Ontogeny of the Furongian (late Cambrian) trilobite Proceratopyge cf. P. Lata Whitehouse from northern Victoria Land,Antarctica, and the evolution of metamorphosis in trilobites

There were multiple origins of metamorphosis‐undergoing protaspides in trilobite evolution: within the superfamilies Remopleuridioidea, Trinucleoidea, and within the Order Asaphida. Recent studies have revealed that the protaspides of the Cambrian representatives of the Remopleuridioidea and the Trinucleoidea did not undergo metamorphosis. However, ontogeny of the Cambrian members of the Order Asaphida has remained unknown. This study documents the ontogeny of the Furongian asaphoidean ceratopygid trilobite, Proceratopyge cf. P. lata Whitehouse, from northern Victoria Land, Antarctica. Two stages for the protaspid phase, five developmental stages for the post‐protaspid cranidia, and ten stages for the post‐protaspid pygidia have been identified. Interestingly, the protaspis directly developed into a meraspis without metamorphosis. A new cladistic analysis resulted in a single most parsimonious tree, according to which the presence of the bulbous commutavi protaspis turns out to be a synapomorphy for Asaphidae + Cyclopygoidea, not a synapomorphy for the Order Asaphida as previously suggested. In addition, it is inferred that there was convergent evolution of indirectly‐developing commutavi protaspides during the Furongian and Early Ordovician. Metamorphosis‐entailing planktonic larvae evolved in many different metazoan lineages near the Cambrian–Ordovician transition, due to the escalating ecological pressure of the Great Ordovician Biodiversification Event. Since the bulbous commutavi protaspid morphology is thought to be an adaptation for a planktonic life mode, the convergent evolution of the indirect development in the three trilobite lineages at this period might have been a result of adaptation to the early phase of the Great Ordovician Biodiversification Event.     

Morphology and ontogeny of the eodiscoid trilobite Sinodiscus changyangensis from the lower Cambrian of South China

Abstract: A large number of complete specimens together with numerous disarticulated sclerites of the eodiscinid trilobite Sinodiscus changyangensis Zhang in Zhou et al., 1977 have been collected from the lower Cambrian Shuijingtuo Formation in Changyang, Hubei Province, South China. An ontogenetic series is established based on the immature and mature exoskeletons including the previously unknown protaspides and meraspides, in particular. No further substages can be differentiated in the protaspid specimens herein. Changes that took place during the meraspid period include the addition of postcephalic segments and prominent pygidial larval notches in early meraspid development which became progressively less distinct and disappeared in degree 2. Two holaspid stages are recognized based on the addition of a new pygidial segment, indicating that the start of the holaspid phase preceded the onset of the epimorphic phase and accordingly, its developmental mode is attributed to the protarthrous pattern. The trunk segmentation schedule of S. changyangensis is discussed, which is similar to other primitive eodiscoid trilobites, that is, as the boundary between the thorax and pygidium migrated posteriorly, there is no change in the number of the trunk segments. The processes of liberation of the thoracic segment and segment insertion into the pygidium are separated from one another, and the two different mechanisms, somitogenesis and tagmosis, progress independently during the ontogenetic development of the postcephalic region of these primitive eodiscinids.     

Phylogenetic support for the monophyly of proetide trilobites

The monophyly of the order Proetida, the only trilobite group to survive the end‐Devonian mass extinction, has been regularly questioned since its erection almost three decades ago. Through analysis of a novel phylogenetic data set comprising 114 characters coded for 55 taxa, including both traditional members of the Proetida along with a number of other trilobite groups, the monophyly of proetide trilobites is rigorously tested for the first time. Proetida is shown to be monophyletic, united by the initial compound eye formation in early protaspids occurring at the lateral margin rather than the anterior margin, and the form of the protaspid glabella being tapering with a pre‐glabellar field. A number of adult characters, including the possession of a quadrate or shield‐shaped hypostome with angular posterior margins, the hypostome median body being divided by a deep groove that entirely traverses the median body, the presence of an enlarged thoracic spine on the sixth tergite and a tergite count of between 7 and 10, also define the basal node. Hystricurid and dimeropygoid trilobites are shown to resolve at the base of the group, while the remaining proetide taxa are divided between large proetoid and aulacopleuroid clades. Some taxa previously allied with Aulacopleuroidea, such as rorringtoniids and scharyiids, are retrieved as basal members of the Proetoidea.     

