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More Orsten-type fossils In recent years, 'Orsten-type' fossils, characterized by remarkable preservation of the soft tissue of putative embryos and arthropod larvae, have transformed our view of the early evolution of metazoans. They are termed 'Orsten' fossils from the name of the oily alum shale deposits in Sweden where they were first found; similarly fine preservation has since been found elsewhere. Now, importantly, elsewhere includes the Lower Cambrian in China. Fossils of 'eucrustacea' — crustaceans of modern aspect — are common in the fossil record from around 500 million years ago. Newly unearthed Orsten-type fossils from China include the earliest known eucrustacean in exquisite three-dimensional detail, significantly extending the fossil record of this group. Fossils of 'eucrustacea' (crustaceans of modern aspect) are common in the fossil record from around 500 million years ago. A remarkable new 'Orsten' type Konservat-Lagerstäette from the Lower Cambrian of China reveals the earliest known eucrustacean in exquisite three-dimensional detail, significantly extending the fossil record of this important group. Crown-group crustaceans (Eucrustacea) are common in the fossil record of the past 500 million years back to the early Ordovician period, and very rare representatives are also known from the late Middle and Late Cambrian periods 1 . Finds in Lower Cambrian rocks of the Phosphatocopina, the fossil sister group to eucrustaceans 2 , imply that members of the eucrustacean stem lineage co-occurred, but it remained unclear whether crown-group members were also present at that time. ‘Orsten’-type fossils are typically tiny embryos and cuticle-bearing animals, of which the cuticle is phosphatized and the material is three-dimensional and complete with soft parts. Such fossils are found predominantly in the Cambrian and Ordovician and provide detailed morphological and phylogenetic information on the early evolution of metazoans. Here we report an Orsten-type Konservat-Lagerstätte from the Lower Cambrian of China that contains at least three new arthropod species, of which we describe the most abundant form on the basis of exceptionally well preserved material of several growth stages. The limb morphology and other details of this new species are markedly similar to those of living cephalocarids, branchiopods and copepods and it is assigned to the Eucrustacea, thus representing the first undoubted crown-group crustacean from the early Cambrian. Its stratigraphical position provides substantial support to the proposition that the main cladogenic event that gave rise to the Arthropoda was before the Cambrian 3 . Small leaf-shaped structures on the outer limb base of the new species provide evidence on the long-debated issue of the origin of epipodites 4 , 5 : they occur in a set of three, derive from setae and are a ground-pattern feature of Eucrustacea.

Background We describe new specimens of Mesozoic mantis shrimps (Stomatopoda, Malacostraca) that exhibit morphological and developmental information previously unknown. Results Specimens assigned to the taxon Sculda exhibit preserved pleopods, thoracopods including all four raptorial limbs as well as details of antennae and antennulae. The pleopods and the antennulae resemble those of the modern mantis shrimps, but the raptorial limbs are not as differentiated as in the modern species. In some specimens, the first raptorial limb (second thoracopod) is not significantly larger than the similar-sized posterior three pairs (as in extant species), but instead these appendages become progressively smaller along the series. In this respect they resemble certain Palaeozoic stomatopods. Another specimen, most likely belonging to another species, has one pair of large anterior raptorial thoracopods, a median-sized pair and two more pairs of small-sized raptorial appendages and, thus, shows a new, previously unknown type of morphology. A single specimen of Pseudosculda laevis also exhibits the size of the raptorial limbs; they are differentiated as in modern species, one large pair and three small pairs. Furthermore, we report additional larval specimens and show also post-larval changes, e.g., of the tail fan. Conclusions These new data are used to reconsider the phylogeny of Stomatopoda. We still need a strict taxonomical revision of the Mesozoic mantis shrimps, but this first examination already demonstrates the importance of these fossils for understanding mantis shrimp evolution and the interpretation of evolutionary pathways of particular features.

The pontogammarid amphipod Dikerogammarus villosus, originally a Ponto-Caspian faunal element, has, in the recent 15-20 years, successfully invaded various aquatic systems in Europe including Lake Constance. In these rivers and lakes it had and still has severe ecological impact on native macro-invertebrates, often eliminating the native and earlier established gammaridean species. In order to test the hypothesis that the mode of food acquisition of D. villosus is of significance for this phenomenon, we focused on the mouthparts of D. villosus, i.e., mandibles, the two pairs of maxillae and the maxillipeds using SEM. Contrary to expectations, provoked by field and laboratory observations, the results of this study show that the mouthparts of D. villosus are not highly specialized just for carnivory and predation. Indeed, the stout mandibles, with their well-developed incisors enable to kill even prey with robust integument, but other modes of feeding are possible. On the maxillulae, maxillae, and maxillipeds we found setae that can be used, together with the gnathopods and the antennae, for filtering suspended algae and other small particles from the respiration current. The same structures are involved in collecting detritus. In contrast, D. villosus does not possess any specific tools for scraping periphyton from the substrate. Feeding on macrophytes may be possibly but not very effective because the surfaces of the molars are not well suited for grinding such plant material. It is shown that D. villosus is neither a shredder, as traditionally predicated for most gammarideans, nor is it a specialized carnivore, as predation experiments proposed, but rather unspecialized. Its ability to be carnivorous and to use a wide spectrum of other food may be an important reason for the success of this invader, being an advantage compared to mainly herbivorous gammarideans, which have been eliminated in many places by D. villosus.

We give an overview of available techniques for imaging and documenting applied to gammarideans and discuss their advantages and disadvantages. Although recent techniques, such as confocal laser scanning microscopy (cLSM), focused ion beam scanning electron microscopy (FIB SEM), or computed microtomography (μCT), provide new possibilities to detect and document structures, these high-tech devices are expensive, and access to them is often limited. Alternatively, there are many possibilities to enhance the capabilities of established techniques such as macrophotography and light microscopy. We discuss improvements of the illumination with polarized light and the possibilities of utilizing the autofluorescence of animals such as the gammarideans. In addition, we present software-based enhancing tools such as image fusion and image stitching.

Fossilized compound eyes from the Cambrian, isolated and three-dimensionally preserved, provide remarkable insights into the lifestyle and habitat of their owners. The tiny stalked compound eyes described here probably possessed too few facets to form a proper image, but they represent a sophisticated system for detecting moving objects. The eyes are preserved as almost solid, mace-shaped blocks of phosphate, in which the original positions of the rhabdoms in one specimen are retained as deep cavities. Analysis of the optical axes reveals four visual areas, each with different properties in acuity of vision. They are surveyed by lenses directed forwards, laterally, backwards and inwards, respectively. The most intriguing of these is the putatively inwardly orientated zone, where the optical axes, like those orientated to the front, interfere with axes of the other eye of the contralateral side. The result is a three-dimensional visual net that covers not only the front, but extends also far laterally to either side. Thus, a moving object could be perceived by a two-dimensional coordinate (which is formed by two axes of those facets, one of the left and one of the right eye, which are orientated towards the moving object) in a wide three-dimensional space. This compound eye system enables small arthropods equipped with an eye of low acuity to estimate velocity, size or distance of possible food items efficiently. The eyes are interpreted as having been derived from individuals of the early crustacean Henningsmoenicaris scutula pointing to the existence of highly efficiently developed eyes in the early evolutionary lineage leading towards the modern Crustacea.

INTRODUCTION: We describe the tagmatization pattern of the anterior region of the extant stomatopod Erugosquilla massavensis. For documentation we used the autofluorescence capacities of the specimens, resulting in a significant contrast between sclerotized and membranous areas. RESULTS: The anterior body region of E. massavensis can be grouped into three tagmata. Tagma I, the sensorial unit, comprises the segments of the eyes, antennules and antennae. This unit is set-off anteriorly from the posterior head region. Ventrally this unit surrounds a large medial sclerite, interpreted as the anterior part of the hypostome. Dorsally the antennular and antennal segments each bear a well-developed tergite. The dorsal shield is part of tagma II, most of the ventral part of which is occupied in the midline by the large, partly sclerotized posterior part of a complex combining hypostome and labrum. Tagma II includes three more segments behind the labrum, the mandibular, maxillulary and maxillary segments. Tagma III includes the maxillipedal segments, bearing five pairs of sub-chelate appendages. The dorsal sclerite of the first of these tagma-III segments, the segment of the first maxillipeds, is not included in the shield, so this segment is not part of tagma II as generally thought. The second and third segments of tagma III form a unit dorsally and ventrally. The tergites of the segments of tagma III become progressively larger from the anterior to the posterior, possibly resulting from a paedomorphic effect during evolution, which caused this reversed enlargement. CONCLUSIONS: The described pattern of tagmosis differs from current textbook knowledge. Therefore, our re-description of the anterior body area of stomatopods is of considerable impact for understanding the head evolution of Stomatopoda. Likewise, it has a bearing upon any comparisons with fossil stomatopods, as mainly sclerotized areas are fossilized, and, on a wider scale, upon larger-scale comparisons with other malacostracans and eucrustaceans in general.

