Known antennae of trilobites are all flagelliform, in marked contrast to the varied first antennae of marine pancrustaceans. An exceptionally preserved specimen of the Early Ordovician (late Tremadocian) asaphid Asaphellus tataensis Vidal, 1998, from the Fezouata Shale in Morocco, exhibits both antennae in situ; they are relatively short, widen distally, and bear a series of round, dome-shaped organs along both their dorsal and ventral surfaces. These organs are vastly larger than chemo- or mechanosensory sensilla on the antennae of other arthropods, rendering their homology and function uncertain. The clavate antennae of Asaphellus reveal the furthest deviation from the inferred ancestral state of the trilobite antenna known to date. This could be an adaptation for detection of prey, because most Asaphidae have been claimed as predators and scavengers on the basis of specialized features of the calcified exoskeleton.

The Upper Famennian (Upper Devonian) Strud locality has yielded very abundant and diversified flora as well as vertebrate and arthropod faunas. The arthropod fauna, mostly recovered from fine shales deposited in a calm, confined floodplain habitat including temporary pools, has delivered a putative insect and various crustaceans including eumalacostracans and notostracan, spinicaudatan and anostracan branchiopods. Here we present the Strud eurypterids, consisting of semi-articulated juvenile specimens assigned to Hardieopteridae recovered from the pool and floodplain deposits, as well as larger isolated fragments of potential adults recovered from stratigraphically lower, coarser dark sandy layers indicative of a higher-energy fluvial environment. The Strud fossils strongly suggest that, as proposed for some Carboniferous eurypterids, juvenile freshwater eurypterids inhabited sheltered nursery pools and migrated to higher-energy river systems as they matured.

A diverse millipede (diplopod) fauna has been recovered from the earliest Carboniferous (Tournaisian) Ballagan Formation of the Scottish Borders, discovered by the late Stan Wood. The material is generally fragmentary; however, six different taxa are present based on seven specimens. Only one displays enough characters for formal description and is named Woodesmus sheari Ross, Edgecombe & Clark gen. & sp. nov. The absence of paranota justifies the erection of Woodesmidae fam. nov. within the Archipolypoda. The diverse fauna supports the theory that an apparent lack of terrestrial animal fossils from ‘Romer's Gap' was due to a lack of collecting and suitable deposits, rather than to low oxygen levels as previously suggested.

The recently described radiodontan Lyrarapax unguispinus Cong et al., 2014 from the Chengjiang biota (Cambrian Series 2, Stage 3) highlighted a new morphological type of frontal appendage and unique mouth structures, a functional combination reinforcing the diversification of feeding strategies of radiodontans during the early Cambrian. Here we describe Lyrarapax trilobus n. sp. from the same fossil Konservat-Lagerstätte. The new species differs from L. unguispinus in the morphology and distribution of endites on the frontal appendage and the strengthening structure of the body flaps. The two species resemble each other in body shape (pattern of flap size), neck segment number, cephalic plates, and most importantly a mouth characterized by concentric wrinkled furrows. The latter confirms that a soft mouth without sclerotized plates is a real feature of Lyrarapax and supports the idea that oral structures provide valid diagnostic characters within Radiodonta.

Pliomerina Chugaeva, 1958, a characteristic element of the peri-Gondwanan Eokosovopeltis-Pliomerina Province, occurs in Llanvirn and Caradoc strata of the Argentine Precordillera. Three protaspid instars are present in the ontogeny of the Early Caradoc Pliomerina peripata new species. A species possibly representing Pliomerella is a rare element in Early Caradoc strata of the Las Aguaditas Formation. Prosopiscus is represented by a Llanvirn species with a first record of protaspid larvae for the enigmatic Family Prosopiscidae. Early growth stages support closest relations of prosopiscids to Phacopina. The presence of Pliomerina and Prosopiscus, along with the cheirurid Pateraspis, demonstrates a peri-Gondwanan influence on the Precordilleran fauna by the Llanvirn, and supports the proximity of the Precordillera terrane to the South American margin by that time.

