Martinssonia elongata gen. et sp.n., a crustacean-like euarthropod from the Upper Cambrian 'Orsten' of Sweden

A tiny arthropod, with five growth stages, is described. Three of the instars are metanauplius-like larvae, having unsegmented bodies and four pairs of appendages. The largest stage, with a length of about 1.5 mm, may still be immature. Its body is divided into three tagmata. The cephalon, including five appendiculate segments, h a projecting forehead with a rostral spine and a small shield with a joint between fourth and fifth segments. Eyes are absent. The trunk is composed of seven annular segments, the anterior two with appendages. The caudal end is a long pleotelson-like segment with the anus on its ventral surface. There are seven pairs of appendages: uniramous antennulae, composed of few tubular podomeres; four pairs of biramous postantennular, almost homeomorphic cephalic appendages; two pairs on the trunk, the anterior pair being similar to the cephalic appendages except for the exopodite, the posterior being much smaller, uniramous and apparently rudimentary. Martinssonia was probably benthic, feeding on detritic particles which it stirred up from the bottom. Besides various crustacean-like features, the new form reveals structures different from Crustacea as well as from all other known arthropodan groups. Martinssonia presumably is a descendant of an euarthropodan group, originating from the crustacean branch long before reaching the eucrustacean level of evolution.     

A novel crustacean swimming stroke: coordinated four-paddled locomotion in the cypridoidean ostracode Cypridopsis vidua (Müller)

Despite the diversity and ecological importance of cypridoidean ostracodes, there have been no kinematic studies of how they swim. We used regular and high-speed video of tethered ostracodes to document locomotion in the cypridoidean species Cypridopsis vidua. Swimming in this species is drag-based, with thrust provided by both antennulae and antennae. About 15 complete power and recovery strokes occur per second; maximal speeds for the limb tips were about 30 mm/s for the antennulae and 50 mm/s for the antennae. These speeds correspond to Reynolds numbers on the order of 10(-1) to 10(0) for the limb tips and 10(-2) to 10(-1) for the setae that extend outward from the swimming limbs and provide much of the surface area of the limb. The strokes of the four thrust-producing limbs are coordinated in a manner that seems to be unique among aquatic arthropods. When viewed from the anterior, power strokes are synchronized diagonally: left antennula and right antenna power strokes start at the same time and terminate just as the power strokes for the right antennula and left antenna begin. Because power strokes occur throughout the stroke cycle, swimming in this species is smoothly continuous, without the rapid accelerations and decelerations characteristic of most small aquatic arthropods.     

The origin of crustaceans: new evidence from the Early Cambrian of China.

One of the smallest arthropods recently discovered in the Early Cambrian Maotianshan Shale Lagerstätte is described. Ercaia gen. nov. has an untagmatized trunk bearing serially repeated biramous appendages (long and segmented endopods and flap-like exopods), a head with an acron bearing stalked lateral eyes and a sclerite and two pairs of antennae. The position of this 520 million-year-old tiny arthropod within the Crustacea is supported by several anatomical features: (i) a head with five pairs of appendages including two pairs of antennae, (ii) highly specialized antennae (large setose fans with a possible function in feeding), and (iii) specialized last trunk appendages (segmented pediform structures fringed with setae). The segmentation pattern of Ercaia (5 head and 13 trunk) is close to that of Maxillopoda but lacks the trunk tagmosis of modern representatives of the group. Ercaia is interpreted as a possible derivative of the stem group Crustacea. Ercaia is likely to have occupied an ecological niche similar to those of some Recent meiobenthic organisms (e.g. copepods living in association with sediment). This new fossil evidence supports the remote ancestry of crustaceans well before the Late Cambrian and shows, along with other fossil data (mainly Early Cambrian in China), that a variety of body plans already coexisted among the primitive crustacean stock.     

