| 1. |
- Altenburger, Andreas, et al.
(författare)
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Metamorphosis in Craniiformea revisited : Novocrania anomala shows delayed development of the ventral valve
- 2013
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Ingår i: Zoomorphology. - : Springer Science and Business Media LLC. - 0720-213X .- 1432-234X. ; 132:4, s. 379-387
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Tidskriftsartikel (refereegranskat)abstract
- We revisited the brachiopod fold hypothesis and investigated metamorphosis in the craniiform brachiopod Novocrania anomala. Larval development is lecithotrophic and the dorsal (brachial) valve is secreted by dorsal epithelia. We found that the juvenile ventral valve, which consists only of a thin layer that was previously described as periostracal, is not a valve and is not secreted by the same epithelia as the dorsal valve. It is secreted by the attachment area of the larva at the posterior-most tip of the posterior larval lobe. The same attachment area is used by larvae of rhynchonelliform brachiopods during metamorphosis to cement their pedicle to the substrate. N. anomala is therefore not initially attached by a valve but by material corresponding to pedicle cuticle. This is different to previous descriptions, which had led to speculations about a folding event in the evolution of Brachiopoda. We show that the “brachiopod fold hypothesis,” which argues that brachiopods are transversely “folded” across the ontogenetic anterior–posterior axis, should be rejected at least with respect to the craniiforms. The data now suggest that the Craniiformea may be a derived group within the Rhynchonelliformea. This interpretation suggests that the last common ancestor of the Craniiformea has lost the pedicle and the ventral valve in early juvenile development. Characters that have previously been considered to be shared between the Craniiformea and the Linguliformea (clade Inarticulata), such as a through-gut and missing hinge articulation, may thus be secondarily derived characters of the Craniiformea within the Rhynchonelliformea.
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| 2. |
- Biressi, A., et al.
(författare)
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Wound healing and arm regeneration in Ophioderma longicaudum and Amphiura filiformis (Ophiuroidea, Echinodermata): comparative morphogenesis and histogenesis
- 2010
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Ingår i: Zoomorphology. - : Springer Science and Business Media LLC. - 0720-213X .- 1432-234X. ; 129:1, s. 1-19
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Tidskriftsartikel (refereegranskat)abstract
- All species of the Ophiuroidea have exceptional regenerative capabilities; in particular, they can replace arms lost following traumatic or self-induced amputation. In order to reconstruct this complex phenomenon, we studied arm regeneration in two different ophiuroids, Ophioderma longicaudum (Retzius, 1805) and Amphiura filiformis O. F. Muller, 1776, which are quite distantly related. These species present contrasting regeneration and differentiation rates and differ in several ecological traits. The aim of this paper is to interpret the primary sequence of morphogenetic and histogenetic events leading to the complete reconstruction of a new arm, comparing the arm regenerative processes of these two ophiuroid species with those described in crinoids. Arm regeneration in ophiuroids is considered an epimorphic process in which new structures develop from a typical blastema formed from an accumulation of presumptive undifferentiated cells. Our results showed that although very different in some respects such as, for instance, the regeneration rate (0.17 mm/week for O. longicaudum and 0.99 mm/week for A. filiformis), morphogenetic and histogenetic aspects are surprisingly similar in both species. The regenerative process presents similar characteristics and follows a developmental scheme which can be subdivided into four phases: a repair phase, an early regenerative phase, an intermediate regenerative phase and an advanced regenerative phase. In terms of histogenesis, the regenerative events involve the development of new structures from migratory pluripotent cells, which proliferate actively, in addition in both cases there is a significant contribution from dedifferentiated cells, in particular dedifferentiating myocytes, although to varying extents. This evidence confirms the plasticity of the regenerative phenomenon in echinoderms, which can apparently follow different pathways in terms of growth and morphogenesis, but nevertheless involve both epimorphic and morphallactic contributions at the cellular level.
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| 3. |
- Buckland-Nicks, John, et al.
