Smithsonian Environmental Research Center
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Fish that live in clams (Astrapogon stellatus, clam cardinalfish), visceral fish that seek shelter in the bodies of sea cucumbers, blennies that live in tubes of tubeworms, there is almost nothing in nature that does not exist.
Every January at low tide for 7 years (1999-2005), tubes of the polychaete Chaetopterus sp. were excavated at Dog Island, Florida, in the northern Gulf of Mexico and examined for the presence of two common crustacean feeders, the anomuran Polyonyx gibbesi and the brachyuran Pinnixa chaetopterana.
Of 114 tubes examined, 4 (3.5 %) contained no crustaceans, 77 (67.5 %) contained only Pinnixa, 23 (20 %) contained only Polyonyx and 10 (9 %) contained both species.
Among the Pinnixa-only tubes, 90% contained a mixed-sex pair; among the Polyonyx-only tubes, 57% contained a mixed-sex pair and the remainder contained a single crab.
All tubes containing both species contained either one or two adult Pinnixa and a small Polyonyx (CW < 3.5 mm, 9 tubes) or a single adult Polyonyx and a small Pinnixa (CW < 3 mm, 1 tube).
No tube contained adults of both species. Of the adult females, 24 % of the Pinnixa and 44 % of the Polyonyx were ovipositing. 7
Experiments in which single adult crabs of either species were introduced into in situ tubes showed that adult crabs of either species expel same-sex conspecifics or heterospecies; over time, most tubes form a mixed-sex pair of a single species.
Source: https://www.jstage.jst.go.jp/article/crustacea/Special2006/6/Special2006_23/_article
The carapace of Polyonyx gibbesi is smooth, oval, about 1/4 to 1/3 wider than long, the front edge is almost straight.
Color: light with some orange or brown, legs and underside of claws speckled;
The antennae are narrow, approx. 1/2 times as long as the body; chelipeds (claws) unequal (different sizes), the inner margin on the 2nd segment (next to the claw) is concave, hollowed out; claws and legs are hairy.
Polyonyx gibbesi lives in pairs in the tubes of the parchment worm, Chaetopterus variopedatus, the porcelain crab is only rarely found outside the tubes.
The relative abundance of the two crabs from Georgetown, South Carolina, compared to other areas identifies Polyonyx as a more southern crab than Pinnixa.
However, the zoeae and adults of Polyonyx are less tolerant of high temperatures than the zoeae or adults of Pinnixa, as indicated by both lethality threshold and metabolic studies.
Adult Polyonyx are also less tolerant to low temperatures than adult Pinnixa. The results suggest that Polyonyx is an obligate commensal of Chaetopterus, whereas Pinnixa is a facultative commensal.
Polyonyx gibbesi is the only species of the genus that occurs in the western Atlantic.
Synonyms:
Polyonix creplini (Müller, 1862)
Polyonix creplinii (Müller, 1862)
Porcellana Creplinii Müller, 1862
Porcellana macrocheles Gibbes in White, 1849
Porcellana macrocheles Gibbes, 1850
Literatur reference:
Werding B, Hiller A (2019)
A new species of Polyonyx (Crustacea, Anomura, Porcellanidae) inhabiting polychaete-worm tubes (Annelida, Chaetopteridae) in the Indo-West Pacific.
ZooKeys 818: 25-34. https://doi.org/10.3897/zookeys.818.30587
Every January at low tide for 7 years (1999-2005), tubes of the polychaete Chaetopterus sp. were excavated at Dog Island, Florida, in the northern Gulf of Mexico and examined for the presence of two common crustacean feeders, the anomuran Polyonyx gibbesi and the brachyuran Pinnixa chaetopterana.
Of 114 tubes examined, 4 (3.5 %) contained no crustaceans, 77 (67.5 %) contained only Pinnixa, 23 (20 %) contained only Polyonyx and 10 (9 %) contained both species.
Among the Pinnixa-only tubes, 90% contained a mixed-sex pair; among the Polyonyx-only tubes, 57% contained a mixed-sex pair and the remainder contained a single crab.
All tubes containing both species contained either one or two adult Pinnixa and a small Polyonyx (CW < 3.5 mm, 9 tubes) or a single adult Polyonyx and a small Pinnixa (CW < 3 mm, 1 tube).
No tube contained adults of both species. Of the adult females, 24 % of the Pinnixa and 44 % of the Polyonyx were ovipositing. 7
Experiments in which single adult crabs of either species were introduced into in situ tubes showed that adult crabs of either species expel same-sex conspecifics or heterospecies; over time, most tubes form a mixed-sex pair of a single species.
Source: https://www.jstage.jst.go.jp/article/crustacea/Special2006/6/Special2006_23/_article
The carapace of Polyonyx gibbesi is smooth, oval, about 1/4 to 1/3 wider than long, the front edge is almost straight.
Color: light with some orange or brown, legs and underside of claws speckled;
The antennae are narrow, approx. 1/2 times as long as the body; chelipeds (claws) unequal (different sizes), the inner margin on the 2nd segment (next to the claw) is concave, hollowed out; claws and legs are hairy.
Polyonyx gibbesi lives in pairs in the tubes of the parchment worm, Chaetopterus variopedatus, the porcelain crab is only rarely found outside the tubes.
The relative abundance of the two crabs from Georgetown, South Carolina, compared to other areas identifies Polyonyx as a more southern crab than Pinnixa.
However, the zoeae and adults of Polyonyx are less tolerant of high temperatures than the zoeae or adults of Pinnixa, as indicated by both lethality threshold and metabolic studies.
Adult Polyonyx are also less tolerant to low temperatures than adult Pinnixa. The results suggest that Polyonyx is an obligate commensal of Chaetopterus, whereas Pinnixa is a facultative commensal.
Polyonyx gibbesi is the only species of the genus that occurs in the western Atlantic.
Synonyms:
Polyonix creplini (Müller, 1862)
Polyonix creplinii (Müller, 1862)
Porcellana Creplinii Müller, 1862
Porcellana macrocheles Gibbes in White, 1849
Porcellana macrocheles Gibbes, 1850
Literatur reference:
Werding B, Hiller A (2019)
A new species of Polyonyx (Crustacea, Anomura, Porcellanidae) inhabiting polychaete-worm tubes (Annelida, Chaetopteridae) in the Indo-West Pacific.
ZooKeys 818: 25-34. https://doi.org/10.3897/zookeys.818.30587