The genus Cordania Clarke, 1892, has been known from the Lower Devonian (Lochkovian-Pragian) of the Appalachian Province and apparently from the Lower-Middle Devonian of China. Probable Lochkovian strata of the Biddabirra Formation in the Amphitheatre Group from near Cobar, New South Wales, Australia, have yielded Cordania buicki new species, extending the range of the genus to eastern Australia. Cladistic analysis of Cordania identifies C. buicki as more closely related to species from Oklahoma than to a northern Appalachian grade.

Alcymene n. gen. comprises a monophyletic group of calymenids known from the Ludlow Series of Sweden and the British Isles. The sister species Alcymene alveus and A. lindstroemi n. gen. and spp. (Hemse Beds, Gotland, Sweden) are most closely related to the type species A. neointermedia (Richter and Richter), which occurs in overlying and underlying strata at nearby localities. Structural modification of A. alveus and A. lindstroemi, especially the development of a greatly broadened and troughed librigenal border, can be interpreted as “snowshoe” adaptations for increased stability on an offshore mud substrate.

Llandovery Encrinurinae from the Whittaker Formation in the central Mackenzie Mountains include Cromus canorus n. sp., Distyrax cooperi n. sp., Distyrax n. sp. A, Perryus bartletti n. sp., and Encrinurus n. sp. Additional diversity of Distyrax Lane, 1988, demands a revised generic diagnosis with emphasis on pygidial homologies; new species are described from the Llandovery of Newfoundland and Ontario. Several characters suggest a sister group relationship between Distyrax and Encrinurus s.s. A lectotype is designated for the Llandovery species Encrinurus elegantulus Billings, 1866. Cromus canorus n. sp. is closely allied to other northern Laurentian Llandovery species. Synapomorphies of Cromus are inclusive for Encrinuraspis as revised by Snajdr, 1985. The long stratigraphic range and morphological conservatism of Cromus are correlated with occurrence in distal mudstone facies. Ontogenetic material for Distyrax n. sp. A, Cromus canorus, and Perryus bartletti is described, with consideration of librigenal spine homologies in Encrinurinae. Humaencrinuroides Nan, 1985, is a pliomerid of the new subfamily Quinquecostinae, and not a subgenus of Encrinuroides Reed.

Protaspides and later growth stages are described and discussed for the Ordovician trinucleid trilobite Cryptolithus tesselatus Green and the raphiophorid Lonchodomas chaziensis Shaw. A small triangular rostral plate is described for a single protaspid instar in both Cryptolithus and Lonchodomas. The presence of this small sclerite in the ontogeny of these taxa supports the origin of the Trinucleoidea from the Ptychopariida through reduction in and then fusion or loss of the rostral plate. Earlier and later growth stages have fused ventral sclerites, with no signs of connective sutures. All members of the Trinucleoidea with known ontogenies share similar small, ovoid asaphoid protaspides, with distinct axes and varying numbers of sharp, conical to subtubular, submarginal spines on the dorsal exoskeleton and marginal spines on the hypostome. Two protaspid instars are identified in both Cryptolithus and Lonchodomas, sharing many characters that indicate homologous levels of development. A single origin for the median suture of the Asaphida is supported, with an anterior rostellum as its precursor.

The hypostome of Glyptambon Holloway, 1981, provides additional morphological evidence that this genus is more closely related to the Siluro-Devonian subfamily Dalmanitinae than to Ordovician “Mucronaspidinae.” New species of Glyptambon are G. amsdeni n. sp., from the Ludlow Brownsport Formation in west-central Tennessee, and G. gassi n. sp., from late Wenlock strata of the Racine Formation in Illinois.

The present note aims to clarify the taxonomic status of the calmoniid trilobite Paranacaste pontagrossensis Popp, 1989, from the Ponta Grossa Formation, Lower Middle Devonian (Eifelian) of the Paraná Basin, Brazil.

