Comatulid Crinoids Research Articles

Response of megabenthic assemblages to different scales of habitat heterogeneity on the Mauritanian slope

The topographically complex deep seabed on the Mauritanian slope, from 990 to 1460m water depth, was imaged with video in an extensive quantitative survey of 17,199m2 of seafloor using a Remote Operated Vehicle (ROV). This study investigated the influence of habitat heterogeneity at two scales on the megafaunal assemblages observed by ROV. Changes in megafaunal assemblages on the Mauritanian slope were assessed at a broad scale, within depth zones, and at a finer scale, in response to changes in local geomorphology associated with submarine landslides. Geomorphology was determined by classification of habitat parameters (slope, aspect, bathymetric position, curvature, fractal dimension and ruggedness) derived from an autonomous underwater vehicle-based multibeam bathymetry survey. Habitat parameters were classified by Iterative Self Organizing Clustering into six major geomorphological groups, four of which were assessed in the ROV video survey. A total of 29 megafaunal taxa were observed along the entire survey, with an overall average faunal density of 0.344 indm−2. Megafaunal assemblage density, species richness and evenness varied significantly across the depth range of the survey in the most common geomorphological zone (sedimentary plains of low slope and complexity). Characteristic species inhabited the shallow areas (asteroid, ophiuroid, anemone, small macrourid), intermediate areas (Benthothuria funabris, black cerianthid, squat lobster) and deeper areas (the holothurians Enypniastes eximia and Elipidia echinata). Megafaunal density, species richness and evenness were not significantly different between geomorphogical groups within one depth zone (1300–1400m). However, the steepest zone, on the edge of a major headwall feature, had four unique taxa (Parapagurus pilosimanus, a comatulid crinoid, a gorgonian and its associated ophiuroid).

Predicting habitat preferences for Anthometrina adriani (Echinodermata) on the East Antarctic continental shelf

The comatulid crinoid Anthometrina adriani is well represented among the suspension-feeding megaepibenthos from the continental shelf of the Dumont D'Urville Sea, Antarctica. Nearly 500 specimens were sampled during the Collaborative East Antarctic Marine Census expedition onboard the RV 'Aurora Australis' (December 2007 to January 2008), from 50 of the 87 stations over a 400 km² area. Abiotic environmental factors were measured and an ocean circulation model was used to generate near-bottom parameters. The ecological niche of A. adri- ani was described by using ecological-niche factor analysis and Mahalanobis distances factor analysis. An environmental suitability map (ESM) was developed to map the optimal habitat. A. adriani prefers moderately deep and relatively cold waters with moderate current velocity, and a substrate with low gravel content and biogenic carbonate. The ESM shows 4 optimal regions: the eastern side of the George V Basin, the eastern side of the Adelie Basin, the southern part of the Adelie Bank, and the coastal area between the Astrolabe and Mertz glaciers. The ecological niche for A. adriani appears very narrow, but the species is widely distributed across the Antarctic shelf. It suggests that local changes in limiting factors have a strong local effect on the distribution of this species and that a total eradication of this species from the shelf would need an Antarctic-wide and synchronic change in these essential parameters. Modeling modifications in environmental conditions under different climate change scenarios could help predict the effect of such changes on the distribution of this selective species.

COULD A STALKED CRINOID SWIM? A BIOMECHANICAL MODEL AND CHARACTERISTICS OF SWIMMING CRINOIDS

Modern stalked crinoids represent a relict fauna of once considerably higher diversity, as seen in their extensive fossil record. Comatulid crinoids, which lack a stalk and dominate modern crinoid diversity, have been interpreted as an evolutionary success story due to the increased mobility afforded by stalk loss. This mobility includes effective crawling and also swimming, often interpreted as anti-predatory escape strategies. Until recently it was assumed that stalked crinoids were incapable of active locomotion, but observations of an extant isocrinid have demonstrated that some can crawl relatively rapidly, perhaps in order to escape from benthic predators. Because the mechanics of crawling in stalked crinoids resemble the mechanics of swimming in comatulids, it is worth investigating whether a stalked crinoid would be capable of swimming. The feasibility of this scenario is tested using a biomechanical model of swimming in a stalkless crinoid and by applying the model to a stalked crinoid. The model demonstrates that the stalk imposes a heavy burden that limits the ability of a stalked crinoid to swim. Evolutionarily this might suggest that stalk loss was a key innovation that facilitated swimming; however, stalk loss alone is not sufficient to allow a crinoid to swim. Swimming would have allowed greater capability for escape from benthic predators than crawling. An evolutionary scenario is considered in which swimming evolved in a stalked crinoid to allow more effective escape from benthic predators subsequent to evolution of rapid crawling, precipitating eventual stalk loss.

Near-bottom current direction inferred from comatulid crinoid feeding postures on the Terre Adélie and George V shelf, East Antarctica

For the first time, comatulid crinoid feeding behaviour is used to infer near-bottom current (NBC) directions on the Terre Adélie and George V shelf, East Antarctica. We analysed 47 still-image and video transects sampled during the Collaborative East Antarctic Marine Census (CEAMARC) expedition in 2007–2008. We recorded the inferred current direction from 1537 comatulid observations and interpolated these data across the shelf using the Natural Neighbour Interpolation (NNI) method. Results revealed a mode current directionality at each station and a close local agreement between the observed and interpolated NBC directions. The interpolated NBC directions show a coherent counter-clockwise gyre in the deep George V Basin, with a northward and westward flow over the northern flank of the basin and eastward flow near the coast, consistent with the distribution of bottom salinity. There also appears to be a clockwise gyre on the relatively shallow Adélie Bank, with an easterly or southeasterly flow along the outer-shelf, south and southwesterly on the east Adélie Bank, and westerly along the Terre Adélie coast.

A crinoid concentration Lagerstätte in the Turonian (Late Cretaceous) Conulus Bed (Miechów-Wolbrom area, Poland)

More than one hundred centrodorsals of the comatulid crinoid Glenotremites paradoxus have been found in Turonian deposits (Upper Cretaceous) in the Miechów-Wolbrom area (southern Poland). This is the first dense occurrence of the genus Glenotremites in the Upper Cretaceous of Poland. Furthermore, so many individuals of this species in one level (the so-called Conulus Bed) forming a crinoid Konzentrat-Lagerstätte are very surprising because only disarticulated remains (cirrals and brachials) are encountered in the older (Cenomanian and earliest Turonian) and younger (late Turonian) deposits. The Glenotremites individuals are accompanied by isocrinids, which prove that stalked forms remained in shallow-water settings for some time after the initiation of the Mesozoic marine revolution.

Larval development of the featherstar Aporometra wilsoni (Echinodermata: Crinoidea)

Abstract. Larval development of a small ovoviviparous comatulid crinoid, Aporometra wilsoni, was investigated using a population from South Australia. The genital pinnules of reproductive females each contain an ovary, within which are oocytes of various stages. Generally, one or more developing larvae lie outside the ovary, but within each pinnule. Larvae pass through “uniformly ciliated” and doliolaria stages before they exit the pinnule via the genital pore. The doliolariae lack the usual ciliary bands and are unable to swim. Doliolariae dissected from pinnules were followed through metamorphosis to the cystidean stage until the pentacrinoid larval stage. While previous reports on Aporometra have noted pentacrinoids attached to the female, virtually no pentacrinoids were found attached to any of the hundreds of adult females observed during this study. Females sampled from the mid‐reproductive season (September and October) were found to bear >2500 developing eggs and larvae at a time. It appears that emerging doliolariae fall from the female and attach to other substrates to complete development. Aporometra is classified in Notocrinida with the Antarctic crinoid Notocrinus. This classification is based in part on their supposedly homologous larval brooding. However, the reproductive mechanism in A. wilsoni is quite different from Notocrinus, calling into question their current status as sister taxa.

