Tatsuo Oji

Larval stages of a living sea lily (stalked crinoid echinoderm).

The embryos and larvae of stalked crinoids, which are considered the most basal group of extant echinoderms, have not previously been described. In contrast, much is known about the development of the more accessible stalkless crinoids (feather stars), which are phylogenetically derived from stalked forms. Here we describe the development of a sea lily from fertilization to larval settlement. There are two successive larval stages: the first is a non-feeding auricularia stage with partly longitudinal ciliary bands (similar to the auricularia and bipinnaria larvae of holothurian and asteroid echinoderms, respectively); the second is a doliolaria larva with circumferential ciliary bands (similar to the earliest larval stage of stalkless crinoids). We suggest that a dipleurula-type larva is primitive for echinoderms and is the starting point for the evolution of additional larval forms within the phylum. From a wider evolutionary viewpoint, the demonstration that the most basal kind of echinoderm larva is a dipleurula is consistent with Garstangs auricularia theory for the phylogenetic origin of the chordate neural tube.

Is predation intensity reduced with increasing depth? Evidence from the west Atlantic stalked crinoid Endoxocrinus parrae (Gervais) and implications for the Mesozoic marine revolution

The number of regenerated arms was counted on specimens of two distinct phenotypes of the stalked crinoid Endoxocrinus parrae (Gervais) from a wide bathymetric range in the Caribbean (178-723 m). In one phenotype, the sample was divided into two groups, one from shallower (< 500 m) depths, the other from deeper (2 500 m); in the other phenotype the group divided at 550 m. In both phenotypes, the frequency of regenerated arms is significantly higher in specimens from shallower water than in those from deeper water. If the regenerated arms in Endoxocrinus parrae were the result of sublethal predation, as previously suggested, then predation intensity is higher in shallow water than deep water. These results are consistent with the idea of the late Mesozoic marine revolution-that there has been stronger predation on various invertebrates in shallow-wa- ter environments since the late Mesozoic. The stalked crinoids may have been unable to cope with increased predation in shelf environments, and they migrated to offshore environments.

Increase of shell-crushing predation recorded in fossil shell fragmentation

Abstract The Mesozoic marine revolution focuses on increased predation by durophagous (shell-crushing) predators and the concomitant evolution of prey organisms that occurred in the Mesozoic. Evidence of this predator/prey revolution is found in the appearance and increase of new types of predators that can crush hard shells of prey organisms, and is also found in the morphological changes of prey organisms, such as the appearance of a protective shell morphology of gastropods. We present new data based on the occurrence of shell fragments that indicate a slower increase in durophagous predation than has been considered previously. The results of an experiment on shell abrasion, in which shells were tumbled in barrels with sediments, indicate that incomplete bivalves and gastropods with angular margins from shallow-marine deposits can be considered as good evidence of durophagous predation. Such angular shell fragments are virtually absent from Japanese Mesozoic shell beds, whereas they are occasionally or commonly found in the Paleogene and are usually abundant in Neogene shell beds. The dominant occurrence of fossil shell fragments in the Cenozoic, as well as the data from shell abrasion experiments using tumbling barrels, indicates that wave agitation or currents do not produce shell fragments with angular margins. Such angular shell fragments are interpreted as the result of durophagous predation that has increased during Cenozoic time, and can be a useful tool in estimating durophagous predation in the fossil record. Revised data on the number of durophagous predator taxa (crustaceans and teleostean fishes) also support this conclusion.

Retrograde community structure in the late Eocene of Antarctica

Current paleobiological models hold that predators eliminated populations of epifaunal suspension feeders from shallow, soft-substrate marine environments beginning in the Mesozoic. Among the suspension feeders affected were dense populations of ophiuroids, which are rare in shallow water today, and isocrinid crinoids, which today occur only in the deep sea. The La Meseta Formation on Seymour Island, Antarctic Peninsula, represents an ecological anomaly: this deposit contains localized, autochthonous, dense assemblages of ophiuroids and isocrinids in a late Eocene, shallow-water setting. The rare occurrence of sublethal arm injuries in both the ophiuroid and crinoid populations suggests low predation levels, as seen in similar populations before the Mesozoic. Sporadic return to a Paleozoic community structure was apparently provoked by changes in temperature and productivity in Antarctica during the late Eocene.

Arm autotomy and arm branching pattern as anti-predatory adaptations in stalked and stalkless crinoids

Arm autotomy was induced in a living specimen of Metacrinus rotundus (Echinodermata: Crinoidea). An arm was autotomized at a ligamentary articulation known as a cryptosyzygy, fol- lowing incision by scissors distal to the break point. Although sessile stalked crinoids cannot entirely escape from a predatory attack by arm autotomy and they do not have an active defense, arm autotomy at cryptosyzygies reduces damage and arm loss by effective distribution, and by mini- mizing trauma and facilitating subsequent regeneration. The paradigmatic distribution of cryptosyzygies in which arm loss is set at a minimum, compared with the actual distribution, shows that these two patterns are similar and that actual specimens successfully reduce arm loss by the effective distribution of cryptosyzygies. The crinoid branching pattern also affects arm loss, and two different paradigms are discussed: anti-predatory and har- vesting. Arm branching patterns of various isocrinids have tended toward the anti-predatory con- figuration from the Jurassic to the Recent, suggesting that the isocrinids have coped with increased predation. Shallow-water comatulids generally adopt the anti-predatory paradigm in their branching pattern, whereas many deep-water, stalked crinoids adopt a harvesting paradigm, reflecting that shallow-water comatulids receive more predatory attacks than do deep-water crinoids.

