浮游被囊动物的分类及其生态学研究进展

被囊动物(Tunicata)是一类低等脊索动物,包括3个纲:有尾纲、海樽纲和海鞘纲;全部生活在海洋里,其中有尾纲和海樽纲营浮游生活。综述了国内外浮游被囊动物分类和生态研究的现状和进展,综述介绍了有尾纲和海樽纲的分类依据、研究现状、趋势和在海洋生态系统中的作用。浮游被囊动物是热带和亚热带海域重要的浮游动物类群,种类和数量的分布变化受物理和生物环境因素的影响;它一方面大量摄食浮游细菌和微小浮游植物,另一方面被一些经济动物摄食,因此在海洋食物链的传递和生态系统的物质循环中占有重要位置。     

Phylogenetic analysis of phenotypic characters of Tunicata supports basal Appendicularia and monophyletic Ascidiacea

With approximately 3000 marine species, Tunicata represents the most disparate subtaxon of Chordata. Molecular phylogenetic studies support Tunicata as sister taxon to Craniota, rendering it pivotal to understanding craniate evolution. Although successively more molecular data have become available to resolve internal tunicate phylogenetic relationships, phenotypic data have not been utilized consistently. Herein these shortcomings are addressed by cladistically analyzing 117 phenotypic characters for 49 tunicate species comprising all higher tunicate taxa, and five craniate and cephalochordate outgroup species. In addition, a combined analysis of the phenotypic characters with 18S rDNA-sequence data is performed in 32 OTUs. The analysis of the combined data is congruent with published molecular analyses. Successively up-weighting phenotypic characters indicates that phenotypic data contribute disproportionally more to the resulting phylogenetic hypothesis. The strict consensus tree from the analysis of the phenotypic characters as well as the single most parsimonious tree found in the analysis of the combined dataset recover monophyletic Appendicularia as sister taxon to the remaining tunicate taxa. Thus, both datasets support the hypothesis that the last common ancestor of Tunicata was free-living and that ascidian sessility is a derived trait within Tunicata. “Thaliacea” is found to be paraphyletic with Pyrosomatida as sister taxon to monophyletic Ascidiacea and the relationship between Doliolida and Salpida is unresolved in the analysis of morphological characters; however, the analysis of the combined data reconstructs Thaliacea as monophyletic nested within paraphyletic “Ascidiacea”. Therefore, both datasets differ in the interpretation of the evolution of the complex holoplanktonic life history of thaliacean taxa. According to the phenotypic data, this evolution occurred in the plankton, whereas from the combined dataset a secondary transition into the plankton from a sessile ascidian is inferred. Besides these major differences, both analyses are in accord on many phylogenetic groupings, although both phylogenetic reconstructions invoke a high degree of homoplasy. In conclusion, this study represents the first serious attempt to utilize the potential phylogenetic information present in phenotypic characters to elucidate the inter-relationships of this diverse marine taxon in a consistent cladistic framework.     

The impact of mitochondrial genome analyses on the understanding of deuterostome phylogeny

Deuterostomia, one of the three major lineages of Bilateria, comprises many well-known animals such as vertebrates, sea squirts, sea stars and sea urchins. Whereas monophyly of Deuterostomia and several subtaxa is well supported, the relationships of these to each other and, hence, deuterostome relationships are still uncertain. To address these issues in deuterostome phylogeny we analyzed datasets comprising more than 300 complete deuterostome mitochondrial genomes. Based on sequence information, the results revealed support for several relationships such as a basal position of Xenoturbella within Deuterostomia or for taxa like Craniota or Ambulacraria, but yielded also problems in some taxa, e.g. Tunicata, Pterobranchia and Ophiuroidea, due to long-branch artifacts. However, within tunicates the relationships are well supported. Variation in the genetic code was also informative and, e.g., supported the taxon Ambulacraria including Pterobranchia.     

Per arborem ad astra: morphological adaptations to exploiting the woody habitat in the early evolution of Hymenoptera

We survey morphological features of larval and adult wasps that undergo their entire larval development inside wood and interpret them in view of the lifestyle. The evolution of some of the characters is explored by mapping them on a recently published phylogeny of Hymenoptera. Based on this phylogeny, it is reasonable to assume that wood-living wasps evolved from a xylophagous/mycetophagous stage as displayed by woodwasps to a carnivorous/parasitoid lifestyle, preying on woodboring insect larvae. The latter mode of life is probably ancestral to the Apocrita which comprise the majority of the order; they share this lifestyle with their sister group, the Orussidae. However, most apocritan wasps have radiated into other habitats, the Orussidae and Stephanidae apparently being the only taxa that have retained the ancestral lifestyle of carnivorous wasps. Other apocritan lineages associated with wood (e.g., Aulacidae, Megalyridae, basal Cynipoidea and some Ichneumonoidea and Chalcidoidea) possibly entered this habitat secondarily and independently acquired morphological traits associated with it. The woody habitat was occupied by Hymenoptera during a crucial stage in their evolution where the transition from the phytophagous to carnivorous lifestyle took place. The anatomy of both larva and adults was extensively transformed in the process.     

Coloniality has evolved once in Stolidobranch Ascidians

Ascidians exhibit a rich array of body plans and life history strategies. Colonial species typically consist of zooids embedded in a common test and brood large, fully developed larvae, while solitary species live singly and usually free-spawn eggs that develop into small, undifferentiated larvae. Ascidians in the order Stolidobranchia include both colonial and solitary species, as well as several species with intermediate morphologies. These include social species, which are colonial but do not live completely embedded in a common test, and a few solitary species that brood embryos and larvae until they are competent to metamorphose. We examined how many times coloniality has evolved within the Stolidobranchia, with phylogenetic analyses using full-length 18S rDNA and partial cytochrome oxidase B sequences for taxa in the families Molgulidae, Styelidae, and Pyuridae. Tunicata orders Phlebobranchia and Stolidobranchia are sister groups, and the family Molgulidae is a monophyletic group and should be raised to the subordinal level, as shown previously by analyses from this lab with partial 18S sequences. In contrast to previous studies, styelids and pyurids are separated into monophyletic groups by ML and Bayesian analyses. We show a single clade within the family Styelidae that contains two colonial (compound) botryllid species, a Symplegma (colonial compound), a colonial (social) species Metandrocarpa taylori, as well as four solitary species, thus confirming that the botryllids are a subfamily of the Styelidae. These results suggest that the ancestor of the Stolidobranchia was solitary and that coloniality has evolved only once within this clade of ascidians. Further phylogenetic analyses of aplousobranch and phlebobranch ascidians will be necessary to understand the number of times that coloniality has evolved within the class Ascidiacea.     

How our view of animal phylogeny was reshaped by molecular approaches: lessons learned

In the late 1980s, researchers began applying molecular sequencing tools to questions of deep animal phylogeny. These advances in sequencing were accompanied with improvements in computation and phylogenetic methods, and served to significantly reshape our understanding of metazoan evolution. Prior to this time, researchers asserted phylogenetic hypotheses based on their experience with taxa and to some degree, their authority. Molecular phylogenetic tools provided discrete methods and objective characters for reconstructing phylogeny. Nonetheless, major changes to widely accepted views, such as animal phylogeny, take time to be accepted. Development and acceptance of our current understanding of animal evolution occurred in three main phases: initial hypotheses based on 18S data, confirmation with additional molecular markers, and continued refinement with phylogenomics. With the advent of ideas such as Lophotrochozoa and Ecdysozoa, flaws in the traditional view became apparent. We now understand that complex morphological and embryological features (e.g., segmentation, coelom formation, development of body cavities) are much more evolutionarily plastic than previously recognized. Here, I explore how the transition from the traditional to the modern phylogenetic understanding of animal phylogeny occurred and examine some implications of this change in understanding. As the field moves forward, the utility of morphological and embryological characters for reconstruction of deep animal phylogeny should be discouraged. Instead, these characters should be interpreted in the light of independent phylogeny.     

The evolution of anural larvae in molgulid ascidians

Ascidians are urochordates, marine invertebrates with non-feeding motile chordate tadpole larvae, except in the family Molgulidae. Urodele, or tailed, Molgulids have typical ascidian chordate tadpole larvae possessing tails with muscle cells, a notochord, and a dorsal hollow nerve cord. In contrast, anural (or tail-less) Molgulids lack a tail and defining chordate features. Molecular phylogenies generated with 18S and 28S ribosomal sequences indicate that Molgulid species fall into at least four distinct clades, three of which have multiple anural members. This refined and expanded phylogeny allows careful examination of the factors that may have influenced the evolution of tail-less ascidians.     

Three‐dimensional reconstruction of the odontophoral cartilages of Caenogastropoda (Mollusca: Gastropoda) using micro‐CT: Morphology and phylogenetic significance

Odontophoral cartilages are located in the molluscan buccal mass and support the movement of the radula during feeding. The structural diversity of odontophoral cartilages is currently known only from limited taxa, but this information is important for interpreting phylogeny and for understanding the biomechanical operation of the buccal mass. Caenogastropods exhibit a wide variety of feeding strategies, but there is little comparative information on cartilage morphology within this group. The morphology of caenogastropod odontophoral cartilages is currently known only from dissection and histology, although preliminary results suggest that they may be structurally diverse. A comparative morphological survey of 18 caenogastropods and three noncaenogastropods has been conducted, sampling most major caenogastropod superfamilies. Three‐dimensional models of the odontophoral cartilages were generated using X‐ray microscopy (micro‐CT) and reconstruction by image segmentation. Considerable morphological diversity of the odontophoral cartilages was found within Caenogastropoda, including the presence of thin cartilaginous appendages, asymmetrically overlapping cartilages, and reflexed cartilage margins. Many basal caenogastropod taxa possess previously unidentified cartilaginous support structures below the radula (subradular cartilages), which may be homologous to the dorsal cartilages of other gastropods. As subradular cartilages were absent in carnivorous caenogastropods, adaptation to trophic specialization is likely. However, incongruence with specific feeding strategies or body size suggests that the morphology of odontophoral cartilages is constrained by phylogeny, representing a new source of morphological characters to improve the phylogenetic resolution of this group. J. Morphol. 2009. © 2008 Wiley‐Liss, Inc.     

Feeding habits may explain the morphological uniqueness of brown bears on Etorofu Island,Southern Kuril Islands in East Asia

The brown bear (Ursus arctos) population on Etorofu Island, Southern Kuril Islands, has several unique morphological features: (1) the presence of white‐pelage bears within the population and (2) a larger body size than bears on a larger neighbour island, Hokkaido Island. Nevertheless, little ecological information is available about Etorofu brown bears. In the present study, we reveal the unique feeding habits of Etorofu brown bears and suggest that their unique morphological features and diet are related. The feeding habits of brown bears on Etorofu Island were assessed using carbon, nitrogen, and sulfur stable isotope analysis, and their feeding habits were compared with those of bears on the eastern side of Hokkaido Island. According to the stable isotope analysis, the dependence on salmon is great for bears on Etorofu but only slight for bears on Hokkaido. Our results suggest that the feeding habits of Etorofu brown bears may explain their unique morphological features because a white pelage colour confers an advantage when catching salmon, and a carnivorous diet can make their body size larger. The variation in feeding habits can be an important driver of the speciation and evolution of animals.     

New developments in vertebrate cytotaxonomy VI. Cytotaxonomy and evolution of lower chordates

A correlation between evolutionary trends and karyotype has been recognized in tunicates. In the ambit of lower chordates and related species, Hemichordata, Cephalochordata and, in the Tunicata, some ascidians seem to maintain a primitive organization of chromosomes: haploid numbers around 20, absence of sex chromosomes, and rod-shaped bivalents. Within the class Ascidiacea, at the karyological level Clavelina depadiformis seems to be very specialized and the family Perophoridae (suborder Phlebobranchiata) very primitive. Thaliacea and Larvacea appear specialized in comparison with the primitive ascidians.This is the sixth in a series of articles, by different authors, to appear in this journal under the editorship of Professor Chiarelli, supplementing the data published in Cytotaxonomy and Vertebrate Evolution (A. B. Chiarelli & E. Capanna, eds, Academic Press, London & New York)-Eds.     

Investment in visual system predicted by floral associations in sap beetles (Coleoptera: Nitidulidae)

Patterns in morphological variation are a central theme of evolution. Uncovering links between morphological character evolution and natural history, specifically feeding behaviour, is important to understanding biological diversity. Species within the sap beetles (Nitidulidae) exhibit a tremendous diversity of feeding behaviours. This immense diversity of feeding can be seen both between major lineages and very closely related taxa. Feeding behaviour diversity may drive morphological variation in several character systems (e.g., eyes). For example, in a shift from feeding on rotting fruit to flower-visiting (anthophily), selective pressures on the visual system may vary and ultimately lead to differences in eye morphology. We tested for potential morphological shifts in relative eye size among adult beetles. We specifically tested for significant relationships between relative eye size and the following factors flower-visiting and sex. We also tested for the influence of phylogeny on the evolution of relative eye size, implementing tests of trait correlation across a topology. We found greater relative eye size in taxa exhibiting anthophilous behaviour, regardless of phylogenetic relatedness or feeding behaviour of sister taxa. We were unable to recover a relationship between relative eye size and sex. Thus, feeding behaviour is currently the strongest predictor of eye size in sap beetles.     

Morphological divergence between three Arctic charr morphs – the significance of the deep‐water environment

Morphological divergence was evident among three sympatric morphs of Arctic charr (Salvelinus alpinus (L.)) that are ecologically diverged along the shallow‐, deep‐water resource axis in a subarctic postglacial lake (Norway). The two deep‐water (profundal) spawning morphs, a benthivore (PB‐morph) and a piscivore (PP‐morph), have evolved under identical abiotic conditions with constant low light and temperature levels in their deep‐water habitat, and were morphologically most similar. However, they differed in important head traits (e.g., eye and mouth size) related to their different diet specializations. The small‐sized PB‐morph had a paedomorphic appearance with a blunt head shape, large eyes, and a deep body shape adapted to their profundal lifestyle feeding on submerged benthos from soft, deep‐water sediments. The PP‐morph had a robust head, large mouth with numerous teeth, and an elongated body shape strongly related to their piscivorous behavior. The littoral spawning omnivore morph (LO‐morph) predominantly utilizes the shallow benthic–pelagic habitat and food resources. Compared to the deep‐water morphs, the LO‐morph had smaller head relative to body size. The LO‐morph exhibited traits typical for both shallow‐water benthic feeding (e.g., large body depths and small eyes) and planktivorous feeding in the pelagic habitat (e.g., streamlined body shape and small mouth). The development of morphological differences within the same deep‐water habitat for the PB‐ and PP‐morphs highlights the potential of biotic factors and ecological interactions to promote further divergence in the evolution of polymorphism in a tentative incipient speciation process. The diversity of deep‐water charr in this study represents a novelty in the Arctic charr polymorphism as a truly deep‐water piscivore morph has to our knowledge not been described elsewhere.     

Molecular and morphological phylogeny of Diplazontinae (Hymenoptera,Ichneumonidae)

Klopfstein, S., Quicke, D. L. J., Kropf, C. & Frick, H. (2011) Molecular and morphological phylogeny of Diplazontinae (Hymenoptera, Ichneumonidae). —Zoologica Scripta, 40, 379–402. Parasitoid wasps are among the most species rich and at the same time most understudied of all metazoan taxa. To understand their diversification and test hypotheses about their evolution, we need robust phylogenetic hypotheses. Here, we reconstruct the phylogeny of the subfamily Diplazontinae using four genes and 66 morphological characters both in separate analyses and in a total evidence approach. The resulting phylogeny is highly resolved, with most clades supported by multiple independent data partitions. It contains three highly supported genus groups, for which we suggest morphological and behavioural synapomorphies. The placement of some of the genera, especially Xestopelta Dasch, is unexpected, but also supported by morphology. Most of the genera are retrieved as monophyletic, with the exception of the morphologically diverse genus Syrphoctonus Förster. We split this genus into three genera, including Fossatyloides gen. n., to restore the phylogeny–classification link. Conflict between the morphological and the molecular topology was mostly resolved in favour of the molecular partition in the total evidence approach. We discuss reasons for this finding, and suggest strategies for future taxon and character sampling in Diplazontinae.     

ELEVATED RATES OF MORPHOLOGICAL AND FUNCTIONAL DIVERSIFICATION IN REEF‐DWELLING HAEMULID FISHES

The relationship between habitat complexity and species richness is well established but comparatively little is known about the evolution of morphological diversity in complex habitats. Reefs are structurally complex, highly productive shallow‐water marine ecosystems found in tropical (coral reefs) and temperate zones (rocky reefs) that harbor exceptional levels of biodiversity. We investigated whether reef habitats promote the evolution of morphological diversity in the feeding and locomotion systems of grunts (Haemulidae), a group of predominantly nocturnal fishes that live on both temperate and tropical reefs. Using phylogenetic comparative methods and statistical analyses that take into account uncertainty in phylogeny and the evolutionary history of reef living, we demonstrate that rates of morphological evolution are faster in reef‐dwelling haemulids. The magnitude of this effect depends on the type of trait; on average, traits involved in the functional systems for prey capture and processing evolve twice as fast on reefs as locomotor traits. This result, along with the observation that haemulids do not exploit unique feeding niches on reefs, suggests that fine‐scale trophic niche partitioning and character displacement may be driving higher rates of morphological evolution. Whatever the cause, there is growing evidence that reef habitats stimulate morphological and functional diversification in teleost fishes.     

