Acta Zoologica

doi: 10.1111/j.1463-6395.1998.tb01153.xpmid: N/A

Hausen, H.; Bartolomaeus, T.

doi: 10.1111/j.1463-6395.1998.tb01154.xpmid: N/A

In Scolelepis squamata and Malacoceros fuliginosus two alternatingly arranged transverse rows of setae are found in each ramus. These are capillary setae in all thoracic setigers, whereas in abdominal setigers they may alternate with hooded hooks. In M. fuliginosus only the abdominal neuropodia bear hooded hooks, whereas in S. squamata these setae are present in both rami in the abdomen. Here every second seta (the capillary one) degenerates before its formation is complete, leading to a single row of hooded hooks. In the transverse rows new setae are formed in a medio‐lateral formative site in both species. Additionally in each ramus there exists one longitudinal row of capillaries which each possesses its own formative site. Ultrastructure and formation of the hooded hooks in S. squamata is very similar to that of hooded hooks in Capitellidae. The hood is preformed by a certain group of microvilli of the chaetoblast, which soon differentiates two layers of microvilli, raising an inner and an outer hood lamella. The hooded hooks and their arrangement are regarded as homologous characters in Spionidae and Capitellidae. This indicates a closer relationship of Spionidae with a taxon consisting of Capitellidae, Arenicolidae, Maldanidae, Oweniida, Terebellida, Sabellida, and Pogonophora.

Weedon, Michael J.

doi: 10.1111/j.1463-6395.1998.tb01155.xpmid: N/A

The calcific protoecia of cyclostome bryozoans have remarkably uniform skeletal ultrastructure in three suborders (Tubuliporina, Cancellata and Rectangulata). The basal wall or floor has a fine outer granular layer succeeded by planar spherulitic fabric, internally lined by irregular semi‐nacre. The roof of the disc comprises an outer granular layer with an inner lining of semi‐nacre continuous with that of the floor; planar spherulitic fabric is absent. Growth of the floor of the disc is initiated around the circular outer rim and continues centripetally to the centre; the inner lining has no prevailing growth direction. The gently domed roof also initiates around the outer rim, and grows in strips, which grow toward the centre, then distally toward the distal tube of the ancestrula which has a fully adult ultrastructure. Protoecia] ultrastructure is independent of adult ultrastructure. The uniformity of skeletal ultrastructure in cyclostomes corresponds with the close similarity of larvae and post‐settlement metamorphosis in the order. The fabric suite of the protoecium resembles the skeletal ultrastructure of Palaeozoic stenolaemates. The primitive fabric condition is retained by some tubuliporines and cancellates. Complex multilayered fabric suites may have evolved in the Mesozoic by addition of new fabric types.

Munk, Ole

doi: 10.1111/j.1463-6395.1998.tb01156.xpmid: N/A

The paper deals with the microscopic structure of tubular light guides in escal appendages of three deep‐sea anglerfishes, Oneirodes eschrichti, Phyllorhinichthys micractis, and Linophryne coronata. The bases of the light guides are located oposite to an aperture in the lightproof cup enclosing the escal light gland. The light guides have an axial light‐transmitting core enclosed by a tubular wall with an opening or window through which light is emitted. The wall consists of a layer of reflecting cells, in two of the three species supplemented by an outer layer of pigmented cells. The window either has a terminal position or is located in the light guide wall near its closed end. A special annular window, situated beneath an inverted cone of reflecting cells, is present at the flattened tip of the light guide within the distal appendage of P. micractis. In one of the species studied (L. coronata) it appears likely that a sphincter of smooth muscle cells may regulate the transmission of light from the light gland to the light guides.

Lundin, Kennet

doi: 10.1111/j.1463-6395.1998.tb01157.xpmid: N/A

Meara stichopi and an undescribed species of Meara, both endosymbiotic in the intestine of aspidochirote holothurians, possess filiform extraepidermal bacteria among the epidermal cilia. Similar bacteria were also observed on one specimen of the free‐living species Nemertoderma westbladi. The bacteria are of the gram‐negative type, as evident by cell wall structure and results from gramstaining. On a few specimens of M. stichopi, the bacteria were found to carry peculiar distal appendages, or buds, on stalked cup‐shaped cell extensions. As the bacteria described here appear to be species specific, they can be used in addition to other features in the often problematic characterization of the nemertodermatid species.

Jamieson, Barrie G. M.; Scheltinga, David M.; Forges, Bertrand Richer

doi: 10.1111/j.1463-6395.1998.tb01158.xpmid: N/A

A total of 17 species, in 14 genera of majids have been examined for sperm ultrastructure. The present account describes the sperm of six of these species, in two subfamilies: Pisinae—Sphenocarcinus orbiculatus and Sphenocarcinus stuckiae and Inachinae—Cyrtomaia furici, Grypacheus hyalinus, Platymaia rebierei and Macropodia longirostris. M. longirostris has the only eubrachyuran sperm in which the acrosome is known to depart radically from a subspheroidal form. The acrosome is semilunar in shape and is bordered by a very thin layer of cytoplasm and an unusually uniform, narrow band of chromatin. The apical surface of the acrosome is almost flat, though slightly concave, whereas the posterior surface forms a hemisphere, and is almost completely occupied by the thin, centrally perforate, electron dense operculum. The bulk of the acrosome consists of a homogeneous, moderately electron dense outer acrosome zone. This surrounds a small inner acrosome zone internal to which is an ellipsoidal, pale perforatorium capped by a central acrosome zone. Majid sperm are distinguished by a flattened and/or centrally depressed operculum; a further characteristic is that the pointed perforatorium is relatively short and frequently does not reach the operculum. They vary inter alia with regard to presence or absence of a posterior median process and, apparently, of centrioles and of microtubules in the nuclear arms, and in the number of these arms. Perforation of the operculum, seen in the Pisinae, is not constant in the Inachinae. Spermatozoal ultrastructure offers no certain support for a close relationship of majids with parthenopids or hymenosomatids.

