Great Appendage Research Articles

Specialized appendages in fuxianhuiids and the head organization of early euarthropods

The organization of the head provides critical data for resolving the phylogenetic relationships and evolutionary history of extinct and extant euarthropods. The early Cambrian-period fuxianhuiids are regarded as basal representatives of stem-group Euarthropoda, and their anterior morphology therefore offers key insights for reconstructing the ancestral condition of the euarthropod head. However, the paired post-antennal structures in Fuxianhuia protensa remain controversial; they have been interpreted as both 'great appendages' and as gut diverticulae. Here we describe Chengjiangocaris kunmingensis sp. nov. and Fuxianhuia xiaoshibaensis sp. nov. from a new early Cambrian (Stage 3) fossil Lagerstätte in Yunnan, China. Numerous specimens of both species show a unique 'taphonomic dissection' of the anterodorsal head shield, revealing the cephalic organization in detail. We demonstrate the presence of a pair of specialized post-antennal appendages (SPAs) in the fuxianhuiid head, which attach at either side of the posteriorly directed mouth, behind the hypostome. Preserved functional articulations indicate a well-defined but restricted range of limb movement, suggestive of a simple type of sweep feeding. The organization of the SPAs in fuxianhuiids is incompatible with the (deutocerebral) anterior raptorial appendages of megacheirans, and argue against the presence of protocerebral limbs in the fuxianhuiids. The positions of the fuxianhuiid antennae and SPAs indicate that they are segmentally homologous to the deutocerebral and tritocerebral appendages of crown-group Euarthropoda respectively. These findings indicate that antenniform deutocerebral appendages with many podomeres are a plesiomorphic feature of the ancestral euarthropod head.

The eyes ofLeanchoilia

Schoenemann, B. & Clarkson, E.N.K. 2012: The eyes of Leanchoilia. Lethaia, Vol. 45, pp. 524–531. Leanchoilia is one of the commonest non-trilobite arthropod taxa of the Lower and Middle Cambrian. It has recently been regarded to be part of the ‘short great appendage arthropods’ clade and is normally considered a predator, both on account of its raptorial appendages and serial midgut digestive glands. The presence or absence of eyes has been one of the most controversial aspects of its morphology, despite pedunculate eyes having been described in the original descriptions of L. superlata (Walcott 1912) and L. illecebrosa Hou 1987. Other authors considered all species of this genus to be blind. There are two pairs of pits on the head, which have been interpreted as eyes attached near the front of the headshield. Pedunculate eyes have been found in four of about fifty specimens of L. illecebrosa from the Chengjiang and Haikou areas. They are delicate and slender, which explains their rare preservation. Distally they are structured like a bunch of grapes, with about 100 spherical units, presumably lenses, each with a diameter of about 55 μm indicating, by calculation, adaptation to dim light. They probably could detect movement, but could not form images. Furthermore, L. illecebrosa possesses two, probably ventral, median eyes, autapomorphies of euarthropods. Thus, like many modern Euarthropoda, L. illecebrosa has two kinds of eyes – two stalked ventral eyes and two pairs of probably ventral (ocellar) median eyes. Its short stalked eyes, orientated downwards and covered by the headshield, suggest that species of Leanchoilia were benthic animals, feeding on benthic or infaunal animals. □Arthropoda, Burgess Shale, Cambrian, Chengjiang, Compound eye, Lagerstatte, Leanchoilia.

Captopodus poschmanni gen. et sp. nov. a new stem-group arthropod from the Lower Devonian Hunsrück Slate (Germany)

A new arthropod from the Lower Devonian Hunsrück Slate is described on the basis of four specimens. The body of Captopodus poschmanni comprises a head, a trunk with an anal portion. The high number of trunk appendages (≥66 segments) is unusual. The function of one pair of cupola-like structures of the head shield is unclear. The presence of large grasping appendages in the head superficially resembles the ‘short great appendages’ of other euarthropods and grasping appendages of thylacocephalans. The phylogenetic position of the arthropod cannot be determined in detail, though several morphological aspects indicate a phylogenetic position as a stem lineage representative of the Euarthropoda, the morphology of the trunk appendages seem to indicate a more advanced phylogenetic position. This new taxon underlines the exceptional diversity of arthropods within the Hunsrück Slate in comparison to other Devonian fossil sites and highlights the significance of the Hunsrück Slate for the evolution of early arthropods.

Morphology and function in the Cambrian Burgess Shale megacheiran arthropod Leanchoilia superlata and the application of a descriptive matrix.

BackgroundLeanchoilia superlata is one of the best known arthropods from the middle Cambrian Burgess Shale of British Columbia. Here we re-describe the morphology of L. superlata and discuss its possible autecology. The re-description follows a standardized scheme, the descriptive matrix approach, designed to provide a template for descriptions of other megacheiran species.ResultsOur findings differ in several respects from previous interpretations. Examples include a more slender body; a possible hypostome; a small specialised second appendage, bringing the number of pairs of head appendages to four; a further sub-division of the great appendage, making it more similar to that of other megacheirans; and a complex joint of the exopod reflecting the arthropod’s swimming capabilities.ConclusionsDifferent aspects of the morphology, for example, the morphology of the great appendage and the presence of a basipod with strong median armature on the biramous appendages indicate that L. superlata was an active and agile necto-benthic predator (not a scavenger or deposit feeder as previously interpreted).

Functional morphology, ontogeny and evolution of mantis shrimp‐like predators in the Cambrian

Abstract: We redescribe the morphology of Yohoia tenuis (Chelicerata sensu lato) from the Cambrian Burgess Shale Lagerstätte. The morphology of the most anterior, prominent, so‐called great appendage changes throughout ontogeny. While its principal morphology remains unaltered, the length ratios of certain parts of the great appendage change significantly. Furthermore, it possesses a special jack‐knifing mechanism, i.e. an elbow joint: the articulation between the distal one of the two peduncle elements and the most proximal of the four spine‐bearing claw elements. This morphology might have enabled the animal to hunt like a modern spearer‐type mantis shrimp, an analogy enhanced by the similarly large and protruding eyes. For comparison, details of specimens of selected other great‐appendage arthropods from the Lower Cambrian Chengjiang Lagerstätte have been investigated using fluorescence microscopy. This revealed that the morphology of the great appendage of Y. tenuis is much like that of the Chengjiang species Fortiforceps foliosa and Jianfengia multisegmentalis. The morphology of the great appendage of the latter is even more similar to the morphology developed in early developmental stages of Y. tenuis, while the morphology of the great appendage of F. foliosa is more similar to that of later developmental stages of Y. tenuis. The arrangement of the elbow joint supports the view that the great appendage evolved into the chelicera of Chelicerata sensu stricto, as similar joints are found in various ingroup taxa such as Xiphosura, Opiliones or Palpigradi. With this, it also supports the interpretation of the great appendage to be homologous with the first appendage of other arthropods.

A restudy of the Burgess Shale (Cambrian) arthropod Emeraldella brocki and reassessment of its affinities

A restudy of the Burgess Shale arthropod Emeraldella brocki suggests novel interpretations of its morphology. We show that the morphology is more plesiomorphic than previously assumed, particularly regarding tagmosis. The cephalon probably only incorporates three limb-bearing postantennular segments. The trunk is not differentiated and consists of 12 tergite-bearing segments and a styliform telson. Limb structure is generally similar to that of other artiopods except for a tripartite exopod and a high degree of differentiation of podomere proportions along the body. A phylogenetic analysis of 20 fossil arthropod taxa based on 36 characters renders E. brocki as a basal taxon within a monophyletic group that comprises all artiopods included. Autapomorphies of this taxon are a filiform antennula and a bilobate exopod that carries lamellae proximally. Trilobites are nested within a group of artiopods sharing a pygidium. Agnostus pisiformis is retrieved as the sister taxon to the stem-lineage crustacean Oelandocaris oelandica, and both constitute the sister taxon of Artiopoda. ‘Great appendage’ arthropods, traditionally included in the Arachnomorpha, are retrieved as sister to the Crustacea sensu lato + Artiopoda clade, which contradicts the arachnomorph concept.

A New Leanchoiliid Megacheiran Arthropod from the Lower Cambrian Emu Bay Shale, South Australia

The Leanchoiliidae is well-known from abundant material of Leanchoilia, from the Burgess Shale and Chengjiang Konservat-Lagerstatten. The first Australian member of the group is Oestokerkus megacholix gen. et sp. nov., described from the Emu Bay Shale (Cambrian Series 2, Stage 4), at Buck Quarry, Kangaroo Island, South Australia, and is intermediate in age between the well known leanchoiliid species from the Burgess Shale and Chengjiang. Phylogenetic analysis of “short great appendage” arthropods (Megacheira) in the context of the chelicerate stem group resolves the Australian species as sister to Burgess Shale, Utah, and Chengjiang Leanchoilia species, but most readily distinguished from Leanchoilia and Alalcomenaeus by a different telson shape, interpreted as being forked, widening distally, and with a few dorsally curved spines at the posterior angle. Leanchoiliid interrelationships are stable to alternative character weights, and Megacheira corresponds to a clade in most analyses.

A new arthropod from the Early Cambrian of North Greenland, with a ‘great appendage’-like antennula

Arthropods have a rich fossil record spanning the Phanerozoic. Biomineralized forms such as the extinct trilobites are particularly common and are proven index fossils for biostratigraphy. Forms with an unmineralized cuticle are more rare, preserved only in so called konservat lagerstatten. Cambrian strata of Greenland have yielded rich trilobite faunas with potential for intercontinental correlation of Cambrian strata, but also an exceptionally preserved fauna, the Sirius Passet Lagerstatte. The first part of this thesis is concerned with trilobite biotratigraphy of the provisional Cambrian Series 2 in Greenland. The second part is concerned with exceptionally preserved arthropods from the Sirius Passet Lagerstatte, but also from 'Orsten' deposits from the Cambrian of Sweden. Perissopyge phenax occurs in the Henson Gletscher and Paralleldal formations spanning the Series 2 and 3 boundary interval in North Greenland. It also occurs in the Sekwi Formation of Yukon Territory, demonstrating that the species may hold potential for correlation within Laurentia. An indeterminate species of Perissopyge is shown to occur in the Ella Island Formation of North-East Greenland together with Olenellus cf. hanseni, which is similar to Olenellus cf. truemani described from the Henson Gletscher Formation. If this correlation is further corroborated it would offer a first tie-point for the An t'Sron Formation of North-West Scotland which yields Fritzolenellus lapworthi, herein reported for the first time from the Bastion Formation which underlies the Ella Island Formation. Oelandocaris oelandica from ‘Orsten’ deposits in the Cambrian series 3 and 4 boundary interval in Sweden is an early representative of the Crustacean stem lineage. Kiisortoqia avannaarsuensis is a new arthropod from the Sirius Passet Lagerstatte with robust antennulae strikingly similar to the 'raptorial' limb of the problematic anomalocaridids. The ventral morphology of the 'bivalved' Isoxys volucris is described for the first time and compared with other species assigned to Isoxys from Cambrian lagerstatten around the world. Finally, Siriocaris trolla, is a new arthropod that similarities with trilobites and certain ‘trilobitomorphs’ but seems to lack important synapomorphies of these taxa, though this may be due to preservational limitations in the material at hand.

Arthropod visual predators in the early pelagic ecosystem: evidence from the Burgess Shale and Chengjiang biotas

Exceptional fossil specimens with preserved soft parts from the Maotianshan Shale (ca 520 Myr ago) and the Burgess Shale (505 Myr ago) biotas indicate that the worldwide distributed bivalved arthropod Isoxys was probably a non-benthic visual predator. New lines of evidence come from the functional morphology of its powerful prehensile frontal appendages that, combined with large spherical eyes, are thought to have played a key role in the recognition and capture of swimming or epibenthic prey. The swimming and steering of this arthropod was achieved by the beating of multiple setose exopods and a flap-like telson. The appendage morphology of Isoxys indicates possible phylogenetical relationships with the megacheirans, a widespread group of assumed predator arthropods characterized by a pre-oral 'great appendage'. Evidence from functional morphology and taphonomy suggests that Isoxys was able to migrate through the water column and was possibly exploiting hyperbenthic niches for food. Although certainly not unique, the case of Isoxys supports the idea that off-bottom animal interactions such as predation, associated with complex feeding strategies and behaviours (e.g. vertical migration and hunting) were established by the Early Cambrian. It also suggests that a prototype of a pelagic food chain had already started to build-up at least in the lower levels of the water column.

REASSESSMENT OF THE GENUS LEANCHOILIA (ARTHROPODA, ARACHNOMORPHA) FROM THE MIDDLE CAMBRIAN BURGESS SHALE, BRITISH COLUMBIA, CANADA

Abstract: The collection, since 1975, of over 1500 specimens of Leanchoilia Walcott by the Royal Ontario Museum has prompted reassessment of the genus and its species from the Middle Cambrian Burgess Shale. Among new characters in Leanchoilia superlata, the type species, are the presence of two pairs of eyes, a dorsal double carina bracketing the axis of the body segments, segmentation of the gill branch of the appendages, and serration along the body edges from the posterior third of the cephalic shield to the last body segment. Leanchoilia persephone Simonetta, previously synonymized with L. superlata, is also well represented in the Burgess Shale, and is re‐established as a valid species, owing to conspicuous differences from the type species. These are the absence of the diagnostic up‐curving snout of the cephalic shield, the absence of carina, the shorter ‘great appendages’, the smooth edges of the body, and its overall shape in dorsal aspect. Leanchoilia superlata and L. persephone may be sexual dimorphs of each other. The ROM collections extend considerably the geographical distribution and stratigraphic range of Leanchoilia in western Canada.

Neuroanatomy of sea spiders implies an appendicular origin of the protocerebral segment

Independent specialization of arthropod body segments has led to more than a century of debate on the homology of morphologically diverse segments, each defined by a lateral appendage and a ganglion of the central nervous system. The plesiomorphic composition of the arthropod head remains enigmatic because variation in segments and corresponding appendages is extreme. Within extant arthropod classes (Chelicerata, Myriapoda, Crustacea and Hexapoda--including the insects), correspondences between the appendage-bearing second (deutocerebral) and third (tritocerebral) cephalic neuromeres have been recently resolved on the basis of immunohistochemistry and Hox gene expression patterns. However, no appendage targets the first ganglion, the protocerebrum, and the corresponding segmental identity of this anterior region remains unclear. Reconstructions of stem-group arthropods indicate that the anteriormost region originally might have borne an ocular apparatus and a frontal appendage innervated by the protocerebrum. However, no study of the central nervous system in extant arthropods has been able to corroborate this idea directly, although recent analyses of cephalic gene expression patterns in insects suggest a segmental status for the protocerebral region. Here we investigate the developmental neuroanatomy of a putative basal arthropod, the pycnogonid sea spider, with immunohistochemical techniques. We show that the first pair of appendages, the chelifores, are innervated at an anterior position on the protocerebrum. This is the first true appendage shown to be innervated by the protocerebrum, and thus pycnogonid chelifores are not positionally homologous to appendages of extant arthropods but might, in fact, be homologous to the 'great appendages' of certain Cambrian stem-group arthropods.

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 phylogeny of arachnomorph arthropods and the origin of the Chelicerata

ABSTRACTA new hypothesis of the relationships between arachnomorph arthropods, and the origin of chelicerates, is presented based on a cladistic analysis of 34 taxa and 54 characters. The present study provides a detailed discussion of primary hypotheses of homology and includes a more complete range of terminal taxa than previous analyses. The analysis provides the first convincing synapomorphies for the Arachnomorpha, and suggests that the marrellomorphs are not arachnomorphs. The assignment of Cambrian ‘great appendage’ (or megacheiran) arthropods to the Arachnomorpha is confirmed, and potential synapomorphies uniting them with chelicerates are discussed and tested. Principal amongst these are the loss of the first cephalic appendages (the antennae), loss of the exopods of the second cephalic appendages and modification of the endopods of these appendages into spinose grasping organs. The Arachnomorpha consists of two major clades: (1) a ‘chelicerate-allied’ clade, including chelicerates, megacheirans, Emeraldella, Sidneyia, cheloniellids and aglaspidids, in which chelicerates and a paraphyletic group of megacherian arthropods form the sister group to the remaining taxa; and; (2) a ‘trilobite-allied’ clade, including trilobites, xandarellids, helmetiids, tegopeltids and naraoiids, the relationships of which are more fully resolved than in previous studies.

The Arthropod Alalcomenaeus cambricus Simonetta, from the Middle Cambrian Burgess Shale of British Columbia

More than 300 specimens of the previously rare arthropod Alalcomenaeus cambricus Simonetta have been collected from a new Burgess Shale locality in the Glossopleura Zone on Mount Stephen, British Columbia. This new material provides much more complete information on its morphology. The cephalon was covered by a shield. A pair of pedunculate eyes and three median eyes were followed by a large anterior appendage, the ‘great appendage’, bearing three long flagella. The two posterior head appendages, like those of the trunk, were biramous. They consisted of a segmented, inner branch, and a flap‐like outer branch, fringed with long filaments. The trunk consisted of 11 somites, each protected by a tergite and bearing a pair of biramous limbs. The telson was paddle‐like and fringed posteriorly with wide flat spines. Alalcomenaeus was probably a predator, moving mainly by swimming. It is now known to be one of the more abundant, widely distributed and longest ranging of Burgess Shale arthropod genera. Its affinities lie with the Arachnomorpha.