A New Bivalved Arthropod from the Early Cambrian Sirius Passet Fauna, North Greenland

A new bivalved arthropod is described from the Lower Cambrian (?Upper Atdabanian) Buen Formation of North Greenland. Pauloterminus spinodorsalis gen. et sp. nov. possesses a bivalved carapace that covers the head, which has a single pair of antennae, and anteriormost thorax. No mouthparts are visible. The five‐segmented abdomen was limbless and terminated in a telson plus a pair of large, lobate uropods. A suite of at least six biramous thoracic limbs are present: the short endopods are made up of small, serial podomeres, while the exopods are lobate and may have functioned as gills as well as in swimming. Partially infilled guts are occasionally visible, suggesting that this animal may have been a sediment feeder. It is compared to other Cambrian bivalved arthropods, especially the waptiids Chuandianella ovata from the Lower Cambrian Chengjiang fauna (China) and Waptia fieldensis from the Middle Cambrian Burgess Shale (British Columbia). Of these three animals, the Greenland and Chinese taxa appear to be the most closely related. P. spinodorsalis possesses many typical arthropod features, but it also demonstrates more primitive characters that are more reminiscent of the lobopodians.     

Crustacea with preserved soft parts from the Upper Cambrian of Sweden

Six monotypic new genera of small crustaceans with phosphatised integument are described from Upper Cambrian, mainly bituminous limestone of southern Sweden. These are Dala peilertae, Bredocaris admirabilis, Walossekia quinquespinosa, Rehbachiella kinnekullensis, Skara anulata and Oelandocaris oelandica. The well-preserved details reveal a nauplius-like organisation of the head region. At least in Bredocaris, Walossekia , and Rehbachiella the head tagma has only three to four specialised pairs of appendages; Skara and Oelandocaris have five pairs of headal limbs. The antennae and the mandibulae served for locomotion and for mastication. All species have a filter apparatus with a distinct filter groove and serially constructed appendages. Four of the six forms had developed a conspicuous median compound eye. Specialisation in the development of the limbs, etc., suggests that some of the forms were benthie, while others may have been epibcnthic and active swimmers, Crustacea , Dala, Bredocaris, Walossekia, Rehbachiella, Skara, Oelandocaris, soft-part preservation, Upper Cambrian, Sweden.     

Phosphatocopina – ostracode-like sister group of Eucrustacea

The Phosphatocopina were long considered as the oldest, Cambrian, record of ostracode Crustacea. However, our detailed analysis of more than 2,500 specimens from the Upper Cambrian ‘Orsten’ of Sweden reveals that Phosphatocopina are neither Ostracoda nor Eucrustacea. The antenna and mandible of the phosphatocopines investigated consist of a prominent limb stem which carries a two-segmented endopod and multi-annulated exopod. This stem portion is now recognised as the fusion product of the coxa and basipod during ontogeny. Phosphatocopina share features, such as the coxa and basipod on antennae and mandibles, as well as ventral body structures such as the prominent pre-oral labrum and a single post-oral cephalic plate, the sternum (with paragnaths on the mandibular sternal portion), exclusively with the Eucrustacea. As a plesiomorphy, the ontogeny of Phosphatocopina starts with a ‘head larva’ with four pairs of limbs, a larva type found in the ground pattern of the Euarthropoda as well as the Crustacea. In contrast, eucrustacean ontogeny begins with a nauplius with three pairs of limbs, a ‘short-head larva’ or orthonauplius. Again, the post-mandibular limbs of phosphatocopines retain the plesiomorphic limb design of a basipod with a setiferous ‘ proximal endite’, whereas Eucrustacea, including the Ostracoda, have their first post-mandibular limb differentiated into a ‘ mouthpart’, the maxillula. Autapomorphies of Phosphatocopina include the small antennula with few terminal setae, a bivalved shield with interdorsum, and the fused coxa and basipod on antenna and mandible. We therefore consider the Phosphatocopina to be the sister group of the Eucrustacea. The respective phosphatocopine species of the Upper Cambrian of southern Sweden are restricted to a particular time zone and may be useful as stratigraphic markers.     

