Reinterpretation of crinoid-platyceratid interaction

The well-known association of platyceratid gastropods with crinoids has traditionally been considered an example of coprophagous commensalism. The Occurrence of several crinoid 'stands' ( Platycrinites sp.) from closely spaced bedding surfaces in the upper Mississippian Wymps Gap Limestone member of the Mauch Chunk Formation of southwestern Pennsylvania encourages reinterpretation of this relationship. Crinoid calyces were collected from five separate clusters, two of which contained associated platyceratids. 'Infested' crinoids either died prematurely or were stunted, compared to crinoids in the 'uninfested' clusters. Platyceratid attachment apparently had an adverse effect upon crinoid growth. Serial acetate peels show positioning of the gastropod on the crinoid tegmen over a highly developed anal tube, or chimney. However, the terminus of the anal tube abuts the gastropod's shell and is poorly situated for fecal ingestion by the snail. We suggest that the snail probably pursued another trophic strategy, perhaps taking advantage of aerosol filtration by the crinoid and elevation above the substrate.     

Escalating predation on crinoids in the Devonian: negative community-level evidence

Previous morphological studies suggest that predation on stalked crinoids increased in the Devonian. However, there was no concomitant decline in the occurrence of dense, shallow-water stalked crinoid assemblages in North America from the Ordovician and Silurian to the Mississippian. The evolution of crinoid defensive adaptations may have kept pace with rising durophagy, forestalling the expected decline of crinoid communities. It is also possible that the demise of reefs after the Frasnian-Famennian mass extinction indirectly decreased predation pressure on crinoids by removing shelter for predatory fish. A third possibility is that stalked crinoid abundance was affected neither by new predators nor by the decline of reefs. □ Crinoidea, dense crinoid assemblages, Echinodermata, North America, Paleozoic, predation.     

Using platyceratid gastropod behaviour to test functional morphology

During the Mississippian (Tournaisian), numerous crinoid genera of the subclass Camerata evolved exaggerated anal tubes, cylindrical extensions of the tegmen with the anus at the distal end. Additionally, camerates exhibit higher frequency of platyceratid gastropod infestation than any other crinoid clade leading some researchers to speculate that anal tubes evolved in response to platyceratid parasitism. To test the infestation avoidance role of anal tubes, platyceratid distribution was analyzed among 636 tubed and 675 tubeless crinoids from Mississippian strata in North America. Results demonstrate significantly higher infestation frequency in tubeless crinoids. Rather than attach to the anal vent, as is typical for platyceratids, the gastropods that infested tubed crinoids are always found at the tube base and acquired nutrients from their hosts via drilling. It is likely that infesting tubeless crinoids was a more cost effective trophic strategy than drilling tubed crinoids.     

Unusual tabulate‐crinoid biocoenosis from the Lower Devonian of Morocco

The Early Devonian (Pragian: sulcatus to pireneae conodont zones) crinoid–coral biocoenosis from Hamar Laghdad, Morocco contains fragments of crinoid stalks of various taxa encrusted by spherical and ellipsoidal coralla of the tabulate coral Hamarilopora minima. These corals were encrusting host crinoids syn vivo, and this is evidenced by pluricolumnals exceeding 30 elements overgrown from all sides. Most known to date crinoid–epibiont associations display various types of reaction to the epibiont, such as swellings and deformations. In the case discussed here, no clear interaction is visible; therefore, this association can be classified as paroecia. It can be inferred, however, that due to a change in mechanical properties of the crinoid stalk (losing flexibility), the epizoan influence on the host was negative, while the coral was profiting from the elevated position over the seafloor and nutrient‐bearing water currents. It can be supposed that this interaction was close to parasitism. No strict species‐specific relationship between the epizoan and the host was observed.     

Observations on the settlement of the brachiolaria larvae of Stichaster australis (Verill) and Coscinasterias calamaria (Gray) (Echinodermata: Asteroidea) in the laboratory and on the shore

The settling behaviour is described and substratum preferences of advances brachiolaria larvae of Stichaster australis (Verrill) and Coscinasterias calamaria (Gray) were determined with larvae reared in the laboratory and the results correlated with field observations of habitat preferences of juvenile starfish at Maori Bay on the west coast of Auckland, New Zealand.C. calamaria larvae settled on almost any hard substratum provided it was coated with a ‘primary’ film. Recently metamorphosed C. calamaria could not be found at Maori Bay and it is inferred that there is low recruitment from the plankton to the Maori Bay population.S. australis larvae would only settle, metamorphose, and feed on the encrusting coralline alga Mesophyllum insigne (Foslie) Adey. Nursery areas of offshore boulders covered with this alga are present at Maori Bay and these were found to support populations of juvenile starfish. M. insigne appears to provide a stable and abundant food source for juvenile S. australis.     

Crinoid stalk flexibility: theoretical predictions and fossil stalk postures

Flexibilities in Lower Mississippian crinoid stalks were inferred from preserved postures and shown not to conform with predictions of a cantilever beam model. Flexibilities were not correlated with hard-part characters such as stalk diameter, stalk length, or columnal height. The lack of correspondence between the predictions of the cantilever model and observed flexibilities implies that the most likely control of stalk flexibility is the ligament, more specifically, its non-constant, mutable properties. Although a few Lower Mississippian crinoids, such as Gilbertsocrinus, Platycrinites , and Camptocrinus , have enhanced flexibility achieved by radical modifications of columnal facet morphology, this study has failed to identify any general morphological characters that consistently predict flexibility. It appears that skeletal morphology is a poor guide to stalk flexibility; mutable collagenous tissue is the key. Crinoidea, taphonomy, constructional morphology, Lower Carboniferous, connective tissues.     

Mississippian crinoid biodiversity,biogeography and macroevolution

Abstract: The biodiversity and biogeography of 217 genera of Mississippian crinoids from North America and the British Isles shed light on the macroevolutionary turnover between the Middle Palaeozoic and Late Palaeozoic Crinoid Evolutionary Faunas. This turnover resulted from steady differential extinction among clades during the middle Mississippian after crinoids reached their Phanerozoic peak of generic richness during the early Mississippian. This peak richness was primarily a function of Mississippian originations rather than Devonian–holdover taxa. North America had 100 per cent higher generic richness than the British Isles, but rarefaction analysis adjusts the difference to only 37 per cent higher. Rarefaction demonstrated that North America had increased biodiversity, compared to the British Isles, almost entirely among monobathrid camerates, disparids and primitive cladids. In contrast, diplobathrid camerates, advanced cladids and flexibles had the same generic biodiversity between regions, when compared using rarefaction. The early Mississippian radiation resulted from two primary causes: (1) the expansion of Tournaisian carbonate ramps following the Frasnian mass extinction of reef faunas and (2) the predatory release in the Tournaisian following the end‐Famennian Hangenberg extinction of durophagous fishes. A majority of crinoid genera from the British Isles are cosmopolitan. When combined with rarefaction analysis and evidence for more first occurrences in North America, this suggests higher origination rates in North America, especially when carbonate ramps were widespread. With the gradual reduction in the area of carbonate ramps from the early to late Mississippian, in conjunction with the radiation of new durophagous fishes, camerate crinoids in particular experienced continuous background extinction, without replacement, beginning during the earliest Viséan (late Osagean). By middle Viséan time (late Meramecian) advanced cladids were dominant in all settings. This resulted in the transition from the Middle Palaeozoic to the Late Palaeozoic Crinoid Macroevolutionary Fauna.     

Interactions between the vermetid Serpulorbis squamigerus (Carpenter) and several species of encrusting bryozoans

Along the southern California coast the vermetid gastropod Serpulorbis squamigerus (Carpenter) frequently recruits onto encrusting cheilostome bryozoans. On experimental substrates 93% of 599 individuals observed recruited onto either the five dominant cheilostome species or the shells of resident juvenile Serpulorbis. Serpulorbis recruitment also varied significantly among the dominant bryozoans. These recruitment patterns were found to result from differential postsettlement mortality as well as from selective settlement of larvae. The longevity of vermetids was also found to differ among substratum types, principally from an increase in the probability of surviving to 3 months of age on bryozoan substrates. No positive or negative effects of this relationship could be found for the bryozoans. By differentially recruiting onto bryozoans the vermetid: (1) aggregated for reproduction while avoiding competition for food with adult conspecifics; and (2) decreased juvenile mortality possibly by an avoidance of competition or by being camouflaged from predators. This relationship was judged to be facultative commensalism.     

