Abstract Morphological identification of planktic crustacean larvae is required in many scientific contexts, such as ecology or taxonomy. Due to a still low availability of genetic sequences for many ingroups of Eumalacostraca, this task is still more feasible by morphological methods. Our understanding of eumalacostracan larval morphology is challenged by phenotypic variability. We investigated four eumalacostracan ingroups: Galatheidae, Hippoidea, Raninidae and Stomatopoda. Representatives of all four groups develop through spine-bearing planktic larval stages. Incorporating dorsal and lateral shield outlines into three-dimensional shape analysis of the shields, we compare specimens from the wild with laboratory-reared specimens. Using graphical and statistical analysis methods, we find that at least the lateral morphology of the shields of Hippoidea and Raninidae seems to be too strongly dependent on phylogeny to show phenotypic variability with our current sample size, but Hippoidea do show phenotypic variability in their dorsal shield morphology. In Galatheidae and Stomatopoda, a clear difference in shield morphology can be found between wild-caught and laboratory-reared specimens. This difference likely represents phenotypic variability. The exact environmental signals causing this phenotypic variability are still unknown, but some candidates are discussed. contexts taxonomy Eumalacostraca methods Stomatopoda spinebearing spine bearing stages threedimensional three dimensional laboratoryreared laboratory reared size wildcaught caught unknown discussed

ABSTRACT Beetles occupy a vast amount of different ecological roles in both terrestrial and freshwater ecosystems. The often very specialised morphology of the adults can frequently be associated with their specific roles. Yet, the ecologically independent larvae of the same species are often unknown; this applies even more so to fossils. Here we report a new fossil beetle larva preserved in Mexican amber. The beetle larva was documented via digital microscopy and X-ray micro-computed tomography (X-ray µCT). The observed features, especially of the trunk, but also the maxillo-labial complex as well as the moulting suture of the head capsule are reminiscent to those of larvae of variegated mud-loving beetles, Heteroceridae. The trunk end is tube-like and protrudes ventro-terminally from abdomen segment 9. While present in other beetle lineages, this morphology is in these lineages, for example, not combined with a simple moulting suture. Some features potentially further supporting an interpretation as a larva of Heteroceridae are not accessible. The interpretation yet remains the most compatible one. Assuming a similar life style to modern larvae of Heteroceridae indicates an original lifestyle associated with running waters, but not within these. Heteroceridae is an ingroup of Byrrhoidea; the fossil record of byrrhoidean larvae is still very scarce. The new fossil hence adds a rare ecological function to the Miocene amber fauna, representing the first fossil record of a larva of Heteroceridae and expanding the fossil record of byrrhoidean larvae.

RESUMEN Los escarabajos ocupan una vasta gama de roles ecológicos diferentes, tanto en ecosistemas terrestres como en cuerpos de agua dulce. La morfología de los adultos, frecuentemente especializada, puede a menudo ser asociada con sus roles ecológicos específicos. Sin embargo, las larvas de una misma especie, que usualmente son ecológicamente independientes, son frecuentemente desconocidas; esto aplica con mayor razón al registro fósil. En este trabajo se reporta una larva de escarabajo preservada en ámbar mexicano. La larva de escarabajo fue documentada vía microscopía digital y tomografía microcomputarizada de rayos X (X-ray µCT). Las características observadas, especialmente las del tronco, además del complejo maxilo-labial y la sutura de muda de la cápsula cefálica, son similares a los de larvas de escarabajos abigarrados del lodo, los Heteroceridae. El extremo posterior del tronco es tubular y se protruye en posición ventro-terminal con respecto al segmento 9 del abdomen. Aunque está presente en otros linajes de escarabajos, esta morfología no está combinada, por ejemplo, con una sola estructura de la sutura de la muda. Algunas características que apoyarían aún más la interpretación de esta larva como un Heteroceridae no son accesibles. La interpretación presentada es la más compatible con las evidencias que se puede proporcionar. Asumiendo un modo de vida similar al de las larvas modernas de Heteroceridae, se puede proponer un hábitat asociado a aguas fluviales, aunque no sumergida en ellas. Heteroceridae es un grupo interno de los Byrrhoidea; el registro fósil de las larvas birroideas es aún muy escaso. En virtud de lo anterior, el nuevo fósil implica una rara función ecológica para la fauna del ámbar del Mioceno y representa el primer registro fósil de larvas de Heteroceridae, a la vez que expande el registro de las larvas birroideas.

Abstract Neuroptera (lacewings) is today a rather small lineage of Holometabola. These representatives of Insecta have mostly predatory larvae with prominent venom-injecting stylets formed by upper and lower jaws. These impressive larvae can be found not only in the modern fauna, but sometimes also as fossils, predominantly preserved in amber. Here we report a new specimen of a lacewing larva from Miocene Mexican amber, most likely a larva of an owlfly (Ascalaphidae) with large prominent stylets, each with three teeth. These stylets arise from a more or less square-shaped head (in dorsal view) that has distinct eye hills with at least three simple eyes (stemmata) each. The trunk is rather short. Trunk segments possess finger-like protrusions carrying numerous setae, which could have been used to attach camouflaging debris to it. Remarkably, the specimen represents only the second report of a lacewing from Miocene Mexican amber, and the first larva. Additionally, we review the Miocene record of lacewing larvae. It includes otherwise only fossils preserved in Dominican amber and remains rather scarce, with only eight specimens in the literature so far. While there seem to be additional specimens in private collec-tions, the overall number is astonishingly low compared to the numbers in Eocene and Cretaceous ambers. Ecological and taphonomic factors possibly explaining the rarity of lacewing larvae in Miocene amber are discussed here.

Resumen Neuróptera (crisopas) es hoy en día un linaje bastante pequeño entre los insectos holometábolos. Estos representantes de Insecta, con larvas que son principalmente depredadoras, tienen prominentes estiletes formados por las mandíbulas superior e inferior que inyectan veneno. Estas impresionantes larvas no solo se pueden encontrar en la fauna moderna, sino a veces también como fósiles, mayoritariamente preservados en ámbar. Aquí presentamos un nuevo espécimen de una larva de crisopa preservada en ámbar mexicano del Mioceno, que es muy probablemente una larva de Ascalaphidae (a veces también denominadas “moscas búho”) con grandes y prominentes estiletes, cada uno con tres dientes. Estos estiletes provienen de una cabeza de forma más o menos cuadrada (en vista dorsal) con colinas visibles que presentan al menos tres ojos simples (stem-mata) cada una. El tronco es más bien corto. Los segmentos del tronco poseen protuberancias en forma de dedos con numerosas setas que podrían haber sido utilizadas para acumular escombros para su camuflaje. Notablemente, este espécimen representa únicamente el segundo reporte de una crisopa en ámbar mexicano del Mioceno y la primera larva. Además, revisamos el registro del Mioceno de larvas de crisopa, que únicamente incluye fósiles preservados en ámbar dominicano y que sigue siendo bastante escaso, con solo ocho especímenes mencionados en la literatura hasta ahora. Si bien parece haber especímenes adicio-nales en colecciones privadas, el número total es sorprendentemente bajo en comparación con la cantidad de ejemplares en ámbar del Eoceno y del Cretácico. Los factores ecológicos y tafonómicos, que posiblemente expliquen la rareza de las larvas de crisopa en el ámbar del Mioceno, son también aquí discutidos.

Abstract Representatives of Hippoidea, often called sand crabs or mole crabs, are an ingroup of Anomala. These marine crustaceans inhabit the tropical and subtropical coasts of the world, yet some also appear in temperate climates. Their adults are specialized for digging and living in sandy substrates. Hippoidean zoea-type larvae are planktic and reach large sizes up to a few centimetres. These larvae transform into megalopa larvae, strongly resembling the adult, mediating the transition to the benthic lifestyle of the adult. We reconstructed outlines in dorsal view of over 80 shields of hippoideans, including representatives of Blepharipodidae (sister group to all others), Albuneidae, and Hippidae and including adults, megalopa-type, and zoea-type larvae from all three ingroups. We conducted a morphological analysis on this data using an elliptic Fourier transformation and principal component analysis. We used the results of the analysis to discuss the life history of hippoideans and the special function of megalopae, which often lack emphasis in current research. Early stage zoea larvae, megalopae, and adults show a linear gradient in their morphological development according to our analysis. However, late stage zoea larvae deviate from this pattern, possibly due to their specialization to a long-lasting planktic life. Lastly, we discuss the influence of phenotypic plasticity in hippoidean zoea larvae.

Abstract We present a documentation of the morphological details of two larval stages of mantis shrimps. Documentation was done using the autofluorescence capacities of the cuticle. This is the first time that morphological details of late mantis shrimp larvae are documented in great detail via photography, including all parts of the body up to the proximal elements of the appendages, and not presented as line drawings; it is the second time for mantis shrimp larvae in general. The description is presented as a standardized descriptive matrix. Documentation and description style are adjusted to facilitate comparison with fossil representatives of mantis shrimps, but also their extant counterparts, as well as specimens in the wider framework of Malacostraca and Eucrustacea. Through an exemplary comparison with fossil mantis shrimps, we provide indications about the early evolutionary history of the group. Through an out-group comparison, we identify several possible evolutionary changes of developmental timing, i.e., heterochrony, which could explain some morphological specialisations of mantis shrimps.

Abstract Mantis shrimps are prominent predatory crustaceans. Their larvae, although morphologically very differently-appearing from their adult counterparts, are already predators; yet, unlike the adults they are not benthic. Instead they are part of the plankton preying on other planktic organisms. Similar to some types of lobsters and crab-like crustaceans the planktic larvae of mantis shrimps can grow quite large, reaching into the centimeter range. Nonetheless, our knowledge on mantis shrimp larvae is still rather limited. Recently new types of giant mantis shrimp larvae with “extreme morphologies” have been reported. Here we describe another type that qualifies to be called “extreme”. Comparative measurements of certain morphological structures on selected known larvae support the exceptionality of the new specimen. It differs in several aspects from the original four types of extreme mantis shrimp larvae described by C. Haug et al. (2016). With this fifth type we expand the known morphological diversity of mantis shrimp larvae and also contribute to our still very incomplete, although growing, knowledge of this life phase.

ABSTRACT Larvae of stomatopods (mantis shrimps) are generally categorized into four larval types: antizoea, pseudozoea (both representing early larval stages), alima and erichthus (the latter two representing later larval stages). These categories, however, do not reflect the existing morphological diversity of stomatopod larvae, which is largely unstudied. We describe here four previously unknown larval types with extreme morphologies. All specimens were found in the collections of the Zoological Museum, University of Copenhagen and were collected during the Danish Dana Expedition round the world 1928-30. These new larval types all represent erichthus-type larvae, especially differing in their shield morphologies. The shield morphology ranges from almost spherical to rather disc-like, with sometimes extremely elongated spines, but only a general systematic assignment of the larvae was possible. Further investigations of these larvae are crucial to understand their life habits and ecological impact, especially as stomatopod and other crustacean larvae might have a much more important position in the marine ecosystems than their corresponding adults.

Construction excavation within member "B" of the middle Eocene-aged Santiago Formation at Bressi Ranch in the southern part of the City of Carlsbad, California, USA, have produced exceptionally preserved upogebiid fossils. While most fossil upogebiids are only known fragmentarily, the specimens described here are preserved as relatively complete articulated specimens. Preserved structures include: the cephalothoracic shield with a short rostrum, a well-developed cervical groove and anterior coarse tuberculation; the pleon, with a characteristic trapezoidal first tergite and the second tergite representing the largest of the series; the appendages including (fragmentary) maxillipeds two and three, and the five walking limbs; the tail fan with uropods with both sub-triangular rami possessing bulging anterior edges and one (endopod) or two (exopod) keels running in parallel to the anterior bulging edge, the exopod lacking a diaresis, and the telson being sub-rectangular with a median suture. Exceptional minute details preserved are the bases of setae on the uropods and muscles in pleomere six. These muscles show fiber bundles about 80 µm in diameter, and individual fibers about 10 µm in diameter. The specimens were documented with up-to-date imaging techniques, including stereo photography or depth-map-based surface reconstructions. Due to the exceptional preservation, the fossils can be recognized as an upogebiid of the species Upogebia aronae sp. nov. As numerous specimens have been found at that locality, this discovery indicates similarly dense populations as seen in modern fauna.

La excavación durante una construcción en el miembro "B" de la Formación Santiago de edad Eoceno medio en el Rancho Bressi, ubicado en la porción sur de la Ciudad de Carlsbad, California, USA, ha producido fósiles de upogébidos excepcionalmente bien preservados. Aunque la mayoría de upogébidos fósiles se conocen de restos fragmentarios, los aquí descritos están preservados como especímenes articulados, relativamente completos. Las estructuras preservadas incluyen: el escudo cefalotorácico con un rostro corto, un surco cervical bien desarrollado y gruesos tubérculos en la porción anterior; pleón con un primer terguito característicamente trapezoidal y el segundo terguito representa el más grande de la serie; los apéndices incluyen los maxilípedos dos y tres (fragmentarios) y las cinco patas ambulacrales; el abanico caudal con urópodos con ambos rami subtriangulares, que poseen márgenes anteriores prominentes y una (en endópodo) o dos (en exópodo) quillas que corren paralelo al margen prominente, el exópodo carece de diéresis y el telson es subrectangular con un sutura media. Detalles diminutos excepcionales son las bases de las setas en los urópodos y los músculos en el pleómero seis. Estos músculos muestran paquetes fibrosos de aproximadamente 80 µm de diámetro, y fibras individuales de aproximadamente 10 µm de diámetro. Los ejemplares se documentarons con técnicas de imagenología de punta, incluyendo estereofotografía y reconstrucciones de superficie basadas en profundidad de mapeo. Debido a la excepcional preservación, los fósiles pueden ser reconocidos como un upogoébido de la especie Upogebia aronae sp. nov. Dado que se han encontrado numerosos especímenes en esta localidad, este hallazgo indica poblaciones similarmente densas como las observadas en la fauna moderna.

We describe 54 fragmentary specimens from the Pliocene of North Carolina that represent isolated dactyli of mantis shrimps. These specimens are preserved uncompressed within three dimensions in calcium phosphate. The dactyli have an estimated maximum length of 15 millimeters and bear six spines. The specimens appear to be hollow and preserve fine details, especially a narrow crest on the dorsal side of the spines, a functional blade edge that has not been previously found on any fossil stomatopod. The specimens are provisionally attributed to the species Squilla empusa, found nowadays along the entire East coast of the United States of America. Fossil occurrences are known from the Pleistocene of Maryland and from the late Pleistocene or early Holocene of Connecticut. Though isolated dactyli are less informative on the taxonomic level, they can be important on the paleo-ecological level, positively demonstrating the presence of ambush predators in an investigated paleo-community. Given the scarce stomatopod fossil record and the exceptional three-dimensional preservation, the finding of these specimens, despite their fragmentary nature, is regarded as significant.

Se describen 54 especímenes fragmentarios del Plioceno de Carolina del Norte, los cuales representan dactilos aislados de mantis marinas. Estos ejemplares se preservaron tridimensionalmenteen fosfato de calcio, sin compresión alguna. Los dactilos tienen una longitud máxima estimada de 15 milímetros y tienen seis espinas. Los especímenes parecen estar huecos y preservan detalles finos, especialmente una cresta estrecha en el lado dorsal de las espinas, que es una hoja afilada funcional no reportada previamente para ningún estomatópodo fósil. Los especímenes son provisionalmente asignados a la especie Squilla empusa, la cual se encuentra actualmente a lo largo de la costa Este de los Estados Unidos de América. Se conocen registros fósiles de esta especie del Pleistoceno de Maryland y del Pleistoceno u Holoceno temprano de Connecticut. Aunque los dáctilos aislados son poco significativos a nivel taxonómico, pueden ser importantes a nivel paleoecológico, puesto que demuestran la presencia de depredadores en una paleocomunidad en estudio. Dado el escaso registro fósil de estomatópodos y la excepcional preservación tridimensional, el hallazgo de estos especímenes, a pesar de su naturaleza fragmentaria, se considera significativo.