Silurian (Llandovery–Ludlow) Encrinurinae from Wisconsin, Indiana, and Illinois include species of Balizoma Holloway, 1980, Curriella Lamont, 1978, Distyrax Lane, 1988, Encrinurus Emmrich, 1844, Mackenziurus Edgecombe and Chatterton, 1990a, and Nucleurus Ramsköld, 1986. Mackenziurus lauriae n. sp. is described from Wenlock strata of the Racine and Sugar Run Dolomites; nine segments in the holaspid thorax are the fewest known for any encrinurid. A square rostral plate is diagnostic of Mackenziurus. New morphological data are provided by Illinois specimens of Balizoma indianensis (Kindle and Breger, 1904) from the Wenlock–Ludlow Racine Dolomite, and of Curriella tuberculifrons (Weller, 1907) from the Llandovery Elwood–Wilhelmi Formations. Nucleurus n. sp. is possibly from Llandovery strata in Wisconsin. Distyrax n. sp. occurs in the Brandon Bridge Member (late Llandovery–early Wenlock) of the Joliet Dolomite in Illinois. The type pygidia and possible topotype material of Encrinurus nereus Hall, 1867, confirm assignment to that genus as currently viewed; this reefal species is distinct from the closely related inter-reef species E. egani Miller, 1880, and appears to be distinct from reefal E. reflexus Raymond, 1916. Lectotypes are selected for these Encrinurus species.

New shumardiid trilobites from Arenig to Early Caradoc deposits of the Argentine Precordillera include species of a revised Kweichowilla (K. salasae, K. sterrenae, and K. piojensis) and the new genus Changchowilla (C. sanjuanina and C. gracielae, and C.? carrerai). Conophrys fabiani new species occurs in the Early Tremadoc of the western Puna region, northwestern Argentina. Leoforteyia new genus is based on L. hintzei new species from the Ibexian of Utah. Published taxa recognized as new species are Conophrys rushtoni, Conophrys wrighti, Leoforteyia ludvigseni and Shumardia whittingtoni. Phylogenetic analysis suggests the differentiation of Shumardia Billings, 1862; Kweichowilla Chang, 1964; Changchowilla new genus; and Leoforteyia new genus as separate taxa and indicates that Conophrys Callaway, 1877, is a grade group. Silicified material provides a nearly complete growth series for Kweichowilla salasae, including the first protaspides known with confidence for the Shumardiidae. Additionally, ontogenetic material for K. sterrenae, C. sanjuanina, C. riojana (Benedetto and Cañas) and C.? carrerai is described.

Leoforteyia is restricted to the Ibexian-Whiterockian of western Laurentia; species of Shumardia are widespread in the Arenig to Early Ashgill of western Europe, Australia, Laurentia, China and Russia. Changchowilla is recorded in the mid-Late Arenig-Llanvirn of the Precordillera and in the Llanvirn-middle Caradoc of China. Argentine species of Kweichowilla are closely allied to Australian species, suggesting biogeographic affinities of the Precordillera to the eastern margin of Gondwana by the Llanvirn and Caradoc.

Functional morphology, occurrence in fine grained sediments, and association mainly with atheloptic and pelagic trilobites suggest that shumardiids were deposit-feeders that inhabited low light levels in low energy settings, with a limited ability to burrow in soft sediments.

The following new Toernquistiidae from Whiterockian (Llanvirn to lower Caradoc) strata of the Precordillera, western Argentina, are described: Chomatopyge canasi new species, Lasarchopyge benedettoi new genus and species, Lasarchopyge correae new genus and species, Lasarchopyge new species A, and Paratoernquistia sanchezae new genus and species. Phylogenetic analysis suggests that the Toernquistiidae Hupé, 1953 (including Chomatopyge, Lasarchopyge, Mesotaphraspis, Paratoernquistia, and Toernquistia) is closely related to but distinct from the Dimeropygidae Hupé, 1953 (including Ischyrotoma, Ischyrophyma and Dimeropyge). It is difficult to find unique synapomorphies that unite toernquistiids and dimeropygids into a monophyletic group that excludes other proetides (e.g., hystricurids), although details of their ontogenies are similar. Several species of Toernquistiidae are known from the Argentine Precordillera (one species previously described), and other species of this family have been described from Australia, Baltica, China, Kazakhstan and Laurentia. Members of the Dimeropygidae are known only from Baltica and Laurentia.

