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.     

Neoarchaeocrinus在我国的发现

根据贵州石阡雷家屯志留系剖面的１块海百合化石标本建立了一新种：Ｎｅｏａｒｃｈａｅｏｃｒｉｎｕｓｓｈｉｑｉａｎｅｎｓｉｓｓｐ．ｎｏｖ。该种以较长大的初级间腕板及辐板脊与腕板脊围成菱形等特征区别于属内其他种。     

Evolutionary history of regeneration in crinoids (Echinodermata)

The fossil record indicates that crinoids have exhibited remarkable regenerative abilities since their origin in the Ordovician, abilities that they likely inherited from stem-group echinoderms. Regeneration in extant and fossil crinoids is recognized by abrupt differences in the size of abutting plates, aberrant branching patterns, and discontinuities in carbon isotopes. While recovery is common, not all lost body parts can be regenerated; filling plates and overgrowths are evidence of non-regenerative healing. Considering them as a whole, Paleozoic crinoids exhibit the same range of regenerative and non-regenerative healing as Recent crinoids. For example, Paleozoic and extant crinoids show evidence of crown regeneration and stalk regrowth, which can occur only if the entoneural nerve center (chambered organ) remains intact. One group of Paleozoic crinoids, the camerates, may be an exception in that they probably could not regenerate their complex calyx-plating arrangements, including arm facets, but their calyxes could be healed with reparative plates. With that exception, and despite evidence for increases in predation pressure, there is no compelling evidence that crinoids have changed though time in their ability to recover from wounds. Finally, although crinoid appendages may be lost as a consequence of severe abiotic stress and through ontogenetic development, spatiotemporal changes in the intensity and frequency of biotic interactions, especially direct attacks, are the most likely explanation for observed patterns of regeneration and autotomy in crinoids.     

Recolonization of the Himerometra robustipinna (Himerometridae, Crinoidea) by macrosymbionts: an in situ experiment

It is generally considered that symbiotic organisms colonize their hosts during their early stages of development. The main goals of the present study were to assess whether post-settled (juvenile and adult) symbionts were able to colonize comatulid crinoids, and whether a hosts’ spatial distribution may influence the colonization pattern through a series of field recolonization experiments. Three series of experiments on recolonization of the comatulid crinoid Himerometra robustipinna were conducted in the Nhatrang Bay, South-China Sea, Vietnam. Ten species of macrosymbiont, 1 polychaetes, 1 gastropods, 1galatheids, 1 ophiurids, and 6 shrimps were found to be associated with H. robustipinna host in the controls and in the 3 experimental series. We found that symbionts rapidly colonized depopulated crinoids in all the experimental series. The prevalence was lower in the experimental series than in the controls butthe abundance, species richness were not significantly different. The presence of post-settled juveniles and adults in experimental series indicated migration from neighboring hosts. Dispersal strategies of symbionts varied: some of them such as the polychaete Paradyte crinoidicola, the gastropod Annulobalcis vinarius, and the galatheid Allogalathea elegans were rapid colonizers. The shrimps Periclimenes commensalis, Pontoniopsis comanthi, and ophiuroid Gymnolophus obscura demonstrated low colonization rate. The 1 and 2 experimental series showed that there was movement of symbionts in dense hosts’ aggregations or over short distances. Unexpectedly, the infestation characteristics of crinoids in the spatially isolated site (series 3) didn’t differ from that of crinoids from aggregations (series 1 and 2), which indicates that long distance (tens meters) migrations of crinoid symbionts also occurs.     