Nonlinear multivariate models of successional change in community structure using the von Bertalanffy curve

von Bertalanffy curves were used to describe the nonlinear relationship between assemblages inhabiting holdfasts of the kelp Ecklonia radiata and the volume of the holdfast. This was done using nonlinear canonical analyses of principal coordinates (NCAP). The volume of the holdfast is a proxy for the age of the plant and, thus, the canonical axis is a proxy for succession in the marine invertebrate community inhabiting the holdfast. Analyses were done at several different taxonomic resolutions on the basis of various dissimilarity measures. Assemblages in relatively large holdfasts demonstrated ongoing variation in community structure with increasing volume when the dissimilarity used was independent of sample size. Smaller holdfasts had proportionately greater abundances of ophiuroids and encrusting organisms (bryozoans, sponges, ascidians), while larger holdfasts were characterised by proportionately greater abundances of crustaceans, polychaetes and molluscs. Such linear and nonlinear multivariate models may be applied to analyse system-level responses to the growth of many habitat-forming organisms, such as sponges, coral reefs, coralline algal turf or forest canopies.     

Treasure with blood: On the discovery of Traumatocrinus (Echinodermata,Triassic) crowns in China

A team of three paleontologists led by the important Triassic worker Te-You Hsu were killed in Guizhou during a field mapping project in 1944. A.T. Mu studied Hsu's crinoid collection and named a new species Traumatocrinus hsui after him in 1949. The first edition of crinoid Treatise did not acknowledge Mu's work and placed Traumatocrinus as junior synonym of Encrinus. However, it is now regarded as a valid taxon in the new edition published in 2011. During this study, original specimens reported by Mu were re-examined. Among them, 21 specimens survived to this day, and the rest of specimens mentioned in Mu were lost during the Second World War. The collection is illustrated with modern standards for the first time. Despite the hard working conditions endured by the Chinese workers during and shortly after the Second World War, this collection, including eleven slabs of crowns, one cup, eight columnals, and one holdfast curated in Nanjing, is the basis for family Traumatocrinidae.     

Spread of introduced Caulerpa species in macroalgal habitats

A short-term field experiment was designed to identify layers of Mediterranean macroalgal assemblage conducive to successful spread of two introduced Caulerpa species (Bryopsidales, Chlorophyta). By manipulation of species presence, three experimental assemblages were obtained: (1) encrusting algae, having removed the turf and erect species; (2) encrusting and turfing algae, having removed erect species; (3) encrusting, turfing and erect algae, that is, unmanipulated assemblages, which served as a control. Fragments of the two introduced species Caulerpa taxifolia (Vahl) C. Agardh and Caulerpa racemosa (Forsskål) J. Agardh were transplanted in each of the three assemblages. Width of the colony, blade density and percentage of the substratum covered by the two species were measured.

The susceptibility of the indigenous community to the spread of Caulerpa species was related to type of assemblage. Blade density and amount of substratum covered by the two Caulerpa species were different between species and generally greater for C. taxifolia than for C. racemosa. Overall, the spread of these species was strongly dependent on the type but not directly on the complexity of the assemblage. Turf was more favourable than encrusting species alone, while the least advantageous habitat was where the macroalgal assemblage is composed of encrusting, turf and erect species. In other words, increased number of species in the assemblage reduces invasion of the Caulerpa species but the type of algae in the assemblage is likely to be more important than number of species. The presence of turf promotes the spread of Caulerpa species.     

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.     

The effects of grazing by gastropods and physical factors on the upper limits of distribution of intertidal macroalgae

