Marginal Plates Research Articles

The ontogeny of cinctans (stem‐group Echinodermata) as revealed by a new genus,GraciaCystis, from the middle Cambrian of Spain

Abstract: A new cinctan echinoderm,Graciacystis ambiguagen. et sp. nov. from Cambrian Series 3 rocks of Spain, is described based on more than 100 articulated specimens that range from 6 to 14.5 mm in thecal length. This material shows thatGraciacystis ambigua, while plastic in thecal shape, is highly conservative in its thecal construction, with a fixed number of marginal plates and very limited addition of plates in the stele and ventral membrane through ontogeny. Ventral swellings on marginal elements are absent from the smallest specimens and become gradually more marked during growth. A cladistic analysis showsGraciacystisto be a basal cinctan, more derived thanSotocinctusand the Trochocystitidae and as sister group to a large clade formed by Sucocystidae + Gyrocystidae. The determinate growth pattern seen inGraciacystisseems to be the general pattern for all cinctans.

A new species of Neoferdina and three new records of sea stars (Echinodermata: Asteroidea) collected from Kumejima Island, southwestern Japan

Sea stars were collected at depths ranging from 91 to 160 m around Kumejima Island situated in the middle of the RyukyuIslands chain in the Western Pacific. Sampling was carried out using a dredge or beam trawl in November 2009, as partof the KUMEJIMA 2009 Expedition. The specimens included an undescribed species of the genus Neoferdina, and threespecies that have never been reported in Japanese waters. Features that characterise this new species, Neoferdina longi-brachia, include: extremely long and narrow arms, no alternating arrangement of large and small superomarginal plates,body surface (except for the marginal plates) completely covered with granules, and an adambulacral armature with 3 furrow spines.

Morphologic and systematic revision of the solute Maennilia estonica (Homoiostelea, Echinodermata) from the Upper Ordovician of Estonia

Maennilia estonica Rozhnov and Jefferies was first described as a stem-chordate but restudy shows it is an unusually large homoiostelean echinoderm. Its feeding structure, an erect ambulacrum, extending exothecally from the peristomial frame plates, bears a large internal tunnel that opens directly into the body cavity. This type of feeding appendage is now recognized to be unique to homoiosteles. It bears no evidence for water vascular system impressions adjacent to its food groove. The theca has poorly developed marginal plates and a narrow rim that, in contrast to some other homoiosteles, does not extend over either lower or upper thecal face. Maennilia appears to have inhabited the deeper portions of a near-shore environment in limey muds adjacent to a linear zone of bryozoan and microbial bioherms.

Roles of EphB3/ephrin-B1 in feather morphogenesis

The ephrin receptor (Eph) tyrosine kinases and their ephrin ligands are involved in morphogenesis during organ formation. We studied their role in feather morphogenesis, focusing on ephrin-B1 and its receptor EphB3. Early in feather development, ephrin-B1 mRNA and protein were found to be expressed in the dermal condensation, but not in the inter-bud mesenchyme. Later, in feather buds, expression was found in both the epithelium and mesenchyme. In the feather follicle, ephrin-B1 protein expression was found to be enriched in the feather filament epithelium and in the marginal plate which sets the boundary between the barb ridges. EphB3 mRNA was also expressed in epithelia. In the feather bud, its expression was restricted to the posterior bud. In the follicle, its expression formed a circle at the bud base which may set the boundary between bud and inter-bud domains. Perturbation with ephrin-B1/Fc altered feather primordia segregation and feather bud elongation. Analyses revealed that ephrin-B1/Fc caused three types of changes: blurred placode boundaries with loose dermal condensations, incomplete follicle invagination with less compact dermal papillae, and aberrant barb ridge patterning in feather filament morphogenesis. Thus, while ephrin-B1 suppression does not inhibit the initial emergence of a new epithelial domain, Eph/ephrin-B1 interaction is required for its proper completion. Consequently, we propose that interaction between ephrin-B1 and its receptor is involved in boundary stabilization during feather morphogenesis.

Henricia pumila sp. nov.: A brooding seastar (Asteroidea) from the coastal northeastern Pacific

A small species of the seastar genus Henricia Gray, 1840 occurs along the cool temperate Pacific coast of North America from near Sitka, Alaska to just south of Ensenada, Baja California, Mexico. Its small adult size, mottled aboral colors, and benthic external brooding reproductive mode have long been noted, but it has never been formally separated from the larger, free-spawning Henricia leviuscula (Stimpson, 1857), with which it has been confused. Here we amplify the description of H. leviuscula, based on examination of the holotype and new specimens, and restrict it to only one of several similar species that co-occur in Puget Sound and vicinity. We also describe the small mottled brooder as Henricia pumila sp. nov., characterize its distribution, and contrast its morphology with H. leviuscula based on the arrangement of marginal plates and the microanatomy of aboral spines.

The morphology ofYujiangolepis liujingensis(Placodermi, Arthrodira) from the Pragian of Guangxi (south China) and its phylogenetic significance

The morphology of the arthrodire placoderm Yujiangolepis liujingensis Wang, Pan & Wang, 1998, from the Lower Devonian of Guangxi is redescribed, and compared to that of the basal arthrodires Antarctaspis White, 1968 from Antarctica, Toombalepis Young & Goujet, 2003 and Wuttagoonaspis Ritchie, 1973 from Australia, and Yiminaspis Dupret, 2008 from south China. A very small plate of the skull roof at the junction of the nuchal, marginal, postorbital, and paranuchal plates is considered as the vestigial homologue of the anterior paranuchal plate in the Petalichthyida and Acanthothoraci. Yujiangolepis is attributed to the family ‘Antarctaspididae’ White, 1968, together with the genera Antarctaspis and Toombalepis. A computerized phylogenetic analysis resolved Yujiangolepis as the most basal arthrodire, and the family ‘Antarctaspididae’ appears paraphyletic, Yujiangolepis being possibly the most basal. The family Wuttagoonaspididae contains the genera Wuttagoonaspis and Yiminaspis, and remains monophyletic. A Chinese origin of the ‘Antarctaspididae’ is proposed, together with a southward dispersal into Gondwana during the Early Emsian.

New stylophorans (Echinodermata) from the upper Cambrian of Guangxi, South China

This paper describes for the first time the cornute stylophorans (Echinodermata) in China. The new material came from the Guole Formation of the Furongian (Late Cambrian) in the Guole area of Jingxi, Guangxi Province, South China. These new cornute specimens are preserved in situ and found along with well-preserved trilobites and brachiopods. One new species, Phyllocystis jingxiensis sp. nov., is proposed to accommodate these unusual materials. The new species is defined by the small, heart-shaped theca with the frame composed of ten narrow, smooth and thick marginal plates, three adoral plates and distinctive zygal and aulacophore. Both supracentrals and infracentrals are polygonal-outlined. The marginal plate M1′ on the inferior face extends posteriorly to form zygal that possesses a broadened proximal end and the proximal portion joining with the conjunction between M4 and M5 on the inferior face. Aulacophore comprises ten segments at its proximal part and is conical at the middle part (named stylocone). Its distal portion is rather long and bears conspicuous ambulacrum grooves. Tectals are horizontally arranged on superior face and obliquely arranged on inferior face. Both cothurnopore and anal pyramid are vaguely seen on the right anterior corner and the extremity of theca’s superior face.

A new species in the genus Ophiomyxa from South-west Australian waters (Echinodermata: Ophiuroidea: Ophiomyxidae)

Franklin, A.M. and O'Hara, T.D. 2008. A new species in the genus Ophiomyxa from South-west Australian waters (Echinodermata: Ophiuroidea: Ophiomyxidae). Memoirs of Museum Victoria 65: 57–62. A new species is described from the genus Ophiomyxa collected from south-west Australia. It is distinguished by the lack of marginal plates, three arm spines, the uppermost reaching up to 2 segments in length, and a characteristic pattern of reduced dorsal arm plates. Current evidence suggests it is endemic to waters around 400m deep off the coast of south-western Australia.