Infestation of Middle Devonian (Givetian) camerate crinoids by platyceratid gastropods and its implications for the nature of their biotic interaction

One of the classic examples of biotic interactions preserved in the fossil record is that between crinoids and infesting platyceratid gastropods. This relationship, spanning an interval from the Middle Ordovician to the end of the Permian, is recognized by the firm attachment and positioning of platyceratids over the anal vent of their hosts. Several hypotheses have been proposed to explain this interaction; the most widely accepted is that the gastropods were coprophagous commensals, feeding on crinoid excrement without any significant detriment to their hosts. The purpose of this investigation was to test this hypothesis. Two species of Middle Devonian camerate (Monobathrida, Compsocrinina) crinoids, Gennaeocrinus variabilis Kesling & Smith 1962 and Corocrinus calypso (Hall 1862), were used in this investigation. The data consisted of 426 individuals of G. variabilis collected near Rockport, Michigan, 30 of which were infested, and 188 individuals of C. calypso collected near Arkona, Ontario, Canada, of which 25 were infested. Length and volume were measured for each crinoid to determine whether a significant difference existed in the size of infested versus uninfested individuals. The results indicated that for both species of crinoids individuals infested by snails were significantly smaller than uninfested individuals (p < 0.05). We explored a variety of scenarios to explain this pattern and conclude that they falsify the null hypothesis that the crinoid-gastropod relationship was strictly commensal. The smaller size of the infested crinoids is interpreted as a consequence of nutrient-stealing by the parasitic gastropods, a strategy that finds analogs in modern seas. Moreover, the absence of platyceratids on the largest crinoids suggests that large size may have inferred immunity from lasting infestation.     

Filtration models, guilds, and biofacies: Crinoid paleoecology of the Stanton Formation (Upper Pennsylvanian), midcontinent, North America

Filtration models make several predictions concerning the distribution of crinoids among benthic habitats: (1) generally, higher energy shoreward settings should contain crinoid assemblages dominated by taxa with dense mesh filtration fans; (2) generally, lower energy offshore settings should be dominated by crinoids with open mesh filtration fans; (3) diversity should be highest in nearshore settings, which generally contain low energy microhabitats within high energy settings where both dense fan and open fan forms can co-occur, whereas offshore assemblages should be dominated by open fan taxa; thus, open fan forms should be more eurytopic than dense fan forms. Also, previous empirical models for crinoid distribution patterns note that nearshore assemblages are dominated by large forms whereas offshore assemblages are dominated by small forms. Filtration fan morphology and body size interact significantly to determine how and where crinoids feed and thus are used here as criteria for distinguishing late Paleozoic crinoid guilds. The distribution patterns of crinoid taxa and guilds among the benthic paleoenvironments of the Upper Pennsylvanian (Missourian) Stanton Formation were used to test the predictions of the filtration models.

The results of quantitative analyses show that large, dense fan crinoids are significantly more abundant in shoreward assemblages than smaller, open fan crinoids, which are more abundant in offshore assemblages; these results are consistent with the aforementioned models. However, diversity patterns are not consistent with the filtration models, indicating that mid-depth and aerobic offshore assemblages are more taxonomically and trophically diverse than nearshore and dysaerobic offshore assemblages, ostensibly due to the overlapping ranges of characteristically nearshore and offshore taxa. Analysis of guild distribution patterns also indicates some contradictions to predicted patterns of stenotopy and eurytopy, indicating additional complexities to late Paleozoic crinoid paleoecology.

Five recurrent crinoid assemblages, or biofacies, have been identified from the Stanton Formation of midcontinent North America. The guild structure and diversity of these biofacies are characterized here as: (1) a moderate diversity nearshore biofacies dominated by large calyx, dense fan guilds; (2) a high diversity midshelf biofacies characterized by equitable contributions of many taxa and guilds; (3) a moderate diversity offshore biofacies dominated by non-pinnulate and small calyx, open fan pinnulate guilds; (4) a low diversity offshore dysaerobic biofacies dominated by small calyx pinnulate guilds; (5) a depauperate offshore biofacies dominated by a unique stalkless species, Paragassizocrinus tarri. Except for Biofacies 5, the number of guilds appears to increase offshore; however, the equitability of taxa among and within the guilds generally decreases offshore. This pattern indicates that the heterogeneity of resources, or the recognition by taxa of different classes of resources, as reflected by the variety of functional types, increased from nearshore to offshore, but that the abundance or accessibility of these resources, and/or the relaxation of competition within guilds, increased from offshore to nearshore.     

