摘要:

Recent work on functional morphology has revealed not only how a wide range of animals work, but shows the significance of their shapes in great detail. Also, sound evidence of evolution is provided. A new approach towards the understanding of Pycnogonida comes from an appreciation of the significance of their general habits and shapes and from the structure and mode of action of their legs. Recent fossil evidence shows that the arachnids had at least two terrestrial landings, occurring millions of years apart in time. At least two, but probably more, separate arachnid lines lived in the sea. It is concluded that pycnogonids evolved from one such aquatic group which never became terrestrial.

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1978.tb02087.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

The Devonian fossil Palaeoisopus appears, in the light of recent evidence from newly found specimens, to be much nearer extant pycnogonids than previously surmised. The fossil record of the Pycnogonida is extended to the Jurassic on the basis of a long overlooked Solenhofen example. Most of the specimens ascribed to the common Solenhofen Phalangites cannot be pycnogonids, but it is possible that we are dealing with a complex of superficially similar fossils. A revision of the classification of the fossil pycnogonids (Order Palaeopantopoda) is suggested in the light of this new material.

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1978.tb02088.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Data were collected for 45 characters from all of the published descriptions of 73 genera of living pycnogonids. Each genus was compared over all characters. equally weighted, with every other genus and similarity values were calculated by means of a restricted version of Gower's Generalized Coefficient (SG). The resulting matrix of intergeneric similarity values was subjected to principal co‐ordinate analysis followed by single nearest‐neighbour analysis at 0.5% SGintervals of the data as described by the first two vectors.Four groupings, at 82.5, 81.5 80.5 and 78.5 SG, were well defined. From this pattern was developed the hypothesis of a classification of the genera into 5 orders containing 30 families.Achelia, Ascorhynchus, Boreonymphon, PentacolossendeisandPhoxichilidium.amongst some other genera, were found to lie in unexpected systematic positions.Rhynchothoraxwas found to be widely different from all other genera.New names are proposed for certain taxa and descriptions are given of suprageneric groups.Further analysis is required to discern character state correlations within the proposed polythetic groups, so that simple keys can be constructed.The researches were supported in part by Scientific Investigations Grants administered by the Royal Society.The computations of the comparisons and the analysis were performed on the ICL 4.70 computer at Rothamsted Experimental Station and I offer my grateful thanks to Mr G. J. S. Ross of that institution for much useful advice and for guiding my data speedily through the system.Without the data there could have been no computations. Through her painstaking help and encouragement in the gathering of data from the multitude of notes and publications, my wife Patricia ensured that the study was accomplished.Without the pycnogonids and their devotees there could have been no data. My debt to scores of pycnogonid‐enthusiasts for their discoveries is self‐evident. However, without Joel Hedgpeth's example and his persisting and friendly encouragement, the joys of pycnogonid studies would have el

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1978.tb02089.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Food choice experiments were carried out with three species of pycnogonids:Nymphon rubrum, N. gracile, andEndeis spinosa.Running sea‐water that had circulated over different possible food‐sources (hydroids, actiniarians, octocorals, synascidians) was offered to the pycnogonids at one side of a basin, pure sea‐water or sea‐water that had flowed over a different source of food at the other.The experiments, though few in number, seemed to indicate that:(1) Pycnogonids are capable of detecting the presence or absence of various coelenterate species.(2) They are able to discriminate between different food‐sources, i.e. the nature of the chemical substances produced by the food determines the degree of attraction.(3) The preferential sequence for the three pycnogonids tested is:Nymphon rubrumprefersDynamenaoverTubulariaandLaomedea; these are preferred overActiniaandMetridium; there is no attraction toAlcyonium. Nymphon gracileprefersLaomedeaoverDynamena. Endeis spinosaprefersLaomedeaoverDynamena; these are preferred overActinia; there is no attraction toMorchellium.(4) Experimental amputation of appendages indicates a high probability that the chemo‐receptors of the pycnogonids are not located on the chelifores, palps, or ovigers. They may be located (a) all over the body, possibly in innervated epidermal bristles; and/or (b) in the distal part of the proboscis, bearing sensory setae; and/or (c) on the w

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1978.tb02090.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

