Morphological design and fossil record of the podocopid ostracod naupliar eye

The naupliar eye of podocopid ostracods is a useful character for considering evolution in photic environments. Based on external morphologies and histological observations, naupliar eyes are here categorized into six types. The fossil record demonstrates that the major evolutionary changes in podocopid naupliar eyes occured after the Ordovician. Eye types 1 and 2 are not joined to the carapace by the hypodermal cells, and these two types are found in Palaeozoic ostracods. Eye type 3, 4, 5 and 6 are extended on eye stalks, tightly joined to the carapace by the hypodermal cells, and use the carapace as the refractive cuticle lens. Eye type 3 appeared in the Permian, and eye types 4, 5 and 6 appeared in the Early Jurassic. The design of the podocopid naupliar eye diversified in the Early Jurassic.     

Homology and homoeomorphy in ostracod limbs

The functional modifications of myodocopan and podocopan ostracod limbs constitute a rich data set with which to carry out phylogenetic analyses, but efforts are hindered by lack of consensus on homologies. Homoeomorphy presents particular difficulties; for example, the furca is post-anal in Myodocopa but pre-anal in Podocopa, suggesting homoeomorphy, not homology. Homoeomorphies also exist between ostracod appendages and those of other Crustacea, for example the oral cone and styliform mandibulae of Paradoxostomatidae (Ostracoda) and Siphonostomatoida (Copepoda), both adaptations to commensal or parasitic lifestyles. Such clear manifestations of homoeomorphy, arising independently in different lineages as a result of similar functional requirements imposed on plesiomorphic appendage structures, warn of the possibility of more subtle examples which, if unrecognized, would lead to misinterpretations of character states used in phylogenetic analysis. For instance, the branchial plates found on third, fourth and fifth limbs of podocopans may not be homologous with the branchial plates on the fifth and sixth limbs of myodocopans. Limb homologies of podocopan ostracods (primarily as represented by various podocopid taxa) are investigated. Evidence is presented, based on studies of morphology and musculature, that podocopid branchial plates are exopodites (arising from the basis), while those of myodocopans are epipodites (arising from the coxa or precoxa). In Podocopida, moreover, the protopodites of post-mandibular limbs appear to be undifferentiated, comprising only a basis, while those of Myodocopa clearly exhibit a basis, coxa and often a precoxa. These differences argue against monophyly of the Ostracoda. The absence of epipodites, combined with the lack of a coxa in post-mandibular limbs, is potentially indicative of closer affinities between podocopans and Cambrian stem-group crustaceans (including Phosphatocopida) than between podocopans and myodocopans. The possible derivation of podocopid third, fourth and fifth limbs from a stem-group crustacean limb is demonstrated. The hypothesis is advanced that podocopan ostracods (represented today by Podocopida, Platycopida and Palaeocopida) are derived from much nearer the base of the crown-group Crustacea than myodocopans.     

First record of preserved soft parts in a Palaeozoic podocopid (Metacopina) ostracod, Cytherellina submagna: phylogenetic implications

The metacopines represent one of the oldest and most important extinct groups of ostracods, with a fossil record from the Mid-Ordovician to the Early Jurassic. Herein, we report the discovery of a representative of the group with three-dimensionally preserved soft parts. The specimen--a male of Cytherellina submagna--was found in the Early Devonian (416 Ma) of Podolia, Ukraine. A branchial plate (Bp) of the cephalic maxillula (Mx), a pair of thoracic appendages (walking legs), a presumed furca (Fu) and a copulatory organ are preserved. The material also includes phosphatized steinkerns with exceptionally preserved marginal pore canals and muscle scars. The morphology of the preserved limbs and valves of C. submagna suggests its relationship with extant Podocopida, particularly with the superfamilies Darwinuloidea and Sigillioidea, which have many similar characteristic features, including a large Bp on the Mx, the morphology of walking legs, Fu with two terminal claws, internal stop-teeth in the left valve, adductor muscle scar pattern, and a very narrow fused zone along the anterior and posterior margins. More precise determination of affinities will depend on the soft-part morphology of the cephalic segment, which has not been revealed in the present material.     

Anchialine podocopid Ostracoda of the Galapagos Islands

Water-filled fissures and lava tubes on Isla Santa Cruz and Isla Isabela provide anchialine habitats for 11 species of podocopid and platycopid Ostracoda, most with Atlantic and West Indian affinities. Their ancestors may have been carried to earlier islands in the Galapagos system by trans-Isthmian currents, on vegetation or larger animals, or by migrating waterfowl. None are derived from present-day Pacific coastal faunas of North, Central or South America. Two species of Cytheracea, a new species of Anchistrocheles (Bairdiacea), and one of Cytherella (Platycopida) are described.     

Functional morphology of Palaeozoic ostracods: phylogenetic implications

Recent discussions of ostracod systematics have focused on soft anatomy, both as seen in extant groups and as recorded by rare examples of special fossil preservation. The position of the fossil Palaeocopina and Leperditicopida, for which no substantial soft part evidence has yet been found, remains in the view of post-Palaeozoic workers uncertain, with some doubt as to whether they should be retained within the Ostracoda. The evolution of carapace bauplans (e.g. the development of brood pouches and lobal structures in palaeocopids as well as the development of adductor muscle scar patterns, calcified inner lamellae and carapace incisures in podocopines) is discussed in relation to presumed soft anatomy. It seems possible to distinguish between plesiomorphic (ancestral, simple) and apomorphic (derived, advanced) characters and consider their significance in ostracod systematics. Although the presumed ‘protostracod’ is not known, the combination of soft anatomy, carapace architecture and behaviour (feeding techniques, brood care) provide evidence of a general body plan which appeared (at the latest) during the Ordovician and continuously evolved towards the anatomy of modern ostracods. In parallel lineages, plesiomorphic forms have died out (leperditicopids and most palaeocopines as well as metacopines), while apomorphic lineages (‘drepanellid archetype’ of palaeocopines; resistant platycopines, podocopines and myodocopines) have survived all extinction events. The evidence supports the retention of the Palaeocopina (and probably the Leperditicopida) in the Ostracoda.     

Recent benthonic ostracod assemblages as indicators of the Tsushima warm current in the southwestern sea of Japan

One hundred and sixty-seven species of podocopid ostracods are reported from 26 recent surface sediment samples collected on the shelf of the Tsushima Strait in the southwestern Sea of Japan. Four biofacies (A–D) are recognised based on Q-mode cluster analysis. Among these, biofacies B is distributed along the Tsushima Warm Current and includes typical East China Sea species. This fact suggests that the migration of the shelf-living ostracods between the open sea and the adjacent semi-enclosed marginal sea mainly occurs in association with the inflow of this sea current. The distribution of the recent ostracod assemblages from the Tsushima Strait are expected to be a sensitive indicator of past and future changes in the Tsushima Warm Current. One new ostracod species of the family Trachyleberididae, Trachyleberis ikeyai, is described and illustrated herein. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: K. Martens     

Homology of Holocene ostracode biramous appendages with those of other crustaceans: the protopod, epipod, exopod and endopod

Unambiguously biramous appendages with a proximal precoxa, well-defined coxa and basis, setose plate-like epipod originating on the precoxa, and both an endopod and exopod attached to the terminal end of the basis are described from several living Ostracoda of the order Halo-cyprida (Myodocopa). These limbs are proposed as the best choice for comparison of ostracode limbs with those of other crustaceans and fossil arthropods with preserved limbs, such as the Cambrian superficially ostracode-like Kunmingella and Hesslandona. The 2nd maxilla of Metapolycope (Cladocopina) and 1st trunk limb of Spelaeoecia, Deeveya and Thaumatoconcha (all Halocypridina) are illustrated, and clear homologies are shown between the parts of these limbs and those of some general crustacean models as well as some of the remarkable crustacean s.s. Orsten fossils. No living ostracodes exhibit only primitive morphology; all have at least some (usually many) derived characters. Few have the probably primitive attribute of trunk segmentation (two genera of halocyprid Myodocopa, one order plus one genus of Podocopa, and the problematic Manawa); unambiguously biramous limbs are limited to a few halo-cyprids. Homologies between podocopid limbs and those of the illustrated primitive myodocopid limbs are tentatively suggested. A setose plate-like extension, often attached basally to a podocopid protopod, is probably homologous to the myodocopid epipod, which was present at least as early as the Triassic. Somewhat more distal, less setose, and plate-like extensions, present on some podocopid limbs (e.g., mandible), may be homologous instead to the exopod (clearly present on myodocopid mandibles). The coxa (or precoxa) is by definition the most basal part of the limb. A molar-like tooth is present proximally on the mandibular protopod of many ostracodes; it is the coxal endite and projects medially from the coxa (or proximal protopod). The Ostracoda is probably a monophyletic crustacean group composed of Myodocopa and Podocopa. All have a unique juvenile (not a larva) initially with three or more limbs. Except that juveniles lack some setae and limbs, they are morphologially similar to the adult. Thus the following suite of characters in all instars may be considered a synapomorphy uniting all Ostracoda: (1) Each pair of limbs is uniquely different from the others. (2) The whole body is completely enclosed within a bivalved carapace that lacks growth lines. (3) No more than nine pairs of limbs are present in any instar. (4) The body shows little or no segmentation, with no more than ten dorsally defined trunk segments. No other crustaceans have this suite of characters. A probable synapomorphy uniting the Podocopa is a 2nd antenna with exopod reduced relative to the endopod.     