In the last 20 years several nonnative amphipod species have immigrated inland waters of Germany and adjacent central European countries. Some of them have been very successful and could establish stabile populations. In some places, they have even replaced native or earlier established species. The gammarid Echinogammarus berilloni originates from the Atlantic region of France and the north-western part of Spain and coexists in some central European waters with the native Gammarus pulex and G. fossarum. Here, we describe and compare the mouthparts and other structures involved in food acquisition of these three sympatric gammaridean species. Our hypothesis was that differences in the mode of feeding of the three species could be the reason for their coexistence and that these differences would be expressed in differences in mouthpart morphology. The results of our SEM study demonstrate that there are indeed interspecific differences in details of the morphology of the feeding structures. This is especially true for the setation of antennae, maxillulae, gnathopods, and third uropods, which can be interpreted as adaptations to special modes of feeding. Generally, all three species are omnivorous, but specializations in details point to the possibility to use some food resources in a special effective way.

Scalidophoran worms diversified in the Cambrian Fortunian, as indicated by recent reports from this stage, with two described species and two more unnamed forms exclusively from Orsten-type Lagerstätten yielding three-dimensionally phosphatized fossils. Here, we report new material of scalidophoran worms in Orsten-type preservation from the Cambrian Fortunian Xinli section in northern Sichuan Province, South China. At least five forms of scalidophoran worms were recovered from this location, including Eokinorhynchus rarus Zhang et al., 2015 and four unnamed taxa—Forms A, B, C, and D. Co-occurring disassociated spinose small shelly fossils might also be isolated cuticular elements of these early scalidophoran worms. The ontogeny of Eokinorhynchus rarus is revised. Forms A, C, and D are assigned to total-group Scalidophora to indicate their uncertain positions within Scalidophora, while Form B might be a close relative of Eokinorhynchus rarus. The current work highlights the significance of Orsten-type Lagerstätten in uncovering the morphology, ontogeny, and taxonomy of early Scalidophora and Cycloneuralia, made particularly available by the new finds in China.

A detailed investigation of Phosphatocopina Fossils and Strata, Number 49: Morphology, Ontogeny, and Phylogeny of the Phosphatocopina (Crustacea) from the Upper Cambrian Orsten of Sweden presents a detailed look at Phosphatocopina through the rigorous lens of modern scientific study. Fully examined here in study form, this monograph details methods, materials, systematics, phylogenetic analysis and more to bolster discussion and back analyses of comparative morphology. Extensive figures and photos clarify qualitative data, while detailed explanation of analysis methods provide a firm foundation for conclusions and future research.

A detailed account of the morphology and ontogeny of the late Middle Cambrian crustacean †Henningsmoenicaris scutula is presented. Ten successive ontogenetic stages could be recognised in the material collected from various localities in Sweden. Morphogenetic changes include the development of a pair of stalked lateral eyes and the increase in the number and size of appendages and their setal armature. Notably, early stages lack ‘proximal endites’ on all post-antennular appendages; such a spine-bearing endite has previously been thought to appear simultaneously on these limbs. In †H. scutula a single functional endite appears on the third limb in an advanced stage; an additional endite appears on the second limb and, subsequently, further endites appear on more posterior limbs. Furthermore, a single specimen of †Sandtorpia vestrogothiensis gen. et sp. nov. is described. Based on this new information and data of other ‘Orsten’ taxa, particularly those assigned already to the early evolutionary lineage of Crustacea, a small-scale computer-based phylogenetic analysis was performed. This resolved the basal branchings of Crustacea s. l. as follows: †Oelandocarididae (=†Oelandocaris oelandica+†H. scutula+†S. vestrogothiensis)+(†Cambropachycopidae (=†Goticaris longispinosa+†Cambropachycope clarksoni)+ (†Martinssonia elongata+Labrophora (=†Phosphatocopina+Eucrustacea))). Plotting ontogenetic data on the phylogram and comparing the ground pattern at every node led to the detection of three peramorphic heterochronic events in the evolutionary lineage towards Eucrustacea.