A pyritized polychaete from the Devonian of Ontario

A polychaete from the Middle Devonian Arkona Shale at Hungry Hollow, Arkona, Ontario is preserved in three dimensions in pyrite. The prostomium bears a single median antenna, a pair of lateral antennae and a pair of ventral palps. It is assumed to be fused to a reduced peristomium. The anteriormost three pairs of trunk appendages are modified as tentacular cirri, the third long and biramous. The remainder of the finely annulated trunk bears at least 21 similar biramous parapodia, some of which preserve evidence of chaetae. The postsegmental pygidium is very small and may bear up to two pairs of cirri. The polychaete, Arkonips topororum, falls within the Palpata, Aciculata, among the crown group Phyllodocida. Its remarkable preservation highlights the potential of the Arkona Shale to yield other examples of soft-tissue preservation.     

The ontogeny of the cypridid ostracod Eucypris virens (Jurine, 1820) (Crustacea,Ostracoda)

The chaetotaxy (shape, structure and distribution of setae) of appendages and valve allometry during the post embryonic ontogeny of the cyprididine ostracod Eucypris virens are described. It is shown that the basic ontogenetic development of E. virens is very similar to that of other species of the family Cyprididae. During ontogeny, the chaetotaxy shows continual development on all podomeres of the limbs with the exception of the last podomere on the antennulae. The long setae on the exopodite and protopodite of the antennae have a natatory function until the actual natatory setae develop in later instars. Aesthetascs (presumed chemoreceptors) ya and y3 are the first to develop and may have an important function in the first instars. Cyprididae require a pediform limb in the posterior of the body presumably to help them to attach to substrates and this is reflected by the pediform nature of one limb at all times throughout all instars. This study has also shown that the fifth limb is most probably of thoracic origin and hence ostracods have only one pair of maxillae.     

A new 'great-appendage' arthropod from the Lower Cambrian of China and homology of chelicerate chelicerae and raptorial antero-ventral appendages

The uniramous ‘great appendages’ of several arthropods from the Early to Middle Cambrian are a characteristic pair of pre‐oral limbs, which served for prey capture. It has been assumed that the morphological differences between the ‘great‐appendage’ arthropods indicate that raptorial antero‐ventral and anteriorly pointing appendages evolved more than once in arthropod phylogeny. One set of Cambrian ‘great‐appendage’ arthropods has, however, very similar short antero‐ventral appendages with a peduncle of two segments angled against each other (elbowed) and with stout distally or medio‐distally directed spines or long flexible flagellate spines on each of the four distal segments. Moreover, the head appendages of all these forms comprise the ‘great appendages’ and three pairs of biramous limbs. To this set of taxa we can add a new form from the Lower Cambrian Maotianshan Shale of southern China, Haikoucaris ercaiensis n. gen. and n. sp. It is known from three specimens, possibly being little abundant in the faunal community. It can be distinguished from all other taxa by the prominence of the proximal claw segment of its ‘great appendages’ and by only three distal spines (one on each of the distal segments). The similarity of the short, spiky ‘great appendages’ of Haikoucaris with the chelicera of the Chelicerata leads us to hypothesize that this particular type of ‘great appendages’ was the actual precursor of the chelicera. Homeobox gene and developmental data recently demonstrated the homology between the antenna of ateloceratans and the antennula of crustaceans on one side and the chelicera of chelicerates on the other. To this we add palaeontological evidence for the homology between the chelicerae of chelicerates and the ‘short great appendages’ of certain Cambrian arthropods, which leads us to hypothesize that the evolutionary path went from the ‘short great appendages’, by progressive compaction, toward the chelicera with only a two‐spined chela. The new form from China is regarded as the possible latest offshoot, whereas the other ‘great appendages’ arthropods with similar short grasping limbs were derivatives of the stem lineage of the crown‐group Chelicerata. Consequently, the chelicera with a chela with one fixed and one mobile finger is an autapomorphy of the crown group of Chelicerata, whereas a raptorial, but more limb‐like antenna, with more distal spine‐bearing segments, characterized the ground pattern of Chelicerata. Further taxa having ‘great appendages’, including the large Anomalocarididae, are also discussed in the light of their possible affinities to the Chelicerata and possible monophyly of all of these arthropods with raptorial anterior appendages.     