Myzostoma fuscomaculatum (Myzostomida), a new myzostome species from False Bay, South Africa

A new myzostome species, described here as Myzostoma fuscomaculatum n. sp. was collected on Tropiometra carinata in False Bay (South Africa), during a survey of symbionts associated with comatulid crinoid species. M. fuscomaculatum n. sp. occurred only on T. carinata and not on the more common crinoid, Comanthus wahlbergi. It infested 61.7% of the 120 host specimens collected, of which 64.9% (48 specimens) hosted more than one individual (maximum of 32). M. fuscomaculatum n. sp. was always located on the host’s arms and pinnules and was cryptically coloured, closely matching the colour pattern of the host. This is the first record of myzostomes from the cool temperate waters of South Africa’s Atlantic coast. The new species is morphologically close to M. gopalai Subramaniam, 1938, collected on T. encrinus in Madras Harbour. M. fuscomaculatum n. sp. differs from M. gopalai in lacking marginal cirri at the adult stage, the presence of three pairs of digestive diverticula, by the position of its lateral organs and by the shape of the manubrium. Molecular phylogenetic analyses based on 18S and 16S rDNA placed M. fuscomaculatum n. sp. into a clade including Hypomyzostoma, Myzostoma and Mesomyzostoma species.

Symbionts of comatulid crinoids in False Bay, South Africa

ABSTRACT This study documents the fauna associated with two common comatulid crinoid species, Comanthus wahlbergi and Tropiometra carinata, in False Bay, South Africa, and describes the patterns of infestation of obligate associate species. A total of 11 invertebrate species was found associated with one or both crinoids. Of these, three were considered obligate: the myzostomidans, Myzostomafuscomaculatum and Myzostoma n. sp., and the shrimp, Hippolyte catagrapha, all of which only occurred on T. carinata. Both frequency and density of infestation were higher for the two myzostomes than for the shrimp. The majority of crinoids infested with myzostomes hosted two or more individuals, while H. catagrapha usually occurred singly. A total of 67.5% of all T. carinata collected were infested by symbionts. Of these 45% hosted only one species, 17% hosted two species and 5.8% hosted all three. Most M. fuscomaculatum (85.2%) and H. catagrapha (82.1%) matched their hosts' colouring, while Myzostoma n. sp. were all ...

Symbionts of comatulid crinoids in False Bay, South Africa

This study documents the fauna associated with two common comatulid crinoid species, Comanthus wahlbergi and Tropiometra carinata, in False Bay, South Africa, and describes the patterns of infestation of obligate associate species. A total of 11 invertebrate species was found associated with one or both crinoids. Of these, three were considered obligate: the myzostomidans, Myzostoma fuscomaculatum and Myzostoma n.sp., and the shrimp, Hippolyte catagrapha, all of which only occurred on T. carinata. Both frequency and density of infestation were higher for the two myzostomes than for the shrimp. The majority of crinoids infested with myzostomes hosted two or more individuals, while H. catagrapha usually occurred singly. A total of 67.5% of all T. carinata collected were infested by symbionts. Of these 45% hosted only one species, 17% hosted two species and 5.8% hosted all three. Most M. fuscomaculatum (85.2%) and H. catagrapha (82.1%) matched their hosts’ colouring, while Myzostoma n. sp. were all yellowish incolour. Infestation by Myzostoma n. sp. increased in both frequency and density with depth. All three obligate symbiont species are new to science, illustrating the biodiversity that can still be uncovered by investigating new niches.

A revision of the comatulid genus Stephanometra AH Clark with a rediagnosis of the genus Lamprometra AH Clark (Echinodermata: Crinoidea)

Several genera in the comatulid crinoid family Mariametridae are currently ambiguously distinguished on the basis of variations in length and robustness of oral pinnules. Previous descriptions have suggested that at least the genera Stephanometra and Lamprometra, both common and widespread on Indo-western Pacific reefs, are imperfectly distinguishable. A detailed morphological re-examination supports distinct Stephanometra and Lamprometra. The five currently recognized species of Stephanometra are reduced to two: S. echinus under S. tenuipinna, and S. spicata (including S. oxyacantha) and S. spinipinna under S. indica. Of specimens examined in the indica-spicata-oxyacantha series, 20% are intermediates that cannot be satisfactorily assigned to species based on current diagnoses. In Lamprometra, L. klunzingeri and L. palmata gyges are formally reduced to infrasubspecific variants of L. palmata.

Syzygial brachials from the upper Muschelkalk (Middle Triassic, Ladinian) of Poland and their implication for an early origin of comatulid crinoids

According to Ubaghs (1978), syzygies are brachial articulations in which radiating ridges and furrows on the two joint faces oppose each other rather than interlock as in symplexies. Cryptosyzygies differ from syzygies by having very short ridges that may be replaced by rows of tubercles or granules, with a tendency toward irregular arrangement and disappearance. Among Triassic crinoids, only representatives of the orders Isocrinida Sieverts-Doreck, 1952 and Comatulida Clark, 1908 had cryptosyzygial or syzygial brachial articulation, respectively. According to Rasmussen (1978), among Isocrinidae the articulations of primibrachial 1 and 2 and secundibrachial 1 and 2 were cryptosyzygial or synarthrial (but see also comments in Simms, 1988a). Among Comatulida, syzygial articulations generally occur between brachials 3 and 4 and in more distal arm parts.

Squat lobsters of the genus Galathea (Decapoda: Anomura: Galatheidae) associated with comatulid crinoids from the Ryukyu Islands, Japan

Squat lobsters of the genus Galathea (Decapoda: Anomura: Galatheidae) associated with comatulid crinoids from the Ryukyu Islands, Japan

KIIMETRA MIOCENICA, A NEW GENUS AND SPECIES OF THE FAMILY CALOMETRIDAE (ECHINODERMATA: CRINOIDEA) FROM THE MIDDLE MIOCENE OF SOUTHWESTERN JAPAN

Extant comatulid (stalkless) crinoids consist of approximately 530 species, classified in 143 genera and 18 families (Clark, 1931, 1941, 1947, 1950; Clark and Clark, 1967; Messing and White, 2001). Recent comatulids account for almost 85% of all the extant crinoid species (comatulids plus stalked crinoids), and their taxonomy is currently being extensively revised (e.g., Hoggett and Rowe, 1986; Rowe et al., 1986; Messing and White, 2001). In stark contrast to such a high extant diversity, records of fossil comatulids are far less common. This is partly due to their low fossilization potential. From the Cretaceous, only 18 genera and nine families of comatulids have been documented (Rasmussen, 1978). The oldest record of a comatulid dates back to the late Triassic ( Paracomatula Hess, 1951; Hagdorn and Campbell, 1993; Simms et al., 1993). Up to the late Cretaceous, the most diverse taxa were notocrinids and solanocrinids (Rasmussen, 1961; Jagt, 1999). The comatulids probably diversified during the Cenozoic (compare Jagt et al., 2002). Cenozoic records of comatulids are thus very important for understanding comatulid diversification. In contrast to stalked crinoids, which occur only at depths below 100 m in modern seas, comatulids are the only crinoid group which flourishes in shallow-water settings. In order to understand the timing and pattern of comatulid survival and diversification, data on Cenozoic comatulids are crucial. Until now, most reports of fossil comatulids chiefly described centrodorsals, because other skeletal parts are easily disarticulated and lost after death (Meyer and Meyer, 1986). In the current paper, we describe a very well-preserved new comatulid species from the Miocene of southwestern Japan, the first report of a fossil member of the Calometridae. It is named Kiimetra miocenica n. gen. and sp. The sample studied contains over 100 specimens …

Isolated Ideas: Crinoid Literature of the Sixteenth Century

The first published accounts of the class Crinoidea (phylum Echinodermata) were from the latter half of the sixteenth century, during which seven or eight works were published. Because this was long before the establishment of modern systematic nomenclature by Linnaeus in 1758, this literature has been largely ignored. The first published work on crinoids was by Agricola in 1546, and the first illustrations of crinoids were by Gessner in 1565-1566. Crinoids were mentioned in these early publications as descriptions of objects dug from the earth, objects that had medicinal uses, and description of collections. The perceived medicinal use of fossil crinoids may have been an important factor for the attention that they received in sixteenth century publications. Little continuity existed from one author to the next, despite communications and mentor-student relationships. During this century, living and fossil crinoids were not allied, neither one was correctly interpreted with living comatulid crinoids (considered starfish), and fossil crinoid columnals were considered inanimate objects. At the close of the sixteenth century, circular and pentalobate columnals and pluricolumnals were related to one another even though they were categorized with an artificial classification scheme, the proposed name for pentalobate pluricolumnals is the valid name today for the Jurassic crinoid Pentacrinus, and living comatulid crinoids were regarded as echinoderms.