Sundin, Lena; Holmgren, Susanne; Nilsson, Stefan

doi: 10.1111/j.1463-6395.1998.tb01159.xpmid: N/A

The gills of the Atlantic cod, Gadus morhua, were studied using immunohistochemical techniques. Primary antibodies directed against serotonin (5‐hydroxytryptamine, 5‐HT) and acetylated α‐tubulin were used to visualise cells containing serotonin and nerve fibres, respectively. Three morphologically different 5‐HT immunoreactive cell types were distinguished: (I) Neuroepithelial cells (NECs), which were abundant along the distal half of the efferent filamental arteries (EFAs), and particularly formed distinct clusters at the individual filamental tips, (II) bipolar neurones running next to the EFAs and (III) multipolar neurones innervating the proximal parts of the EFA. In addition, the study revealed a well‐developed system of nerve fibres, some of which form plexuses in association with the NECs. A relatively rich innervation of the proximal part of the EFAs, in conjunction with the EFA sphincters was also observed. Delicate varicose terminals surround the bases of the efferent lamellar arterioles. The localisation of distinct clusters of NECs at the individual filamental tips and the close connection with nerve terminals suggests a function as external branchial oxygen receptors.

Orrhage, Lars; Eibye‐Jacobsen, Danny

doi: 10.1111/j.1463-6395.1998.tb01160.xpmid: N/A

A reinvestigation of the central nervous system of the Phyllodocidae appeared necessary as the existing literature proved insufficient for detailed comparisons with other polychaete families. Many earlier opinions turned out to be quite contradictory, especially as concerns the morphological value of the anterior end appendages. In the present paper the microanatomy of the brain and the anterior ventral cord, as well as the innervation of, inter alia, the cephalic appendages, the nuchal organs and the alimentary canal of Eulalia viridis (main object of study), Eumida sanguinea, Pterocirrus macroceros, Sige fusigera, Eteone picta, E. foliosa, Phyllodoce groenlandica, P. longipes, P. mucosa, Paranaitis wahlbergi, Notophyllum foliosum and Nereiphylla lutea are described. The results are summarized in schematic diagrams and compared with corresponding observations on other polychaete families. Thereby, some earlier opinions about the nature of the cephalic appendages of the Phyllodocidae are strengthened while others are rejected. Most significantly, it is concluded that the so‐called ventrolateral antennae of phyllodocids are homologous with the palps of other polychaetes and the median antenna found in certain genera is homologous with the nuchal papilla found in most other genera of the family. These partly new or revised characters and character states formed the basis for a reconsideration of earlier ideas about the phylogeny of the Phyllodocidae: a new alternative.

Justine, Jean‐Lou; Iomini, Carlo; Raikova, Olga I.; Mollaret, Isabelle

doi: 10.1111/j.1463-6395.1998.tb01161.xpmid: N/A

Spermatozoa of certain acoels, a group of primitive Platyhelminthes, and spermatozoa of the most derived Platyhelminthes, the Cercomeridea (parasitic Platyhelminthes), show a general morphological resemblance in that they are long filiform cells with two incorporated axonemes and longitudinal cortical microtubules. A possible way to test the homology of these cortical microtubules in the different groups is to analyze the presence/absence of post‐translational modifications of tubulin. An indirect immunofluorescence study showed that the doublet microtubules of the sperm axonemes are labelled by an anti acetylated‐alpha‐tubulin antibody in all groups, irrespective of the axoneme pattern (9 + 0, 9 + 2 and non‐trepaxonematan 9 + “1” in various acoels, and trepaxonematan 9 + “1” of the temnocephalid Troglocaridicola sp., the digenean Echinostoma caproni and the monopisthocotylean monogenean Pseudodactylogyrus sp.). Significant differences are found in the sperm cortical microtubules: they are acetylated in the acoel Actinoposthia beklemischevi, but not in the digenean E. caproni and the temnocephalid Troglocaridicola sp. These results suggest that the sperm cortical microtubules of the acoels are not homologous with the morphologically similar elements found in the higher Platyhelminthes.

Bedini, Celina; Lanfranchi, Alberto

doi: 10.1111/j.1463-6395.1998.tb01162.xpmid: N/A

The brain of Strongylostoma simplex shows the organization typical of the most evolutionary groups of free‐living plathelminths. Three types of neurons, two types of neurosecretory cells, and a certain number of glia‐like cells are present. Somato‐axonic synapses and axo‐dendritic contacts with a “spine apparatus”, like those described in vertebrates, have been identified. These two types of synapses have never been reported in other plathelminth brains. Local thickenings and dense bars attached to the presynaptic membrane are also observed, together with the paramembranous density common in many flatworm synapses.