| 1. |
- Borg, Bertil, et al.
(författare)
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The Parapineal Organ of Teleosts
- 1983
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Ingår i: Acta Zoologica. - : Wiley. - 0001-7272 .- 1463-6395. ; 64:4, s. 211-218
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Tidskriftsartikel (refereegranskat)abstract
- A parapineal organ was found to be present in 21 teleost fishes belonging to 20 different families, but was absent in poecilids and cyprinodontids. The parapineal organ was situated on the left side of the brain and sent a nerve tract to the left habenular nucleus, except in Gadus, where a “parapineal organ” appeared to send a nerve tract into the pineal stalk. The parapineal organ of adult Gasterosteus consisted of glial elements and parapinealocytes. The latter were small neurons which sent off the unmyelinated axons that formed the parapineal tract. A single photoreceptor cell was found in a stickleback parapineal organ. 1983 The Royal Swedish Academy of Sciences
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| 2. |
- Ekström, Peter, et al.
(författare)
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The Monoaminergic Paraventricular Organ in the Teleost Ictalurus nebulosus LeSueur, with Special Reference to Its Vascularization
- 1982
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Ingår i: Acta Zoologica. - : Wiley. - 0001-7272 .- 1463-6395. ; 63:1, s. 45-54
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Tidskriftsartikel (refereegranskat)abstract
- Specific, fluorescent, subependymal perikarya were found in the pars anterior of the paraventricular organ (PVOpa), in the nucleus recessus lateralis (NRL) and in the nucleus recessus posterioris (NRP). No fluorescent perikarya were present in the nucleus lateralis tuberis (NLT). Fluorescent nerve tracts connect the PVOpa and the NRL with the NRP, and interconnect the paired NRP. The nucleus preopticus (NPO) and the NLT receive a large input of aminergic nerve fibers. The monoaminergic nuclei are well vascularized, and their vascular plexes seem to be connected. A capillary plexus is situated dorsal to the NRP and exhibits no contact with the pituitary. It is surrounded by the prominent fluorescent tracts connecting the aminergic nuclei. 1982 The Royal Swedish Academy of Sciences
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| 3. |
- Elofsson, Rolf, et al.
(författare)
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Compound eyes of some deep-sea and fiord crustaceans
- 1977
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Ingår i: Acta Zoologica. - : Wiley. - 0001-7272 .- 1463-6395. ; 58, s. 169-177
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Tidskriftsartikel (refereegranskat)abstract
- The compound eyes of the deep-sea mysid Boreomysis scyphops and the two mysid species Amblyops abbreviata and Pseudomma affine, which are indigenous to deep fiords in Norway, have been investigated. The eye stalks are greatly transformed, but contain hypertrophied retinas. The ommatidia of all three species lack a dioptric apparatus, possessing only retinular cells, which are arranged in a cylinder-like fashion. Folds from the retinular cells project into the “cylinder” and are covered with microvilli. The arrangement is explained functionally by an increase in the photopigment-bearing surface as an adaptation to low-light intensities. The orderly arrangement of microvilli in most arthropod compound eyes has been lost, and the arrangement is thus multidirectional in these mysids. With the photopigment dipoles arranged along the microvillar axis, the disorderly arrangement of microvilli signifies a more efficient capture of non-polarized light. It is concluded that the mysid compound eyes show adaptations to low-light intensities probably acquired during the species' evolutionary descent into deep-sea habitats. Amblyops abbreviata and Pseudomma affine, belonging to genera with entirely transformed eyes and with an ultrastructure less “normal” than that of Boreomysis scyphops are believed to be earlier descendants into the deep-sea habitats than the latter species, which belongs to a genus in which most of the species have well-developed eyes.
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| 4. |
- Elofsson, Rolf, et al.