Functional morphology and palaeontological significance of the conchiolin layers in corbulid pelecypods

The Corbulidae, which today are slow, cumbersome, very shallow burrowers, developed special morphological features by which they obtained an outstanding capability to withstand the physical and biological stresses characteristic of their preferred habitat. These features are: an inequivalve, globose shape, thick shells, and conchiolin layers (at least one) embedded within their valves in a unique way. These features enable the corbulids to close their valves tightly during the unfavourable environmental conditions (e.g. low salinity, low oxygen content) which may prevail in the marginal marine regions inhabited by several corbulid species. The conchiolin layers act as a barrier preventing all chemically boring organisms from penetrating into the bivalve shell, or shell dissolution by sea water undersaturated with respect to calcium carbonate. The layered conchiolin weakens the shell mechanically, however, especially during fossilization, when the conchiolin is decomposed. The valve splits apart into two shells so completely different in appearance that they may be attributed to different taxa. The conchiolin layers are therefore of great ecological and palaeontological significance. The nature of these conchiolin layers in Corbula (Varicorbula) gibba (Olivi) is described and illustrated and their functional significance discussed in relation to other living and fossil corbulid species.     

Heterochrony of the ostracod hingement and its significance for taxonomy

The hingement of cytheracean ostracods is a very significant character for taxonomy. In some taxa, adult hinge characters develop abruptly at the last moult, whilst in others no significant change of hingement is observed throughout ontogeny. These two types of hinge development are regarded to as 'leap type' and 'gradual type', respectively. In the five major cytheracean families examined, heterochronic relationships were detected in 11 pairs, i.e. in each family, the adult hinge character of the gradual-type taxon corresponds to the A-1 hingement of the leap-type taxon. Furthermore, these 11 heterochronic pairs can be classified into two categories. The first are 'complete pairs', in which the adult hinge character of gradual-type taxa can be almost completely identified in the A-1 of the counterpart leap-type taxa. The second group are 'incomplete pairs', in which the relationship is not so complete. Palaeontological evidence indicates that in most cases the heterochronic evolution is characterized by paedomorphosis, because the leap type always has the older fossil record than the gradual type in each pair. Most of the gradual-type species of complete pairs originated in the Miocene, while all the gradual-type species of incomplete pairs appeared in and after the Pleistocene. Heterochronic changes must occur universally in the cytheracean ostracods, but the degree of completeness of the heterochronic pair seems to be related to the age of speciation.     

Vicariance and dispersal in southern hemisphere freshwater fish clades: a palaeontological perspective

Widespread fish clades that occur mainly or exclusively in fresh water represent a key target of biogeographical investigation due to limited potential for crossing marine barriers. Timescales for the origin and diversification of these groups are crucial tests of vicariant scenarios in which continental break‐ups shaped modern geographic distributions. Evolutionary chronologies are commonly estimated through node‐based palaeontological calibration of molecular phylogenies, but this approach ignores most of the temporal information encoded in the known fossil record of a given taxon. Here, we review the fossil record of freshwater fish clades with a distribution encompassing disjunct landmasses in the southern hemisphere. Palaeontologically derived temporal and geographic data were used to infer the plausible biogeographic processes that shaped the distribution of these clades. For seven extant clades with a relatively well‐known fossil record, we used the stratigraphic distribution of their fossils to estimate confidence intervals on their times of origin. To do this, we employed a Bayesian framework that considers non‐uniform preservation potential of freshwater fish fossils through time, as well as uncertainty in the absolute age of fossil horizons. We provide the following estimates for the origin times of these clades: Lepidosireniformes [125–95 million years ago (Ma)]; total‐group Osteoglossomorpha (207–167 Ma); Characiformes (120–95 Ma; a younger estimate of 97–75 Ma when controversial Cenomanian fossils are excluded); Galaxiidae (235–21 Ma); Cyprinodontiformes (80–67 Ma); Channidae (79–43 Ma); Percichthyidae (127–69 Ma). These dates are mostly congruent with published molecular timetree estimates, despite the use of semi‐independent data. Our reassessment of the biogeographic history of southern hemisphere freshwater fishes shows that long‐distance dispersals and regional extinctions can confound and erode pre‐existing vicariance‐driven patterns. It is probable that disjunct distributions in many extant groups result from complex biogeographic processes that took place during the Late Cretaceous and Cenozoic. Although long‐distance dispersals likely shaped the distributions of several freshwater fish clades, their exact mechanisms and their impact on broader macroevolutionary and ecological dynamics are still unclear and require further investigation.     

