A new species of Megaesthesius Rathbun, 1909 (Crustacea: Brachyura: Chasmocarcinidae) from deep water off Western Australia.

A new species of Megaesthesius Rathbun, 1909, M. westralia, is described from shelf waters off Western Australia. It can be separated from its two congeners by differences in carapace shape and dentition, as well as differences in the male abdomens and gonopods.

A new species of Mictyris Latreille, 1806 (Crustacea: Decapoda: Brachyura: Mictyridae) from the Andaman coast of Thailand, with notes on its ecology and behavior.

A new species of soldier crab (genus Mictyris Latreille, 1806) is described from the Andaman Sea coast of Thailand. Mictyris thailandensis sp. nov. differs morphologically from its described congeners by its pale plain colouring, the differently shaped apex of the male first gonopod, and by chela features. It also has significant genetic divergence (cytochrome oxidase I > or = 11.95%) from other described species.

A review of Chiromantes obtusifrons (Dana, 1851) (Decapoda: Brachyura: Sesarmidae), with descriptions of four new sibling-species from Christmas Island (Indian Ocean), Guam and Taiwan.

The identity of Chiromantes obtusifrons (Dana, 1851), previously considered widespread in the tropical West Pacific region to the eastern Indian Ocean, is revised and found to be a species-complex. Chiromantes obtusifrons is now considered endemic to the Hawaiian Is., and four new species are described from Guam, Taiwan and Christmas Island. Two species live sympatrically in Taiwan. Species separation is based on carapace and frontal shape and granulation, leg proportions, abdominal somite proportions, and distinctive live colouration.

A new species and new record of Samadinia Ng & Richer de Forges, 2013 (Crustacea: Brachyura: Epaltidae) from deepwater off north-eastern Queensland, Australia.

A new species of Samadinia Richer de Forges & Ng, 2013, is described from deep-water off northeastern Queensland, Australia. Samadinia hela n. sp. is distinctive in having pseudorostral spines longer than the maximum carapace length, slender preorbital spines that are curved inwards over the base of the rostrum, and long and laterally flattened hepatic and lateral bracnchial spine plates. A new record of S. despereaux (Lee, Richer de Forges & Ng, 2019) from Queensland is also reported in this study.

Two new species of Tmethypocoelis Koelbel, 1897 (Decapoda, Brachyura, Dotillidae) from Sulawesi, Indonesia.

Tmethypocoelis Koelbel, 1897, is a central Indo-West Pacific genus of small intertidal, soft sediment dotillid crabs that includes five recognised species. Two new species, Tmethypocoelissimplexsp. nov. and T.celebensissp. nov., are here described from Sulawesi, Indonesia. Tmethypocoelissimplexsp. nov. is found on the west coast of Central Sulawesi, while T.celebensissp. nov. occurs in the north-eastern part of Sulawesi. Both new species differ from each other and known congeners by the male cheliped, male pleon, and male first gonopod characters. The differences in gastric mill morphology further confirm the two species as new. The distinct water current patterns in the Makassar Strait and the Maluku Channel might have contributed to the evolution of these two sibling species.

Redescription of Austrothelphusa wasselli (Bishop, 1963) (Crustacea: Brachyura: Gecarcinucidae), and designation of a new species from the Gilbert River, north Queensland, Australia.

A new species of freshwater crab, Austrothelphusa gilbertensis, is described from Gilbert River Catchment, north-western Queensland. It is morphologically most similar to A. wasselli Bishop, 1963, described from the eastward flowing Stewart Drainage Basin, much further to the north-east on Cape York. It differs from A. wasselli by several morphological characters including, better defined gastro-cardiac carapace grooves, cervical groove relatively deeper, postfrontal lobes more prominent and bearing striated crests, larger and fewer spots on carapace and legs, epibranchial tooth more prominent, walking legs more slender, and G1 more strongly curved. A CO1 genetic divergence of greater than 6% confirms its novel status. Intraspecific CO1 divergence within catchments is also discussed.

The magnitude of global marine species diversity.

BACKGROUND: The question of how many marine species exist is important because it provides a metric for how much we do and do not know about life in the oceans. We have compiled the first register of the marine species of the world and used this baseline to estimate how many more species, partitioned among all major eukaryotic groups, may be discovered. RESULTS: There are ∼226,000 eukaryotic marine species described. More species were described in the past decade (∼20,000) than in any previous one. The number of authors describing new species has been increasing at a faster rate than the number of new species described in the past six decades. We report that there are ∼170,000 synonyms, that 58,000-72,000 species are collected but not yet described, and that 482,000-741,000 more species have yet to be sampled. Molecular methods may add tens of thousands of cryptic species. Thus, there may be 0.7-1.0 million marine species. Past rates of description of new species indicate there may be 0.5 ± 0.2 million marine species. On average 37% (median 31%) of species in over 100 recent field studies around the world might be new to science. CONCLUSIONS: Currently, between one-third and two-thirds of marine species may be undescribed, and previous estimates of there being well over one million marine species appear highly unlikely. More species than ever before are being described annually by an increasing number of authors. If the current trend continues, most species will be discovered this century.