Adult members of the decapod Infraorder Anomura are crustaceans with a variously shaped carapace. The group includes hermit crabs, porcelain crabs, mole and sand crabs. The abdomen is either soft and asymmetrically twisted (as in hermit crabs, which inhabit gastropod shells), or not soft, short, symmetrical and flexed underneath the thorax (porcelain crabs, for instance).
The first pereiopod is usually and the second pereiopod is occasionally chelate. The third pereiopod is never chelate; the fourth and fifth pereiopods are usually chelate or subchelate, and one or both are frequently reduced and do not function as a walking leg — the fifth pereiopods function as gill cleaners and are often not visible from outside.
The pleopods are rarely well developed, often reduced or present on only one side of the animal. The uropods often are reduced or modified or may be occasionally absent.
The telson is occasionally reduced or absent; sometimes together with the uropods forming a tailfan.
The larval development is metamorphic, including zoeal and megalopal stages.
In general, Anomura are marine, but a few semiterrestrial and freshwater species are known. Adult anomurans are benthic, therefore they are not included in the present system.
In the present keys, anomuran larvae are only identified as zoeal and megalopal stages and not further keyed out to lower systematic level. Larvae of the families Galatheidae and Porcellanidae may be further identified with the aid of Pike and Williamson, 1972. Larvae of the families Paguridae and Lithodidae may be further identified with Pike and Williamson, 1958.
Distribution in the North Sea
Twenty-seven species of the Infraorder Anomura occur in the North Sea. Adults of few species have been reported from the pelagic, yet as occasional guests in plankton catches, i.e. Pisidia longicornis (Linnaeus, 1767) Family Porcellanidae [Pisida longicornis ]; see Van der Baan et al., 1972. Anomuran species are not keyed out here.
Anomurans from the North Sea are:
Axius stirynchus Leach, 1815
Calocaris macandreae Bell, 1846
Callianassa subterranea (Montagu, 1803)
Callianassa tyrrhena (Petagna, 1792)
Diogenes pugilator (Roux, 1829)
Galathea dispersa Bate, 1859
Galathea intermedia Liljeborg, 1851
Galathea nexa Embleton, 1834
Galathea squamifera Leach, 1814
Galathea strigosa (Linnaeus, 1767)
Munida rugosa (Fabricius, 1775)
Munida sarsi Huus, 1935
Munida tenuimana G.O. Sars, 1872
Lithodes maja (Linnaeus, 1767)
Anapagurus chiroacanthus (Liljeborg, 1856)
Anapagurus hyndmanni (Bell, 1845)
Anapagurus laevis (Bell, 1845)
Pagurus alatus Fabricius, 1775
Pagurus bernhardus (Linnaeus, 1758)
Pagurus cuanensis Bell, 1845
Pagurus prideauxi Leach, 1815
Pagurus pubescens Krøyer, 1838
Pagurus variabilis (A. Milne-Edwards and Bouvier, 1892)
Pisidia longicornis (Linnaeus, 1767)
Porcellana platycheles (Pennant, 1777)
Upogebia deltuara (Leach, 1815)
Upogebia stellata (Montagu, 1803)
[Description after McLaughlin, 1980; Brusca and Brusca, 1990]