Eye morphology and optics of the double-eyed mysid Euchaetomera typica

The structure and optics of the mesopelagic double-eyed mysid crustacean Euchaetomera typica Sars, 1884 are described for the first time. The lateral eye is a typical refracting superposition eye with a wide field of view (172°) and low resolution (interommatidial angle of 7.3°). The antero-dorsal part of the eye is elongated due to the extension of the clear zone. This dorsal eye has a restricted field of view (33°) but much higher resolution (1.5°). The dorsal eye also uses refracting superposition optics, although the optical array is unusual as many of the peripheral ommatidia lack crystalline cones. The centre of curvature of the cornea is in front of the flattened rhabdom layer whereas the axes of the crystalline cones are centred on a point about twice as deep as the rhabdom layer. This results in a well-focused eye, free of spherical aberration. There is a remarkable similarity in eye structure between this species and some mesopelagic double-eyed euphausiid crustaceans.     

Functional morphology of the shell in platycope ostracodes - a study of arrested evolution

Shell morphology in relation to soft parts is described in the modem species Cytherella abyssorum G. O. Sars, based on microtome sections, serial peels and thin sections. Functionally important features of the cytherellids include the extensive development of the intervalvar cuticle ('ligament') along a strongly curved Line, the consequently very narrow ventral slit between valves in opened carapaces, and a special mode of egg care which is associated with a distinctive (domatial) type of sexual shell dimorphism. Platycope ostracodes represent a pronouncedly conservative evolutionary lineage; their essential characters are fully developed already in the earliest known true platycopes from the Silurian Period. The cause of the slow evolutionary change is suggested to have been the virtual impossibility to change their specific morphological organisation to fit some other mode of life or to diversify widely within the given morphological framework. The same obviously applies to the lingulaccan brachiopods and probably also other bradytelic groups.     

Phylogeny of Holothuroidea (Echinodermata) inferred from morphology

Holothuroids, or sea cucumbers, are an abundant and diverse group of echinoderms with over 1400 species occurring from the intertidal to the deepest oceanic trenches. In this study, we report the first phylogeny of this class, based on a cladistic analysis of 47 morphological characters. We introduce several previously unconsidered synapomorphic characters, examine the relationships between representatives from all extant families and assess the assumptions of monophyly for each order and subclass. Maximum-parsimony analyses using three rooting methods recovered well-supported and identical topologies when two small and apparently derived families, Eupyrgidae and Ge-phyrothuriidae, were removed. The results suggest that the higher-level arrangement of Holothuroidea warrants a considerable revision. Apodida was sister to the other holothuroids. The monophyly of Dendrochirotida was not supported and the group may be paraphyletic. A randomization test using Wills' gap excess ratio found significant congruence between the phylogeny and the stratigraphic record of fossil members, suggesting that the fossil record of holothuroids is not as incomplete as is often stated. The fossil-calibrated tree indicated that several groups of holothuroids survived the end-Permian mass extinction and that the clade composed of Dendrochirotida, Dactylochirotida, Aspidochirotida and Molpadiida rapidly radiated during the Triassic.     