New rare bivalved arthropods from the Lower Cambrian Chengjiang fauna, Yunnan, China

Five new bivalved arthropods are described from the Lower Cambrian Chengjiang fauna, Yunnan, China. All of them are rare in the fauna, represented by one or two individuals among thousands of specimens. Four of the five new taxa are preserved with soft parts that show a clear distinction between them. The new taxa provide new important information concerning the soft bodied and limb characters of the early bivalved arthropods. A significant lesson is that, not knowing any soft parts, it is virtually impossible to place systematically a new type of bivalved carapace. It is often impossible even to tell if it is a crustacean or not. A second antenna in the shape of a “great appendage” is identified for the first time among the bivalved arthropods. The new taxa include representatives of the order Pectocaridida, the families Pectocarididae, Clypecarididae and Occacarididae, the genera and speciesPectocaris spatiosa, Clypecaris pteroidea, Occacaris oviformis, Forfexicaris validaandYunnanocaris megista.

EmeraldellaandLeanchoilia,two arthropods from the Burgess Shale, Middle Cambrian, British Columbia

The type species of two much discussed but hitherto poorly known genera of arthropods are described in detail from new preparations. Illustrations are by photographs, explanatory line drawings, and reconstructions including three-dimensional models. The convex body ofEmeraldella brockiwas not trilobed, and was divided into a cephalon with labrum and 13 trunk somites, the first 11 having pleurae which were progressively narrower (transversely (tr.)) and more backwardly curved posteriorly, the last two somites being cylindrical, with a long posterior spine inserted into the 13th. A bilobed, spinose, ventral anal plate was probably attached to the 12th somite; the alimentary canal may have terminated in the 13th somite. The cephalon bore long antennae and five pairs of limbs, the first short, uniramous and jointed, the second to fifth biramous, the outer branch elongate-oval and having marginal filaments, the inner branches jointed and progressively longer. Trunk somites 1—11 each bore a pair of biramous limbs, the outer branch bilobed and with filaments on the distal margins, the jointed inner branches long on the anterior six or seven pairs. The coxae of the entire limb series bore a spinose gnathobase on the mesial edge, and the proximal podomeres of the leg branches were spinose. The outer branches were attached to the coxa and possibly the first podomere of the inner leg branch. The maximum known length of the body (excluding the posterior spine) was 65 mm; the animal lacked eyes, and was a benthonic predator and scavenger, walking on and digging into the muddy bottom, the gnathobases enabling soft food to be squeezed, shredded and passed forward along the midline to the backward-facing mouth. The outer branches were presumably gills, and may have aided in feeble swimming.Leanchoilia superlatahad a smooth, convex, faintly trilobate exoskeleton. The head shield was subtriangular with an upturned snout. The 11 tergites had broad (tr.) pleurae, behind the fifth progressively narrower (tr.) and more backward-curving; the 11th was curved back beside a short, triangular tail spine, which bore lateral spines. Anteriorly the cephalon bore the great appendage, which consisted of a basal section and four additional stout podomeres shaped to curve through 90°. The second and third podomeres were each extended by a tapering shaft continued by a longer, annulated portion. The distal podomere consisted of a tapering shaft terminating in three claws and a long, annulated extension. The remainder of the body had 13 pairs of biramous appendages (two on the cephalon, one on each trunk somite), the outer branch a lobe having overlapping lamellae on the distal and posterior margins, the inner branch tapering, of some eight podomeres and terminal spines. The proximal portions of the appendages are not preserved, but the outer branch was attached so that the inner branch lay below the anterior border of the outer branch; the two branches were of similar length (tr.) and hung down below the body. The alimentary canal is preserved, filled anteriorly with apatite, the filling showing segmentation and annulation. The mouth was apparently downward- and forward-facing, and led into a bulbous foregut situated beneath the cephalon. The anus opened on the 11th trunk somite. The maximum known length of the body was 68 mm. The animal lacked eyes and was probably benthonic in habit, able to rest on the sediment surface on the great appendage and the tips of the inner branches and to swim over it by metachronal movements of the outer branches (which also acted as gills), the great appendage swung back beneath the body to reduce resistance. It was probably a detritus feeder, the food pushed into the midline by the limbs, the mouth presumably suctorial. There is no evidence of a labrum, or of gnathobasic basal podomeres, but the inner margin of the leg branch was setiferous. The single species ofEmeraldella, E.brocki, is recognized, and the type and only specimen of ‘Emeraldoides’ is referred to it. Synonymous withLeanchoilia superlataare Walcott’s three species L.major, Bidentia difficilisandEmeraldellamicrura, and Simonetta’sLeanchoilia amphiction, L.persephoneand L.protogonia.Emeraldellabrockimay be allied withMolaria spinifera; problematical is any relationship to aglaspidids.Leanchoilia superlatamay be most closely related toActaeus armatus.Emeraldella and Leanchoiliaare very different from one another, and from eitherSidneyia or Naraoia; these four genera are so heterogeneous that Stormer’s grouping of them into the taxon Merostomoidea is rejected as no longer useful.