Studies on the renal sac of the ascidian Molgula manhattensis. I. Development of the renal sac

The renal sac of the ascidian family Molgulidae (Tunicata, phylum Chordata) has been thought to function as a kidney, yet its structure, contents and activities seem incompatible with current generalizations regarding excretory processes in marine animals. The development of the renal sac is described here as part of a general effort to reexamine the organ's role in Molgula manhattensis. Light microscopy of living animals and fixed material has shown the following: (1) The renal sac begins to sequester concretions before the heart starts beating and before feeding begins. Therefore, blood circulation by heartbeat is not necessary for production or transport of the initial concretions, whatever its effects may be on the renal sac in older individuals. Ingested food cannot provide the initial concretion material. (2) In laboratory-raised animals, concretions appear in the renal sac before “renal sac organisms” (fungus-like organisms seen in the renal sac of all field-collected adults) can be detected. Thus, at least some portion of the concretions can be produced by Molgula in the absence of renal sac organisms. (3) No openings have been detected in the renal sac at any stage of its development, nor is there any evidence that concretions are dissolved or transported out of the renal sac. (4) The development and morphology of the renal sac are consistent with the hypothesis that the organ is an epicardial derivative, except that the renal sac arises from post-pharyngeal (presumptive gut) endoderm, rather than pharyngeal endoderm.     

Energetics and the evolution of carnivorous plants--Darwin's 'most wonderful plants in the world'

Carnivory has evolved independently at least six times in fiveangiosperm orders. In spite of these independent origins, thereis a remarkable morphological convergence of carnivorous planttraps and physiological convergence of mechanisms for digestingand assimilating prey. These convergent traits have made carnivorousplants model systems for addressing questions in plant moleculargenetics, physiology, and evolutionary ecology. New data showthat carnivorous plant genera with morphologically complex trapshave higher relative rates of gene substitutions than do thosewith simple sticky traps. This observation suggests two alternativemechanisms for the evolution and diversification of carnivorousplant lineages. The ‘energetics hypothesis’ positsrapid morphological evolution resulting from a few changes inregulatory genes responsible for meeting the high energeticdemands of active traps. The ‘predictable prey capturehypothesis’ further posits that complex traps yield morepredictable and frequent prey captures. To evaluate these hypotheses,available data on the tempo and mode of carnivorous plant evolutionwere reviewed; patterns of prey capture by carnivorous plantswere analysed; and the energetic costs and benefits of botanicalcarnivory were re-evaluated. Collectively, the data are moresupportive of the energetics hypothesis than the predictableprey capture hypothesis. The energetics hypothesis is consistentwith a phenomenological cost–benefit model for the evolutionof botanical carnivory, and also accounts for data suggestingthat carnivorous plants have leaf construction costs and scalingrelationships among leaf traits that are substantially differentfrom those of non-carnivorous plants. Key words: Carnivorous plants, competition, construction costs, cost–benefit model, Darwin, energetics, niche overlap, phylogeny, prey capture, universal spectrum of leaf traits Received 6 May 2008; Revised 5 June 2008 Accepted 16 June 2008     

Molecular phylogeny of Abyssocladia (Cladorhizidae: Poecilosclerida) and Phelloderma (Phellodermidae: Poecilosclerida) suggests a diversification of chelae microscleres in cladorhizid sponges

Vargas, S., Erpenbeck, D., Göcke, C., Hall, K. A., Hooper, J. N. A., Janussen, D. & Wörheide, G. (2012) Molecular phylogeny of Abyssocladia (Cladorhizidae: Poecilosclerida) and Phelloderma (Phellodermidae: Poecilosclerida) suggests a diversification of chelae microscleres in cladorhizid sponges. —Zoologica Scripta, 42, 106–116. The taxonomic placement of Abyssocladia Lévi, 1964 (Poecilosclerida) is controversial, having been assigned at various times to three different families (Mycalidae, Cladorhizidae and Phellodermidae) in two different suborders (Mycalina and Myxillina, respectively), since its inception in 1964. It shares the general body plan with the carnivorous sponge family Cladorhizidae (Mycalina), including the lack of an aquiferous system. Nevertheless, it also has chela spicules apparently identical to those in Phelloderma Ridley & Dendy 1886 (Phellodermidae, Myxillina). The ongoing debate on the position of Abyssocladia ultimately reduces to a discussion on the use of chelae morphology to infer phylogenetic relationships within Poecilosclerida. Here, we infer the phylogenetic relationships of the genera Phelloderma and Abyssocladia using two independent molecular markers (28S rDNA and COI), showing that Abyssocladia is not closely related to Phelloderma and belongs in Cladorhizidae. We suggest that despite their complexity, chelae morphology can evolve independently in different poecilosclerid lineages and as such might be potentially misleading as indicator of the phylogenetic history of the group. We also provide the first phylogenetic analysis of the carnivorous sponge family Cladorhizidae and give first insights into the evolution of this feeding mode in Poecilosclerida and, more generally, in Porifera.     

Key novelties in the evolution of the aquatic colonial phylum Bryozoa: evidence from soft body morphology

Molecular techniques are currently the leading tools for reconstructing phylogenetic relationships, but our understanding of ancestral, plesiomorphic and apomorphic characters requires the study of the morphology of extant forms for testing these phylogenies and for reconstructing character evolution. This review highlights the potential of soft body morphology for inferring the evolution and phylogeny of the lophotrochozoan phylum Bryozoa. This colonial taxon comprises aquatic coelomate filter‐feeders that dominate many benthic communities, both marine and freshwater. Despite having a similar bauplan, bryozoans are morphologically highly diverse and are represented by three major taxa: Phylactolaemata, Stenolaemata and Gymnolaemata. Recent molecular studies resulted in a comprehensive phylogenetic tree with the Phylactolaemata sister to the remaining two taxa, and Stenolaemata (Cyclostomata) sister to Gymnolaemata. We plotted data of soft tissue morphology onto this phylogeny in order to gain further insights into the origin of morphological novelties and character evolution in the phylum. All three larger clades have morphological apomorphies assignable to the latest molecular phylogeny. Stenolaemata (Cyclostomata) and Gymnolaemata were united as monophyletic Myolaemata because of the apomorphic myoepithelial and triradiate pharynx. One of the main evolutionary changes in bryozoans is a change from a body wall with two well‐developed muscular layers and numerous retractor muscles in Phylactolaemata to a body wall with few specialized muscles and few retractors in the remaining bryozoans. Such a shift probably pre‐dated a body wall calcification that evolved independently at least twice in Bryozoa and resulted in the evolution of various hydrostatic mechanisms for polypide protrusion. In Cyclostomata, body wall calcification was accompanied by a unique detachment of the peritoneum from the epidermis to form the hydrostatic membraneous sac. The digestive tract of the Myolaemata differs from the phylactolaemate condition by a distinct ciliated pylorus not present in phylactolaemates. All bryozoans have a mesodermal funiculus, which is duplicated in Gymnolaemata. A colonial system of integration (CSI) of additional, sometimes branching, funicular cords connecting neighbouring zooids via pores with pore‐cell complexes evolved at least twice in Gymnolaemata. The nervous system in all bryozoans is subepithelial and concentrated at the lophophoral base and the tentacles. Tentacular nerves emerge intertentacularly in Phylactolaemata whereas they partially emanate directly from the cerebral ganglion or the circum‐oral nerve ring in myolaemates. Overall, morphological evidence shows that ancestral forms were small, colonial coelomates with a muscular body wall and a U‐shaped gut with ciliary tentacle crown, and were capable of asexual budding. Coloniality resulted in many novelties including the origin of zooidal polymorphism, an apomorphic landmark trait of the Myolaemata.     

Palaeobotryllus from the Upper Cambrian of Nevada — a probable ascidian

Phosphatic microfossils etched from Upper Cambrian (Trempealeauan Stage) Limestones of the Whipple Cave Formation, Nevada, and other contemporaneous formations in western North America, are colonies, the individuals of which are arranged irregularly around one or more nuclei. No secondary growth has occurred. During their lifetime, however, the individuals partially filled their chambers with phosphatic matter. The highly differentiated morphology of the colonies is strikingly similar to the living ascidian tunicate Botryllus. Ecological conditions and size range of the fossils are likewise similar to those of the Ascidiacea. If recognized as an ascidian, Palaeobotryllus taylori n.g., n.sp. extends the known occurrence of Tunicata into the Upper Cambrian.