Summary The cover of foliose algae is sparse to non-existent above a low-level algal zone on many shores in N.S.W., except in rock-pools. Above this algal zone, encrusting algae, mostly Hildenbrandia prototypus, occupy most of the primary substratum on sheltered shores. Experimental manipulations at midtidal levels were used to test hypotheses about the effects of grazing by molluses and of physical factors during low tide on this pattern of algal community structure.Fences and cages were used to exclude grazers: molluscs grazed under roofs and in open areas. Cages and roofs provided shade, and decreased the harshness of the environment during low tide: fences and open areas had the normal environmental regime.In the absence of grazers, rapid colonization of Ulva and slower colonization by other foliose algae occurred in all experimental areas. The rate of colonization by Ulva sporelings was initially retarded on existing encrusting algae, but after a few months, cover of Ulva equalled that on cleared rock.Most species of algae only grew to maturity inside cages, and remained as a turf of sporelings inside fences. No foliose algae grew to a visible size in open, grazed areas. Grazing thus prevents the establishment of foliose algae above their normal upper limit on the shore, but the effects of physical factors during low tide prevent the growth of algae which become established when grazers are removed. Physical factors thus limit the abundance of foliose algae at mid-tidal levels.The recolonization of cleared areas by Hildenbrandia was not affected by the presence of a turf of sporelings, nor by the shade cast by roofs, but was retarded in cages where mature algae formed a canopy. Even under such a canopy, Hildenbrandia eventually covered as much primary substratum as in open, grazed areas. This encrusting alga is able to escape from the effects of grazing by having a tough thallus, and by its vegetative growth which allows individual plants to cover a lot of substratum, and by the tendency for new individuals to start growing from small cracks and pits in the rock, which are apparently inaccessible to the grazers.Mature foliose algae are removed from the substratum by waves, and many individual plants died during periods of hot weather. Sporelings in a turf were eliminated, after experimental fences were removed, by the combined effects of macroalgal grazers, which invaded the areas, and microalgal grarers which ate the turt from the edges inwards.The results obtained here are discussed with respect to other studies on limits to distribution of intertidal macroalgae, and the role of grazing in the diversity and structure of intertidal algal communities. Some problems of these experimental treatments are also discussed.     

Larger foraminifera as a substratum for encrusting bryozoans (Late Oligocene,Tethyan Seaway,Iran)

Considering the diversity and abundance of larger foraminifera examined from a wide range of Late Oligocene to Early Miocene palaeoenvironments in the Tethyan Seaway, encrusting bryozoans make extremely little use of their tests as substratum. Significant encrustations by bryozoans were exclusively found on large (ø c. 6 cm), undulating tests of Lepidocyclina spp., on which, however, a remarkable 34 taxa of encrusting bryozoans were recorded. This shallow-water fauna of Chattian age was analyzed in respect of the bryozoan taxa present, colony growth type, and mode of budding, colony size, as well as onset of reproduction. Taxic and morphological similarities between the fossil assemblage and modern faunas encrusting mobile substrata indicate a long history of bryozoans as part of the interstitial habitat, while the tests of certain larger foraminifera may have played a significant role in the evolution of shallow-water bryozoans by providing substrata for encrusting species in otherwise unfavorable environments.     

Train crash crinoids revisited

‘Train crash crinoids’ represent an unusual mode of preservation of crinoid columns, superficially resembling to the carriages of a crashed train. They were exhumed from the White Peak (Mississippian limestones) of the Peak District in the Treak Cliff area of Castleton, Derbyshire, north‐central England, and were presented by Broadhurst & Simpson as part of a varied suite of observations supporting the recognition of an ancient apron reef (= fore‐reef slope). A re‐examination of these specimens shows that they were not live crinoids at or near the reef crest, but were recently dead specimens, recumbent on the sediment surface. Something triggered their movement into deeper water, and some travelled downslope parallel to the direction of movement and broke into a ‘train crash pattern’ when the lower end impacted on an immovable object.     

Relationship between cover of Chondrus crispus (Gigartinales,Rhodophyta) and Phymatolithon (Corallinales,Rhodophyta) on friable rock substrata

Field observations in sublittoral Prince Edward Island, Canada, indicated that on a friable sandstone substratum Chondrus crispus was more commonly associated with Phymatolithon sp. than with bare rock. Thus, a substantial proportion of the population of Irish moss along the coast of Prince Edward Island occurs on this encrusting coralline. These observation may be explained on the basis of the relative stability of the substratum in contrast to other studies in which sloughing of epithallial cells by species of both Phymatolithon and Lithothamnium has been reported to limit epiphytism by fleshy macrophytes.Issued as NRCC 31426.     

Survival of crinoid stems following decapitation: evidence from the Ordovician and palaeobiological implications

It was recently discovered that the stems of extant crinoids may survive after detachment of the crown, presumably feeding by the absorption of nutrients through the ectoderm. Previously, only one analogous, albeit morphologically dissimilar, pattern of crownless survival has been recognized from the fossil record. Certain Upper Ordovician (Cincinnatian) crinoid pluricolumnals from Kentucky, Ohio and Indiana, derived from the disparids Cincinnaticrinus spp., have rounded terminations reminiscent of some modern bourgueticrinid overgrowths. Such specimens have hitherto been interpreted as distal terminations of mature individuals that have become detached from their attachment structures and taken to an eleutherozoic existence. However, it is considered more probable that they represent overgrowths of the column following predatory decapitation. If this new interpretation is correct, then post-decapitation survival of crinoid stems is now recognized for most of the history of the crinoids, 'lethal' predation on crinoid crowns occurred at least as early as the Late Ordovician and ancient crinoid populations can no longer be determined merely by counting crowns.     