Gorgonians (Anthozoa: Octocorallia) of the northwestern Sea of Japan

Three species of gorgonians (Primnoa pacifica, Calcigorgia japonica, and Thouarella superba) are reported as new records for the northwestern Sea of Japan; one of them (Calcigorgia japonica sp. n.) has been described as a new species. Variations of colony morphology in some species are described; the taxonomical value of specific characters is discussed. The geographical range of Primnoa pacifica in the northwestern Pacific is shown to be wider than was considered earlier. Variations of sclerite morphology (number of marginal plates, presence of additional basal plates, and number of marginal spines on the basal plate) are regarded as intracolonial or intraspecific variability. The distribution range of Thouarella superba described earlier from the Aleutian Islands (Nutting, 1912) was shown to extend into the low-boreal part of the boreal Pacific. An examined specimen of Paragorgia sp. differed from all known species and appeared similar only to P. regalis Nutting, 1912 reported from the eastern coast of Japan. The most distinctive characters of Calcigorgia japonica sp. n. were the shape of polyp, with a thin lower part looking like folded podia (in fixed specimens) and the presence of two types of clubs scattered among the sclerites of the polyp.

ABNORMALITIES IN THE LOWER ORDOVICIAN CORNUTE PHYLLOCYSTIS THORAL, 1935 (ECHINODERMATA: STYLOPHORA) FROM MONTAGNE NOIRE (SOUTHERN FRANCE): IMPLICATIONS FOR PLATE HOMOLOGY AND PHYLOGENY

Two specimens of the cornute Phyllocystis crassimarginataThoral, 1935 from the Lower Ordovician of Southern Montagne Noire (Languedoc, France) showing abnormal numbers of marginal plates are described. The first one (UM 310) is characterized by the insertion of one extra plate between the fourth right marginal and the zygal plate Z. Comparison with a new, undescribed Tremadoc boot-shaped cornute suggests that 1) the extra plate of UM 310 is equivalent to M4, and 2) the three right marginals located between M1 and Z in “normal” specimens of Phyllocystis can be identified as M2, Mc, and M3. Plate configurations of the right thecal margin are thus identical in “normal” Phyllocystis, chauvelicystids, and cothurnocystids. This result indicates that Phyllocystis is probably more closely related to these two clades than to scotiaecystids. Consequently, the identification of the four marginals forming the left thecal margin of Phyllocystis (M′2, M′3, M′5, and M5) is deduced from a comparison with the cothurnocystid plate pattern. The second abnormal specimen of P. crassimarginata (R64546) is characterized by the loss of M′3. It confirms that reduction in the number of marginals is a general trend in boot-shaped cornutes.

Cell interactions in barb ridges of developing chick downfeather and the origin of feather branching

The epidermis of developing feathers comprises outer and inner periderm, subperiderm and germinal layer. The inner periderm gives origin to sheath and barb ridge vane cells that contain alpha‐keratin and form a belt around feather filaments. This produces mechanical resistance, forcing the inner epidermal cell layers to fold inward and form barb ridges. Mesenchymal‐epidermal contacts occur from the mesenchymal core to external regions of barb ridges and involve thin cytoplasmic processes (filopodia) from mesenchymal cells. Subperiderm cells produce feather keratin that remains in derived barb and barbule cells displaced into two barbule plates and a ramus. Barb medullary cells undergo lipid degeneration while barbule cells accumulate feather keratin and cornify. Supporting cells surround barb and barbule cells and later degenerate leaving separate barbules, while marginal plate cells disappear leaving separate barbs. Caspase‐3, a marker for apoptosis, is absent in cells of barb ridges. Degenerating cells in developing feathers are eliminated by necrosis following vascular retraction. Caspase‐14 is present in cornifying sheath cells as well as in the corneous layer of the follicular epidermis. The sheath detaches from barbs through the formation of a sloughing layer. The differentiation of supporting cells among barb/barbule cells allows the origin and evolution of the branching pattern of feathers.