(författare)
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The sperm of Xenacoelomorpha revisited : implications for theevolution of early bilaterians
- 2019
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Ingår i: Zoomorphology. - : SPRINGER. - 0720-213X .- 1432-234X. ; 138:1, s. 13-27
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Tidskriftsartikel (refereegranskat)abstract
- Sperm structure of the Xenacoelomorpha (Acoelomorpha plus Xenoturbellida) is updated in the light of new discoveries or new interpretations of existing data. Nemertodermatida and Acoela (Acoelomorpha) have introsperm with certain basic features in common, but all acoels lack acrosomes and usually have two flagella with unusual combinations of microtubules, whereas all nemertodermatids have small, simple acrosomes and a typical 9+2 flagellum. Xenoturbellida is currently considered as the sister taxon to Acoelomorpha. Xenoturbella bocki has an aquasperm that has almost nothing in common with the sperm of Acoelomorpha. We argue that the aquasperm ultrastructure of X. bocki has much in common with sperm of hemichordates and to some extent echinoderms, which was previously disputed. Molecular analyses have on the one hand supported a connection with deuterostomes but on the other hand have negated it, suggesting that the closest common ancestor of Xenacoelomorpha is either the Nephrozoa, Deuterostomia or Protostomia. Sperm structure is highly diverse among Xenacoelomorpha, with protostome-like traits in Acoelomorpha and deuterostome-like traits in Xenoturbella. Assuming Xenacoelomorph monophyly and ancestral introsperm in this taxon, however, suggests that the re-expression of the aquasperm form of Xenoturbella, involving some key changes in sperm morphology, is a secondarily derived state that could have occurred through progenetic spermiogenesis with the precocious development of round spermatids to maturity.
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| 4. |
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| 5. |
- Meyer-Wachsmuth, Inga, et al.
(författare)
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The muscular system of Nemertoderma westbladi and Meara stichopi (Nemertodermatida, Acoelomorpha)
- 2013
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Ingår i: Zoomorphology. - New York/Heidelberg : Springer. - 0720-213X .- 1432-234X. ; 132:3, s. 239-252
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Tidskriftsartikel (refereegranskat)abstract
- Nemertodermatida is a small taxon of marine worm-like animals; its position in the tree of life is highly contested The musculature of Nemertoderma westbladi and Meara stichopi is studied here in detail using fluorescent phalloidin and confocal microscopy.In both species the musculature is composed of an outer layer of circular and an inner layer of longitudinal musculature, diagonal muscles form a distinct layer in N westbladi but in M. stichopi these fibres connect to both other layers. The supraterminally opening male pore and antrum are formed by invagination of the whole body-wall in both species and the seminal vesicle is lined by a thin net of musculature only in full male maturity. Modifications of the ventral body-wall adjacent to the mouth are small and transient in N. westbladi including no extra musculature whereas it consists of additional strong U-shaped musculature in M. stichopi. Myogenesis in N. westbladi is not finished in hatchlings and will be completed dorsally in juvenile specimens and ventrally in male mature ones, after the loss of the mouth.Musculature between the two species differs considerably and might give insights into the internal relationships of Nemertodermatida and might prove to be useful in studies investigating their phylogenetic position. More data of other species and developmental changes are needed.
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| 6. |
- Pleijel, Fredrik, 1955, et al.
(författare)
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Chambered chaetae in nereidiform polychaetes (Annelida)
- 2010
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Ingår i: Zoomorphology. - : Springer Science and Business Media LLC. - 0720-213X .- 1432-234X. ; 129:2, s. 93-98
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Tidskriftsartikel (refereegranskat)abstract
- The nereidiform polychaete taxa Chrysopetalidae, Hesionidae and Nereididae are characterized by the presence of chambered chaetae. The medullae (inner part) of all examined annelid chaetae are provided with internal longitudinal canals, but in these taxa there are additional thin, transverse walls (diaphragms), giving the chaetae a barred or chambered appearance in light microscopy. We investigate this structure in chrysopetalids, hesionids, nereidids, with light, scanning and transmission electron microscopy and compare it to phyllodocids and syllids, which are outside this clade. We conclude that chambered chaetae likely constitute an synapomorphy for chrysopetalids, hesionids and nereidids, although further study are required of some aphroditids and nephtyids.
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| 7. |
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| 8. |
- Tekle, Yonas I., et al.