The soft anatomy of Isoxys minor from the Guanshan fauna,lower Cambrian of Southwest China

Isoxys is a very common Cambrian bivalved arthropod, specimens of which are normally preserved only as valves. The discovery of the soft anatomy of Isoxys may greatly assist understanding affinities and functional morphology. Isoxys minor Luo and Hu in Luo et al., 2008 is the most common representative of all animal species known from the lower Cambrian Guanshan fauna (Cambrian Series 2, Stage 4) at the Shitangshan Section, near Kunming, Yunnan Province, Southwest China. Here we describe and reconstruct the morphology of I. minor on the basis of newly illustrated fossils and a few new specimens that bear soft-parts including new discovery of frontal grasping appendages. Like the soft anatomy of other known Isoxys, it bears a pair of large stalked eyes, a pair of specialized frontal grasping appendages, approximately 12–14 paired biramous limbs, and a helm-like tail exposed outside the valves.     

A second type A-nauplius from the Upper Cambrian 'Orsten' of Sweden

Walossek, Dieter & Müller, Klaus J. 1989 07 15: A second type A-nauplius from the Upper Cambrian 'Orsten' of Sweden. Lethaia , Vol. 22, pp. 301–306. Oslo. ISSN 0024–1164.
Among newly sorted material, two specimens at first considered as nauplius-like larva A (Müller & Walossek 1986, Transactions of the Royal Society of Edinburgh: Earth Sciences 77 ) differ from this type in their larger sized body and appendages, much smaller caudal spines, and lack of the dorsal hook-like plates. They are regarded as a similar but distinct type, named 'larva A2'. * Crustacea, ontogeny, phosphatization, 3D-preservation .     

A new arthropod from the Silurian Konservat-Lagerstätte of Herefordshire, UK

A small, non-biomineralized, macrophagous arthropod with chelicerate affinities, Offacolus kingi gen. et sp. nov., from the Silurian (Wenlock Series) of Herefordshire, UK, is described. The dorsal exoskeleton comprises an arch-like cephalic shield, a thorax of three free tergites and a triangular posterior tagma of five fused tergites, the last with a stout postero-dorsally directed medial spine. Seven pairs of appendages beneath the cephalic shield surround a postero-medially sited oral cavity on the ventral surface of the head. Appendages I and, probably II are uniramous and project antero-ventrally; I was sensory and II sensory and/or ambulatory. Appendages III-VI are biramous, each with an antero-ventrally projecting ramus and a robust, highly geniculate, horizontally oriented ramus that projects through an anterior gape. The former rami were ambulatory and the latter have spinose terminal podomeres and functioned as a unit for trapping food and transferring it towards the oral cavity. Appendage VII, which is probably uniramous, is posteroventrally directed and flap like. Each tergite of the thorax and posterior tagma covers at least a pair (probably two pairs) of probably biramous appendages with each ramus flap like and setose.     

A Silurian 'marrellomorph' arthropod

Xylokorys chledophilia, a new arthropod with three-dimensionally preserved soft tissues, is described from the Herefordshire (Silurian) Lagerstätte of England. The head and trunk are covered by a relatively featureless ovoid carapace, which comprises a domed central part and a flange-like border. The head bears five pairs of appendages. The first is uniramous, with dorsal and ventral projections distally. Appendages two to four are biramous and each endopod terminates in two projections. Appendage five is possibly biramous. The hypostome is very long and subrectangular in outline. There are approximately 35 pairs of biramous trunk appendages. Each exopod comprises a long slender shaft bearing numerous fine filaments; each endopod comprises a ribbon-like shaft bearing paddle-like endites. Morphological comparisons and cladistic analyses of X. chledophilia indicate affinity with Vachonisia rogeri from the Lower Devonian Hunsrück Slate, within the marrellomorphs, but assignment to Marrellomorpha is provisional pending revision of other members of this clade. Xylokorys is the first ‘marrellomorph’ to be reported from the Silurian. It is interpreted as a benthic particle filter feeder, which may also have consumed prey items.     