Signs of predation in the Middle Jurassic of south‐central Poland: evidence from echinoderm taphonomy

Distinct faunal aggregates are described from the Middle Jurassic (uppermost Bajocian/lowermost Bathonian and Middle Bathonian) clay deposits of Częstochowa area, south-central Poland. These aggregates are composed of molluscs (scaphopods, gastropods, bivalves, ammonites and belemnites), articulate brachiopods and echinoderms (asteroids, crinoids and echinoids). A large percentage of the fossils, especially bivalves, are fragmented, but some fossils are complete. Although most of the fossils are crushed and fragmented, they are still identifiable to at least the genus level. Thorough statistical analysis of taphonomic features indicates that the preservation of asteroid marginal plates is distinct from the ossicles derived from the host clays. The high frequency of bite marks and the good state of preservation suggest that the accumulations are the products of predation activities and most probably are the effect of regurgitation. Taking into account the rich and diverse fauna, the predator was a bottom-feeding generalist. Possible predators include palaeospinacid sharks, a tooth of which was collected from the same bedding surface, but not associated with regurgitated remains. Although the bite marks on the asteroid ossicles point to sharks as potential producers of regurgitates, other vertebrates, like durophagous pycnodontiform fish, cannot be excluded.

Cell organization of barb ridges in regenerating feathers of the quail: implications of the elongation of barb ridges for the evolution and diversification of feathers

AbstractThis ultrastructural study on the regenerating feathers of quail describes the cellular organization of the barb ridges responsible for the ramification of adult feathers. Bilateral symmetry of the barb ridges determines the organization of feather cells into feather branching. The length of the barb ridges, derived from the number of cells associated to form the barbule plates, determines the length of the barbule branching. Long chains of barb cells form long barbs that branch from the rachis with an increase of feather size. Supportive cells function as spacers between the barbule cells. New cells derive from stem cells localized in the collar region of the feather follicle, as indicated from the re‐organization of collar cells into barb ridges (a morphogenetic process inherited from that of embryonic feathers), production of an embryonic type of keratin (feather keratin), permanence of periderm granules (typical embryonic organelles) in barb vane ridge cells. Variations in the process of barb ridge morphogenesis allow the fusion of ridges into a rachis. The differentiation of hooklets contributes to the origin of planar feathers. Separation between rachis and merging barb ridges is by supportive cells, derived from the marginal plates of the barb ridges. Speculations on the evolution and diversification of feathers are presented.

Wedge cells during regeneration of juvenile and adult feathers and their role in carving out the branching pattern of barbs

The present ultrastructural study on regenerating feathers emphasizes the role of supportive cells in determining the branching pattern of barbs. Supportive cells are localized among developing barb and barbule cells, in marginal plates, and underneath the feather sheath, and their differentiative fate, in general, is a form of lipid degeneration. The Latter process determines the carving out of barb branching in both downfeathers and pennaceous feathers. In the latter feathers, some supportive cells (barb vane cells and cylindrical cells of marginal plates) degenerate within each barb ridge leaving separate barbules. Other supportive cells, here termed wedge cells, form columns of cornified material that merge into elongated corneous scaffolds localized among barbs and the rachis. This previously undescribed form of cornification of supportive cells derives from the aggregation of periderm and dense granules present in wedge cells. The latter cells give origin to a corneous material different from feather keratin that may initially sustain the early and soft barbules. After barbules are cornified the supportive cells scaffolds are eventually sloughed as the sheath breaks allowing the new feather to open up and form a planar vane. The corneous material of wedge cells may also contribute to molding of the overlapped nodes of barbule cells that form lateral spines or hooklets in mature barbules. Eventually, the disappearance of wedge cell scaffolding determines the regular spacing of barbs attached to the rachis in order to form a close vane.