The ontogenies of three new species of Telephinidae, Telephina calandria, Telephina chingolo, and Telephina problematica are described from Arenig-Caradoc strata in the Argentine Precordillera, and compared with the larval stages of some other Proetida, including other telephinids.

New findings reveal 1) a radical metamorphosis in the ontogenies of these Telephina species late in the meraspid period, not previously described among Trilobita; and 2) distinctive hypostomes of Telephinidae containing long, thin anterolaterally and dorsally splayed anterior wings. Early ontogenies of different species currently assigned to the genus Telephina fall into at least two distinct morphological and life history groups, and hypostomes (if correctly assigned in previous works) vary significantly. The three new species strengthen the hypothesis of a phylogenetic connection between Oopsites and Telephina.

Three morphological types of protaspid instars are described for proetide trilobites. Two are anaprotaspides, and the third is a metaprotaspis. They always occur in the same sequence in the ontogeny, but no cases are known of all three types in the same species. These larval types are important for understanding the systematics and life cycles of the Proetida. Benthic/pelagic transitions identify four life history patterns among the the Proetida. The best larval synapomorphy for the Proetida is the distinctive metaprotaspid larval type, which is absent in very few proetides (some Telephinidae), perhaps as a result of heterochronic displacement of this stage into the meraspid period.

Phylogenetic parsimony analysis forms a basis for classification of the Siegenian–Eifelian “Malvinella group,” a monophyletic taxon within the “Metacryphaeus group” of the family Calmoniidae. Fifty-one exoskeletal characters for Metacryphaeus Reed and 12 taxa of the “Malvinella group” yield a shortest length cladogram with a consistency index of 0.51. A classification based on retrieving the structure of this cladogram recognizes six genera: Malvinella Wolfart, Vogesina Wolfart, Palpebrops n. gen. (type P. donegalensis n. sp.), the sister taxa Parabouleia Eldredge and Bouleia Kozlowski, and Plesiomalvinella n. gen. [type P. pujravii (Wolfart)]. Palpebrops is more closely related to Vogesina than to Malvinella; Amazonian species are nested within this group as sister taxa to Andean or Amazon/Andean clades. Bolivian Belén Formation Malvinella buddeae n. sp. is an allopatric species distinct from Icla Formation M. haugi (Kozlowski). “Metacryphaeus” of recent revisions is a paraphyletic grade group including primitive species of the “Malvinella group.” Metacryphaeus australis (Clarke), M. tuberculatus (Kozlowski), and M. caffer (Salter) are endemic to the Paraná Basin, Andean Bolivia–Parnaíba Basin, and South Africa, respectively.

The family Emuellidae Pocock, 1970 was established for Emuella Pocock, 1970 and Balcoracania Pocock, 1970 from the Lower Cambrian of South Australia. Based on their peculiar trunk tagmosis, emuellids have been interpreted as the sister group of all other trilobites with dorsal facial sutures, and classified as high as the ordinal level. Cladistic analysis with a range of exemplar taxa of the Olenellina and Redlichiina instead resolves the emuellids within the Redlichiina, with tagmosis into a prothorax and opisthothorax (“telosoma”) nonhomologous in olenellines and emuellids. A taxonomic revision of Australian species identifies Balcoracania flindersi as a junior subjective synonym of B. dailyi, whereas the two named species of Emuella are considered to be distinct. Balcoracania dailyi possesses up to 103 thoracic segments, the maximum number recorded in any trilobite.