Cambrocaris baltica n. gen. n. sp., a possible stem-lineage crustacean from the Upper Cambrian of Poland

Bodily preserved, secondarily phosphatized arthropods discovered in drill cores on He***l Peninsula, northern Poland, and in its vicinity date from the Upper Cambrian. Comparisons between a group of arthropods of the Upper Cambrian of Sweden recognized as stem-lineage crustaceans indicate that one of these new forms, Cambrocaris baltica n. gen. n. sp., also represents a derivative of the early phase of crustacean evolution prior to the crown-group level. The material also yielded a specimen identified as Skara minuta Müller & Walossek, 1985, hitherto known only from Västergotland, Sweden, and two limb fragments which cannot be assigned to species. □ Crustacea, stem-lineage derivatives. Phosphatization, three-dimensional preservation, Upper Cambrian, Alum shales, 'Orsten', northern Poland.     

A new specimen ofWeinbergina opitzi (Chelicerata: Xiphosura) from the Lower Devonian Hunsriick Slate, Germany

A new specimen of the synziphosurine arthropodWeinbergina opitzi is described from the Lower Devonian (Lower Emsian) Hunsrück Slate of Germany (Rhenish Slate Mountains). It is the smallest and only the fifth specimen of this taxon to be described and is preserved in ventral aspect with exceptional preservation of prosomal and opisthosomal appendages. This specimen confirms the presence of a seventh appendage, similar in morphology to the preceding prosomal appendages, associated with opisthosomal segment one. In addition, at least three opisthosomal plates fringed with teeth are confirmed. Correlation of prosomal appendage podomeres betweenWeinbergina and selected chelicerate taxa shows that appendage structure is most similar to eurypterid appendages III–IV and Araneae appendages III–VI. This is in contrast to modern horseshoe crabs which have fewer podomeres in appendages II–V due to an undifferentiated tibiotarsus.      

The Early Cambrian colonization of pelagic niches exemplified by Isoxys (Arthropoda)

The anatomy of the bivalved arthropod Isoxys (Early and Middle Cambrian) is reconstructed, based on new evidence from soft parts and exoskeletal design and on a critical review of previous work. Isoxys had a long segmented body flanked with a pair of short antennules, followed by a series of 14 biramous appendages provided with long paddle-like exopods concealed under a widely open bivalved carapace folded dorsally and bearing long cardinal spines. The close resemblance between Isoxys and Recent pelagic crustaceans (halocyprid ostracods, larval stages of malacostracans) indicates that Isoxys was probably an active epipelagic swimmer (evidence from soft parts, carapace design and distributional pattern). Some species (e.g. I. auritus and I. paradoxus from the Maotianshan Shale biota; Early Cambrian) may have lived in the vicinity of the bottom either permanently or temporarily, whereas others may have had ecological preferences for more open-marine settings. The spinosity of Isoxys had a possible role in predatorial deterrence rather than in buoyancy control or in retarding sinking within the water column. The presence of Isoxys in the Maotianshan Shale of S. China indicates that arthropods had already colonized midwater niches by the Early Cambrian. The midwater communities of the Maotianshan Shale comprised numerous other invertebrates, such as abundant medusiform eldonids, vetulicolids, chordates and possibly early vertebrates. This contradicts the opinion that pelagic communities remained poorly developed until late Cambrian/Ordovician times and that the occupation of the midwater niches largely post-dates the initial diversification of the benthic faunas.     

A Larval Sea Spider (Arthropoda: Pycnogonida) from the Upper Cambrian 'orsten' of Sweden, and the Phylogenetic Position of Pycnogonids

Among a set of small, secondarily phosphatised larval arthropods from the Upper Cambrian 'Orsten' of Sweden, described by Müller and Walossek in 1986, one form bears a remarkable resemblance to the hatching protonymph larva of extant Pantopoda. This 'larva D' shares with protonymphs their gross body form, the anteroventral mouth on a slightly off-set forehead region, the cheliceral morphology, two homeomorphic pairs of post-cheliceral limbs, and further detailed similarities. It is described herein as Cambropycnogon klausmuelleri gen. et sp. nov. and is proposed as the oldest unequivocal record of both Pycnogonida and Chelicerata. Plesiomorphic features such as a pair of rudimentary pre-cheliceral limbs and the gnathobasic basipods of the two post-cheliceral limbs distinguish it from all known larvae of extant Pantopoda and lead us to propose a phylogeny of the Pycnogonida of the form ( Cambropycnogon klausmuelleri + ( Palaeoisopus + ( Palaeopantopus + Pantopoda))). The fossil may help to resolve the long debate about the relationships of Pycnogonida to other Arthropoda and supports a (Pycnogonida + Euchelicerata) relationship within the Chelicerata. The pre-cheliceral limbs in this fossil support traditional morphological studies in which the chelicera represent the second (a2) head appendage, corresponding to the crustacean 'second antennae', and contradict recent data based on homeobox genes implying that the chelicerae are the first (a1) head appendages homologous with crustacean first antennae.     