Ontogeny of the Upper Cambrian (Furongian) Olenid trilobite Protopeltura aciculate (Angelin, 1854) from Skåne and Västergötland,Sweden

Abstract: The ontogeny of the trilobite Protopeltura aciculata (Angelin, 1854) is described on the basis of material from the upper Cambrian (Furongian) of Andrarum (Skåne) and Hjelmsäter (Västergötland), Sweden. P. aciculata is present in the Parabolina brevispina and Parabolina spinulosa zones. Protopeltura aciculata is represented by all stages of growth, from early protaspides to holaspides, although most of the specimens are disarticulated and precise degrees are unknown. The cranidia have therefore been allocated to five morphological groups. Cuticular sculpture of the cranidia changes throughout ontogeny. Large tubercles are present in earlier stages, disappear gradually in middle meraspid stages and are replaced with a very faint granulation. The transitory pygidium, relatively large and shield‐shaped with upwardly and backwardly directed marginal spines in early meraspides, later becomes very small, triangular‐shaped and lacking spines as a late meraspid and holaspid. The development of hypostomes and librigenae is also described. Protopeltura aciculata shows major intraspecific variations throughout development, especially regarding the pygidium where variation is much less constrained than in many other olenids. This high developmental plasticity may be a survival strategy for a trilobite living in a stressed environment. Protopeltura inhabited a dysoxic environment, possibly unusually prone to localised spreading of anoxic or toxic water. Some morphs may have been less vulnerable than others to such stresses, surviving by chance and thus enabling the species to continue.     

Phylogenetics links monster larva to deep‐sea shrimp

Mid‐water plankton collections commonly include bizarre and mysterious developmental stages that differ conspicuously from their adult counterparts in morphology and habitat. Unaware of the existence of planktonic larval stages, early zoologists often misidentified these unique morphologies as independent adult lineages. Many such mistakes have since been corrected by collecting larvae, raising them in the lab, and identifying the adult forms. However, challenges arise when the larva is remarkably rare in nature and relatively inaccessible due to its changing habitats over the course of ontogeny. The mid‐water marine species Cerataspis monstrosa (Gray 1828) is an armored crustacean larva whose adult identity has remained a mystery for over 180 years. Our phylogenetic analyses, based in part on recent collections from the Gulf of Mexico, provide definitive evidence that the rare, yet broadly distributed larva, C. monstrosa, is an early developmental stage of the globally distributed deepwater aristeid shrimp, Plesiopenaeus armatus. Divergence estimates and phylogenetic relationships across five genes confirm the larva and adult are the same species. Our work demonstrates the diagnostic power of molecular systematics in instances where larval rearing seldom succeeds and morphology and habitat are not indicative of identity. Larval–adult linkages not only aid in our understanding of biodiversity, they provide insights into the life history, distribution, and ecology of an organism.     

Enrolment and trunk segmentation of a Cambrian eodiscoid trilobite

Completely enrolled, phosphatized, 3‐D specimens of the eodiscinid trilobite Tsunyidiscus yanjiazhaiensis from Cambrian Stage 3 of South China exhibit much morphological detail and show variation in delicate coaptative structures associated with their trunk segmentation. The relationship between enrolment mechanism and trunk segmentation during ontogeny confirms a unique developmental pattern among the early Cambrian eodiscoid trilobites, revealing how these animals controlled the rate of segment increase and release during post‐embryonic development in their life cycles.     

Rugiloricus bacatus sp. nov. (Loricifera ‐Pliciloricidae) and a ghost‐larva with paedogenetic reproduction

Abstract

A new species of Loricifera, Rugiloricus bacatus sp. nov. is described together with the diagnoses of two other Rugiloricus species, Rugiloricus sp. nov. A and B, from the Faroe Bank (North Atlantic). Characteristic for all three species is the presence of a new type of reduced larva, a ghost‐larva. This type of reduced larva was discovered in 1986 by Jeanne Renaud‐Mornant, but it was with the Faroe Bank material that it was first discovered that the ghost‐larvae belonged to the phylum Loricifera. The ghost‐larvae are eitherfound inside late instar Higgins‐larvae, called penultimate Higgins‐larvae, or in the sediment. The three types of Higgins‐larvae from the Faroe Bank can be distinguished by characters such as anterior setae, posterior setae and toes. The adults of Rugiloricus bacatus sp. nov. are characterised by a prominent ruff resembling a pearl necklace; two of the eight clavoscalids are modified in the 1st row; the 2nd row of leg‐shaped scalids are very large and robust, and the 9th row with 30 beak‐like scalids alternating with 30 alternating plates. The postlarvae are free‐living and their scalids on the introvert are reduced to protoscalids. Postlarvae and adult stages have not been found for Rugiloricus sp. nov. A and B and therefore only diagnoses of these two species are presented here.     