Fixed, free, and fixed: the fickle phylogeny of extant Crinoidea (Echinodermata) and their Permian-Triassic origin.

Although the status of Crinoidea (sea lilies and featherstars) as sister group to all other living echinoderms is well-established, relationships among crinoids, particularly extant forms, are debated. All living species are currently placed in Articulata, which is generally accepted as the only crinoid group to survive the Permian-Triassic extinction event. Recent classifications have recognized five major extant taxa: Isocrinida, Hyocrinida, Bourgueticrinina, Comatulidina and Cyrtocrinida, plus several smaller groups with uncertain taxonomic status, e.g., Guillecrinus, Proisocrinus and Caledonicrinus. Here we infer the phylogeny of extant Crinoidea using three mitochondrial genes and two nuclear genes from 59 crinoid terminals that span the majority of extant crinoid diversity. Although there is poor support for some of the more basal nodes, and some tree topologies varied with the data used and mode of analysis, we obtain several robust results. Cyrtocrinida, Hyocrinida, Isocrinida are all recovered as clades, but two stalked crinoid groups, Bourgueticrinina and Guillecrinina, nest among the featherstars, lending support to an argument that they are paedomorphic forms. Hence, they are reduced to families within Comatulida. Proisocrinus is clearly shown to be part of Isocrinida, and Caledonicrinus may not be a bourgueticrinid. Among comatulids, tree topologies show little congruence with current taxonomy, indicating that much systematic revision is required. Relaxed molecular clock analyses with eight fossil calibration points recover Articulata with a median date to the most recent common ancestor at 231-252mya in the Middle to Upper Triassic. These analyses tend to support the hypothesis that the group is a radiation from a small clade that passed through the Permian-Triassic extinction event rather than several lineages that survived. Our tree topologies show various scenarios for the evolution of stalks and cirri in Articulata, so it is clear that further data and taxon sampling are needed to recover a more robust phylogeny of the group.

Complex tsunami waves suggested by the Cretaceous-Tertiary boundary deposit at the Moncada section, western Cuba

The Moncada Formation in western Cuba is an 2-m-thick weakly metamorphosed complex characterized by repetition of calcareous sandstone units that show overall upward fining and thinning. The Moncada Formation contains abundant shocked quartz, altered vesicular impact-melt fragments, and altered and deformed greenish grains of possible impact glass origin. In addition, a high iridium (0.8 ppb)

Photographic observations of the stalked crinoid Metacrinus rotundus Carpenter in Suruga Bay, Central Japan

Photographic observations were carried out at depths of the shelf edge at the mouth of Uchiura Inlet, Suruga Bay, central Japan in order to clarify the life style of the isocrinid stalked crinoid,Metacrinus rotundus (Echinodermata). The distribution of the species was found to be restricted to a narrow area where boulders and rock outcrops were locally present. Mean density of the crinoid was 0.05 m−2, and this value was an order of magnitude smaller than that of the deeper isocrinid,Diplocrinus wyvillethomsoni, reported from the Bay of Biscay.Metacrinus rotundus formed a parabolic filtration fan with its arms recurved into the bottom current, and was thought to be a passive suspension feeder elevating the fan into the water column by its stalk. The distal half of the stalk lay along the hard substratum and about ten groups of cirri grasped the substratum. This mode of attachment was similar to that ofCenocrinus rather than that ofDiplocrinus. Metacrinus rotundus collect food at the layer between 10 and 50 cm above the sea floor, and do not utilize a higher layer even when this layer could be utilized by climbing over a larger boulder. Resuspended benthic materials are thought to be important as a food source forM. rotundus, and the crinoids seek not only locations of stronger currents but also the position where much resuspended matter is available.

Low-diversity shallow marine benthic fauna from the Smithian of northeast Japan: paleoecologic and paleobiogeographic implications

Abstract An unusually low-diversity shallow marine benthic community in a siliciclastic setting was identified and described from the Lower Triassic (Smithian) Hiraiso Formation (Southern Kitakami Mountains, northeast Japan). The Hiraiso fauna includes bivalve species of widespread genera, such as Eumorphotis, Entolium, Bakevellia (Maizuria), Unionites, Neoschizodus, and the oldest record of the crinoid genus Holocrinus. Facies analysis enabled reconstruction of an environmental gradient ranging through storm-dominated sedimentary settings of various depths, thus allowing us to estimate the probable habitats of the shelly fossil assemblage. Regional comparison of contemporaneous shallow marine fossil localities (i.e., Southern Primorye, Maizuru Terrane, and Chichibu Terrane) demonstrated particularly striking similarity among the shallow marine benthic communities of these siliciclastic settings. We thus infer no substantial ecological recovery among these tropical shallow marine benthic communities in Smithian time.

Development and growth of the feather star Oxycomanthus japonicus to sexual maturity

Abstract Crinoids, including feather stars, are the most basal group among extant echinoderm classes and share a basic body plan. In spite of their importance for evolutionary developmental study, information on the development of crinoids has been limited, because there are not many species whose spawning season is known, and artificial spawning is impossible. Therefore, it is not easy to obtain fertilized eggs of crinoids. We have observed the spawning and development of the feather star Oxycomanthus japonicus for 7 years. We have established a cultivation system that has enabled us to culture large numbers of O. japonicus from eggs through to sexually mature adults. In the present study, we show that (1) individuals take 2 years to reach sexual maturity; (2) the skeleton of the theca of a stalked juvenile consists of five orals, five basals, five radials, five infrabasals, and an anal plate; and (3) the onset of spawning has shifted by about two weeks since 60 years ago. Our cultivation system can provide enough embryos, larvae, juveniles, and adults for further experiments, extending the possibilities for crinoid research.