Crustacea in the Biosphere1)

CHAPTER 26 CRUSTACEA IN THE BIOSPHERE1) BY PIERRE NOËL, THÉODORE MONOD (†) AND LUCIEN LAUBIER (†) Contents. – Introduction: the presence of Crustacea in the biosphere. The extremes: sizes and environmental conditions – Size – Temperature – Altitude – Deep sea – Salinity. Habitats of crustaceans. The oceanic environment – Coastal zone: littoral and neritic bottoms – Deep benthos – The pelagic realm. Fresh waters – Continental waters – Thermal waters – Subterranean waters – Temporary waters – Hypersaline water bodies – Phytothelmes – Muscicolous crustaceans. Terrestrial habitats – “Flying” Crustacea. Commensal and parasitic associations of Crustacea. Epizoonts, commensals and parasites of crustaceans. Appendices. Bibliography. INTRODUCTION: THE PRESENCE OF CRUSTACEA IN THE BIOSPHERE P. J. van Beneden wrote in 1861: « Aucune classe du règne animal ne nous semble présenter une diversité plus remarquable. Tous les genres d’habitation possibles semblent avoir été épuisés, et, depuis l’état de libre vagabondage en pleine mer jusqu’à la dépendance la plus complète de l’hôte qui les héberge ou du gîte qui les abrite, toutes les nuances intermédiaires imaginables semblent avoir été épuisées.»[“Not a single class of the animal kingdom appears to present a more remarkable diversity [than Crustacea]. All types of possible lodging seem to have been exhausted, from the state of vagrancy in open sea until full dependence on the host that feeds them, or on the accommodation that houses them. All intermediate possibilities that could be imagined seem to have been exhausted.”] Crustaceans show an extraordinary diversity for their ways of life and their diets. What is actually shared between the appearance of a sacculinid cirripede and a water flea, between a crab and a brine shrimp? As such, they rank among the most diverse groups 1) The original, 1996 text has been updated by Pierre Noël in March 2013; latest additions December 2013. © Koninklijke Brill NV, Leiden, 2014 Crustacea 4B (26): 3-115 4 P. NOËL, TH. MONOD (†) & L. LAUBIER (†) of the Animal Kingdom. A large number of habitats has been occupied by crustaceans; however, they are basically aquatic and mainly marine. Very few of them adapted to a life style outside the water. Some crustaceans are sessile (cirripedes); none is really able to fly. Among arthropods, crustaceans fulfil the same role in the water that insects have in terrestrial and aerial habitats. However, their numbers of species are by far smaller, i.e., some 68 000 only (fossils not included), with the following distribution over the various classes (classification according to Forest, 2004; numbers adapted from Ahyong et al., 2011, and further literature): Cephalocarida 13 Branchiopoda ±1180 Remipedia 27 Tantulocarida 36 Mystacocarida 13 Thecostraca ±1400 Copepoda ±16 000 Branchiura ±200 [Pentastomida 130] Ostracoda ±7600 Malacostraca ±40 000 The number of described species of Crustacea increases with time. For instance, this number was successively estimated as 30 000 (Forest, 1969), 40 000 (Heywood & Watson, 1995), 52 000 (Monod & Laubier, 1996; Martin & Davis, 2001), and 68 000 (Brusca & Brusca, 2003). The average of new, valid species described every year is ca. 300. Furthermore, it is often considered that for groups of small size only half of the species actually present may have been described already (see Noodt, 1971 for copepods), which means that substantial numbers of species of crustaceans in nature still await scientific discovery and proper description. For amphipods, Bousfield (1978) stated that approximately 25 000 species would exist, whereas only 5000 species had by then been described. Furthermore, the growing application of molecular techniques is uncovering much cryptic speciation. THE EXTREMES: SIZES AND ENVIRONMENTAL CONDITIONS Size Crustacean adult size varies from 0.1 mm (Stygotantulus stocki), less than 1 mm for copepods (0.18 mm), ostracodes, mystacocarids, and even peracarids such as isopods of the families Microcerberidae and Microparasellidae, or 1-2 mm (Isopoda: Chauliodonis- cus reyssi: 1.3 mm, Haploniscus unicornis: 1.7 mm; Carpias minutus: 1.9-2.16 mm; Am- phipoda: Galapsiellus leleuporum: 1-1.15 mm), to up to 65 cm (body length) for the De- capoda: Homarus americanus. These are selected minimal sizes as examples, but here are,.

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