(författare)
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The anostracan rhabdom and the basement membrane. An ultrastructural study of the Artemia compound eye (Crustacea)
- 1975
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Ingår i: Acta Zoologica. - : Wiley. - 0001-7272 .- 1463-6395. ; 56, s. 141-153
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Tidskriftsartikel (refereegranskat)abstract
- The ommatidia of the compound eyes of Artemia salina L. are normally composed of four crystalline cone cells containing glycogen. The cells are enveloped by two so-called “cellules épidermiques juxta-cristallines”. There are also six pigmented retinula cells, all contributing to the rhabdom.A peculiar feature of the Artemia crystalline cone cells is that their elongated parts, the so-called cone cell roots, widen and flatten proximally, forming interdigitating “endfeet”. The basement membrane thus consists of a cellular portion combined with the basal lamina.The main mass of the rhabdom of the Artemia eye is built up by five retinula cells, two contributing a smaller part. The microvilli are oriented in four directions, two being orthogonal. The sixth cell contributes on two small portions to the rhabdom in the distalmost and a more proximal position. The rest of it runs axon-like outside the omnatidium. Where the sixth cell wedges in, the direction of the microvilli is changed and has no orthogonal pattern.Two rhabdom types of compound eyes are distinguished: the decapod or banded or layered rhabdom: and the anostracan rhabdom with continuous rhabdomeres.
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| 5. |
- Elofsson, Rolf
(författare)
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The ultrastructure of a chemoreceptor organ in the head of copepod crustaceans
- 1971
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Ingår i: Acta Zoologica. - : Wiley. - 0001-7272 .- 1463-6395. ; 52, s. 299-315
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Tidskriftsartikel (refereegranskat)abstract
- The ultrastructure of the paired nerves, previously called frontal organ or X-organ, in copepod crustaceans was investigated. These nerves, run- ning from the anterior margin of the brain to the frontal edge of the animals, are found to contain the dendrites of three types of morpho- logically different sensory neurons. The first unit consists of two dendrites (distinguished by their myelinization) leading to two small hairs on the front. Their detailed structure was not investigated. The second unit consists of a few large dendrites ending in b’ranching cilia. The latter are surrounded by a specialized glial cell. The ciliary branches are reg- ularly sized and arranged. The third unit consists of c. 17 dendrites ending with cilia at the cuticle. The cilia are split into irregular branches which are buried in modified epidermal cells which, in the case of Calanus, are connected with cuticular pores. By analogy with other presumed chemosensory organs in the Arthro- poda, the second and the third unit are considered, on a morphological basis, to be chemoreceptors. The second unit receives internal stimuli. Because it resembles other X-organs in the Crustacea, all X-organs could have the same function. The third unit is thought of as receiving external stimuli.
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| 6. |
- Elofsson, Rolf
(författare)
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To the question of eyes in primitive crustaceans
- 1992
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Ingår i: Acta Zoologica. - : Wiley. - 0001-7272 .- 1463-6395. ; 73, s. 369-372
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Tidskriftsartikel (refereegranskat)abstract
- Based on a review of studies of functional and comparative anatomy of crustacean eyes, a hypothesis is formed on eyes in primitive crustaceans. It is suggested that they were similar to present-day frontal eyes of the malacostracan type. Neuronal architecture suggests that the development to apposition compound eye followed two main routes, one seen in malacostracansand the other in non-malacostracans. Within the two subgroups different and separate lines have been followed to form specialized apposition types and, within the Malacostraca, superpositioneyes as pointed out by Nilsson (Nilsson, D. E. 1989. Facets of vision, pp. 30-73).
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| 10. |
- Boisvert, Catherine, 1978-
(författare)
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The humerus of Panderichthys in three dimensions and its significance in the context of the fish-tetrapod transition
- 2009
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Ingår i: Acta Zoologica. - : Wiley. - 0001-7272 .- 1463-6395. ; 90:suppl 1, s. 297-305
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Tidskriftsartikel (refereegranskat)abstract
- The humerus of Panderichthyshas been considered to represent a transitionalform between that of tetrapodomorph fish such asEusthenopteronandtetrapods such asAcanthostega. The previous description was based onflattened material and was analysed in the context of the few fossils known atthe time. Since then, several new forms have been described such asGogonasus,Tiktaalikand an isolated humerus from the Catskill Formation. The humeralmorphology ofPanderichthys rhombolepisand its interpretation in this newcontext are therefore reassessed with the help of a three-dimensional modelproduced with themimicssoftware based on a computed tomography scan ofan unflattened specimen as well as comparisons with the originally describedmaterial. The humerus ofPanderichthysdisplays a combination of primitive,derived, intermediate and unique characteristics. It is very similar to themorphology ofTiktaalikbut when it differs from it, it is most often morederived despite the more basal phylogenetic position thatPanderichthysoccupies. What emerges from this study is a much more gradual transformationof the humerus morphology from fish to tetrapods and the ability to distinguishautapomorphies more easily. The picture is more complex than previouslybelieved, with many morphological specializations probably reflecting thebreadth of ecological specializations already present at the time.
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