Clustered trilobite assemblages in the Middle Devonian Hamilton Group

Clusters of well-preserved trilobites occur throughout lower and middle Paleozoic strata. This phenomenon, however, remains poorly understood. Several thin, regionally persistent beds in the Middle Devonian (Givetian) Hamilton Group of New York State display taphonomic and sedimentary features which indicate rapid burial by storm-generated clouds of fine-grained sediment. Furthermore, components in these units display little or no post-mortem disturbance and, therefore, reflect in faunal associations. These beds contain two types of clustered assemblages of the trilobites Phacops (Green), Greenops boothi (Green) and Dechenella rowi (Green). Body clusters comprise dense assemblages of three or more complete trilobite corpses. Moult clusters , in contrast, are composed of three more moult ensembles; i.e., articulated thoracopygidia in close proximity to corresponding cephala. Clusters are species-segregated and contain only a small portion of the total size range exhibited by trilobite species. Moreover, body clusters and moult clusters are morphometrically undifferentiated indicating that these two cluster modes represent related phenomena. Analogy with modern marine arthropods suggests that trilobites assembled into monospecific, age-segregated clusters and moulted prior to en masse copulation.     

Global Invasions of Marine and Estuarine Habitats by Non-Indigenous Species: Mechanisms, Extent, and Consequences

Non-indigenous species (NIS) are increasingly conspicuous inmarine and estuarine habitats throughout the world, as the number,variety, and effects of these species continue to accrue. Mostof these NIS invasions result from anthropogenic dispersal.Although the relative importance of different dispersal mechanismsvaries both spatially and temporally, the global movement ofballast water by ships appears to be the largest single vectorfor NIS transfer today, andmany recent invasions have resultedfrom this transfer. The rate of new invasions may have increasedin recent decades, perhaps due to changes in ballast water transport.Estuaries have been especially common sites of invasions, accumulatingfrom tens to hundreds of NIS per estuary that include most majortaxonomic and trophic groups. We now know of approximately 400NIS along the Pacific, Atlantic and Gulf coasts of the U.S.,and hundreds of marine and estuarine NIS are reported from otherregions of the world. Although available information about invasionsis limited to a few regions and underestimates the actual numberof NIS invasions, there are apparent differences in the frequencyof NIS among sites. Mechanisms responsible for observed patternsamong sites likely include variation in supply of NIS, and perhapsvariation in properties of recipient or donor communities,butthe role of these mechanisms has not been tested. Although ourpresent knowledge about the extent, patterns and mechanismsof marine invasions is still in its infancy, it is clear thatNIS are a significant force of change in marine and especiallyestuarine communities globally. Taxonomically diverse NIS arehaving significant effects on many, if not most, estuaries thatfundamentally alter population, community, and ecosystems processes.The impacts of most NIS remain unknown, and the predictabilityof their direct and indirect effects remains uncertain. Nonetheless,based upon the documented extent of NIS invasions and scopeof then effects, studies of marine communities that do not includeNIS are increasingly incomplete     

Debris cloaking in Endomychidae: a new species from Peru (Goleoptera)

Adults and immature stages of the mychothenine endomychid Bystus decorator sp. nov. from Peru are described. All life stages occur together on rotting logs and feed on fungal spores. Larval debris cloaking and morphological adaptations associated with it are discussed in detail. Some larval setae are apically clubbed and barbed along the shafts to facilitate particle adhesion. Pronation of the thoracic lateral lobes bring the setae into contact with the substrate to gather particles of debris. The anatomy and functional morphology of the thoracic musculature is considered in the context of cloaking behaviour. Variations in debris cloaking behaviours among mychothenine endomychids are discussed and compared to other debris-cloaking insects.     

Epi- and endobiontic organisms on Late Jurassic crinoid columns from the Negev Desert, Israel: Implications for co-evolution

Columns of the articulate crinoids Millericrinus and Apiocrinites from the Upper Jurassic (Upper Callovian) Zohar and Matmor formations of the Negev Desert of Israel display abundant encrusting organisms of about ten species, as well as diverse trace fossils produced by endobionts. Pluricolumnals were colonized by epi- and endobiontic organisms both during life and post-mortem. Skeletonized encrusting organisms include abundant ostreid bivalves (which evidently colonized both live and dead crinoid columnals), two types of serpulid worms, encrusting foraminifera, three species of bryozoans, and small encrusting sclerosponges. Several types of borings are present: Trypanites (possibly produced by sipunculids), Gastrochaenolites (crypts of boring lithophagid bivalves), elliptical barnacle? borings, and channel-like annelid? borings. In addition, approximately 16% of the pluricolumnals display circular parabolic embedment pits assignable to the ichnogenus Tremichnus. They are associated with substantial deformation of the containing columnals and were probably the work of host-specific ectoparasitic organisms. Discovery of Tremichnus on Jurassic crinoids extends the range of this trace by almost 100 million years, providing evidence for one of the longest-ranging host-parasite interactions documented thus far (over 200 million years). The relationship of epibionts to the Jurassic crinoids thus ranged from simple utilization of dead hard substrate to probable opportunistic commensalism in forms that colonized the live upright stems, as in some oysters, through host-specific parasitism in the case of Tremichnus.     

Host-specific pit-forming epizoans on Silurian crinoids

Brett, Carlton E. 197807 15: Host-specific pit-forming epizoans on Silurian crinoids. Lethaia , Vol. 11. pp. 217–232. Oslo. ISSN 0024–1164.
Circular-parabolic pits occur commonly on the endoskeletal remains of certain Paleozoic crinoids. Detailed study of several hundred specimens, representing about 30 pelmatozoan species from the Upper Silurian Rochester Shale of New York and Ontario, reveals that such pits occur exclusively in seven species of crinoids. Furthermore, there are consistent differences in the morphology and orientation of holes occurring on the different crinoid species. This suggests that distinct epizoan species settled selectively on given hosts. The relationship between the hole-producing epizoans and crinoid hosts is inferred to have been a form of dependent commensalism. Preliminary surveys of other Paleozoic crinoid assemblages reveal similar host-selectivity by pit-producing epizoans. Crinoidepizoan pairs apparently co-evolved through considerable spans of geologic time as related genera and species of different ages, from Silurian to Pennsylvanian, exhibit similar pits.