Behavioral stereotypy and some ecological consequences of entrance-shaft placement of the domichnium Sanctum laurentiensis in Ordovician trepostomate Bryozoa

Abstract

The ichnofossil Sanctum laurentiensis from the Late Ordovician (Cincinnatian) of Laurentia is a domichnium tunneled into live colonies of ramose and frondose trepostome Bryozoa. A preferred entrance location was chosen by the trace-making endoskeletozoan. The organism chose to tunnel in positions near growing tips of branches where one of two conditions prevailed. At stereotypical sites, here considered “determinate”, domicile entrances were made where a trepostome branch was in the growth process of bifurcation; sites considered “indeterminate” were chosen where one blade or branch was impinging on another, or on some other nearby substrate, thus interfering with normal colony growth in a random, or non-ontogenetic, manner. This stereotypy is a rare example of demonstrable entrance-siting behavior by an unknown invertebrate organism. A skeleto-structural condition was present at both determinate and indeterminate locations on ramose trepostome colonies. Stereotypical entrance-site choices included a location where bryozoan freewall membrane was compromised or thinned and exozone was incompletely developed. Sanctum producers preferred incomplete exozone in order to access the endozone for excavation to form a domichnium. Middle and Late Ordovician diversification of ramose bryozoan forms stimulated escalation of bioeroder and symbiont taxa in living zoaria thus encouraging further trepostome evolution.     

The inference of extrazooidal feeding currents in fossil bryozoan colonies

Taylor, Paul D. 1979 01 15: The inference of extrazooidal feeding currents in fossil bryozoan colonies. Lethaia , Vol. 12, pp. 47–56. Oslo. ISSN 0024–1164.
Previous studies on live bryozoan colonies have shown that the feeding autozooids in a colony may cooperate in differing ways to produce an extrazooidal watercurrent system organised on a colony-wide or subcolony-wide basis. The presence of an extrazooidal current system may be inferred in fossil stenolaemate bryozoans which exhibit either a differential spacing of open autozooecial apertures or a systematic variation across the marial surface in the orientation of automoecial distal portions. By inference, aggregations of autozooecial apertures represented loci of inhalant extrazooidal flow whereas zoarial protuberances (e.g. monticules) with outwardly leaning autozooecia acted as loci of exhalant extrazooidal flow. Bryozoans having automoecia opening obliquely into gaps or fenestrules in their zoaria probably drew a unidirectional extrazooidal current of water through the fenestrules. Extrazooidal water currents may function to accelerate colony clearance rate, decrease the chances of recycling filtered water, aid spermatoman and larval dispersal, and clear sediment from the colony surface.     

Zooidal anatomy in Ordovician and Carboniferous trepostome bryozoans

Fossil bryozoans sometimes contain fossilised brown bodies which remain after polypide degeneration. Position and shape of brown bodies as well as different skeletal diaphragms within living chambers allow outlining of autozooid anatomy in Palaeozoic trepostome bryozoans. In some trepostome bryozoans short autozooids were restricted by complete basal diaphragms to distal parts of autozooecia. In species with alternating hemiphragms, as in the specimen ofHemiphragma sp. described here, long autozooids occupied the entire autozooecial chambers. Their short polypides were positioned in distal parts of the autozooid. Both anatomic types correspond to the progressive polypide cycle afterBoardman. For species with ring septa, non-alternating hemiphragms (studied in an example ofNipponostenopora karatauensis) as well as without any diaphragms the stationary type of polypide cycle seems also to be possible. In that case, the polypides should be as long as the cystid.      

新疆西准噶尔晚泥盆世法门期的苔藓虫动物群及其形态特异性和古环境意义*

本文重新研究了产自新疆西准噶尔晚泥盆世法门期洪古勒楞组和铁列克提组的苔藓虫动物群, 重点关注其形态学特征和古生态学意义。该苔藓虫动物群由隐口目(Cryptostomata)、窗格苔藓虫目(Fenestrata), 变口目 (Trepostomata)和泡孔目(Cystoporata)组成。优势类群隐口目苔藓虫是具有中轴或中板的细枝状和双叶状群体。 它们的虫室具有加厚的外区体壁, 弯曲强烈的自虫室, 数量众多的大虫室(metazooecia)或隐蔽虫室(tectizooecia), 以及径向刺突和/或棘状刺突。多样化的异虫室、刺突、自虫室等结构, 以及不同生长环境中的不同生态组合是新疆西准噶尔法门期苔藓虫成功演化的基础。洪古勒楞组下段和铁列克提组下部的苔藓虫动物群可以划分为三类生态组合(即: No. 1, No. 2和No. 3), 代表前滨—近岸—远岸的沉积环境。其中, 近岸环境的枝状—双叶状—网状苔藓虫组合的属种丰度、分异度最高。     

新疆西准噶尔晚泥盆世法门期的苔藓虫动物群及其形态特异性和古环境意义*

本文重新研究了产自新疆西准噶尔晚泥盆世法门期洪古勒楞组和铁列克提组的苔藓虫动物群, 重点关注其形态学特征和古生态学意义。该苔藓虫动物群由隐口目(Cryptostomata)、窗格苔藓虫目(Fenestrata), 变口目 (Trepostomata)和泡孔目(Cystoporata)组成。优势类群隐口目苔藓虫是具有中轴或中板的细枝状和双叶状群体。 它们的虫室具有加厚的外区体壁, 弯曲强烈的自虫室, 数量众多的大虫室(metazooecia)或隐蔽虫室(tectizooecia), 以及径向刺突和/或棘状刺突。多样化的异虫室、刺突、自虫室等结构, 以及不同生长环境中的不同生态组合是新疆西准噶尔法门期苔藓虫成功演化的基础。洪古勒楞组下段和铁列克提组下部的苔藓虫动物群可以划分为三类生态组合(即: No. 1, No. 2和No. 3), 代表前滨—近岸—远岸的沉积环境。其中, 近岸环境的枝状—双叶状—网状苔藓虫组合的属种丰度、分异度最高。     

Unusual compound zooecia in the trepostome bryozoan Eostenopora from the Devonian of Guizhou,China

Enlarged, ‘compound zooecia’ are described for the first time in a trepostome bryozoan. Several of these zooecia are visible in tangential sections of Eostenopora guizhouensis (Hu) from the Devonian (Eifelian) Houershan Formation of Houershan, Dushan, southern Guizhou, China. They are broad and occupy the space of two or occasionally three or four normal autozooecia. Some have bridging walls extending partway across the enlarged zooecial chamber. Without serial sectioning, the origin of compound zooecia in E. guizhouensis is debatable. However, the existence of irregular gaps in some zooecial walls leads to the hypothesis that compound zooecia originated from the loss by resorption of the skeletal walls between two normal autozooecia. The bridging walls are interpreted as a response by the bryozoan to restore the integrity of the constituent zooecia. By analogy with the ‘Doppelgänger’ zooids of some modern cheilostome bryozoans, compound zooecia of E. guizhouensis may have housed the lophophores of more than one zooid.     

Symbiosis between gastropods and bryozoans in the late Ordovician of Cumbria, England

Five examples of symbiosis between gastropods and trepostome bryozoans are described from the Ashgill (late Ordovician) of Cumbria (England). The gastropods are invariably found associated with the bryozoans. whereas the bryozoans may be free-living. Encrustation is considered to have taken place, in most cases, on mature, living gastropod shells, resulting in the trepostome utilizing the shell as a surrogate basal disc. Three specimens show encrustation on an empty gastropod shell, causing the trepostome to develop a basal disc similar to non-encrusting forms. The bryozoan colony probably benefited from the symbiotic relationship by increased water flow over the colony, caused by gastropod locomotion, whereas the gastropod was afforded protection from predators. The new species Spiroecus nidhoeggi. Diplotrypa hvergelmi and Monotrypa fontinalis are described.     

Borings in trepostome bryozoans from the Ordovician of Estonia: two ichnogenera produced by a single maker, a case of host morphology control

The evolution of borings has shown that the morphology of borings is a function of both the borer and its substrate. This study investigated the effect of bryozoan internal skeletal morphology on the dimensions and distribution of borings. One hundred and forty-three trepostome colonies from the Middle and Upper Ordovician strata of northern Estonia were examined. Of these, 80% were matrix entombed, longitudinally sectioned ramose and hemispherical colonies, and 20% were matrix-free hemispherical colonies that allowed examination of the colony surfaces. Seventy-one percent of the ramose colonies were bored, whereas 88% of the hemispherical colonies were bored. On average, only 8% of colony surface areas were bored out. Borings were more randomly oriented in the hemispherical colonies. In contrast in the ramose colonies, the borings tended to more restricted to the thin-walled endozone and thus parallel to the branch axis. This is interpreted to be a function of the thick-walled exozones controlling to some extent where the borer could bore. Based on morphology, the borings in the hemispherical colonies are referred to Trypanites and those in the ramose colonies to Sanctum . Sanctum is revised to include two possible openings and to recognize that boring shapes were inherently constrained by the thick-walled exozones of the host bryozoan colonies. Both trace fossils were probably produced by a boring polychaete that used the tubes as domiciles.     