Functional morphology of the hallucal metatarsal with implications for inferring grasping ability in extinct primates

Primate evolutionary morphologists have argued that selection for life in a fine branch niche resulted in grasping specializations that are reflected in the hallucal metatarsal (Mt1) morphology of extant “prosimians”, while a transition to use of relatively larger, horizontal substrates explains the apparent loss of such characters in anthropoids. Accordingly, these morphological characters—Mt1 torsion, peroneal process length and thickness, and physiological abduction angle—have been used to reconstruct grasping ability and locomotor mode in the earliest fossil primates. Although these characters are prominently featured in debates on the origin and subsequent radiation of Primates, questions remain about their functional significance. This study examines the relationship between these morphological characters of the Mt1 and a novel metric of pedal grasping ability for a large number of extant taxa in a phylogenetic framework. Results indicate greater Mt1 torsion in taxa that engage in hallucal grasping and in those that utilize relatively small substrates more frequently. This study provides evidence that Carpolestes simpsoni has a torsion value more similar to grasping primates than to any scandentian. The results also show that taxa that habitually grasp vertical substrates are distinguished from other taxa in having relatively longer peroneal processes. Furthermore, a longer peroneal process is also correlated with calcaneal elongation, a metric previously found to reflect leaping proclivity. A more refined understanding of the functional associations between Mt1 morphology and behavior in extant primates enhances the potential for using these morphological characters to comprehend primate (locomotor) evolution. Am J Phys Anthropol 156:327–348, 2015. © 2014 Wiley Periodicals, Inc.     

柚木野螟成虫复眼外部形态和超微结构观察

【目的】柚木野螟Eutectona machaeralis主要取食危害珍贵树种柚木。本研究旨在观察研究柚木野螟成虫复眼的形态、组织结构和超微结构,分析其复眼结构特征,为更好了解该物种复杂的视觉行为与感光、趋光机制的关系奠定基础。【方法】运用光学显微镜以及扫描和透射电子显微镜技术观察了柚木野螟成虫复眼的形态、组织结构和超微结构。【结果】柚木野螟成虫复眼着生于头部触角基部,呈椭球形,属对称性复眼。雌、雄成虫复眼分别有2 300~2 755和1 950~2 316个小眼。小眼呈正六边形,表面密被角膜乳突,间隙偶有感觉毛。每个小眼由1个角膜、4个晶锥细胞、1对初级色素细胞,6个次级色素细胞、不同水平面分布的12个视网膜细胞和基膜等组成。沿小眼纵轴11个视网膜细胞的向心侧细胞膜特化成细丝状微绒毛,形成放射状排列的视小杆,组合呈融合型视杆;第12个视网膜细胞位于小眼基部。基膜上方,视网膜细胞和次级色素细胞末端膨大,以轴突形式穿过基底膜。【结论】柚木野螟复眼为典型的重叠像眼,雌、雄成虫小眼排列方式及内部结构无明显差异,但雌、雄虫小眼数量和大小具有明显的性二型现象。     

星天牛成虫复眼外部形态和内部超微结构

星天牛Anoplophora chinensis能够取食上百种植物,以幼虫蛀干危害为主。本研究使用扫描电镜、透射电子显微镜和光学显微镜研究了星天牛成虫复眼外部形态和内部超微结构。结果表明星天牛复眼着生于触角基部,为不规则的肾形,表面光滑,由1 211~1 270个小眼组成,大部分小眼呈六边形,少数位于复眼边缘的小眼为不规则的五边形,小眼间角为6.90~9.56°。每个小眼由角膜、晶锥、视网膜细胞和基膜组成。角膜厚度为84.03±3.82 μm,晶锥被初级色素细胞包围,色素颗粒直径为0.41~0.97 μm。每个小眼包括8个视网膜细胞,其中6个周缘细胞（R1~R6）包围2个中央细胞（R7~R8）,视网膜细胞的感杆小体在向心侧形成半融合的感杆束,次级色素细胞色素颗粒将相邻小眼的视网膜细胞隔离,色素颗粒直径为0.41~1.06 μm。星天牛成虫复眼为并列像型,复眼分辨率较低,但视觉角度广,能够感受强度较低的光照。     

Carapace formation of the podocopid ostracode Semicytherura species (Crustacea: Ostracoda)

Details of ostracode carapace structures were examined by SEM and TEM. The podocopine ostracode Semicytherura kazahana has major ridges on the carapace surface and develops its prismatic layer inside the adult carapace. Electron microscopy at the final molt reveals that the major ridges arise from the highly dense formation of pits within the underlying swollen epidermis, and that disappearance of the epidermis in the presumptive area of the prismatic layer occurs after the calcification of the outer lamella cuticle, and just before synthesis of the membranous layer. These facts suggest that the formation of the carapace in Semicytherura takes place via a more complex process than that of the other podocopid ostracodes.