(författare)
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Ultrastructural and immunocytochemical investigation of acoel sperms with 9 + 1 axoneme structure : New sperm characters for unraveling phylogeny in Acoela
- 2007
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Ingår i: Zoomorphology. - : Springer Science and Business Media LLC. - 0720-213X .- 1432-234X. ; 126:1, s. 1-16
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Tidskriftsartikel (refereegranskat)abstract
- Acoel sperm characters proved useful in deciphering acoel taxonomy. The phylogenetic value of sperm characters in closely related sub-groups or in a monophyletic taxon has not yet been assessed. We have investigated sperm ultrastructure in seven members of the monophyletic taxon Childia sensu (Tekle et al. J Zool Sys Evol Res 43(1):72-90, 2005) and in their closest relatives, the Mecynostomidae (four taxa). All members of Childia examined show little variation in their sperm ultrastructure. The common characters of Childia taxa are: 9 + 1 axoneme structure, the presence of six distal cytoplasmic microtubules in the absence of axial or cortical ones, long nucleus and extensive nucleus-flagella overlap. We have identified a new set of cytoplasmic microtubules lying in the centriolar end of the sperm cell, distal microtubules. The origin and phylogenetic significance of this character is discussed. The types and arrangement of cytoplasmic granules could be used as phylogenetic characters at a low taxonomic level. A loose membrane amorphous core type of granule was found to be a synapomorphy for the following clade within the taxon Childia: C. crassum + C. groenlandica + C. vivipara + C. brachyposthium + C. macroposthium. Sausage shaped granules are plesiomorphic among the taxa examined. The rest of the granule characters were found to be homoplasious. Sperm ultrastructural characters have again proven their concordance with molecular phylogeny. The only morphological synapomorphies known for the sister taxa Childia-Mecynostomidae, in the molecular phylogeny, are characters derived from sperm ultrastructure: distal microtubules arranged in two groups of three microtubules each and a 9 + 1 axoneme structure. The spermatozoa of Childia and Mecynostomidae show 9 + 1 axoneme configuration, seemingly similar to the 9 + `1' axoneme pattern of the Platyhelminthes—Trepaxonemata. Using electron-microscope immunocytochemistry, we have demonstrated that, unlike the central cylinder of trepaxonematans, the central cylinder of the 9 + 1 axonemal pattern in acoels is immunoreactive to tubulin and contains a single central microtubule. Therefore, the 9 + 1 patterns in acoels and trepaxonematans are homoplasious.
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| 9. |
- Wernström, Joel Vikberg, et al.
(författare)
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Geometric morphometrics of macro- and meiofaunal priapulid pharyngeal teeth provides a proxy for studying Cambrian "tooth taxa"
- 2023
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Ingår i: Zoomorphology. - : Springer. - 0720-213X .- 1432-234X. ; 142, s. 411-421
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Tidskriftsartikel (refereegranskat)abstract
- Priapulids are marine, benthic ecdysozoan worms that feed using a distinctive toothed pharynx. While only a handful of lineages have survived to the present day, the Cambrian priapulid stem group left behind a rich record of articulated body fossils and characteristic trace fossils in the form of burrows. Recently, the fossil record of isolated priapulid cuticular elements including pharyngeal teeth has gained increased attention as a means of revealing cryptic priapulid taxa otherwise unknown among macrofossils. In this study, we focus on the ecological implications of shape variation in the teeth of extant and extinct priapulids, which display substantial morphological differences between taxa and life stages. We define a landmarking scheme to capture shape variation in priapulid teeth and apply it to our dataset, which includes a breadth of tooth specimens from extant macrofaunal and meiofaunal lineages alongside numerous Cambrian priapulid teeth preserved as isolated small carbonaceous fossils. Through ordination of the principal components of shape, we explore the priapulid tooth morphospace and find evidence that its occupancy has expanded since Cambrian times, indicating a corresponding expansion of the group's ecological niche. We also employ our geometric morphometric approach to make linear discriminant analysis-based taxon assignments based on tooth morphology, which can be helpful for classifying enigmatic "tooth taxa" known solely from fossil teeth. Finally, we use discriminant analysis to study tooth shapes from a functional perspective, considering known ecologies to characterize the ecological functions of unclassified isolated teeth.
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| 10. |
- Elofsson, Rolf, et al.
(författare)
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Evolutionary aspects on the construction of the first optic neuropil (lamina) in Crustacea
- 1986
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Ingår i: Zoomorphology. - 0720-213X. ; 106, s. 174-178
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Tidskriftsartikel (refereegranskat)abstract
- A Golgi study of the neuronal morphology of the first optic neuropil (lamina) in three anostracan species revealed a close similarity in the lamina construction and neuron types. The lamina architecture of decapod and mysid crustacean species, as revealed by the Golgi method, conformed to previous studies and differed from the anostracans. The comparison was made at the level of resolution comprising retinal projection on the lamina, structural entities such as columns and layers and neuron position, branching pattern and terminal fields. It was shown that different types of compound eyes and variation in the habitat of the animals were of less importance for the lamina design than common descent as expressed in the present taxonomic groups.
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