Pistol shrimps: How to recognise them in the fossil record

Matúš Hyžný (Slovakia), Andreas Kroh (Austria), Alexander Ziegler (Germany) and John WM Jagt (The Netherlands) Alpheid shrimps, colloquially referred to as “pistol shrimps”, exhibit a remarkable anatomical adaptation. These tiny marine crustaceans use their enlarged and highly modified claw to ‘shoot’ at their prey – hence their name. It is astonishing that the snapping claw evolved at least 30 million years ago. How do we know that? Because the fossils tell us. Fig. 1. Habitus (body form) of alpheid snapping shrimps, exemplified by the extant species Alpheus thomasi from the Caribbean Sea. (Photo: Arthur Anker.) The famous snapping claw Alpheid pistol shrimps represent a super-diverse group of benthic marine crustaceans (that is, living on the bottom of the sea, including the sediment surface and some sub-surface layers). There are more than 600 living species, nearly half of which belong to the genus Alpheus. Its representatives possess a snapping claw, a multifunctional tool used for various types of behaviour such as aggression, warning or defence, as well as for hunting prey. Although snapping claws evolved independently several times within various decapod crustaceans, only in pistol shrimps did this organ attain true perfection. Fig. 2. Pistol shrimps ‘shoot’ with an enlarged, modified claw. (Photo: Arthur Anker.) The process of snapping involves a cracking sound reaching up to 210 decibels, one of the loudest produced by any animal. This noise originates from the collapse of a cavitation bubble in front of the claw, which, in addition, is accompanied by a short flash of … Read More

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Boxstones: In search of Miocene Suffolk

Tim Holt-Wilson (UK) The date is 24 May 2014 and I am browsing across East Lane Beach at Bawdsey in southeast Suffolk. A brown lump of sandstone with a white fossil shell impression catches my eye. A boxstone. This is the first one I have ever found with a fossil in it. Looking closely, I see that the sea has abraded the shell’s outlines, although the margins have survived better than the rest, so it should be possible to identify the specimen (Fig. 1). Fig. 1. Boxstone, found 24 May 2014. Boxstones are fragments of a vanished world. They are all that remains of a lost geological stratum in Suffolk called the ‘Trimley Sands’ (Balson, 1990), although deposits of similar age are still present across the sea in Belgium and other parts of Europe. Boxstones are lumps or concretions of brown sandstone, which may contain shell fossils and – if you are extremely lucky – bones and teeth. They are beach-rolled and rounded, and typically measure between 5 and 15cm in diameter. The sand is mostly quartzose, with a rich assemblage of secondary minerals, and is cemented with carbonate-fluorapatite (a phosphate mineral) and calcite (Mathers and Smith, 2002). Boxstones can be found scattered sparsely across the shingle beaches at Bawdsey and Felixstowe Ferry (Fig. 2), and in situ as a common component of the basement beds (nodule beds) at the base of the Coralline Crag and Red Crag formations of southeast Suffolk (Fig. 3). They are eroding out of the … Read More

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Fossil crustaceans as parasites and hosts

Adiël Klompmaker (USA) Who would like to carry a parasite? I bet not many people would like to have one or more. They are nevertheless very common in humans and in other organisms, and can affect entire food webs including keystone species. They tend to be small compared to the host and the vast majority of them are soft-bodied. Despite their small size and soft appearance, they can affect the host substantially, for example, leading to a reduced growth rate and less offspring. Much of the same holds true for crustaceans – they are affected by parasites and can act as parasites themselves. For example, parasitic crustaceans are found among the isopods and copepods. Given the widespread occurrence of parasitism in and by crustaceans today, a fossil record of such parasitism may be expected. Swellings in fossil crabs and squat lobsters So what does the fossil record look like? I have been fortunate to have worked on this under-studied field of research. During my PhD research, I found various swellings in fossil crabs and squat lobsters (decapods from the superfamily Galatheoidea) during and after field work in northern Spain in reef carbonates from the mid-Cretaceous (upper Albian). They appeared to occur regularly in the back part of the carapaces of these crustaceans. Fig. 1. Bopyrid isopods from the species Orthione griffenis (large female and small male), removed from the right gill chamber of a modern mud shrimp (Upogebia pugettensis). (Photo by Stephen Ausmus, USDA Agricultural Research Service, http://www.bugwood.org.) This swelling … Read More

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Cryptic crab caves in Caenozoic corals

Adiël A Klompmaker (USA) Modern coral reefs harbour a large number of cryptic species: species that are either small and/or well hidden in the nooks and crannies of the reef framework. Examples include certain fish, stomatopods, shrimps and crabs. One such group consists of members of the Cryptochiridae family or cryptic crabs. These are small, usually much less than 10mm carapace length, and fragile, because much of their exoskeleton is poorly calcified. The phylogeny, systematics and ecology of these crabs have been an active field of research during the last few years, especially due to work of Sancia van der Meij (Naturalis Biodiversity Center, now at the Oxford University Museum of Natural History) and colleagues. The number of species known has increased notably from about about 45 in 2011 to 52 species in 2016. Along with the discovery of new taxa of these cryptic species, the placement in the Grapsoidea superfamily has been rejected and the Cryptochiridae are now firmly placed in the Cryptochiroidea superfamily. Domiciles in corals This group relies heavily on corals for protection, because all of the more than 50 species live in domiciles within the corals. Most of them can be found in circular to oval or crescent-shaped holes or pits (Fig. 1), whereas only two species make true galls in which the females reside. All species that live in holes are oriented face-forward. The holes are probably caused by a combination of the crabs’ ability to kill a polyp and plus subsequent removal of some … Read More

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Jamaican fossil crabs

Stephen K Donovan (The Netherlands) and Joe SH Collins (UK) Decapod crustaceans (crabs) are among the most attractive of fossils. Yet, the beautifully preserved specimens seen in museum displays and dealers’ catalogues are in stark contrast with the usual haul of the collector, that is, scraps, commonly claws or (more rarely) bits of carapace, which we all find in (mainly) Cretaceous and Cenozoic sedimentary rocks. However, these bits and pieces represent most of the fossil record of crabs and, as such, are of importance to the systematist and anyone with an interest in aspects such as taphonomy and palaeoecology. Just as it is possible to identify a shark from a tooth or a cidaroid echinoid from a spine, so a crab claw can commonly provide data that permits its identification to the level of genus or species (Collins, 1999). The present authors, in collaboration with Roger Portell of the Florida Museum of Natural History at the University of Florida in Gainesville, have been collecting and studying the fossil crabs of Jamaica (and the wider Antilles) for over 20 years. Until the 1990s, reports of fossil crabs from the island were limited to a few fragmented specimens and rare, well-preserved carapaces (some retaining claws) or the isolated claws of mud shrimps (=Callianassa sensu lato), which were collected mainly from the Upper Cretaceous and Eocene by visiting geologists as an aside to their own research. They were sent to the British Museum (Natural History) for description. These early records were reviewed and … Read More

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