Extreme protomeric development in a burlingiid trilobite from Cambrian glacial erratics of Denmark

Pengia Geyer & Corbacho is a Cambrian burlingiid trilobite with fused trunk segments devoid of any articulation in the anamorphic and epimorphic phases of development. The type species is Pengia fusilis (Peng et al.) from the Wanshania wanshanensis Zone of China. Here we describe a second species, Pengia palsgaardia sp. nov., from the Lejopyge laevigata Zone of the Paradoxides forchhammeri Superzone. It comes from a glacial erratic in Denmark which probably originated in the Alum Shale Formation of Västergötland, Sweden. Pengia palsgaardia is a large burlingiid (~10 mm in length), with 14 fused segments in the trunk whose boundaries are marked by ridges. The axis is narrow, with the axial furrows faintly indicated or effaced across the median. Laterally along the axis and the tapering glabella, symmetrical globular lobes are developed that are pinched at their base. During ontogeny the glabellar furrows are pit‐like adaxially but shallow towards the axial furrow as the globular lobes develop. Their pit‐like appearance in Pengia palsgaardia and some other burlingiid species is not considered similar to the condition seen in oryctocephalid trilobites. A median preglabellar ridge resembling that of Schmalenseeia Moberg develops late in ontogeny but in early ontogeny the preglabellar field resembles that of Burlingia Walcott, Alumenella Geyer & Corbacho and Niordilobites Geyer & Corbacho. This gives Pengia a more basal position in the schmalenseeid lineage, outside the derived Schmalenseeia. In mature specimens the facial sutures in P. palsgaardia are fused, but an ocular suture may have been present. During ontogeny Pengia would have gone through the anamorphic and protomeric protaspid segmental conditions, but articulation between either the cephalon and pygidium, or pygidium and thoracic segments of the trunk never developed so it did not progress beyond the protaspid phase. This extreme protomeric development is considered to be a derived feature in Pengia.     

COMPOSITION,ABUNDANCE AND SEASONALITY OF LARVAL FISH IN RICHARDS BAY HARBOUR,KWAZULU-NATAL,SOUTH AFRICA

Summary

The present study examined the composition, abundance and seasonality of fish larvae occurring in Richards Bay Harbour, over an 18-month period from June 1991 to November 1992. Ichthyoplankton samples were collected every six weeks at top, mid and bottom depths in the dredged channel 100 to 200 m from the harbour entrance. A total of 7 163 fish larvae, representing 105 taxa and 53 families, was collected throughout the study period. The dominant families were the Engraulidae and Gobiidae representing 50% and 37% of the total catch, respectively. The most abundant larvae were those of the thorny anchovy, Stolephorus holodon, and an unidentified goby, Gobiid 12 (32% and 30% of the total catch, respectively). Estuarine-associated taxa dominated the total catch in terms of density (61%), with 11 out of the 28 taxa being totally dependent on estuaries at some stage in their life cycle. Turbidity and temperature were significant variables accounting for 27% of the variation in larval densities of estuarine-dependent species. The main peak in larval density occurred in January 1992 (summer) with a mean larval density of 160 larvae per 100 m³. Larvae of estuarine-associated taxa were predominantly at the flexion and postflexion developmental stages. Since larval densities of certain estuarine-associated species were significantly greater in bottom samples and on flood tides, it is suggested that selective tidal stream transport is a recruitment mechanism used by these species. The present study concluded that it is important to maintain and preserve the estuarine component of Richards Bay Harbour so that the system can function as an estuarine nursery for many of the fish species depending on it at certain stages in their life cycle.     

Aseptic rearing of Epiphyas postvittana (Lepidoptera: Tortricidae) on a meridic diet

The light brown apple moth, Epiphyas postvittana (Walker), was reared aseptically from newly hatched larvae to adults for three generations on a meridic diet. Growth and development on this diet were comparable with that on oligidic diets and on host‐plants. At 25 ± 1°C, 50–60% R.H., and 12‐h photophase, the average larval period was approx. 28 days, pre‐pupal and pupal 11–12 days, and pre‐oviposition approx. 2 days; the incuva‐tion period of eggs was approx. 7 days. The average developmental period from egg to adult was thus about 49 days; 89 % of larvae reached the adult stage. The average fecundity was 598 eggs per female, and the sex ratio was nearly 1:1. There were no differences in the rate of development or in fecundity of insects reared on media with and without a mould inhibitor.     

Bystrow’s Paradox – gills,fossils, and the fish‐to‐tetrapod transition

Schoch, R.R. and Witzmann, F. 2011. Bystrow’s Paradox – gills, fossils, and the fish‐to‐tetrapod transition. —Acta Zoologica (Stockholm) 92 : 251–265. The issue of which breathing mechanism was used by the earliest tetrapods is still unsolved. Recent discoveries of stem tetrapods suggest the presence of internal gills and fish‐like underwater breathing. The same osteological features were used by Bystrow to infer a salamander‐like breathing through external gills in temnospondyl amphibians. This apparent contradiction – here called Bystrow’s Paradox – is resolved by reviewing the primary fossil evidence and the anatomy of the two gill types in extant taxa. Rather unexpectedly, we find that internal gills were present in a range of early crown tetrapods (temnospondyls), based on the anatomy of gill lamellae and location of branchial arteries on the ventral side of gill arch elements (ceratobranchials). Although it remains to be clarified which components are homologous in external and internal gills, both gill types are likely to have been present in Palaeozoic tetrapods – internal gills in aquatic adults of some taxa, and external gills in the larvae of these taxa and in larvae of numerous forms with terrestrial adults, which resorbed the external gills after the larval phase. Future developmental studies will hopefully clarify which mechanistic pathways are involved in gill formation and how these might have evolved.     

Identification of β integrin‐like‐ and fibronectin‐like proteins in the bivalve mollusk Mytilus trossulus

Integrins play a key role in the intermediation and coordination between cells and extracellular matrix components. In this study, we first determined the presence of the β integrin‐like protein and its presumptive ligand, fibronectin‐like protein, during development and in some adult tissues of the bivalve mollusc Mytilus trossulus. We found that β integrin‐like protein expression correlated with the development and differentiation of the digestive system in larvae. Besides the presence of β integrin‐like protein in the digestive epithelial larval cells, this protein was detected in the hemocytes and some adult tissues of M. trossulus. The fibronectin‐like protein was detected firstly at the blastula stage and later, the FN‐LP‐immunoreactive cells were scattered in the trochophore larvae. The fibronectin‐like protein was not expressed in the β integrin‐positive cells of either the veliger stage larvae or the adult mussel tissues and the primary hemocyte cell culture. Despite the β integrin‐ and fibronectin‐like proteins being expressed in different cell types of mussel larvae, we do not exclude the possibility of direct interaction between these two proteins during M. trossulus development or in adult tissues.     

Pædomorphic patterns of the Cambrian genus Alueva (Trilobita, Ellipsocephalidae) from the Iberian Chains (NE Spain)

Three hundred protaspid and meraspid specimens of the trilobite species Alueva undulata Sdzuy, 1961 from the uppermost Bilbilian limestones of the Valdemiedes Formation (Iberian Chains, NE Spain) have been released by the action of acid. A pædomorphocline is proposed embracing the different species of Alueva, based on the comparison of the ontogenic patterns of the species Alueva undulata Sdzuy, 1961, and the adult morphologies of Alueva moratrix (Sdzuy, 1958). This analysis suggests that the species Alueva? hastata (Sdzuy, 1958) is not related to the pædomorphocline, and provides an approach for evaluating the phylogenetic relationships between the species A. undulata and A. moratrix, which occur across the Lower-Middle Cambrian transition in the Iberian Chains, directly linked with the Valdemiedes event.     