Disarticulation patterns in Ordovician crinoids: Implications for the evolutionary history of connective tissue in the Crinoidea

Taphonomic information is examined to evaluate the early history of connective tissues in the Crinoidea. The pattern of stalk segmentation of Middle and Late Ordovician crinoids is consistent with the two-ligament (intercolumnal and through-going ligaments) pattern present in living isocrinid crinoids and interpreted for fossil isocrinids, holocrinids, and Lower Mississippian crinoids. A single rhombiferan was also examined; its taphonomic pattern is also indicative of this style of tissue organization. Furthermore, the taphonomy of all Middle and Late Ordovician crinoids may reflect that they lacked discretely organized muscles between arm brachials, which is consistent with the hypothesis that muscles evolved as a connective tissue between plates only once within the Crinoidea, during the Early Devonian. These data indicate that the two-ligament organization of the stalk is a primitive feature among the Crinoidea and perhaps even among stalked echinoderms. Therefore, the autotomy function of this column-tissue organization among living crinoids is an exaptation. On the other hand, discretely organized muscles as connective tissue in crinoid arms is a derived trait that first appeared during the middle Paleozoic; this adaptation proved very successful for the advanced cladid crinoids.     

Development of cyanobacterial build-up and evolution of river bed morphology in the chalk stream Eaulne (Upper-Normandy, France)

In some hardwater rivers of the Seine basin (France), the development ofan encrusting cyanobacterial microflora may gradually lead to a cementation ofriver bed sediments, to a reduction of spawning ground areas and to a loss ofbenthic floral and faunal diversity. Current methods for build-up management arebased on mechanical dredging of the stream bed. In the short term, the habitatdiversity and microfaunal diversity are improved, but in 1–3years the cyanobacterial growth resumes and the bed sediments arecemented again. The early growth stages of stromatolitic structures on newlyavailable substrata were studied for three years in the river Eaulne(Upper-Normandy, France) in relation with microfloral development, sedimentaryprocesses and water quality. Seasonal current velocity variations appeared tocontrol the construction process (colonization dynamics and dependency ofstromatolite growth to mat extension) through substratum availability andnutrient renewal. Under the conditions allowing an optimal microfloraldevelopment, the carbonate precipitation rates were inversely correlated withsubstratum grain size, i.e. the maximal encrusting biomass was hosted bygravels. Homogeneous substrata showed the highest short-term potentialities forhigh sediment cementation rate, whereas heterogeneous, mixed grain size had thehighest potentialities for long-term colonization by the encrusting microflora.     

An evaluation of the mortality of the brown seaweed <Emphasis Type="Italic">Ascophyllum nodosum</Emphasis> (L.) Le Jol. produced by cutter rake harvests in southern New Brunswick,Canada

Ascophyllum nodosum (rockweed) landings in the Atlantic Maritime provinces of Canada totalled 36,500 wet tonnes in 2009. Due to the relative slow growth, stochastic recruitment, and the importance of habitat protection, strict harvest regulations are in place in the region to maintain the integrity of this resource. Special harvesting rakes have been designed to cut the plants and not to dislodge the clumps and their holdfasts from the substratum. However, for various reasons, close to 6% of the biomass harvested annually contains holdfast material. This proportion is closely monitored by the province as it is assumed to represent clump mortality. However, due to the complex structure of A. nodosum clumps, this relationship with mortality is not simple. A study was carried out to evaluate the real impact of this detachment on the A. nodosum population of southern New Brunswick in 2004. The structure of harvested A. nodosum clumps with associated holdfast material was analyzed and compared to non-harvested clumps from the same harvest area. Results showed that when a rake strips a clump, it only detaches 17.4% of the holdfast surface, leaving 36.8% of the plant biomass and 80.3% of the shoot density intact. An analysis of storm-cast material from the same study area showed a similar effect in the clump structure, although the incidence of holdfast in the detached biomass could be as high as 30%. Due to the high biomass detached each year by coastal storms in New Brunswick, their impact on the A. nodosum resource is 21 times higher than the annual harvest.