摘要:

Three new specimens which preserve the soft parts of conodonts are described from the Lower Carboniferous of Granton, Edinburgh. The animal was apparently laterally flattened in life and the somites were V‐shaped. The nature of the preserved axial lines is equivocal; some may represent the walls of the gut. The elements of one of the new specimens show that it does not belong toClydagnathus, to which the other soft‐bodied specimen from Granton was tentatively assigned. The possibility of a relationship between the euconodonts and the Chaetognatha is discounted. Nor do the conodonts constitute a phylum, but are a separate group of primitive jawless crania

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb00741.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb00742.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Rhabdotubus johanssonin.gen., n.sp., is described from the early Middle CambrianEccaparadoxides pinusZone of Närke, southern Sweden. The colonies encrusted shells of inarticulate brachiopods, and occasionally trilobites, on otherwise soft substrates. The tubarium consists of repent and erect tubes. The former branch irregularly and produce a thecorhiza‐like structure; the latter are erect and mostly isolated, up to 10 mm in length and widening gradually to about 1 mm width. Both repent and erect tubes are composed of fusellar bands, mostly irregularly arranged. Branching of repent tubes takes place through resorption or perforation of fusellar tissue in the parent tube. Branching of erect tubes occurs sporadically. There is no thecal dimorphism. No sclerotized stolon is present.Rhabdotubusis interpreted as the earnest known rhabdopleurid (Class Pterobranchia, Phylum Hemichordata). In general habitus it is similar to sessile graptolites of the Order Tuboidea. These similarities may well have phylogenetic significance, but further knowledge of the Tuboidea and other sessile orders of the Graptolithina is required to clarify the early evolution of graptolit

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb00743.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

In the dorsal median anterior region of the head, the larvae of decapod Crustacea possess a discrete organ: a glandular‐sensory complex which is not present in post‐larval juvenile forms. Its external topography reveals the presence of one or two central pores (Brachyura, Anomura) or a poreless central area (Macrura) surrounded by four equidistant plate‐pits which contain a central pimple or ‘nipple’. The Macrura plate‐pits lack the central pimple but develop a row of diminutive pegs. No definite function can yet be ascribed to the organ. The dorsal organ described here in Decapoda larvae closely resembles the median sensory tubercle found on the cephalon of some trilobites, especially Trinucleidae. In view of the possible homology between these structures in the two groups, previous interpretation of the trilobite organ as a median eye tubercle must

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb00744.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb00745.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

The trilobiteAmpyxina bellatula(Savage) occurs in monospecific accumulations within dolomitic strata of the shaly Upper Ordovician Maquoketa Group of northeastern Missouri. A dolomitic stratum containing 97 complete individuals and considerable amounts of pyrite exhibited no associated benthic megafauna. The strata appear to be equivalent to the Scales Formation of the Maquoketa Group of northern Illinois and eastern Iowa which have been interpreted as having been deposited in a muddy environment with severe circulation restrictions. The presence of the monospecific trilobite association in what otherwise would be an unfossiliferous stratigraphic sequence is interpreted as being the result of opportunistic strategy by this trilobite in a resource‐rich unstable environmental setting. The association was apparently cat‐astrophically buried, thus preserving the age structure of the holaspid population. A size‐distribution histogram of the holaspid population indicates that reproduction may have occurred in periodic bursts with lesser reproductive events occurring during the intervening periods. Holaspid survivorship information indicates that mortality was low during the early holaspid stage and increased with age. Anomalous single bed trilobite accumulations of various age rocks have been documented by numerous authors. These may in part be analogous to theAmpyxinaoccurrence in the Maquoketa Group of Missouri, and be attributable to opportunistic strat

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb00746.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb00747.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Semitubina sakoin. sp. from the late Silurian of Japan represents the second species of this genus and also the first record of a Silurian gastropod in Japan. The gastropod shells occur in a thin mudstone bed and were found to be encrusted exclusively by corallites of? Favositessp. These corallites reveal that encrustation proceeded as the gastropod shells grew. The ecological relationship between the two organisms is considered to be symbiotic. This mode of life allowed the coral to live on a muddy substrate because clear sea water passed over the colony as the gastropod moved along. The gastropod benefited from this relationship by being protected from shell‐boring or shell‐crushing predators by the encrusting corallite. InSemitubina sakoithe body whorl is separated from the penultimate one by a considerable gap in a later growth stage andS. sakoihas been cited as one of the uncoiled gastropods. The uncoiling of this gastropod results primarily from rapidly increasing whorl translation rate in the latest growth stage. Taking the symbiotic relationship with? Favositessp. into consideration, a deposit feeding or benthic scavenging mode of life is suggested for this gastro

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb00748.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb00749.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Remains of jawed polychaetes were recovered from stomach contents of queen triggerfish (Balistes vetulaL.) collected by spearing from Came Bow Cay, Belize, Central America. Jaws in the nereidids, glycerids, and arabellids recovered are perfectly preserved, and might be passed by the fish without noticeable alteration. Jaws in the onuphids are fully articulated, but the outer wall‐layer has been digested away, leaving only the inner aragonitic layer intact. A low fossilization potential for onuphid jaws is indicated, consistent with laboratory studies of jaw composition. Based on literature accounts, fish predation may have a considerable influence on polychaete jaw (scolecodont) assemblages in sedimen

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb00750.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY