Arthropods (animals of the Phylum Arthropoda) are an extremely diverse group readily identified by their chitinous exoskeleton, multiple joined appendages, and segmented bodies. Early estimates of arthropod diversity (predicting number of unknown species) ranged as high as 30-100 million. That figure has since been dramatically revised and conservative estimates put the number of extant species at between 2 and 10 million, only just over one million of which have been described. These one million species account for over 80% of all extant animal species. Arthropods inhabit almost every habitat, from the deep ocean to extreme altitudes; from Arctic ice packs to the Australian deserts. Unfortunately, global habitat degradation and destruction continues apace and it is inevitable that a great many species will be, and indeed have been lost before they could be discovered.
As was the case with the dicots (and will be again with subsequent lists), the taxon has been split between the groups detailed here and the insects in part 2. It should be noted that a great many arthropod species are data deficient and thus are unclassified (that is to say, except as ‘data deficient’ (DD)). It is highly probable that a great many of these species are critically endangered.
Follow the link for ‘Arthropods Part 2 – Insects‘.
 Understanding Evolution. (2010). The Arthropod Story. University of California Museum of Paleontology. [online]
 Odegaard, F. (2000). How many species of arthropods? Erwin’s estimate revised. Biol J Linn Soc. 71:583 – 597. [available online]
 Hamilton, A. et al. (2010). Quantifying uncertainty in estimation of tropical arthropod species richness. Am Nat. 176: 90 – 95
Peacock tarantula (Poecilotheria metallica)
The beautiful metallic blue peacock tarantula was first discovered in a timber yard of Gooty, India in 1899. Despite frequent and resolute surveys, the species was not rediscovered for another 102 years when individuals were found in a forest some distance from the original site. They are arboreal creatures, living in tall trees where they feed on insects. There is no information available on the current size of the population. However, P. metallica exists within a restricted range of less than 100km^2. Habitat quality is declining and, due to the striking colouration, it is a highly sought-after species for the international pet trade.
 Molur, S., Daniel, B.A. & Siliwal, M. 2008. Poecilotheria metallica. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.2
 Gurley, R. (2009). Metallic bluie ornamental tree spider. Animal-world. [online]
Noel’s amphipod (Gammarus desperatus)
Like all amphipods, G. desperatus is small and shrimp-like, lacking a carapace and exhibiting lateral compression. It is a freshwater species of well-oxygenated streams, ponds and springs. Primary threats are habitat loss, degredation and pollution. Two of the three known sub-populations have been lost in the last century; the only known surviving population exists at Bitter Lake National Wildlife Refuge, New Mexico, USA.
 Lang, B. & Pollock, C.M. 2000. Gammarus desperatus. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.2.
 Cole, G.A. (1979). Gammarus desperatus, a new species from New Mexico (Crustacea: Amphipoda). Hydrobiologia. 76 (1-2): 27 – 32.
Image © Brian K. Lang
Ingolfiellidae is not an especially speciose taxon as amphipods go, comprising 39 known species. However, the taxon as a whole has a global distribution, inhabiting deep-sea mud floors, fresh and brackish waters and high altitude river beds. I. longipes was discovered in a brackish cave pool (Walsingham Sink Cave) on the island of Bermuda. To date, only a single female has been collected.
 Iliffe, T.M. 1996. Ingolfiella longipes. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.2.
 CaveBiology.com (2007). Ingolfiella (Tethydiella) longipes Stock, Sket & Iliffe, 1987. CaveBiology.com. [online]
 Vonk. R., Schram, F. R. (2003). Ingolfiellidea (Crustacea, Malacostraca, Amphipoda): a phylogenetic and biogeographic analysis. Contib Zool. 72(1) [online]
Shasta crayfish (Pacifastacus fortis)
Crayfish are freshwater relatives of lobsters; the famous langoustine or spiny lobster is a marine crustacean which is sometimes referred to by the name ‘crayfish’ though to call it such is, taxonomically speaking, a misnomer. The Shasta crayfish is endemic to Shasta County, California where it exists in fragmented sub-populations of the Pit River drainage. Migration between sub-populations, while being disturbed by natural barriers, is also inhibited by hydroelectric development and habitat degradation. Further threats come in the form of invasive crayfish species, including the infamous signal crayfish (Pacifastacus leniusculus). Based on previous surveys, the current population may be as low as 3,000.
 American Fisheries Society Endangered Species Committee 1996. Pacifastacus fortis. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.2.
 U.S. Fish and Wildlife Service. (2009). Shasta Crayfish (Pacifastacus fortis); 5 Years Review: Summary and Evlauation. U.S. Fish and Wildlife Service. [online]
Image © B. Moose Petersen
All the freshwater crab species which comprise the genus Perbrinckia are endemic to Sri Lanka. Of the 13 Perbrinckia species, one is listed as least concern (LC), two are listed as vulnerable (VU) and the remaining ten are listed as critically endangered. P. punctata is listed thus due to a limited range of occurrence (50km^2) within which it is known only from one location (Horton Plains, Agara Oya Basin). Though the range is protected, human impacts and habitat degradation are primary threats.
 Bahir, M.M., Ng, P.K.L., Crandall, K., Pethiyagoda, R. and Cumberlidge, N. 2008. Perbrinckia punctata. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.2.
Singapore freshwater crab (Johora singaporensis)
The worst case scenario in the most recent IUCN Red List survey of freshwater crabs suggested that around two-thirds of all species are at risk of extinction as a result of habitat destruction, pollution and drainage. While the most optimistic scenario is that only 16% of species are thus endangered (227 identified), the prevalence of stated threats and the fact that 628 species are data deficient means that this lower estimate is highly unlikely to be accurate. The Singapore freshwater crab was originally known from two locations, though one of these has been extirpated due to water acidification. The second population occurs in area of less than 100km^2 in a streamlet near Buit Batok where it hides beneath rocks and in vegetation. This remaining population is under severe threat from habitat development and degradation.
 Lara Esser, Cumberlidge, N., and Darren Yeo 2008. Johora singaporensis. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.2.
 Walker, M. (2009). Freshwater crabs ‘feel the pinch’. BBC Earth News. [online]
Image © Peter Ng
Major black millipede (Doratogonus major)
The millipedes of the genus Doratogonus are relatively large at between 80 and 200 millimetres and are distributed across South Africa at varying levels of abundance. D. major is a species of woodland; specifically, Gwaliweni Forest in northern KwaZulu-Natal, an area of around 11km^2, where it lives in the soil and leaf litter. Only a small number of specimens have been collected despite their size, leading to the suggestion that the population density may be very low. The primary threats to this species are habitat destruction (for fuel and building materials locally) and the various problems faced by species which exist in low numbers.
 Hamer, M. 2006. Doratogonus major. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.2.
 ARKive (2010). Major black millipede (Doratogonus major). ARKive.org. [online]
Image © Bolleque