Isoxys (Arthropoda) with preserved soft anatomy from the Sirius Passet Lagerstätte,lower Cambrian of North Greenland

Stein, M., Peel, J.S., Siveter, D.J. & Williams, M. 2009: Isoxys (Arthropoda) with preserved soft anatomy from the Sirius Passet Lagerstätte, lower Cambrian of North Greenland. Lethaia, Vol. 43, pp. 258–265. Isoxys volucris is the most commonly occurring species in the lower Cambrian Sirius Passet Lagerstätte of North Greenland. Newly identified material allows a first, limited, account of the ventral morphology of this species, hitherto known only by the morphology of its shield. The antennula is large and robust, composed of about seven articles armed with spines, and was probably not sensorial. The postantennular limbs are serially similar, biramous with a large paddle‐shaped exopod fringed with setae. It is possible that the animal possessed a furca. The inner lamella, lining the ventral surface of the shield is recognised in Isoxys for the first time. Comparisons with other congeneric species of which aspects of the ventral morphology are known, show similarities with Isoxys auritus from China, reconsidered here, but indicate differences in antennular morphology with other species as currently understood. □Cambrian, Greenland, Isoxys, soft anatomy, Sirius Passet, palaeoecology.     

Anatomy and lifestyle of Kunmingella (Arthropoda, Bradoriida) from the Chengjiang fossil Lagerstätte (lower Cambrian; Southwest China)

An updated reconstruction of the body plan, functional anatomy and life attitude of the bradoriid arthropod Kunmingella is proposed, based on new fossil specimens with preserved soft parts found in the lower Cambrian of Chengjiang and Haikou (Yunnan, SW China) and on previous evidence. The animal has a single pair of short antennae pointing towards the front (a setal pattern indicates a possible sensory function). The following set of seven appendages (each composed of a 5-segmented endopod and a leaf-like exopod fringed with setae) is poorly differentiated, except the first three pairs (with possible rake-like endopodial outgrowths, smaller exopods) and the last pair of appendages (endopod with longer and more slender podomeres). The endopods are interpreted as walking legs with a possible role in handling food particles (marginal outgrowth with setae). The leaf-like exopods may have had a respiratory function. The trunk end is short, pointed, flanked with furcal-like rami and projects beyond the posterior margin of the carapace. The attachment of the body to the exoskeleton is probably cephalic and apparently lacks any well-developed adductor muscle system. The inferred life attitude of Kunmingella (e.g. crawling on the surface of the sediment) was that of a dorsoventrally flattened arthropod capped by a folded dorsal shield (ventral gape at least 120°), thus resembling the living ostracode Manawa. The animal was also probably able to close its carapace as a response to environmental stress or to survive unfavourable conditions (e.g. buried in sediment). The anterior lobes of the valves are likely to have accommodated visual organs (possibly lensless receptors perceiving ambient light through the translucent head shield). Preserved eggs or embryos suggest a possible ventral brood care. The presence of Kunmingella in coprolites and its numerical abundance in Chengjiang sediment indicate that bradoriids constituted an important source of food for larger predators. Kunmingella differs markedly from the representatives of the crown group Crustacea (extant and Cambrian taxa) and from the stem group derivatives of Crustacea (exemplified by phosphatocopids and some ‘Orsten’ taxa) in showing no major sign of limb specialization (e.g. related to feeding strategies). Although it resembles other Chengjiang euarthropods in important aspects of its body plan (e.g. uniramous antennae, endopod/exopod configuration), Kunmingella possesses several features (e.g. antennal morphology, post-antennular appendages with 5-segmented endopods) which support the view that bradoriids may be very early derivatives of the stem line Crustacea.