The process of digestion was studied in some polar pycnogonids, mainly the Antarctic formsNymphon australeandNymphon orcadense.Our findings did not support the theory of the digestive process proposed by Schlottke (1933) and this led to a re‐examination of his ideas. We propose a new scheme for digestion in pycnogonids and fit Schlottke's observations into this framework. It is suggested that Antarctic pycnogonids may possess behavioural adaptations peculiar to their supply of food. Some directions for further study are indicate

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1978.tb02091.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

A new species of ammotheid pycnogonid(Ascorhynchus endoparasiticussp. nov.) has been found parasitic inside the pallial cavity of an opisthobranchiate mollusc (Scaphander punctostriatus) from the Azores. One adult and three young individuals were living in three different molluscs, probably feeding upon the rectum contents of their hosts.Many features of the parasites' morphology show various adaptations to this curious habitat.

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1978.tb02092.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

There is little information concerning the reproductive biology of the Pycnogonida. Information obtained by the authors concerning the female reproductive system of British pycnogonids is discussed and evaluated.Oögenesis and vitellogenesis are similar to the processes described in some annelids and crustaceans. Vitellogenesis contrasts with the process in insects where the majority of the yolk is produced extra‐oöcytically and is transported to the developing oocyte, whereas in the Pycnogonida the majority of the yolk is produced intra‐öocytically with only a small extra‐oocyte contribution. This represents a fairly primitive arthropodan type of vitellogenesis.The reproductive cycles of several British pycnogonid species have been studied by regular sampling at different localities over long periods of time. This has provided information on population dynamics, particularly life‐span, migratory movements and fecundity.Although similarities exist between species there are also marked differences in that some species produce only a single new generation each year, whereas in others the presence of a second population of mature ova in the same year may enable the production of a second brood, if conditions are

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1978.tb02093.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

A large sample of the pycriogonidAnoplodactylus portus, collected from the Pacific side of the Panama Canal Zone, contains a high percentage of gynandromorphs. The literature on aquatic arthropod gynandromorphs is outlined. The nature and variations of the sexual mosaic population are described and discussed. The several morphological differences between normal and mosaic members of the population are illustrated, and the possible origin of these gynandromorphs is discussed.

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1978.tb02094.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Patterns of walking, modes of joint movement, and individual limb diversity were analysed with the aid of ciné film of several living Antarctic pycnogonids, including the 8‐leggedColossendeis australis, C. angusta, Pallenopsis patagonica, andNymphonsp., the 10‐leggedDecolopoda australis, and the 12‐leggedDodecolopoda mawsoni.Appendage musculature of several of these species and also of the 10‐leggedPentapycnon charcotiandPentanymphon antarcticurnwas dissected. At least two distinct morphotypes were identified: a short‐legged, crawling variety (P. charcoti); and the more typical long‐legged, large bodied, walking forms. No gross differences in musculature of joints were noted in the species examined. All joints are, at least superficially, hinge joints. The coxa‐body joint is largely immobile, the coxa 1‐coxa 2 joint alone exhibits promotion‐remotion and all other joints are flexion‐extension joints. The 8‐legged forms move in an imprecise manner, there being irregularity of leg raising and lowering and where legs touch down in relation to the body and to other legs. The 10‐ and 12‐legged forms exhibit more precise patterns of metachronal leg movements. Although legs move in a basic promotion‐remotion, extension‐flexion mode, there is a certain degree of twisting of a leg as it is picked up, brought forward, and set down; models indicating how such joint movement occurs were constructed. The possibility that hydrostatic pressure is employed in extension is considered and is found to be remote. Lateral placement of legs, orientated in almost all directions in the horizontal plane of the trunk, achieves a versatility of movement similar to that in crabs. Comments on pycnogonid ta

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1978.tb02095.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

The transportation off‐shore of the littoral pycnogonidNymphon gracileduring the winter months is facilitated by the ebb tide swimming of this otherwise benthic animal. The energy cost of migration has been estimated from measurements of oxygen consumption and drag forces acting on the different segments of the leg during swimming. The swimming patterns ofN. gracileboth under constant conditions and in response to tidal pressure cycles are considered in relation to the animals' energy reserve

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1978.tb02096.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY