Embryonic growth and trophotaenial development in goodeid fishes (Teleostei: Atheriniformes)

Embryonic growth and trophotaenial development are examined in two species of goodeid fish, Ameca splendens and Goodea atripinnis. During gestation of A. splendens, embryonic dry mass may increase from 0.21 mg at the onset of development to 31.70 mg at term. In G. atripinnis, embryonic dry mass ranges from 0.25 mg at the onset of development to 3.15 mg at term. Increase in mass is primarily due to the uptake of maternally derived nutrients by trophotaeniae, externalized embryonic gut derivatives. Trophotaenial development in both species is divisible into five phases. During the first phase, the anus is formed. The second phase involves dilation of the anus, enlargement of the perianal lips, differentiation of the hindgut absorptive epithelium, and formation of the trophotaenial peduncle. The third phase is characterized by a further marked hypertrophy and lateral expansion of the perianal lips that results in the formation of short trophotaenial processes. During the fourth phase, there is continued outward expansion of the inner mucosal surface of the trophotaenial peduncle that results in its eversion and lobulation. Placental function is established by this phase. Axial elongation and dichotomous branching of trophotaenial processes occurs during the fifth phase. Development of rosette and ribbon trophotaeniae differ in the degree of axial elongation during the fifth and final phase.     

Structure and function of placental exchange surfaces in goodeid fishes (Teleostei: Atheriniformes)

The species of the family Goodeidae have evolved reproductive strategies involving intraovarian gestation, early evacuation of nearly yolk‐exhausted embryos from the ovigerous tissue into the ovarian cavity, placental matrotrophy during intraluminal gestation, and the birth of highly developed fry. The inner ovarian lining becomes hypervascularized during gestational periods and functions as the maternal component of the placental association. Embryotrophic liquid is secreted by the inner ovarian epithelium into the ovarian cavity. Comparative electrophoretic analyses of embryotrophe and maternal blood serum provide evidence for the transfer of maternal serum proteins into the embryotrophe. Trophotaeniae, proctodaeal processes of the embryos, provide a surface for nutrient absorption. Endocytic activity was demonstrated by ingestion of unspecific tracer proteins in various species. Moreover, the trophotaenial absorptive cells (TACs) in Ameca splendens ingest various proteins or random copolymers conjugated to colloidal gold as well as radioiodinated proteins in a way that satisfies the criteria of receptor‐mediated endocytosis. Several aminopeptidases (APs) on the surface of TACs were identified as protein binding sites as evidenced by inhibition of binding and uptake of marker proteins in the presence of AP substrates or AP inhibitors. Morphological adaptations of the embryonic circulatory system pertaining to nutrient and gas exchange were characterized. The embryonic epidermis comprises two layers of squamous cells closely underlain by a dense capillary net. Efficient gas exchange is facilitated by a thin embryotrophe‐blood barrier of both the embryonic skin and the intraovarian lining. J. Morphol. 276:991–1003, 2015. © 2014 Wiley Periodicals, Inc.     

Scavenger receptors facilitate protein transport in the trophotaenial placenta of the goodeid fish,Ameca splendens (Teleostei: Atheriniformes)

In the goodeid placental analogue, trophotaeniae provide extraembryonic gut-derived exchange surfaces. Ameca splendens embryos possess endocytosing trophotaeniae that are capable of absorbing a dazzling array of proteinaceous substances. The iron core protein, native ferritin (NF), and several radioiodinated proteinaceous substances were used to study ligand and binding site pathways in the trophotaenial absorptive cells (TACs). Time sequence analysis of NF trafficking indicated an exclusively lysosomal pathway. Binding to TACs of NF was completely inhibitable by proteins containing multiple lysine residues such as apoferritin, bovine serum albumin (BSA), human transferrin (HTf), fetuin, hemoglobin, myoglobin, cytochrome c, ubiquitin, parvalbumin as well as the random copolymers, poly(Glu,Lys,Tyr)6:3:1 and poly(D-Glu,D-Lys)6:4. Peptide hormones and pepsin that contains only one lysine residue did not produce inhibitory effects. Radiolabels such as (125)I-BSA, (125)I-HTf and (125)I-poly(Glu,Lys,Tyr) bound to trophotaeniae in a specific saturable manner. Any two proteins were shown to hinder one another in getting hold of a binding site. Concentration-dependent (125)I-BSA binding and Scatchard analysis of the data revealed both low- and medium-affinity binding with apparent dissociation constants, K(d)s, of 3.4 x 10(-5) M and 2 x 10(-7) M, respectively. Binding of NF and radioiodinated proteins was inhibited in the presence of a large excess of L-Lys, D-Lys, and several dipeptides containing Lys. Both Ca(2+)-depletion and low pH dramatically reduced the TACs' capacity to bind proteins. The effects of acidotropic agents included a reversible loss of surface protein binding sites, tremendous vacuolation, and the arrest of lysosomal degradation. Collectively, present results demonstrate that TACs bind and absorb multiple proteinaceous substances through a mechanism satisfying the criteria of receptor-mediated endocytosis. It is concluded that scavenger protein binding sites are used to ingest proteins for lysosomal degradation, helping to meet the embryos' amino acid requirement.     

The trophotaenial placenta of a viviparous goodeid fish. II. Ultrastructure of trophotaeniae, the embryonic component

Embryos of the viviparous goodeid fish Ameca spendens develop within the ovarian lumen, where they establish a placental association with the maternal organism and undergo a 15,000% increase in embryonic dry weight. The placenta consists of an embryonic component, the trophotaeniae, and a maternal component, the internal ovarian epithelium. Examination with light microscopy and with transmission and scanning electron microscopy reveals that trophotaeniae of A. splendens are extraembryonic membranes consisting of five ribbon-like processes originating from a tube-like mass of tissue that extends outward from the perianal region of developing embryos. There are two sets of lateral processes and a longer single median process. Trophotaeniae possess an outer epithelium that surrounds a highly vascularized core of loose connective tissue. Epithelial cells possess apical microvilli and a pronounced endocytotic apparatus. Cells of the trophotaenial epithelium are either tightly apposed along their lateral margins or separated by enlarged intercellular spaces. Regions of the trophotaenial epithelium possessing enlarged intercellular spaces are distributed in patches. The trophotaenial epithelium is continuous with the embryonic hindgut epithelium and is considered to be derived from it. Comparison of trophotaenial morphology in A. splendens with that reported in Xenotoca eiseni reveals differences in histological organization. The former possess unsheathed trophotaeniae, whereas the latter are sheathed. We postulate that the apposition of trophotaenial epithelium to the internal ovarian epithelium constitutes a placental association equivalent to a noninvasive, epithelioform of an inverted yolk sac placenta. Structural relationships of embryonic and maternal tissues of the trophotaenial placenta are discussed in relation to maternal-embryonic nutrient transfer processes.     

The trophotaenial placenta of a viviparous goodeid fish. III: Protein uptake by trophotaeniae, the embryonic component

Protein uptake and degradation by trophotaenial cells of the viviparous goodeid fish Ameca splendens were studied colorimetrically and ultrastructurally using horseradish peroxidase (HRP) as a tracer and acid (ACPase) and alkaline (ALPase) phosphatase cytochemistry. Trophotaeniae are ribbon-like external projections of the embryonic gut that are equivalent to greatly hypertrophied intestinal villi. During gestation within the ovarian lumen, trophotaeniae are directly apposed to the internal ovarian epithelium (IOE) where they establish a placental association between the developing embryo and maternal organism. Trophotaenial absorptive cells possess an ALPase reactive brush border, an endocytotic apparatus, and ACPase reactive standing lysosomes. Ultrastructural studies of protein uptake indicate that cells of the trophotaenial epithelium take up HRP by micropinocytosis and degrade it within lysosomes. Initially (from 1.5-10 min), HRP is taken up in vitro at 22 degrees C at the apical cell surface and passes via endocytotic vesicles into an apical canalicular system. From 1.5 to 10 min exposure, HRP passes passes from the apical canalicular system to a series of small collecting vesicles. After 10 min, HRP is detected within large ACPase reactive supranuclear lysosomes. Three hours after an initial 1 h exposure to HRP, most peroxidase activity within supranuclear lysosomes is no longer detected. Presence of Golgi complexes, residual bodies, and secretory granules in the infranuclear cytoplasm suggest that products of protein uptake and hydrolysis are discharged across basal and lateral cell surfaces and into the trophotaenial circulation. Trophotaeniae of embryos incubated in vitro in HRP-saline take up HRP at an initial rate of 13.5 ng HRP/mg trophotaenial protein/min. The system becomes saturated after 3 h. Trophotaeniae incubated at 4 degrees C show little or no uptake. In trophotaeniae continuously pulsed with HRP for 1 h, then incubated in HRP-free saline, levels of absorbed peroxidase declined at a rate of 0.5 ng/mg trophotaenial protein/min. HRP does not appear to enter the embryo via extra-trophotaenial routes. These findings are consistent with the putative role of trophotaeniae as the embryonic component of the functional placenta of goodeid fishes. Trophotaenial uptake of maternal nutrients accounts for a massive (15,000%) increase in embryonic dry weight during gestation.     

Aminopeptidases function as endocytic receptors in the trophotaenial placenta of the goodeid fish,Ameca splendens (Teleostei: Atheriniformes)

Viviparity in goodeid teleosts is characterized by the elaboration of trophotaeniae, extraembryonic proctodaeal appendages facilitating maternal-embryonic nutrient transfer. The trophotaenial absorptive cells (TACs) express aminopeptidases (APs) such as APA, APN, gamma-glutamyltransferase (gamma-GT), dipeptidyl aminopeptidase (DAP) IV, and neutral endopeptidase (NEP) as inferred from the results of cleavage experiments with, respectively, Glu-alpha-(4M beta NA), Ala-(4M beta NA), Glu-gamma-(4M beta NA), Gly-Pro-(4M beta NA), and Gl-(Ala)(3)-(4M beta NA). Enzyme reaction product was localized to the apical and basolateral plasma membrane as well as to some intracellular compartments. In the accompanying report (Schindler, 2003) evidence is presented that the trophotaeniae of Ameca splendens embryos randomly, yet specifically, bind and ingest proteins as well as certain copolymers of amino acids. Present results demonstrate that endocytosis is significantly inhibitable by unspecific proteinase inhibitors, such as diisopropylphosphorofluoride, phenylmethanesulfonylfluoride, antipain, 1.10-phenanthroline, and dithiothreitol. The specific microbial AP inhibitors amastatin, bestatin, and phosphoramidon suppressed protein binding to TACs more effectively when added in combination than did either agent alone. Moreover, in the presence of 4M beta NA assay substrates of APs the capability of TACs to bind proteins was significantly reduced. Conversely, the rate at which 4M beta NA substrates were cleaved by trophotaenial APs was modified in the presence of proteins. Depending on protein concentrations the AP-catalyzed reactions either decreased or increased in velocity. Analysis of the enzyme kinetics by methods of linear transformation suggests that proteins bind to APs competitively, thereby adopting the role of enzyme inhibitors. On the other hand, protein binding to APs appears to be a signal to translocate enzymes from an internal pool to the surface membrane. In the presence of primaquine, the rate of AP-catalyzed cleavage of 4M beta NA substrates was significantly reduced. That can be put down to the fact that weak bases disrupt the recycling of endocytosed membrane constituents. In conclusion, there is evidence that APs in the trophotaenial placenta of A. splendens function as scavenger receptors mediating in the delivery of embryotrophic proteins for lysosomal degradation.     

Interrelationships of the ostariophysan fishes (Teleostei)