Allocrioceras from the Cenomanian (mid‐Cretaceous) of the Lebanon and its bearing on the palaeobiological interpretation of heteromorphic ammonites

Specimens of the mid‐Cretaceous heteromorphic ammonite Allocrioceras cf. annulatum (Shumard, 1860) from the Upper Cenomanian lithographic limestones of the Lebanon provide an in situ record of aptychi and interpreted remnants of internal soft tissue and stomach content. Based on this exceptionally well‐preserved material, Allocrioceras is interpreted as a pelagic, aperture‐upwards drifter that probably fed on comatulid crinoids.

Re-evaluation of the systematics of two deep-sea species of Thalassometra (Echinodermata: Crinoidea) and its biogeographical implications

Biogeography of deep-sea comatulid crinoids is poorly understood owing partly to the lack of detailed taxonomic studies. Recent cruises off Peru dredged up two new, well-preserved specimens of Thalassometra bispinosa, a deep-sea comatulid species which was heretofore only known from the Southern Ocean. These new records enabled re-evaluation of intra-specific variation for both quantitative and qualitative morphological characters. We thus provide a new description of the species, including these new specimens, and discuss the affinities with closely related species. As a consequence, we re-evaluate the systematic position of material previously assigned to T. bispinosa dredged from the Campbell Plateau, Southern Ocean. Discrete morphological characters, measurements and SEM photographs justify reassignment of these specimens to Thalassometra villosa. This species, another poorly known deep-sea comatulid crinoid previously known only from the Aleutian Islands in the North Pacific, is also redescribed. The biogeography of these two deep-sea comatulid species is discussed and hypotheses of their geographical distribution are proposed. La biogeographie des comatules profondes reste mal connue. Cette lacune est essentiellement due au manque de matériel. Deux campagnes IFREMER récentes, effectuées au large du Pérou, ont permis la récolte de deux spécimens exceptionnellement conservés de Thalassometra bispinosa. Cette espèce de comatule du bathyal profond était connue uniquement de l'Océan Austral. L'étude de la variation morphologique intraspécifique de ces nouveaux spécimens, tant quantitative que qualitative, a permis de donner une description détaillée de l'espèce. Sur la base de cette nouvelle description, nous avons réexaminé la position systématique du matériel provenant du Plateau Campbell (Océan Austral), auparavant attribuée à T. bispinosa. La comparaison des caractères morphologiques externes et des articulations des spécimens concernés a fourni les arguments de l'attribution des spécimens du Plateau Campbell à Thalassometra villosa. En conséquence, nous donnons une nouvelle description de cette seconde espèce bathyale jusqu'alors uniquement connue dans le Pacifique Nord. La biogéographie de ces deux espèces est discutée. Nous proposons un scénario explicatif de leur distribution.

Comatulid crinoids from Late Jurassic reefal deposits of NW Germany (Lower Saxony Basin)

Comatulid crinoids from Late Jurassic reefal deposits of NW Germany (Lower Saxony Basin)

Fossil record of echinoderm regeneration with special regard to crinoids.

