Decapod crustaceans from hydrothermal vents and cold seeps: a review through 2005

The taxonomic status, biogeographical distributions and existing collections are reviewed for all species of decapod crustaceans known from the vicinity of hydrothermal vents and cold (hydrocarbon or brine) seeps. To date, more than 125 species representing 33 families of decapods have been reported. Represented families are, in alphabetical order within infraorder, the penaeoid families Benthesicymidae and Sergestidae; the caridean families Alvinocarididae (all of which are vent or seep endemics), Crangonidae, Glyphocrangonidae, Hippolytidae, Nematocarcinidae, Oplophoridae, Palaemonidae, Pandalidae and Stylodactylidae; the anomuran families Chirostylidae, Galatheidae, Lithodidae and Parapaguridae; the brachyuran crab families Atelecyclidae, Bythograeidae (all of which are vent endemics), Cancridae, Epialtidae, Geryonidae, Goneplacidae, Homolidae, Majidae, Ocypodidae, Oregoniidae, Parthenopidae, Pisidae, Portunidae and Varunidae; the lobster (astacidean) family Nephropidae; and the thalassinidean families Axiidae, Callianassidae and Calocarididae. Some species appear to be vagrants, here defined as opportunistic species occasionally found in the vicinity of vent sites but not restricted to them. Other species, notably members of the shrimp family Alvinocarididae and the crab family Bythograeidae, are clearly endemics, known only from vent or seep sites and presumably restricted to them. All endemic vent shrimps, most of which were originally treated as members of the family Bresiliidae, are now treated as members of the family Alvinocarididae. The family Mirocarididae proposed earlier is no longer recognized following a recent review of the characters that define the genus Mirocaris and the family Alvinocarididae. Currently recognized vent-associated species of shrimp belong to six genera: Alvinocaris, Chorocaris, Mirocaris, Nautilocaris, Opaepele and Rimicaris; the genus Iorania is no longer recognized. Several more genera and species are in various stages of description (manuscripts in press or in review). Of the endemic shrimp genera, only Alvinocaris has been reported from both hydrothermal vents and cold seeps. Vagrant shrimp species include members of the families Crangonidae (one species), Hippolytidae (several species in the genus Lebbeus), Nematocarcinidae (genus Nematocarcinus, often seen but rarely collected), Oplophoridae (five genera), Palaemonidae (one species) and Pandalidae (one species of Chlorotocus questionably included). Within the Anomura, vent-associated species of the family Galatheidae (squat lobsters), most belonging to the genera Munida and Munidopsis, are probably vagrants rather than endemics, although some species are known only from vent sites to date and may prove to be true endemics. The galatheid genus Munidopsis is the most speciose and widespread of all vent-associated taxa and has been reported from both hot vents and cold seeps, although this probably reflects only the fact that it is a widespread and speciose deep-sea genus. Other galatheid genera reported from vent sites are Alainius, Phylladiorhynchus and Shinkaia. Also in the Anomura, three chirostylids in two genera (Eumunida and Uroptychus) are known, and the family Lithodidae is represented at several sites (by species in five genera). All of these anomurans are assumed by us to be vagrants rather than endemics, although some species are known only from one or two sites and may prove to be true endemics. The anomuran hermit crab family Parapaguridae is represented by a single species described recently from an active hydrothermal vent; however, the family (or at least a hermit crab assumed to belong to this family) is also known from other locations where it has not been collected. Among the Brachyura, endemic crab species are all members of the family Bythograeidae, which currently consists of five genera (with the number of recognized species in parentheses): Bythograea (6), Cyanagraea (1), Segonzacia (1), Austinograea (4) and Allograea (1). Vagrant crab species in the Atelecyclidae, Cancridae, Epialtidae, Geryonidae, Goneplacidae, Homolidae, Majidae, Ocypodidae, Oregoniidae, Parthenopidae, Pisidae and Portunidae reported from or near vents or seeps are assumed to be vagrants. One genus of Varunidae (Grapsoidea), Xenograpsus, is restricted to shallow-water volcanic systems off Japan and Taiwan and is apparently endemic to shallow thermal sites. The lobster family Nephropidae (known from the Mid-Atlantic Ridge) is represented by one recently described species of the genus Thymopides, the only other species of which is known from Antarctic waters. The thalassinoid (‘mud shrimp’) families Axiidae, Callianassidae and Calocarididae (all reported from the Gulf of Mexico) are represented by species as yet undescribed, with the exception of one recently described axiid from the Gulf and one vagrant callianassid species reported from a shallow volcanic system in the Aegean Sea. Unresolved taxonomic problems, some of which are presently under study by traditional morphological methods and/or comparative studies employing allozymes as well as mtDNA data, are mentioned, and limited genetic information as it relates to biogeography is included where known. A discussion of vent biogeography as it pertains to information on the Decapoda is included. Biogeographical trends include the apparent overall similarity of the Indian Ocean sites to those of the Mid-Atlantic with respect to decapods. Both Indian Ocean and Mid-Atlantic systems exhibit a relatively low endemic crab diversity (one species each, though in different genera) and a relatively high diversity and density of shrimp, including the alvinocarid shrimp genera Mirocaris and Rimicaris, which are found nowhere else. Collection trends include the unfortunate tendency for oceanographic researchers to store vent and seep specimens in university or personal laboratory freezers and other non-recognized repositories, making access to specimens, as well as accurate assessment of their systematic and biogeographical status, difficult. © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society, 2005, 145, 445–522.