New observations on the skeletons of the earliest bryozoans from the Fenhsiang Formation (Tremadocian,Lower Ordovician), Yichang,China

The earliest unequivocal bryozoans occurred in the Fenhsiang Formation (upper Tremadocian, Lower Ordovician) of Yichang, South China, providing important clues about the early evolution of primitive bryozoans. In this study, SEM and EDAX were used to analyze the microstructure of the walls of two bryozoan genera, Nekhorosheviella and Orbiramus, from the Fenhsiang Formation. All walls of Nekhorosheviella and endozonal walls of Orbiramus show poor preservation in thin sections, with a granular appearance reflecting extensive neomorphism, whereas exozonal walls of Orbiramus are distinctly laminated. These preservational differences may reflect skeletal chemistry, particularly the magnesium content of the calcite. Phosphatic skeletal linings were found to be distributed unevenly in the autozooecia of Nekhorosheviella, but were absent in Orbiramus.     

Wachstums- und Knospungsstrategie vonGrammothoa filifera Voigt & Hillmer (Bryozoa,Cheilostomata, Ob. Kreide)

The genusGrammothoa, growing on the interior walls ofThalassinoides burrows in the Maastrichtian Chalk-tuff, has developed a special growth strategy for spatial competition with other encrusting species which has not been previously recorded in bryozoans. The zoarium consists of auto-zooecia, gynozooecia and chains of smaller zooeciules, the latter forming stolon-like outgrowths from the distal edge of the colony. New areas of substratum are explored and colonized by the growth of these zooeciules. At the branching points of the zooeciules, autozooecia and gynozooecia are budded and may coalesce to form the main part of the colony.     

Note on the Bryozoan Pustulopora pustulosa (Goldfuss)

Topotype material of Pustulopora pustulosa (Goldfuss), the type species of Pustulopora Blainville, is investigated and its structure described. It has a distinctive budding pattern in which autozooecia are formed from an axial bundle of zooecia. The gonozooecium is of ' Mecynoecia '- shape.     

Structure of Adnate Colony Portions in Crisiidae (Bryozoa Cyclostomata)

The “rhizoidsrdquo; surrounding the base of the erect “colony” emanating from the ancestrula in the Crisiidae, especially the simple species Crisidia cornuta (L.), are a regular adnate system of autozooids. Each autozooid is composed of a proximal adnate part and a distal peristome (in some species kenozooids are possibly intercalated). The autozooid peristomes support erect branches identical in budding and structure with the branch emanating from the erect peristome of the ancestrula. Thus, the complete crisiid colony consists of an adnate system of ancestrula and autozooids, which form erect branches from their peristomes. The adnate zooid system is comparable in autozooid morphology and budding pattern with simple uniserial stomatoporids. The tentative hypothesis is proposed that the crisiid group has developed from primitive stomatoporids; the adnate zooid system of the stomatoporids apparently evolved peristomial budding to produce the erect colony branches characteristic of crisiids.     

Colony Budding and its Effects on Food Allocation in the Highly Polygynous Ant, Monomorium pharaonis

To advance our understanding of the causes and the consequences of budding (colony multiplication by fragmentation of main nests), we investigated nest movement in the facultatively polydomous Pharaoh ant, Monomorium pharaonis. Demographic data revealed that Pharaoh ants are highly polygynous and have a relatively low worker to queen ratio of 12.86. Budding experiments demonstrated that the number of available bud nests has a significant effect on colony fragmentation and increasing the number of bud nests resulted in smaller colony fragments. The overall distribution among bud nests was uneven, even though there was no evidence that the different life stages and castes partitioned unevenly among the bud nests and the analysis of individual colonies revealed no evidence of an uneven split in any of the colonies. This demonstrates that Pharaoh ants have the ability to exert social control over colony size and caste proportions during budding, which may contribute to their success as an invasive ant. The intensity of nest disturbance had a significant effect on whether or not the ants migrated into bud nests. Major disturbance resulted in the ants abandoning the source nest and migrating to bud nests and minor disturbance did not stimulate the ants to abandon the source nest. The results of the successive budding experiment which allowed the ants the opportunity to bud into progressively smaller nest fragments demonstrate that Pharaoh ants maintain a preferred minimum group size of 469 ± 28 individuals. Food allocation experiments utilizing protein marking revealed that nest fragmentation in Pharaoh ants has no negative impact on intracolony food distribution. Overall, our results suggest that nest units in the Pharaoh ant behave like cooperative, rather than competitive, entities. Such cooperation is most likely facilitated by the fact that individuals in all bud nests are genetically related, remain in close proximity to each other, and may continue to exchange individuals after budding.     