Assessment of hidden diversity of crinoids and their symbionts in the Bay of Nhatrang,Vietnam

Crinoid associates represent an abundant and diverse, but poorly explored, component of the hidden biodiversity of coral-reef ecosystems. We studied data from 5 years of collecting in the Bay of Nhatrang (BN), Vietnam, to assess the diversity of crinoids and their symbionts, to compare it with other areas of the Indo-West Pacific, and to elucidate the extent to which the observed diversity of crinoids and their symbionts corresponds to their true diversity. In total, about 2,287 specimens of symbionts belonging to 70 species were found on 203 specimens of crinoids belonging to 33 species. Among the crinoids, the most numerous species were Himerometra robustipinna (36 specimens) and Cenometra bella (29 specimens), among the symbionts the polychaete Paradyte crinoidicola (c. 850 specimens) and the galatheid crustacean Allogalathea elegans (180 specimens). Species accumulation curves suggest that we have sampled most of the crinoid diversity in the BN, whereas the diversity of their symbionts remained undersampled. Estimated species richness of crinoids was higher than previously observed richness, and varied from 39 (estimated by bootstrap) to 46 (jackknife 2). Estimated species richness of symbionts was higher than observed richness, and varied from 71 (bootstrap) to 93 (jackknife 2). We suggest a slight increase in the number of crinoid species to result from more detailed studies of nocturnal species, and an increase in the number of symbiotic species when studies of nocturnal crinoid associates and sibling species among decapods are included. Our study revealed a rather rich crinoid fauna in the bay compared to other areas of the Indo-West Pacific, and the highest species richness of crinoid associates known from anywhere in the World Ocean.     

Paleobiology of the oldest known articulate crinoid

The evolutionary and ecological recovery of benthic marine invertebrate faunas from the devastating Permian-Triassic mass extinction is poorly understood. In particular. Paleozoic crinoids were decimated, creating an evolutionary bottleneck, so that Early Triassic (Scythian) and Anisian representatives of the genus Holocrinus may be considered the stem group for the monophyletic crinoid subclass Articulata, which includes all post-Paleozoic crinoids. Crinoid ossicles in limestones of the Scythian (Spathian) Virgin Limestone Member (Moenkopi Formation) of southern Nevada and southwestern Utah, identified as Holocrinus? smithi, respresent the oldest known Holocrinus. Limestone units of the virgin were deposited in nearshore and inner shelf environments of an arid epeiric seaway. Although these crinoids are generally completely disarticulated and occur commonly in storm-generated deposits. they are interpreted to have been deposited near their living sites in ‘disturbed neighborhood’ assemblages. Counts of ossicles in bulk samples indicate a relatively low number of individuals, suggesting that populations of H.? smithi occurred in scattered clumps or as isolated individuals. attached to hardgrounds or shell beds. Bivalves are the most common associates, and are commonly more numerous than the estimated number of crinoid individuals, although bivalve species richness is never greater than three. Virgin Limestone fossil assemblages probably represent the first redevelopment of relatively complex tiered epifiaunal communities in the Mesozoic. *Echinodermata, mass extinction, Early Triassic, paleoecology, Crinoida, Articulata.     

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.     

Biodiversity and historical biogeography of stalked crinoids (Echinodermata) in the deep sea

About 95 species of stalked crinoids are now described from 60m to hadal depths, but our knowledge remains far from complete. Depending on which species concept is used, estimates of species richness can be dramatically different. It is necessary to have a homogeneous concept for taxonomic units. The abundance of the crinoid fossil record allows a discussion of the ancestry of deep sea crinoid fauna. Stalked crinoids have a horizontal diversity pattern with three regional centres of high diversity (i.e. western tropical Pacific, western tropical Atlantic and north-eastern Atlantic). Vertical patterns show two faunal strata which vary in importance among provinces. The epibathyal stratum has apparently remained relatively similar in intertropical areas since the Mesozoic. Despite environmental changes related to glaciation since the Middle Miocene, the deepest crinoid fauna (i.e. the deep sea fauna sensu stricto at depths more than 1000 ± 200 m) have a very ancient origin with a dispersion closely related to plate tectonics. The bathyal fauna on hard substrates includes a few living fossils and has a high historical interest.     

Crinoids, hardgrounds, and community succession: The Silurian Laurel—Waldron contact in southern Indiana

Halleck, Margaret S.: Crinoids, hardgrounds, and community succession: The Silurian Laurel-Waldron contact in southern Indiana.
The uppermost surface of the Silurian Laurel Limestone at its contact with the Waldron Shale in southeastern Indiana was a hardground lithified prior to the deposition of the Waldron. Evidence for this conclusion is the presence of attached palmate crinoid roots, auloporid corals, and craniid brachiopods on the Laurel surface; the irregularity of the contact with the Waldron; and a pyritic veneer at this contact. The hardground apparently had a submarine origin. In addition to the attached epifauna mentioned above, algal-sediment 'clods' formed on this surface. Some of these accumulated around the crinoid stems, causing them to produce cirral extensions. The resulting community was a crinoid 'meadow' with algal growths forming sediment traps around and between the crinoids. Later stages of Waldron Shale deposition led to the development of a soft-bottom community.     

New crinoids from the Baltic region (Estonia): fossil tip‐dating phylogenetics constrains the origin and Ordovician–Silurian diversification of the Flexibilia (Echinodermata)

This study documents previously unknown taxonomic and morphological diversity among early Palaeozoic crinoids. Based on highly complete, well preserved crown material, we describe two new genera from the Ordovician and Silurian of the Baltic region (Estonia) that provide insight into two major features of the geological history of crinoids: the early evolution of the flexible clade during the Great Ordovician Biodiversification Event (GOBE), and their diversification history surrounding the end‐Ordovician mass extinction. The unexpected occurrence of a highly derived sagenocrinid, Tintinnabulicrinus estoniensis gen. et. sp. nov., from Upper Ordovician (lower Katian) rocks of the Baltic palaeocontinent provides high‐resolution temporal, taxonomic and palaeobiogeographical constraints on the origin and early evolution of the Flexibilia. The Silurian (lower Rhuddanian, Llandovery) Paerticrinus arvosus gen. et sp. nov. is the oldest known Silurian crinoid from Baltica and thus provides the earliest Baltic record of crinoids following the aftermath of the end‐Ordovician mass extinction. A Bayesian ‘fossil tip‐dating’ analysis implementing the fossilized birth–death process and a relaxed morphological clock model suggests that flexibles evolved c. 3 million years prior to their oldest fossil record, potentially involving an ancestor–descendant relationship (via ‘budding’ cladogenesis or anagenesis) with the paraphyletic cladid Cupulocrinus. The sagenocrinid subclade rapidly diverged from ‘taxocrinid’ grade crinoids during the final stages of the GOBE, culminating in maximal diversity among Ordovician crinoid faunas on a global scale. Remarkably, diversification patterns indicate little taxonomic turnover among flexibles across the Late Ordovician mass extinction. However, the elimination of closely related clades may have helped pave the way for their subsequent Silurian diversification and increased ecological role in post‐Ordovician Palaeozoic marine communities. This study highlights the significance of studies reporting faunas from undersampled palaeogeographical regions for clade‐based phylogenetic studies and improving estimates of global biodiversity through geological time.     

Aspects of crinoid palaeontology of the North Esk Inlier,Scotland (Silurian,Llandovery, Telychian)

Abstract: The described fauna of well‐preserved Llandovery (Telychian) echinoderms from the North Esk Inlier, including six crinoids, one echinoid and seven starfish species, is mainly allochthonous. Most of these taxa are known only from starfish beds, channel fill deposits probably representing submarine mass flows and preserving a biota probably derived from elsewhere, presumably shallower water. Only one crinoid species, Pisocrinus cf. campana Miller, is recognized as a common fossil away from the starfish beds and is a biostratigraphic marker for the base of the Wether Law Linn Formation, forming part of the Skenidioides‐Cyrtia Association. Crinoid columnals preserved perpendicular to bedding (that is, in putative life position) in Lamont’s bivalve bed, Deerhope Formation, are tentatively interpreted as being in situ by comparison with a similar occurrence in the Silurian of Arisaig, Nova Scotia. Two new species of crinoid are described, the cladid Dendrocrinus? sp. and the columnal morphospecies Pentagonocyclicus (col.) lamonti sp. nov.     

Host‐specific acrothoracid barnacles on Middle Devonian platyceratid gastropods

Borings, attributed to acrothoracic barnacles, occur on the platyceratid gastropod Naticonema lineatum (Conrad) from the Middle Devonian Hamilton Group of western New York and rarely in specimens as old as the Early Devonian. These latter are the oldest known acrothoracid borings are in the fossil record. The borings are consistently developed as laterally compressed, inequilateral pouches exclusively on these gastropods, commonly as dense infestations.

Naticonema shells yielding borings typically occur associated with partially articulated qrinoid remains, and they are sometimes found attached to crinoids in a manner similar to coprophagous Platyceras. In addition to barnacle borings, Naticonema shells often bear thin encrustations of bryozoans which are usually perforated by these borings but sometimes also overgrow them. Barnacles bored live hosts; gastropods prevented shell penetration by producing cyst‐like secondary secretions of calcite beneath acrothoracid boreholes.

The relative antiquity of these borings and their association with coprophagous platyceratids makes their discovery particularly significant in revealing aspects of the early ecology of barnacles. Attachment to the host commensal gastropods was one of the first successful life modes of these crustaceans prior to their later diversification to other habitats. Mississippian and Pennsylvanian occurrences of similarly bored gastropods demonstrate continuity of the barnacle‐gastropod‐crinoid ecological association from the Middle to Late Paleozoic.     

NEW CLADID AND FLEXIBLE CRINOIDS FROM THE MISSISSIPPIAN (TOURNAISIAN, IVORIAN) OF ENGLAND AND WALES

Abstract:  The modern study of fossil crinoids began with J. S. Miller who, in 1821, described specimens from southern England, nearby Wales and other regions, and named several common Early Carboniferous genera. Later, in 1950–60, James Wright monographed all known Early Carboniferous crinoids from the British Isles. In spite of such previous scrutiny, we recognize here two new genera among species already described: Glamorganocrinus gen. nov. (type species: Ophiurocrinus gowerensis Wright, 1960) from South Wales and Mendipocrinus gen. nov. (type species: Poteriocrinus latifrons Austin and Austin, 1847) from southern England. These new genera increase the number of advanced cladid genera in the Ivorian Substage of the Tournaisian in western Europe to 18, and the total number of crinoid genera to 36. A review of species assigned to Mespilocrinus has led to the recognition of M. granulifer De Koninck and LeHon, 1854 as a nomen dubium. A new species of Mespilocrinus , M. wrighti sp. nov., is described from the Ivorian of South Wales; this is the most highly derived species of the genus, as based on a phylogenetic analysis including ten species and 13 characters, with Pycnosaccus as the outgroup. A single, well-ordered tree resulted from this analysis. Interpretation of this tree suggests that the centre of evolution for Mespilocrinus was North America, where three species appeared during the Kinderhookian (early Tournaisian), rapidly achieving morphological disparity within the genus. This radiation event was part of the overall explosive radiation of crinoids following the Late Devonian mass extinction event when crinoid diversity was at a global minimum during the Frasnian. Recovery began during the Famennian, followed by an explosive radiation in the Tournaisian.     

Preservation of hypericin and related polycyclic quinone pigments in fossil crinoids

The fringelite pigments, a group ofphenanthroperylene quinones discovered in purple coloured specimens of the Upper Jurassic crinoid Liliocrinus, demonstrate exceptional preservation of organic compounds in macrofossils. Here we report the finding of hypericin and related phenanthroperylene quinones in Liliocrinus munsterianus from the original 'Fringeli' locality and in the Middle Triassic crinoid Carnallicrinus carnalli. Our results show that fringelites in fact consist ofhypericin and closely related derivatives and that the stratigraphic range of phenanthroperylene quinones is much wider than previously known. The fossil occurrence of hypericin indicates a polyketide biosynthesis of hypericin-type pigments in Mesozoic crinoids analogous to similar polyketides, which occur in living crinoids. The common presence of a characteristic distribution pattern of the fossil pigments and related polycyclic aromatic hydrocarbons further suggests that this assemblage is the result of a stepwise degradation of hypericin via a general diagenetic pathway.     

