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.     

The first tomopterid, a polychaete from the Carboniferous of Scotland

Briggs, Derek E. G. & Clarkson, Euan N. K. 1987 07 15: The first tomopterid, a polychaete from the carboniferous of Scotland.
The first known example of a fossil tomopterid, Eotomopteris aldridgei , is described from the Lower Carboniferous of Granton, Edinburgh. The head bears tentacular cirri, and the trunk preserves evidence of at least 20 pairs of parapodia. The polychaete is associated with other soft-bodied and lightly skeletalized organisms including crustaceans, conodonts, an additional chordate, and branching structures which resemble hydroids. It is similar to living tomopterids and was probably pelagic. This discovery indicates that these polychaetes were well established by the early Carboniferous and probably before.     

A new probable stem lineage crustacean with three-dimensionally preserved soft parts from the Herefordshire (Silurian) Lagerstätte, UK

A new arthropod with three-dimensionally preserved soft parts, Tanazios dokeron, is described from the Wenlock Series (Silurian) of Herefordshire, England, UK. Serial grinding, digital photographic and computer rendering techniques yielded 'virtual fossils' in the round for study. The body tagmata of T. dokeron comprise a head shield and a long trunk. The head shield bears six pairs of horn-like spines and the head bears five pairs of appendages. The antennule, antenna and mandible are all uniramous, and the mandible includes a gnathobasic coxa. Appendages four and five are biramous and similar to those of the trunk: each comprises a limb base with an endite, an enditic membrane, and two epipodites, plus an endopod and exopod. The hypostome bears a large cone-like projection centrally, and there may be a short labrum. The trunk has some 64 segments and at least 60 appendage pairs. A very small telson has the anus sited ventrally in its posterior part and also bears a caudal furca. Comparative morphological and cladistic analyses of T. dokeron indicate a crustacean affinity, with a probable position in the eucrustacean stem group. As such the epipodites in T. dokeron are the first recorded in a eucrustacean stem taxon. The new species is interpreted as a benthic or nektobenthic scavenger.     

Cambrian stem-group annelids and a metameric origin of the annelid head

The oldest fossil annelids come from the Early Cambrian Sirius Passet and Guanshan biotas and Middle Cambrian Burgess Shale. While these are among the best preserved polychaete fossils, their relationship to living taxa is contentious, having been interpreted either as members of extant clades or as a grade outside the crown group. New morphological observations from five Cambrian species include the oldest polychaete with head appendages, a new specimen of Pygocirrus from Sirius Passet, and an undescribed form from the Burgess Shale. We propose that the palps of Canadia are on an anterior segment bearing neuropodia and that the head of Phragmochaeta is formed of a segment bearing biramous parapodia and chaetae. The unusual anatomy of these taxa suggests that the head is not differentiated into a prostomium and peristomium, that palps are derived from a modified parapodium and that the annelid head was originally a parapodium-bearing segment. Canadia, Phragmochaeta and the Marble Canyon annelid share the presence of protective notochaetae, interpreted as a primitive character state subsequently lost in Pygocirrus and Burgessochaeta, in which the head is clearly differentiated from the trunk.     

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.     

An Early Cambrian stem polychaete with pygidial cirri

The oldest annelid fossils are polychaetes from the Cambrian Period. They are representatives of the annelid stem group and thus vital in any discussion of how we polarize the evolution of the crown group. Here, we describe a fossil polychaete from the Early Cambrian Sirius Passet fauna, Pygocirrus butyricampum gen. et sp. nov., with structures identified as pygidial cirri, which are recorded for the first time from Cambrian annelids. The body is slender and has biramous parapodia with chaetae organized in laterally oriented bundles. The presence of pygidial cirri is one of the characters that hitherto has defined the annelid crown group, which diversified during the Cambrian-Ordovician transition. The newly described fossil shows that this character had already developed within the total group by the Early Cambrian.     

An early Cambrian chelicerate from the Emu Bay Shale,South Australia

The Emu Bay Shale Lagerstätte (Cambrian Series 2, Stage 4) occurs on the north coast of Kangaroo Island, South Australia. Over 50 species are known from here, including trilobites and non‐biomineralized arthropods, palaeoscolecids, a lobopodian, a polychaete, vetulicolians, nectocaridids, hyoliths, brachiopods, sponges and chancelloriids. A new chelicerate, Wisangocaris barbarahardyae gen. et sp. nov., is described herein, based on a collection of some 270 specimens. It is up to 60 mm long, with the length of the cephalic shield comprising about 30% that of the exoskeleton. The cephalic margin has three pairs of bilaterally‐symmetrical small triangular spines. A pair of small eyes is placed well forwards on the ventral margin of the cephalic shield. The trunk comprises 11 segments that increase in length while narrowing posteriorly, each possibly bearing a pair of biramous appendages; the most posterior segment is almost square whereas the others are transversely elongated. The spatulate telson is proportionately longer than in taxa such as Sanctacaris, Utahcaris and Leanchoilia. Up to eight (?four pairs) of 3 mm‐long elements bearing alternating inward‐curving short and long spines beneath the cephalic shield are interpreted as basipodal gnathobases, part of a complex feeding apparatus. A well‐developed gut includes a stomach within the cephalic shield; it extends to the base of the telson. In a few specimens there are shell fragments within the gut, including those of the trilobite Estaingia bilobata (the most common species in the biota); these fragments have sharp margins and extend across the gut lumen. The species may have been a predator or a scavenger, ingesting material already broken up by a larger predator/scavenger. The morphology of this taxon shares many overall body features with Sanctacaris, and some with Sidneyia, particularly its gnathobasic complex. These chelicerate affinities are corroborated by phylogenetic analyses.     

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.     

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 soft-bodied euarthropod from the early Cambrian Xiaoshiba Lagerstätte of China supports a new clade of basal artiopodans with dorsal ecdysial sutures

We describe the exceptionally well-preserved non-trilobite artiopodan Zhiwenia coronata gen. et sp. nov. from the Cambrian Stage 3 Xiaoshiba Lagerstätte in Yunnan, China. The exoskeleton consists of a cephalic shield with dorsal sutures expressed as lateral notches that accommodate stalked lateral eyes, an elongate trunk composed of 20 tergites—the first of which is reduced—and a short tailspine with marginal spines. Appendicular data include a pair of multi-segmented antennae, and homonomous biramous trunk limbs consisting of an endopod with at least seven podomeres and a flattened exopod with lamellae. Although the presence of cephalic notches and a reduced first trunk tergite invites comparisons with the petalopleurans Xandarella, Luohiniella and Cindarella, the proportions and exoskeletal tagmosis of Zhiwenia do not closely resemble those of any major group within Trilobitomorpha. Parsimony and Bayesian phylogenetic analyses consistently support Zhiwenia as sister-taxon to the Emu Bay Shale artiopodan Australimicola spriggi, and both of them as closely related to Acanthomeridion from the Chengjiang. This new monophyletic clade, Protosutura nov., occupies a basal phylogenetic position within Artiopoda as sister-group to Trilobitomorpha and Vicissicaudata, illuminates the ancestral organization of these successful euarthropods, and leads to a re-evaluation of the evolution of ecdysial dorsal sutures within the group.     

The morphology of Opabinia regalis and the reconstruction of the arthropod stem-group

Opabinia regalis Walcott is an enigmatic fossil from the Middle Cambrian Burgess Shale of uncertain affinities. Recent suggestions place it in a clade with Anomalocaris Whiteaves from the Burgess Shale and Kerygmachela Budd from the Greenlandic Sirius Passet Fauna; these taxa have been interpreted as 'lobopods'. Consideration of available Opabinia specimens demonstrates that reflective extensions from the axial region, previously thought to be either gut diverticula or musculature, can be accommodated in neither the trunk nor the lateral lobes that arise from it. They must therefore be external structures independent of the lateral lobes. On the basis of their sub-triangular appearance, size and taphonomy, they are considered here to represent lobopod limbs. Some evidence for the existence of terminal claws is also presented. The question of whether Kerygmachela, Opabinia and Anomalocaris constitute a monophyletic or paraphyletic grouping is considered. While they share several characters, most of these are plesiomorphies. Further, Opabinia and Anomalocaris share several arthropod-like characters not possessed by Kerygmachela. It is concluded that these three taxa probably form a paraphyletic grouping at the base of the arthropods. Retention of lobopod-like characters within the group provides important documentation of the lobopod-arthropod transition. A proper understanding of Opabinia and its close relatives, which may include the tardigrades, opens the way for a reconstruction of the arthropod stem-group. This in turn allows the construction of a speculative but satisfying scenario for the evolution of major arthropod features, including the origin of the biramous limb, tergites and arthropod segmentation. 'Arthropodization' may thus be seen not to be a single event but a series of adaptive innovations. OPABINIA, ANOMALOCARIS, KERYGMACHELA, Burgess Shale, problematica, Lobopodia, Arthropoda.     

A new species of Euzonus (Polychaeta: Opheliidae) from subtidal zones in Japan

A new opheliid polychaete, Euzonus japonicus sp. nov., is described. This species was collected from subtidal zones in Japanese coasts, while most Euzonus species inhabit intertidal sandy beaches. E. japonicus sp. nov. is morphologically most similar to another subtidal species, E. flabelliferus (Ziegelmeier, 1955) collected from northern Europe, but different from that in the form of branchiae. They share a unique characteristic on setiger 10, i. e., a pair of lateral transverse rows of conical cirri, instead of a pair of lateral smooth ridges that are common to all intertidal Euzonus species.     

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.     

Phosphatocopine ostracodes with preserved appendages from the Upper Cambrian of Sweden

Mülkr. Klaus 1. 1979 01 IS: Phosphatocopine ostracodes with preserved appendages from the Upper Cambrian of Sweden. Lethaia . Vol. 12. pp. 1–27. Oslo. ISSN 0024–1164.
More than 400 specimens of phosphatocopine ostracodes. representing different moult stages of Vestrogothia. Falites and Hesslandona have been recovered, with body and appendage structures preserved in minute detail. from anthraconites in the Upper Cambrian of Sweden and drift boulders deriving from that area. The secondary phosphatization of these structures, leading to preservation. is extensively discussed. It comprises even the inner lamella, but the abdomen is not preserved. Hypostome and lower lip are well developed. The large antennula is composed of a basipodite with probably two podomeres and a long exopodite with up to 18 podomeres bearing long spines, forming a natatory organ, and a broad endopodite of two to three podomeres. The biramous organization of the antennula is a unique, most primitive feature of phylogenetic significance. The antennae and up lo four additional pairs of appendages are also biramous and similar to the antennulae, not yet differentiated for specialized functions. Only the last pair is uniramous, but a second branch may have developed in subsequent moult stages not represented in the material. The movement of food into the mouth was achieved by the endites of antennulae and antennae, a function transferred backwards to other appendages during the course of ostracode phylogeny and reflected in ontogenetic trends among Recent ostracodes. The phosphatocopines were nectobenthic, filtering plankton feeders.     

Phylogeny of benthic Phyllodocidae (Polychaeta) based on morphological and molecular data

A combined molecular (18S rDNA, 28S rDNA, 16S rDNA and COI) and morphological analysis of the benthic phyllodocids is presented for the first time. Nineteen phyllodocids and two outgroup taxa are assessed using parsimony, maximum likelihood and Bayesian analyses. We demonstrate high degrees in homoplasy in the traditionally used morphological phyllodocid characters, and show that all the three current subfamilies Phyllodocinae, Eteoninae and Notophyllinae are non-monophyletic. The genera Eulalia, Eumida, Protomystides, Pseudomystides, Pterocirrus and Sige form a well-supported group, as does Mystides and Nereiphylla. Another clade with strong support includes Eteone and Paranaitis, although with Eteone nested within a paraphyletic Paranaitis. The relationship between these two taxa indicate that the unusual arrangement of modified cirri on the first segments in Eteone is due to a fusion of segment 1 and 2 where the cirri of segment 1 have been reduced. Eulalia is non-monophyletic and should be split, minimally into two groups. Our results are ambiguous regarding the ancestral phyllodocid condition of absence-presence of median antenna or nuchal papilla and uniramous or biramous parapodia, but shows that the absence of cirri on segment 3 (previously an apomorphy, for e.g., Mystides, Pseudomystides and Hesionura) is maximally homoplastic.     

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.     

The larval development of an Australian limnadiid clam shrimp (Crustacea, Branchiopoda, Spinicaudata), and a comparison with other Limnadiidae

The adult morphology of the Australian Limnadopsis shows some remarkable differences to that of other Limnadiidae. These differences are not reflected in its larval development. In Limnadopsis parvispinus, larval development comprises six stages. In stages I and II only the three naupliar appendages are present: the antennule as a small bud, the biramous antenna as the main swimming organ, and the mandible. The antennal protopod bears two endites, the proximal naupliar process and a more distal endite. In stage III a bifid naupliar process (in earlier stages not bifid) and the first signs of the carapace and trunk limb anlagen (undifferentiated rudiments) appear. In stage IV the carapace anlagen become more pronounced. The number of trunk limb anlagens increases to five, and differentiation has commenced. In stage V the first five pairs of trunk limbs are differentiated to varying degrees. The anterior-most four pairs of trunk limbs are subdivided into five endites, a small endopod, an exopod and an epipod. The bivalved carapace covers the anterior-most limbs. In larval stage VI the carapace is larger and the trunk limbs are further differentiated. A general pattern in the sequence of larval stages is the increasing number of sensilla on the antennules. From the last larval to the first postlarval stage, a significant change in morphology takes place. The trunk limbs are now used for swimming. Typical larval organs are much smaller than in the last larval stage. A comparison with other representatives of the Limnadiidae shows a high degree of correspondence, with most differences explained by the heterochronous appearance of characters during development. Five to seven stages are described for all studied Limnadiidae, including one particular stage in which four fully developed setae, a bifid naupliar process and the first signs of carapace anlagen are present. These characters are found in stage III in L. parvispinus, Limnadia stanleyana, Eulimnadia texana, and Imnadia yeyetta but in stage IV in E. braueriana and L. lenticularis. Based on a comparison of the larval stages of six limnadiid and one cyzicid species, we conclude that at least six naupliar stages belong to the limnadiid ground pattern.     

Expression of Distal-less, dachshund, and optomotor blind in Neanthes arenaceodentata (Annelida, Nereididae) does not support homology of appendage-forming mechanisms across the Bilateria

The similarity in the genetic regulation of arthropod and vertebrate appendage formation has been interpreted as the product of a plesiomorphic gene network that was primitively involved in bilaterian appendage development and co-opted to build appendages (in modern phyla) that are not historically related as structures. Data from lophotrochozoans are needed to clarify the pervasiveness of plesiomorphic appendage-forming mechanisms. We assayed the expression of three arthropod and vertebrate limb gene orthologs, Distal-less (Dll), dachshund (dac), and optomotor blind (omb), in direct-developing juveniles of the polychaete Neanthes arenaceodentata. Parapodial Dll expression marks pre-morphogenetic notopodia and neuropodia, becoming restricted to the bases of notopodial cirri and to ventral portions of neuropodia. In outgrowing cephalic appendages, Dll activity is primarily restricted to proximal domains. Dll expression is also prominent in the brain. dac expression occurs in the brain, nerve cord ganglia, a pair of pharyngeal ganglia, presumed interneurons linking a pair of segmental nerves, and in newly differentiating mesoderm. Domains of omb expression include the brain, nerve cord ganglia, one pair of anterior cirri, presumed precursors of dorsal musculature, and the same pharyngeal ganglia and presumed interneurons that express dac. Contrary to their roles in outgrowing arthropod and vertebrate appendages, Dll, dac, and omb lack comparable expression in Neanthes appendages, implying independent evolution of annelid appendage development. We infer that parapodia and arthropodia are not structurally or mechanistically homologous (but their primordia might be), that Dll's ancestral bilaterian function was in sensory and central nervous system differentiation, and that locomotory appendages possibly evolved from sensory outgrowths.     

Morphology,morphogenesis and molecular phylogeny of a new marine ciliate,Trichototaxis marina n. sp. (Ciliophora,Urostylida)

The live morphology, infraciliature and morphogenesis of a new urostylid ciliate, Trichototaxis marina n. sp., collected from coastal water in Qingdao, China, were studied based on the observations of live and silver stained specimens. The new species is characterised as follows: body very flexible and contractile, slight to brick-reddish in colour due to irregularly-shaped, brick-red pigments; ca. 70 adoral membranelles; about 17 frontal cirri arranged in a bicorona; average 67 midventral pairs, the right base of each pair being conspicuously larger than the left base; five to seven transverse cirri; constantly two frontoterminal, one buccal and two pretransverse ventral cirri; two or three left marginal rows; right and innermost left marginal rows with 56–92 and 66–106 cirri, respectively; six bipolar dorsal kineties; more than 100 macronuclear nodules. The characteristic morphogenetic feature in T. marina is the development of the left marginal rows, that is, only one left marginal row is newly built the other one or two being retained from the parental cell. Phylogenetic analyses based on small subunit ribosomal gene sequence data reveal a close relationship of T. marina with members of family Pseudokeronopsidae.     

A new species of Amphictene (Annelida,Pectinariidae) from the Gulf of Mexico,with a redescription of Amphictene guatemalensis (Nilsson, 1928)

The genus Amphictene is reported for the first time from Mexico. Previous records for America are restricted to Brazil (Amphictene catharinensis) (Grube, 1870), and Guatemala (Amphictene guatemalensis) (Nilsson, 1928). In this paper we describe a new species, Amphictene helenae sp. n., characterized by the presence of three pairs of tentacular cirri, while other species have only two pairs. The new species is closely similar to Amphictene catharinensis, and can be distinguished by the presence of a circular group of glandular papillae inserted between the lines of glandular cirri present from the second segment. Amphictene guatemalensis is redescribed based on type material; it differs from the new species in the presence of two pairs of tentacular cirri on segments 1 and 2, six pairs of glandular cirri on the third segment, and four glandular lobes fused in pairs on the fourth segment.