Regeneration of skeletal parts of fossil echinoderms is reviewed. Among regenerations of various fossil echinoderms, those of crinoids are most common and many examples have been reported. Mesozoic and Cenozoic crinoids, the subclass Articulata, are characterized by the dominance of muscular articulations in the arms and they have only a small number of ligamentary articulations in localized positions that are specialized for autotomy. The dominance of muscular articulations is most conspicuous in the family Isocrinidae and comatulid (stalkless) crinoids. Most of the regenerated arms of articulate crinoids start on this ligamentary articulation. In contrast, most Paleozoic crinoids have many more ligamentary articulations and fewer muscular articulations in their arms than the Mesozoic to Recent crinoids. The ligamentary articulations of Paleozoic crinoids were probably not capable of autotomy. Fossil and recent stalked crinoids provide data on the degree and style of regeneration after loss of body parts. If the aboral nerve center in the basal part of crown is retained, the entire calyx and arms can be regenerated. In contrast, if the aboral nerve center is lost and only the stalk is preserved, some skeletal parts can only be generated imperfectly and irregularly. This type of imperfect regeneration is better termed as overgrowth.

The Antillean Tertiary crinoid fauna

Fossil crinoids are described from the Lesser Antilles for the first time. Crinoids are now known to occur in the Miocene of Carriacou, the Grenadines (four species), and in the Eocene and Miocene of Barbados (three species). Taxa include: isocrinid sp. indet., hyocrinid sp. indet. (both Eocene); the isocrinids Neocrinus decorus (Wyville Thomson, 1864) and Isocrinus sp., the bourgueticrinid Democrinus? sp., and the comatulid Horaeometra sp. (all Miocene). Despite the preponderance of taxa in open nomenclature, these are among the very few records of fossil crinoids from the Antillean region. Faunas are dominated by the columnals of isocrinids; bourgueticrinid and millericrinid columnals, and comatulid centrodorsals, are very rare, despite comatulids being both the most diverse crinoids in the modern fauna and the only group that occurs in shallow-water environments. Post-Eocene crinoid faunas in the Antillean region include taxa that are similar, at least at the generic level, to those of the present day. Democrinus? sp. from Carriacou is the first pre-Quaternary bourgueticrinid from the Antilles. Horaeometra sp. is the first fossil comatulid from the Antilles to be classified to generic level.The extant crinoid fauna of the tropical western Atlantic includes 23 genera/34 species of “stalkless” comatulid crinoids and eight genera/ten species of stalked crinoids. This is far greater than the known diversity of fossil crinoids from the Antillean region, which spans circa 120 Ma. The apparent rarity of fossil crinoids is probably part artefact, produced by collection bias, taphonomic effects, and the relative rarity of exposures of sedimentary units deposited in 150+ m, i.e., the environment of extant stalked crinoids.

THE ANTILLEAN TERTIARY CRINOID FAUNA

Fossil crinoids are described from the Lesser Antilles for the first time. Crinoids are now known to occur in the Miocene of Carriacou, the Grenadines (four species), and in the Eocene and Miocene of Barbados (three species). Taxa include: isocrinid sp. indet., hyocrinid sp. indet. (both Eocene); the isocrinids Neocrinus decorus (Wyville Thomson, 1864) and Isocrinus sp., the bourgueticrinid Democrinus? sp., and the comatulid Horaeometra sp. (all Miocene). Despite the preponderance of taxa in open nomenclature, these are among the very few records of fossil crinoids from the Antillean region. Faunas are dominated by the columnals of isocrinids; bourgueticrinid and millericrinid columnals, and comatulid centrodorsals, are very rare, despite comatulids being both the most diverse crinoids in the modern fauna and the only group that occurs in shallow-water environments. Post-Eocene crinoid faunas in the Antillean region include taxa that are similar, at least at the generic level, to those of the present day. Democrinus? sp. from Carriacou is the first pre-Quaternary bourgueticrinid from the Antilles. Horaeometra sp. is the first fossil comatulid from the Antilles to be classified to generic level.The extant crinoid fauna of the tropical western Atlantic includes 23 genera/34 species of “stalkless” comatulid crinoids and eight genera/ten species of stalked crinoids. This is far greater than the known diversity of fossil crinoids from the Antillean region, which spans circa 120 Ma. The apparent rarity of fossil crinoids is probably part artefact, produced by collection bias, taphonomic effects, and the relative rarity of exposures of sedimentary units deposited in 150+ m, i.e., the environment of extant stalked crinoids.