The morphology of prehatching embryos of Caecilia orientalis (Amphibia: Gymnophiona: Caeciliidae)

The state of development of advanced embryos of the direct‐developing Ecuadorian caecilian Caecilia orientalis (Caeciliidae: Gymnophiona: Amphibia) was examined. Because it is established that development is correlated with reproductive modes in a number of features, we included comparison with taxa that represent the major reproductive modes and all of the modern normal tables and ossification sequences. The embryos of C. orientalis most closely resemble those of stage 47/48 Gegeneophis ramaswamii, an Indian caeciliid, and stage 47/48 Hypogeophis rostratus, a Seychellian caeciliid, both direct developers, in details of bone mineralization, chondrocranial degeneration, and vertebrogenesis. They are most like stage 45 H. rostratus in external features (gills, pigmentation, etc.). They are less similar to prehatchings of Ichthyophis kohtaoensis, an ichthyophiid with free‐living larvae, and to fetuses of the viviparous caeciliid Dermophis mexicanus and the viviparous typhlonectid Typhlonectes compressicauda at comparable total lengths in both skeletal development and external features. The similarity of developmental features among the direct‐developers suggests a correlation with mode of life history. A noteworthy feature is that C. orientalis has an armature of multiple rows of teeth on the lower jaw with tooth crowns that resemble the “fetal” teeth of viviparous taxa and that are covered with a layer of oral mucosal epithelium until full development and eruption, but the upper jaw bears a single row of widely spaced, elongate, slightly recurved teeth that resemble those of the adult. J. Morphol., 2009. © 2009 Wiley‐Liss, Inc.     

Life history shifts and alterations in the early development of parasitic wasps

Summary

In insects, the regulation of embryonic development has been intensively studied in model species like Drosophila melanogaster. Previous comparative studies have suggested that the developmental processes documented in Drosophila well describe embryogenesis of holometabolous insects generally. However, there have been few attempts to take into account how life history has influenced insect embryogenesis or to characterize early development of species with life histories fundamentally different from flies. Our studies of advanced insects in the order Hymenoptera suggest that punctuated shifts in life history can profoundly influence these events. In particular, alterations associated with the evolution of endoparasitism argue that departures from the fly paradigm may occur commonly among insects that develop under conditions different from typical terrestrial species.     

Mansuyia Sun,and Tsinania Walcott,from the Furongian of North China and the evolution of the trilobite family Tsinaniidae

The Furongian trilobite family Tsinaniidae is characterized by a highly effaced surface and forms an important constituent of the Furongian trilobite faunas of east Gondwana. However, the origin of the characteristic morphology of this family has remained unclear. Only recently has the tsinaniid trilobite Lonchopygella megaspina been suggested to represent an intermediate stage in the evolutionary transition to other tsinaniids on the basis of the trunk segmentation. Here, we report successive occurrences of four species of the kaolishaniid genus Mansuyia and a tsinaniid trilobite Tsinania canens from the Furongian (late Cambrian) Chaomidian Formation in Shandong Province, China. A cladistic analysis including these taxa reveals that the four species of Mansuyia constitute stem‐group taxa to the family Tsinaniidae, rendering Mansuyia and the Kaolishaniidae paraphyletic. The youngest species of Mansuyia, M. taianfuensis, turns out to be the immediate sister taxon of the Tsinaniidae, displaying a closely similar morphology to the tsinaniid trilobite, Shergoldia laevigata. The generic and familial boundary therefore situated between M. taianfuensis and S. laevigata.     

Compound eyes and ocular pigments of crustacean larvae (Stomatopoda and decapoda,brachyura)

Larvae of decapod and stomatopod crustaceans possess paired compound eyes not unlike those of adult crustaceans. However, the visual demands of larval and adult life differ considerably. Furthermore, the eyes of adult stomatopods appear to be far more specialized than those of the larvae. We examined eyes of several stomatopod species just before and after larval metamorphosis. At this time, the entire larval retina is joined by a new, adult‐type retinal array which gradually replaces the remnants of the larval retina. The new retina of the postlarva is anatomically similar to that of the full‐grown adult, and has virtually identical assemblages of intrarhabdomal filters. We determined the photopigments of Gonodactylus aloha, the only species for which we were able to obtain both larval and adult specimens, using microspectrophotometry. The single middle‐wavelength larval rhodopsin (λ_max= 499 nm) disappears at metamorphosis; none of the 10 classes of adult rhodopsins has λ_max between 473 and 510 nm. This metamorphic change of visual pigment does not occur in a comparison species of decapod crustacean, the blue crab Callinectes sapidus. Here, rhodopsins both of the megalops larva and the adult had λ_max at 503–504 nm. The difference between these two species can be explained by the varying ecological requirements of their larvae and adults, and more study of visual pigments in retinas of larval and adult crustaceans is warranted.     