Estimating Cetacean Carrying Capacity Based on Spacing Behaviour

Conservation of large ocean wildlife requires an understanding of how they use space. In Western Australia, the humpback whale (Megaptera novaeangliae) population is growing at a minimum rate of 10% per year. An important consideration for conservation based management in space-limited environments, such as coastal resting areas, is the potential expansion in area use by humpback whales if the carrying capacity of existing areas is exceeded. Here we determined the theoretical carrying capacity of a known humpback resting area based on the spacing behaviour of pods, where a resting area is defined as a sheltered embayment along the coast. Two separate approaches were taken to estimate this distance. The first used the median nearest neighbour distance between pods in relatively dense areas, giving a spacing distance of 2.16 km (±0.94). The second estimated the spacing distance as the radius at which 50% of the population included no other pods, and was calculated as 1.93 km (range: 1.62–2.50 km). Using these values, the maximum number of pods able to fit into the resting area was 698 and 872 pods, respectively. Given an average observed pod size of 1.7 whales, this equates to a carrying capacity estimate of between 1187 and 1482 whales at any given point in time. This study demonstrates that whale pods do maintain a distance from each other, which may determine the number of animals that can occupy aggregation areas where space is limited. This requirement for space has implications when considering boundaries for protected areas or competition for space with the fishing and resources sectors.     

Responses to damage in an arborescent bryozoan: Effects of injury location

A common consequence of the predation or physical disturbance of sessile modular animals is the removal of part of the colony. This damage is often sub-lethal, and leaves the remainder of the colony to repair and regenerate lost tissue. Damage may, however, have lasting effects on the life history characteristics of a colony. We examined the effects of damage on growth and reproduction in the arborescent bryozoan Bugula neritina (Linnaeus), with a particular focus on the effects of the location of that damage. We predicted that a damaged colony would initially allocate more energy to damage repair and subsequent growth, increasing in size to decrease the risk of mortality, at the expense of its short-term reproductive potential. A short-term experiment assessed the immediate regenerative capacities of colonies, while a longer-term experiment measured overall colony responses to damage at different colony locations. In this experiment, zooids were removed in three colony regions; all on one colony branch, spread evenly across all growing tips, and a third, intermediate pattern. A third experiment tested the effects of predator-induced damage versus damage alone, by measuring the recovery of colonies subjected to either a predation event by the nudibranch Polycera hedgpethi, or to an imitation predation event, where an equivalent section of the colony was removed manually. Regeneration was rapid, with budding resuming a few days after damage occurred. Removing around 20% of the colony did not consistently alter colony growth rates in any experiment, but the onset of reproduction was delayed by 7 to 20 days, and subsequent colony fecundity reduced by as much as 70% in one damage treatment. The removal of the same amount of tissue by nudibranch predators, or manually removed in a treatment that mimicked this predation, had no detrimental effect on the onset of reproduction or the eventual reproductive output. Nudibranchs removed tissue by consuming whole colony branches, and the experimental treatment that removed one branch also had the least effect of three damage treatments. These results suggest the severity of long-term effects depends on the location of the injury, and that B. neritina does not modify its growth or reproductive patterns to minimise these effects.     

Arrangement of pili in colonies of Neisseria gonorrhoeae.

The morphology and arrangement of pili in the P++ colony phenotype of Neisseria gonorrhoeae were examined by a variety of electron microscopic techniques. The apparent structure and organization of gonococcal pili varied depending upon the method of specimen preparation. Pili as thin, individual, unbranched structures were demonstrated by negative staining and in sections of epoxy-embedded specimens. Pili forming thick structures which branch, subdivide, and rejoin to form an irregular lattice were demonstrated in specimens processed by the critical-point drying method and by rapid freezing and low temperature sublimination. We propose that in gonococcal colonies of the P++ phenotype, pili exist as individual threadlike structures only on the bacterial surfaces; as the pili leave the bacterial surfaces, they form thick bundles which branch, subdivide, and rejoin to form a supporting framework interconnecting the colony members. This arrangement of pili is usually disrupted by the commonly used method of negative staining and cannot be clearly detected within epoxy-embedded specimens. These data are summarized in a model depicting the organization of pili in the P++ colony phenotype of N. gonorrhoeae.     

Schischcatella (Fenestrata,Bryozoa) from the Devonian of the Rhenish Massif,Germany

Abstract: The Devonian fenestrate bryozoan, Schischcatella Waschurova, 1964 , possessed colonies in the form of low, erect bifoliate fronds that grew from an encrusting sheet‐like base with autozooecia arranged in biserial, bifurcating rows. This growth habit is unique in fenestrates, which normally had unilaminate arborescent colonies. Originally, Schischcatella was described from the Lower Devonian of Tajikistan. This article describes a new species, S. heinorum sp. nov., from the Middle Devonian of the Eifel (western Rhenish Massif, Germany) with additional material from the Lower Devonian of the Kellerwald (eastern Rhenish Massif, Germany). External and internal morphologies of this bryozoan have been studied using abundant material. The growth habit of Schischcatella suggests a completely different pattern of feeding currents than that in the normal fenestrate colony. The outflow of the filtered water occurred only on edges of colonies between rami. In the absence of chimneys (areas of vertical water expelling), such a functional morphology may have restricted extension of the colony in a distal direction. The evolution of Schischcatella is apparently an example of paedomorphosis, the genus evolved from an unknown semicosciniid species by the early ontogenetic interruption of colony development and further changes in the mode of growth.     

Linking ice structure and microscale variability of algal biomass in Arctic first-year sea ice using an in situ photographic technique

Microscale photographs were taken of the ice bottom to examine linkages of algal chlorophyll a (chl a) biomass distribution with bottom ice features in thick Arctic first-year sea ice during a spring field program which took place from May 5 to 21, 2003. The photographic technique developed in this paper has resulted in the first in situ observations of microscale variability in bottom ice algae distribution in Arctic first-year sea ice in relation to ice morphology. Observations of brine channel diameter (1.65–2.68 mm) and number density (5.33–10.35 per 100 cm²) showed that the number of these channels at the bottom of thick first-year sea ice may be greater than previously measured on extracted ice samples. A variogram analysis showed that over areas of low chl a biomass (≤20.7 mg chl a m⁻²), patchiness in bottom ice chl a biomass was at the scale of brine layer spacing and small brine channels (∼1–3 mm). Over areas of high chl a biomass (≥34.6 mg chl a m⁻²), patchiness in biomass was related to the spacing of larger brine channels on the ice bottom (∼10–26 mm). Brine layers and channels are thought to provide microscale maxima of light, nutrient replenishment and space availability which would explain the small scale patchiness over areas of low algal biomass. However, ice melt and erosion near brine channels may play a more important role in areas with high algal biomass and low snow cover.     

A bryozoan buildup from the Lower Carboniferous of North Wales

A carbonate buildup dominated by trepostome Bryozoa is described from Dinantian (Asbian) strata near Llandudno in North Wales. A three-phase ecological succession is recognised within the buildup: (i) a basal diverse community with fenestrate, ramose, encrusting trepostome and cystoporate bryozoans in a mud rich wackestone; (ii) a bulk facies, dominated by encrusting and foliaceous, trepostome bryozoans in a fine packstone, and (iii) a thin capping phase, dominated by unilaminar, encrusting trepostome bryozoans in a slightly coarser lithology, including skeletal debris derived from the mound top and possible flanking beds. The buildup probably had topographic relief and developed in a shallow marine environment. The internal tripartite zonation reflects the growth of the structure into a shallower, higher energy regime, with the capping beds being deposited just below wave base. The buildup developed to the north of St. George's Land, on a carbonate shelf edge bordering the deeper basinal facies of the Irish Sea Basin. Dinantian, Asbian, buildup, trepostome Bryozoa, Foraminifera, corals, calcareous algae, Carboniferous, North Wales .     

A comparison between coral colonies of the genus Madracis and simulated forms

In addition to experimental studies, computational models provide valuable information about colony development in scleractinian corals. Using our simulation model, we show how environmental factors such as nutrient distribution and light availability affect growth patterns of coral colonies. To compare the simulated coral growth forms with those of real coral colonies, we quantitatively compared our modelling results with coral colonies of the morphologically variable Caribbean coral genus Madracis. Madracis species encompass a relatively large morphological variation in colony morphology and hence represent a suitable genus to compare, for the first time, simulated and real coral growth forms in three dimensions using a quantitative approach. This quantitative analysis of three-dimensional growth forms is based on a number of morphometric parameters (such as branch thickness, branch spacing, etc.). Our results show that simulated coral morphologies share several morphological features with real coral colonies (M. mirabilis, M. decactis, M. formosa and M. carmabi). A significant correlation was found between branch thickness and branch spacing for both real and simulated growth forms. Our present model is able to partly capture the morphological variation in closely related and morphologically variable coral species of the genus Madracis.