Cell structure of developing downfeathers in the zebrafinch with emphasis on barb ridge morphogenesis

The present ultrastructural and immunocytochemical study on the embryonic feathers of the zebrafinch, an altricial passerine bird, describes cellular differentiation of developing downfeathers. Barb ridges are folds of the original epidermis of the embryonic feather germ in which the basal-apical polarity of epidermal cells is upset. The result is the loss of most germinal activity of basal cells of the barb ridges so that only the embryonic epidermal layers remain. The more external layer is the primary periderm, followed by 4-6 layers of inner-periderm cells that mature into feather sheath and barb vane ridge cells. The following layer, the subperiderm, produces a small type of beta-keratin typical of feathers. In barb ridges, the subperiderm layer is displaced to form barbule plates and barb cells. The formation of branching barbules occurs by the presence of barb vane ridge cells that function as spacers between barbule cells. The fourth layer is homologous to the germinal layer of the epidermis, but in barb ridges it rapidly loses the germinal capability and becomes the cyclindrical layer of marginal plates. The study indicates that a necrotic process determines the carving out of the final feather shape, although apoptosis may also play a role. In fact, after barb and barbule cells have formed a keratinized syncitium, retraction of the vascular bed determines anoxia with the resultant necrosis of all feather cells. Only those of the keratinized syncitium remain to form the feather while supportive cells disappear. The sheath covering the barb and barbule syncitium is lost by the formation of a sloughing layer following degeneration of external barb ridge vane cells and loss of the sheath. It is proposed that the evolution of the morphogenetic process of barb ridge formation was peculiar to tubular outgrowths of the integument of archosaurian reptiles that evolved into birds. Once established in the embryonic programmes of skin morphogenesis of ancient birds, variations in the process of barb ridge morphogenesis allowed the fusion of ridges into large or branched ridges that originated the rachis. This process produced pennaceous feathers, among which were those later used for flight. The present study stresses that the morphogenetic process of barb ridge formation determines the concomitant appearance of barbs and barbules. As a consequence, intermediate forms of evolving feathers with only barbs but not barbules are unlikely or are derived from alteration of the above basic morphogenetic mechanism.

Sculpting skin appendages out of epidermal layers via temporally and spatially regulated apoptotic events.

Complex skin appendages are built from the epidermal cells through various cell events. Here we used TUNEL and caspase-3 immuno-localization to examine apoptosis in feather morphogenesis. We deduced three modes. In Mode 1A, apoptosis occurs within the localized growth zone (LoGZ) to regulate growth (feather buds). In Mode 1B, morphogen secreting cells are present adjacent to LoGZ and apoptosis may work to remove such signaling centers (barb ridges). In Mode 2, keratinocytes apoptosed before terminal differentiation and left spaces between branches (marginal plate). In Mode 3A, keratinocytes cornified and flaked off to free skin appendages (feather sheath, pulp epithelium). In Mode 3B, keratinized apoptosed epithelial cells became permanent structures (rachis, ramus, barbules). Thus, different apoptotic modes can have different impacts on morphogenesis. We further tested effects of imbalanced Shh on apoptosis. Shh suppression reduced marginal plate apoptosis and caused abnormal differentiation of barbule plates. Shh over-expression enhanced proliferation in barb ridges. Expression of Patched in the barbule plate epithelia implies a paracrine mechanism. The current work complements our recent work on LoGZ to show how adding and removing cell masses in temporally and spatially specific ways are coordinated to sculpt skin appendages from epidermal layers.

Microeledone mangoldi n. gen. and n. sp., a deep-water pygmy octopus from the Norfolk Ridge, New Caledonia (Cephalopoda:Octopodidae)

Microeledone mangoldi n. gen. and n. sp. is described from a male specimen collected from approximately one kilometre deep on the Norfolk Ridge south of New Caledonia in the south-west Pacific Ocean. This tiny octopus is characterised by a single row of suckers that are functional to the tips of the arms, the absence of an ink sac, the presence of a pair of chitinous stylets, a UU-shaped funnel organ, a copulatory organ with distinct ligula and calamus, and a distinctive radula. The radula has seven teeth per row. The unique central (rachidian) tooth has a long, sharp mesocone with a curved and grooved tip. The remaining rows of teeth are also unique, being flattened and plate-like. Marginal plates are absent. The body is smooth, without papillae, cartilaginous tubercles, or a lateral ridge. Functional chromatophores are absent. This octopus appears related to several other genera of deep-sea octopods with a single row of suckers, namely Thaumeledone Robson, 1930, Bentheledone Robson, 1932 and Graneledone Joubin, 1918, to which the new genus is compared. Definitions of the genus Thaumeledone are reviewed.

