isolation on the behavioral interaction of juvenile land hermit crab (Coenobitidae) from the Motus of Mo’orea French, Polynesia

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