Parthenopidae

Horrid elbow crab Daldorfia horrida, photographed by Francesco De Marchi.

Belongs within: Heterotremata.

The Parthenopidae, elbow crabs or pebble crabs, are a family of tropical and subtropical marine crabs, notable for having particularly long chelipeds relative to the other legs. Most species have a subtriangular body shape, though the Indo-Pacific Lambrachaeus ramifer has the front of the carapace extended forward into a long neck.

Crabs that cannot scratch their heads
Published 12 October 2009
An elbow crab amongst seaweed, showing both its long reach and well-developed camouflage. Photo from Wild Shores of Singapore.

Lift up one arm, and bend your elbow. Reach with your fingers to a point on your back, between your shoulder-blades. Scratch. Not only will that work wonders for any annoying tingle that you might have been feeling, but you have just demonstrated your superior flexibility to an elbow crab.

Crabs of the family Parthenopidae are found in tropical and subtropical coral reefs and shelly sea bottoms. Most species have bodies that are roughly triangular in shape, and often highly ornamented with lumps, bumps and spines (this ornamentation makes them very difficult to see among coral and rocks; it also encourages the growth of algae and other camouflaging organisms on the crab). They also usually have very large and long chelipeds (pincers), which make it easy to see how they got the name of ‘elbow crabs’. The merus (the ‘upper arm’ part of the cheliped) is proportionally much longer than in many other crab families, giving parthenopids a real gorilla-ish look (I found one website that labelled a parthenopid of the genus Daldorfia as the “King Kong crab”). Despite their extraordinary size and length, however, the range of mobility of an elbow crab’s chelipeds is limited, hence the point about back-scratching above. An elbow crab cannot reach the middle part of the top of its carapace.

Furtipodia petrosa, a rather adorable-looking parthenopid from Guam that resembles a sponge-covered rock. Furtipodia is also one of a number of parthenopids in which the walking legs are hidden by the carapace, improving the disguise. Photo from here.

This lack of cheliped mobility is one of the features distinguishing members of the Parthenopidae from the spider crabs of the Majidae, which have a broadly similar superficial appearance (Ng & McLay 2003). Other distinct features of the family include the fusion of the third to fifth segments of the male abdomen* (Tan & Ng 2007); also, while female majids have a high-domed abdomen that forms an entirely enclosed brood chamber for her eggs, the parthenopid female’s abdomen does not entirely seal the eggs away from the outside world. The similar adult appearance of Parthenopidae and Majidae, with their triangular bodies and pointed snouts, lead most early authors to regard them as closely related, but the similarities are now thought to be convergent. The larvae of parthenopids are more similar to those of other families than majids (Yang 1971), while phylogenetic studies do not support their association (Brösing 2008).

*If you don’t know where to find the abdomen of a crab, then look at the underside of one the next time you’re able to. The much reduced abdomen is turned forwards and held on the underside of the cephalothorax. In males, it is a small, narrow segmented strip. In females, it is much larger and broader, and is used to hold her eggs.

Normal parthenopids are remarkable enough, but Lambrachaeus ramifer looks like something out of a Japanese video game (making it appropriate that I found this photo on a Japanese website). This individual is a female carrying eggs—they’re the orange mass on her underside.

The subfamilial classification of Parthenopidae was reviewed by Tan & Ng (2007) who recognised only two subfamilies of elbow crabs, the Parthenopinae and Daldorfiinae (earlier authors recognised more—some have been moved to other families, others have been synonymised). The two subfamilies are distinguished by only a single character, the relative length of the antennal segments, and a more formal analysis is still required to test their distinction. A separate subfamily had previously been recognised for the very distinctive Indo-Pacific species Lambrachaeus ramifer which has the front of the carapace extended forward into a long neck (Ng & McLay 2003), but Tan & Ng (2007) placed this species in Parthenopinae, noting that it had been separated on the basis of its own peculiar autapomorphies rather than by lack of the features of other subfamilies.

Systematics of Parthenopidae

Characters (from Gore & Scotto 1979): Eyes usually retractile within small circular well-defined orbits; floor of orbit nearly continued to fron, leaving a hiatus usually filled by second article of antennary peduncle which is small, short, not fused with epistome or front. Basal antennal article small, deeply embedd between inner angle of orbit and antennulary fossae. Antennules folding a little obliquely. Chelipeds not especially mobile, usually much longer and heavier than other legs, with fingers bent on the hand at an angle toward side with fixed finger. Palp of external maxilliped articulated at anterointernal angle of merus. Male openings coxal.

<==Parthenopidae
    |  i. s.: Rhinolambrus Milne-Edwards 1878NM03
    |           |--*R. contrarius (Herbst 1804) [=Cancer contrarius]NM03
    |           |--R. cybelis (Alcock 1895)NM03
    |           |--R. pelagicus (Ruppell 1830) [=Parthenope (Rhinolambrus) pelagicus]J90
    |           |--R. sisimanensis Serène & Umali 1972NM03
    |           `--R. turriger (White 1847)NM03
    |         Mimilambrus [Mimilambridae, Mimilambroidea]MD01
    |         AulacolambrusMG-H11
    |--Lambrachaeus Alcock 1895 [Lambrachaeinae, Lambrachaeini]NM03
    |    `--*L. ramifer Alcock 1895NM03
    |--DaldorfiaTSH09 [Daldorfiidae, DaldorfiinaeNM03]
    |    |--D. garthiV77
    |    |--D. horrida (Linnaeus 1758)TSH09 [=Parthenope horridaGS79]
    |    |--D. investigatorisV77
    |    |--D. rathbunaeV77
    |    |--D. semicircularisV77
    |    `--D. spinosissimaV77
    `--ParthenopinaeGS79
         |--Garthambrus Ng 1996NM03
         |--Tutankhamen Rathbun 1925GS79
         |    `--T. cristatipes (Milne Edwards 1880) [=Mesorhoea cristatipes, Lambrus cristatipes]GS79
         |--ThyrolambrusGS79
         |    |--T. astroides Rathbun 1894GS79
         |    `--T. excavatus Baker 1905MG-H11
         |--PlatylambrusGS79
         |    |--P. carinatusGS79
         |    `--P. validus De Haan 1837MG-H11
         |--Mesorhoea Stimpson 1871GS79
         |    |--M. belli (Milne Edwards 1878)GS79
         |    `--M. sexspinosa Stimpson 1871 [=M. sexpinosa; incl. Solenolambrus fastigatus Milne Edwards 1878]GS79
         |--Leiolambrus Milne Edwards 1878GS79
         |    |--L. nitidus Rathbun 1901GS79
         |    `--L. punctatissimus (Owen 1839)GS79
         |--Cryptopodia Milne Edwards 1834GS79
         |    |--C. concava Stimpson 1871GS79
         |    |--C. hassleri Rathbun 1925GS79
         |    `--C. spatulifrons Miers 1879J90
         |--Heterocrypta Stimpson 1871GS79
         |    |--H. aloysioi Rodriques da Costa 1968GS79
         |    |--H. colombiana Garth 1940GS79
         |    |--H. granulata (Gibbes 1850) [=Cryptopodia granulata; incl. H. lapidea Rathbun 1901]GS79
         |    `--H. tommasii Rodriques da Costa 1959GS79
         |--Solenolambrus Stimpson 1871GS79
         |    |--S. arcuatus Stimpson 1871GS79
         |    |--S. brasiliensis Rodrigues da Costa 1961GS79
         |    |--S. decemspinosus Rathbun 1894GS79
         |    |--S. portoricensis Rathbun 1924GS79
         |    |--S. tenellus Stimpson 1871 [incl. Pisolambrus nitidus Milne Edwards 1878, Lambrus (Pisolambrus) nitidus]GS79
         |    `--S. typicus Stimpson 1871GS79
         `--Parthenope Weber 1795GS79
              |--P. agona (Stimpson 1871) [=Lambrus agonus, P. agonus (l. c.)]GS79
              |--P. angulifrons Latreille 1825KK03
              |--P. aylthoni Righi 1965GS79
              |--P. charlottensis Rathbun 1935GS79
              |--P. chondrodes Davie & Turner 1994MG-H11
              |--P. depressiuscula (Stimpson 1871) [=P. (Platylambrus) depressiuscula]GS79
              |--P. excavata (Stimpson 1871)GS79
              |--P. exilipes (Rathbun 1893)GS79
              |--P. fraterculus (Stimpson 1871) [=Lambrus fraterculus, Platylambrus fraterculus]GS79
              |--P. granulata (Kingsley 1879) [=Lambrus granulatus]GS79
              |--P. guerini (Brito Capello 1871)GS79
              |--P. hyponca (Stimpson 1871)GS79
              |--P. macrochelos (Herbst 1790)KK03
              |--P. massena Roux 1830 [=Lambrus massena]GS79
              |--P. meridionalis (Boschi 1965)GS79
              |--P. nodosus (Jacquinot 1853)J90
              |--P. pourtalesii (Stimpson 1871) (see below for synonymy)GS79
              |--P. serrata (Milne Edwards 1834) (see below for synonymy)GS79
              |--P. stimpsoni Garth 1958GS79
              `--P. triangula (Stimpson 1860) [=P. (Pseudolambrus) triangula]GS79