Revision Of Late Devonian (Famennian) And Some Early Carboniferous (Tournaisian) Crinoids And Blastoids From The Type Devonian Area Of North Devon

The crinoids and blastoids from the Pilton (Beds) Formation of the type Devonian of north Devonshire are revised. These fossils were monographed by the Rev. G. F. Whidborne in 1898, but have not been studied since that time. Recent studies on various groups of fossils from the Pilton and related rocks in North Devon confirm that the great majority of these fossils are Famennian, although three specimens from Fremington are probably Early Carboniferous (Tournaisian). We identify four blastoid taxa from a fauna that is sparse and poorly preserved; two spiraculates, one fissiculate, and one taxon unidentifiable at the ordinal level. Mesoblastus cf. M. crenulatus from the Gattendorfia Zone (Lower Carboniferous) near Fremington is the oldest known representative of this genus. The crinoid fauna is somewhat more diverse, but the preservation is equally poor. No changes are made in the flexible crinoids. Among camerate crinoids, one species is reassigned to Eumorphocrinus and one is retained in Actinocrinites. Specimens of some crinoids, such as Rhodocrinites and Megistocrinus, are so poorly preserved that certain identification was not possible. The hexacrinoid Adelocrinus, relegated to uncertainty for 150 years, is here shown to be a valid genus that is very similar to Arthroacantha, but not synonymous with it. Among the cladid crinoids, the dominant groups are those within the Superfamily Scytalocrinacea, which includes Bridgerocrinus, Sostronocrinus, and Scytalocrinus, all of which are placed in the new family Sostronocrinidae. One new species, Glossocrinus whidbornei, is named. Non‐pinnulate cladids, common in older Devonian rocks, do not occur. The fauna shows considerable similarity with faunas from eastern North America and Germany. It shows less resemblance to the extensive Famennian crinoid and blastoid fauna of north‐western China, despite some remarkable congruencies, especially the occurrence of very similar species of Actinocrinites in these widely separated areas.     

Radial perforations in crinoid stems from the Silurian of Gotland

Radiating intracolumnal canals are a characteristic feature of large (diameter 10 mm or more) crinoid stems from the Silurian of Gotland. They are found in nodals as well as in internodals where the columnal height exceeds one millimetre. They were formed secondarily in the median and distal portions of crinoid stems with pseudocirriferous holdfasts. Intercolumnal canals are found in the distal parts of stems with true cirri regardless of the size of the stem. It is suggested that these canals played an important role in crinoid physiology. The crinoids are believed to have sustained a large proportion of their tissues through cutaneous digestion and uptake of dissolved substances from the surrounding sea water. The intra- and intercolumnal canals increased the surface of the axial canal in relation to volume. They provided a connection between the axial canal and the surrounding sea water, thus facilitating nutrient transport to the tissues.     

Haemal and coelomic circulatory systems in the arms and pinnules ofFlorometra serratissima (Echinodermata: Crinoidea)

Summary The haemal and coelomic circulatory systems in arms and pinnules of a stalkless crinoid are described by transmission electron microscopy, and the coelomic topography is revealed by scanning electron microscopy of corrosion casts and peritoneal surfaces. In addition, the route of the coelomic circulation in the living crinoid is shown by injection of carmine particles, and sites of peritoneal phagocytosis are demonstrated by injection of latex beads. The most important morphological findings are: the controversial hyponeural circulation is haemal and not coelomic; peritoneal ciliation is general and not limited to the cells of the ciliated pits; and occur smooth muscle cells occur below the peritoneum. Carmine particles injected into the central body coelom rapidly travel outward toward the arm and pinnule tips via the aboral canals; the particles return to the central body via the subtentacular canals. Latex beads injected intracoelomically are taken up by peritoneal cells throughout the subtentacular, genital and aboral canals. The possible functions of the haemal and coelomic circulatory systems of crinoids are discussed.     

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.