Species of the superfamily Acastacea constitute a minor element of North and South American Silurian trilobite faunas. Phacopidina? obsoleta (Ulrich and Delo) (Llandovery, Tennessee) provides the sole Silurian record of the “kloucekiine” grade (Acastacea s.l.); a lectotype is designated for this species. Acaste birminghamensis Norford (mid Llandovery, Alabama) lacks synapomorphies of post-Llandovery Acastidae s.s. (=Acastinae + “Acastavinae” + Asteropyginae), and is the basis for Llandovacaste n. gen. (Acastidae s.l.). A well-preserved sample of Andinacaste cf. A. ledgrandi Eldredge and Braniša from the Catavi Formation (Ludlow–Přídolí), Bolivia, displays apomorphic characters of the genal spines and hypostome shared with Devonian calmoniids. Coaptative structures, including vincular furrow/pits and “bifurcated” thoracic pleural tips, are documented for Andinacaste; similar enrollment morphologies arose in other acastomorph calmoniids. Poorly known Llandovery acastaceans from Paraguay and Venezuela may represent Andinacaste. Acaste zerinae n. sp. from the Pembroke Formation (Přídolí) of Maine is closely comparable to British late Wenlock A. downingiae (Murchison). The Australian Gedinnian acastine placed in Phacopinae indet. longisulcata (Shergold) is designated Acaste lokii n. sp.

The Emu Bay Shale Konservat-Lagerstätte (Cambrian Series 2, Stage 4) on Kangaroo Island, South Australia, is the source of two new non-biomineralized artiopodan arthropods. Squamacula buckorum n. sp. is the first record outside of China of a genus otherwise known only from its type species, S. clypeata, from the Chengjiang biota. The Australian species displays the long cephalic doublure and spiniform exopod setae that are apomorphic for this genus, provides new information on the alimentary tract and midgut glands (the latter preserved as three-dimensional, permineralized structures), and indicates interspecific variability in trunk segment numbers. The distribution of Squamacula strengthens the biogeographic connections between early Cambrian “Burgess Shale-type” biotas of Australia and South China. Australimicola spriggi n. gen. n. sp. represents a monotypic genus resolved in a cladistic analysis of Cambro-Ordovician artiopodans as most closely related to or within Conciliterga (a clade containing Helmetia, Kuamaia, Kwanyinaspis, Rhombicalvaria, Saperion, Skioldia, and Tegopelte). Compared with other members of this clade from Chengjiang and the Burgess Shale, the new genus is diagnosed by an elongate trunk with 23 thoracic tergites having spatulate pleural tips and a small pygidium possessing a single, elongate pair of pleural spines, with specimens also showing a hypostome attached to an anterior (or prehypostomal) sclerite, antennae, short endopods, an annulated alimentary tract, and a series of three-dimensional, permineralized midgut glands. An alternative relationship between Australimicola and the Early Ordovician–Early Devonian Cheloniellida explains the shared anterior flexure of trunk pleurae but forces dubious homologies in other characters, such as dorsally-articulated furcae versus spines.

Protamphisopus wianamattensis (Chilton, 1918) from the Middle Triassic (Anisian) Ashfield Shale in the Sydney Basin, Australia, is the earliest-known freshwater representative of the basal isopod suborder Phreatoicidea. In contrast, the late Paleozoic Palaeophreatoicidae species, which are morphologically distinct from extant families, are found in marine or estuarine facies. Comparison of Protamphisopus wianamattensis with living Phreatoicidea permits the external morphology of the fossils to be reconstructed and the species to be coded for cladistic analysis using a revised and expanded character set developed for living phreatoicideans. In resulting parsimonious trees as well as immediately suboptimal trees, Protamphisopus is nested within clades related to the family Amphisopodidae. Although not included in the analysis, the Late Permian Protamphisopus reichelti Malzahn (in Glaessner and Malzahn, 1962) appears to be a member of the Palaeophreatoicidae, rather than among the crown group of the Phreatoicidea. Therefore, a minimum age of Middle Triassic can be assigned to the basal branches within the phreatoicid crown group. The minimum age for the colonisation of fresh water by the suborder is also established although, given the advanced position of Protamphisopus wianamattensis in the cladograms, the habitat shift may have occurred earlier. The biogeographic distribution of extant Phreatoicidea on fragments of Gondwana is consistent with early Mesozoic origins for the major clades of this isopod suborder.