Parthenope pourtalesii (Stimpson 1871) [=Lambrus pourtalesii, Lambrous (l. c.) pourtalesii, Lambrus ponstalesi (l. c.), Platylambrus pourtalesii; incl. Lambrus verrillii Smith 1881, Parthenope verrillii]GS79

Parthenope serrata (Milne Edwards 1834) [=Lambrus serratus, Platylambrus serratus; incl. L. crenulatus Saussure 1858, Parthenope crenulata, L. lupoides White 1847 (n. n.), L. melanodactylus Desbonne in Desbonne & Schramm 1867 (n. n.)]GS79

*Type species of generic name indicated

References

Brösing, A. 2008. A reconstruction of an evolutionary scenario for the Brachyura (Crustacea) in the context of the Cretaceous-Tertiary boundary. Crustaceana 81 (3): 271–287.

[GS79] Gore, R. H., & L. E. Scotto. 1979. Crabs of the family Parthenopidae (Crustacea Brachyura: Oxyrhyncha) with notes on specimens from the Indian River region of Florida. Memoirs of the Hourglass Cruises 3 (6): 1–98.

[J90] Jones, D. S. 1990. Annotated checklist of marine decapod Crustacea from Shark Bay, Western Australia. In: Berry, P. F., S. D. Bradshaw & B. R. Wilson (eds) Research in Shark Bay: Report of the France-Australe Bicentenary Expedition Committee pp. 169–208. Western Australian Museum.

[KK03] Kocataş, A., & T. Katağan. 2003. The decapod crustacean fauna of the Turkish seas. Zoology in the Middle East 29: 63–74.

[MD01] Martin, J. W., & G. E. Davis. 2001. An updated classification of the Recent Crustacea. Natural History Museum Los Angeles County, Science Series 39: 1–124.

[MG-H11] McEnnulty, F. R., K. L. Gowlett-Holmes, A. Williams, F. Althaus, J. Fromont, G. C. B. Poore, T. D. O’Hara, L. Marsh, P. Kott, S. Slack-Smith, P. Alderslade & M. V. Kitahara. 2011. The deepwater megabenthic invertebrates on the western continental margin of Australia (100–1100 m depths): composition, distribution and novelty. Records of the Western Australian Museum Supplement 80: 1–191.

[NM03] Ng, P. K. L., & C. L. McLay. 2003. On the systematic position of Lambrachaeus Alcock, 1895 (Brachyura, Parthenopidae). Crustaceana 76 (8): 897–915.

Tan, S. H., & P. K. L. Ng. 2007. Descriptions of new genera from the subfamily Parthenopinae (Crustacea: Decapoda: Brachyura: Parthenopidae). Raffles Bulletin of Zoology Supplement 16: 95–119.

[TSH09] Titelius, M. A., A. Sampey & C. G. Hass. 2009. Crustaceans of Mermaid (Rowley Shoals), Scott and Seringapatam Reefs, north Western Australia. Records of the Western Australian Museum Supplement 77: 145–176.

[V77] Vermeij, G. J. 1977. Patterns in crab claw size: the geography of crushing. Systematic Zoology 26 (2): 138–151.

Yang, W. T. 1971. The larval and postlarval development of Parthenope serrata reared in the laboratory and the systematic position of the Parthenopinae (Crustacea, Brachyura). Biological Bulletin 140: 166–189.

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