Carcinization in the Anomura – fact or fiction? II. Evidence from larval, megalopal and early juvenile morphology

In this second of a two-part series, carcinization in the Anomura has been reviewed from early juvenile, megalopal, and larval perspectives. Data from megalopal and early juvenile development in ten genera of the Lithodidae have provided unequivocal evidence that earlier hypotheses regarding evolution of the king crab pleon were erroneous. A pattern of sundering, and decalcification has been traced from the megalopal stage through several early crabs stages in species of Lithodes and Paralomis, with supplemental evidence from species in eight other genera. Of major significance has been the attention directed to the Marginal plates of the second pleomere, which when separeted in lithodids are not homologous with the adult so-called “marginal plates” of the following three tergites. Auxiliary megalopal and early juvenile lithodid data, as well as equivalent data from other paguroids, support the evolutionary direction indicated by lithodid pleonal plate development. Therefore, while carcinization, or development of a crab-like body form, has occurred in the Lithodidae, it has not proceeded from a hermit crab ancestor. Rather the data suggest the reverse, thus effectively refuting the “hermit to king” myth. Brief reviews of data available from the Lomisidae and Porcellanidae support the proposition of independent anomuran carcinization events in these taxa as well. Results of cladistic analysis of megalopal and juvenile data, although somewhat unconventional, do not support the claim of a sister-group relation of the lithodid genera Lithodes and Paralithodes with the pagurid genus Pagurus. Attempts to subject larval phase data to similar analysis were thwarted by the tendency in paguroids, including lithodids, for lecithotrophic development. Additionally, presumed initial and terminal stage deletions disallow the ontogenetic stage homologies required for meaningful phylogenetic results.

Groenlandaspidid placoderm fishes from the Late Devonian of North America

Two new taxa of groenlandaspidid fish (Placodermi: Arthrodira) from non-marine deposits of the Catskill Formation (Upper Devonian) at Red Hill, Clinton County, Pennsylvania, USA, are the first to be described from North America outside of Greenland. Groenlandaspis pennsylvanica n.sp. is known only from isolated trunk elements that are quite similar to Groenlandaspis antarctica Ritchie, 1975. Groenlandaspis pennsylvanica n.sp. is characterized by distinct features of the median dorsal (MD), posterior dorsolateral (PDL), and anterior dorsolateral (ADL) plates. Turrisaspis elektor n.gen. and n.sp. is a smaller form with a high median dorsal plate (MD) and tall, narrow elements of the dorsolateral trunk shield, particularly the PDL, giving this taxon a distinctively short, high trunk shield. The head shield of Turrisaspis elektor has a divided pineal plate and the postmarginal plate makes contact with the postorbital plate, excluding the marginal plate from the lateral margin of the head shield. Groenlandaspis pennsylvanica n.sp. is a rare faunal component at the Red Hill site whereas Turrisaspis elektor is very common. The large sample size of Turrisaspis elektor provides a glimpse at ontogenetic and individual variation within this taxon.

Re-evaluation of Graneledone setebos (Cephalopoda: Octopodidae) and allocation to the genus Megaleledone

The holotype of the Antarctic octopodid Graneledone setebos was re-examined and found to lack the epidermal warts characteristic of the genus Graneledone. It is similar in its large size to another Southern Ocean species, Megaleledonesenoi. A comparative study of G. setebos and specimens attributed to M. senoi led us to conclude that M. senoi is a junior synonym of G. setebos. Although M. senoi is not valid, the genus Megaleledone can be separated from other genera by the structure of the radula (which lacks marginal plates) and we therefore consider the genus to be valid. We propose the new combination of Megaleledone setebos and have refigured the beaks and radula of the holotype herein and expanded the description. A search of museum specimens and the literature shows that Megaleledone setebos is more common in Antarctic waters than previously supposed.