OBSERVATIONS ON THE DISTRIBUTION,EMERGENCE AND BEHAVIOUR OF CENTRAL AFRICAN CHAOBORIDAE

SUMMARY

The distribution of four species of Chaoboras over selected parts of Zimbabwe is given. The effect of temperature on the duration of the larval life cycle is discussed in relation to the generation time and the lunar periodicity of the adult emergence period. There were apparently two generations of larvae present in the habitat at any one time, although these generations were not distinct due to the variations in the time taken by the larvae to complete development at any temperature. The emergence was synchronized to the lunar cycle, but the actual moon phase at which emergence occurred was variable, as the two populations under observation both changed from new moon emergences to full moon emergences during the study. Some observations on the behaviour of adult Chaoboras edulis are given.     

Rib and vertebral micro‐anatomical characteristics of hydropelvic mosasauroids

Houssaye, A. & Bardet, N. 2011: Rib and vertebral micro‐anatomical characteristics of hydropelvic mosasauroids. Lethaia, Vol. 45, pp. 200–209. Mosasauroids are squamates secondarily adapted to an aquatic life that dominated the sea during the Late Cretaceous. Mosasauroids display distinct types of morphologies illustrating steps in the adaptation of this lineage to increasing obligatory habits. Hydropelvic mosasauroids (sensu Caldwell & Palci) were the most highly adapted to an open‐sea environment. Contrary to plesiopelvic forms, they are considered to have relied on a hydrodynamic, rather than hydrostatic buoyancy and body trim control strategies. This led previous authors to consider that these taxa would favour bone lightening (osteoporotic‐like condition) rather than bone mass increase. Although an osteoporotic‐like state was indeed described in Clidastes and Tylosaurus, bone mass increase was reported in Platecarpus. As a matter of fact, the new analysis of vertebral thin sections of various taxa combined with the reanalysis of the rib sections available in Sheldon’s PhD thesis in a micro‐anatomical perspective reveals the absence of both bone mass increase and bone lightening in these organisms. These taxa in fact display a vertebral micro‐anatomy much peculiar within squamates. It characteristically corresponds to a true network of thin trabeculae whose tightness varies between taxa, probably as a result of both species and individual size differences, particularly the latter. In addition, analysis of the pattern of vascularization as observed in hydropelvic mosasauroids, which is unique amongst squamates, suggests that large size in hydropelvic mosasauroids would mainly rely on protracted rather than faster growth rates. □Histology, hydropelvic mosasauroids, micro‐anatomy, ribs, vascularization, vertebrae.     

The function of forks: Isotelus‐type hypostomes and trilobite feeding

Hegna, T.A. 2010: The function of forks: Isotelus‐type hypostomes and trilobite feeding. Lethaia, Vol. 43, pp. 411–419. Despite previous investigations, the function of the forked morphology of asaphid trilobite hypostomes is enigmatic. The focus of this study is the large and robust forked hypostome of the largest known genus of trilobite, Isotelus, and the independently‐derived forked hypostome of Hypodicranotus, the longest hypostome relative to body size of any trilobite. Although the trilobite hypostome is analogous to the labrum in other arthropods, forked hypostomes lack an obvious modern functional counterpart. The Isotelus hypostome is distinguished from other trilobite hypostomes by closely‐spaced terrace ridges on a greatly thickened inner surface of the forked posterior margin, with the scarp of the terrace facing antero‐ventrally. This is compatible with a grinding function, suggesting possible limb differentiation to complement this structure. The inner face of the tine (one of the two, prominent, sub‐parallel posterior projections) is also unique in that it has a microstructure which is evident in section, running perpendicular to the surface. Macropredatory and filter‐feeder roles are ruled out, and previous characterizations of the hypostome as knife‐like or serrated are rejected. Its function is incompatible with that of other non‐asaphid trilobites with forked hypostomes, like the remopleuridid Hypodicranotus, which lack similar terrace ridges and thickened inner‐edge cuticle. □Arthropoda, Asaphida, ecology, functional morphology, Trilobita.