Sylvain Le Bris, Frankreich
Info
There are some interesting aspects to this Caribbean porcelain crab concerning its coloration and morphological variations.
In Petrolisthes amoenus, the color patterns vary greatly depending on size.
Small specimens (cl 3.9, cw 3.5) have brownish to orange spots on a predominantly white background; these small spots group together to form larger spots or slender stripes on the carapace and chelipeds.
The walking legs P2–5, also known as pereiopods, feature a net-like pattern of brownish to orange thick stripes.
In larger specimens (cl 5.7, cw 5.3), the carapace is regularly and densely covered with a net-like pattern of slender, carmine-red stripes on a much more subtle white background.
The carpus, merus, and proximal half of the propodus of the chelipeds have carmine-red stripes of varying size and thickness on a predominantly white background, while the distal half of the propodus, the solid finger, and the dactylus are carmine-red.
On P2–5, the net-like pattern of thick stripes is carmine-red.
Adult specimens (cl 9.4, cw 8.5) are mostly reddish to dark orange on the carapace and chelipeds; the reticulate pattern on P2–5 is carmine red and is crossed by 3 or 4 transverse white stripes alternating with the rest of the red.
A large carmine red spot on a light orange background is characteristic of the Mxp 3 merus (Fig. 5C). The ventral surface of the body is also distinctly reddish with small light yellow areas.
The distinguishing features of the crabs are particularly easy to see here:
https://www.researchgate.net/ publication/318793782_A_new_species_of_Pachycheles_Crustacea_Anomura_Porcellanidae_with_taxonomic_remarks_on_two_other_porcelain_crabs_from_the_remote_oceanic_archipelago_of_Trindade_and_Martin_Vaz_South_Atlantic_Ocean , page 555
A certain degree of morphological variation can be observed in Petrolisthes amoenus, which is partly related to the size of the specimens:
The presence of dense, short, robust setae on the back of the carapace, mainly in small specimens (such setae are usually absent in larger specimens and completely absent in adult specimens); and the degree of development of the outer corner of the eye, which in large specimens may be equipped with a spine of varying size (or even appear only as a slight elevation) (in small specimens, the outer corner of the eye is equipped with a conspicuous spine).
However, even in specimens of the same size and sex, some morphological variations can be observed:
The antennule basal segment with 4 to 6 distal spines (usually 4); (2) 4 or 5 spines on the mesial margin of the P1 carpus; and a fringe of setae on the lateral margin of the P1 propodus, which is either slightly pronounced and only present on its proximal half or clearly pronounced along the entire lateral margin of the P1 propodus.
It is not uncommon for specimens of Petrolisthes amoenus in museum collections to be misidentified as Petrolisthes galathinus.
Reproduction:
Members of the order Decapoda are mostly gonochoric and courtship rituals (through olfactory and tactile signals) often take place before copulation; indirect sperm transfer usually occurs.
Length of carapace: 1.5 cm
Similar species: Petrolisthes marginatus Stimpson, 1859
Synonyms:
Petrolisthes serratus Henderson, 1888 · unaccepted > junior subjective synonym
Porcellana Amoena Guérin-Méneville, 1855 · unaccepted > superseded combination
In Petrolisthes amoenus, the color patterns vary greatly depending on size.
Small specimens (cl 3.9, cw 3.5) have brownish to orange spots on a predominantly white background; these small spots group together to form larger spots or slender stripes on the carapace and chelipeds.
The walking legs P2–5, also known as pereiopods, feature a net-like pattern of brownish to orange thick stripes.
In larger specimens (cl 5.7, cw 5.3), the carapace is regularly and densely covered with a net-like pattern of slender, carmine-red stripes on a much more subtle white background.
The carpus, merus, and proximal half of the propodus of the chelipeds have carmine-red stripes of varying size and thickness on a predominantly white background, while the distal half of the propodus, the solid finger, and the dactylus are carmine-red.
On P2–5, the net-like pattern of thick stripes is carmine-red.
Adult specimens (cl 9.4, cw 8.5) are mostly reddish to dark orange on the carapace and chelipeds; the reticulate pattern on P2–5 is carmine red and is crossed by 3 or 4 transverse white stripes alternating with the rest of the red.
A large carmine red spot on a light orange background is characteristic of the Mxp 3 merus (Fig. 5C). The ventral surface of the body is also distinctly reddish with small light yellow areas.
The distinguishing features of the crabs are particularly easy to see here:
https://www.researchgate.net/ publication/318793782_A_new_species_of_Pachycheles_Crustacea_Anomura_Porcellanidae_with_taxonomic_remarks_on_two_other_porcelain_crabs_from_the_remote_oceanic_archipelago_of_Trindade_and_Martin_Vaz_South_Atlantic_Ocean , page 555
A certain degree of morphological variation can be observed in Petrolisthes amoenus, which is partly related to the size of the specimens:
The presence of dense, short, robust setae on the back of the carapace, mainly in small specimens (such setae are usually absent in larger specimens and completely absent in adult specimens); and the degree of development of the outer corner of the eye, which in large specimens may be equipped with a spine of varying size (or even appear only as a slight elevation) (in small specimens, the outer corner of the eye is equipped with a conspicuous spine).
However, even in specimens of the same size and sex, some morphological variations can be observed:
The antennule basal segment with 4 to 6 distal spines (usually 4); (2) 4 or 5 spines on the mesial margin of the P1 carpus; and a fringe of setae on the lateral margin of the P1 propodus, which is either slightly pronounced and only present on its proximal half or clearly pronounced along the entire lateral margin of the P1 propodus.
It is not uncommon for specimens of Petrolisthes amoenus in museum collections to be misidentified as Petrolisthes galathinus.
Reproduction:
Members of the order Decapoda are mostly gonochoric and courtship rituals (through olfactory and tactile signals) often take place before copulation; indirect sperm transfer usually occurs.
Length of carapace: 1.5 cm
Similar species: Petrolisthes marginatus Stimpson, 1859
Synonyms:
Petrolisthes serratus Henderson, 1888 · unaccepted > junior subjective synonym
Porcellana Amoena Guérin-Méneville, 1855 · unaccepted > superseded combination