The history of ostariophysan classification is summarized and it is noted that traditional concepts of relationships have never been supported by characters found to be unique to the taxa. We present a new hypothesis of relationships among four of the five major ostariophysan lineages: Cypriniformes, Characiformes, Siluroidei, and Gymnotoidei (Otophysi). Cypriniforms are the sister-group of the remaining three (Characiphysi), and characiforms are the sister-group of siluroids plus gymnotoids (Siluriformes). Placement of the Gonorynchiformes as the sister-group of the Otophysi is supported by additional evidence. Each of the five lineages is monophyletic. Analysis was concentrated upon species thought to be the least specialized within each lineage; choices of these species are discussed. Chanos is determined to be a relatively primitive gonorynchiform morphologically and the sister-group of all other Recent members of the order. Opsariichthys and Zacco are found to be morphologically primitive cypriniforms. We propose that a monophyletic group comprising the Citharinidae and Distichodontidae forms the sister-group of all other characiforms. Within the two families, Xenocharax is the least specialized. We suggest that Hepsetus, the erythrinids, and the ctenoluciids are more derived than the distichodontids and citharinids, and may form a monophyletic group within die characiforms. The traditional hypothesis that Diplomystes is the primitive sister-group of all Recent siluroids is substantiated. Our evidence suggests that Sternopygus is the most primitive gymnotoid morphologically; but rather than being the sister-group of all other gymnotoids, it is the primitive sister-group within a lineage called the Sternopygidae by Mago-Leccia. Previous explanations of otophysan distribution have been based on notions of relationships which are unsupported by the evidence presented herein. Our own analysis of relationships serves primarily to make clear the extent of sympatry, and therefore the probability of dispersal, among the major ostariophysan lineages. The extent of sympatry, together with the widespread distribution of ostariophysans, suggests that the group is older than previously supposed, and our hypotheses of relationships among the characiforms implies that many of the extent characiform lineages evolved before the separation of Africa and South America. Further understanding of ostariophysan distribution must await phylogenetic analysis within each of the five major lineages so that distributions linked with vicariance patterns and dispersal events can be sorted out.     

Systematics of Tanganyikan cichlid fishes (Teleostei: Perciformes)

The relationships among 53 genera of Tanganyikan cichlid fishes were analyzed based on internal and external morphological features. Comparison of the morphological cladistic tree with a previously proposed classification showed 5 of 12 tribes to be nonmonophyletic. Sixteen tribes were recognized, the changes in classification being that Trematocarini was treated as a junior synonym of Bathybatini; 5 new tribes were established for each of the following genera, Benthochromis, Boulengerochromis, Ctenochromis benthicola, Cyphotilapia, and Greenwoodochromis; Ctenochromis horei was transferred from Haplochromini to Tropheini; and Gnathochromis pfefferi was transferred from Limnochromini to Tropheini. The revised classification was supported by previously proposed molecular trees.     

Phylogenetic inference in Odontesthes and Atherina (Teleostei: Atheriniformes) with insights into ecological adaptation

This contribution provides an insight into Atheriniformes systematics based on four mitochondrial regions: 12S rRNA, cytb, COI and control region (2794bp in total). In the Atherinopsoidei (New World silversides), comparisons among five species of Odontesthes, O. argentinensis, O. bonariensis, O. smitti, O. hatcheri and O. incisa revealed a putative marine-freshwater pairing pattern of Odontesthes species, possibly driven by sea level fluctuations of South American waters. This study represents the first data on molecular phylogeny of Odontesthes species that can be of usefulness to biodiversity conservation policies. In the Atherinoidei (Old World silversides), Atherina boyeri was corroborated as a species complex constituted by a marine form, a marine with dark spots form and a brackish form. Concretely, Odontesthes and Atherina may represent geographically replicated models to study genetic adaptation and speciation of marine species to brackish and freshwater habitats. In addition, phylogenetic analyses supported Odontesthes and Atherina as monophyletic taxa and their separation into two differentiated suborders Atherinopsoidei and Atherinoidei, respectively.     

Phylogenetic relationships among atheriniform fishes (Teleostei: Atherinomorpha)

We present evidence from adult and larval morphology for the monophyly and relationships of Atheriniformes, using other atherinomorphs, mugilids and acanthomorph fishes as outgroups. Atheriniformes is diagnosed by ten characters (larval: short preanal length, single mid-dorsal row of melanophores; adult: vomerine ventral face concave, long Al muscle tendon to lacrimal, two anterior infraorbital bones, pelvic-rib ligament, pelvic medial plate not extended to anterior end, and second dorsal-fin spine flexible). We recognize six families within the order, the hierarchical relationships among which are: (Atherinopsidae (Notocheiridae (Melanotaeniidae (Atherionidae (Phallostethidae, Atherinidae))))). Other major conclusions include: (1) Atherinopsidae (Menidiinae, Atherinopsinae) is diagnosed by 20 characters (e.g. ethmomaxillary ligament attached to palatine dorsal process, ventral postcleithrum with two dorsal rami); (2) Melanotaeniidae (Bedotiinae (Melanotaeniinae (Telmatherinini, Pseudomugilini))) is diagnosed by six characters (e.g. absence of second dorsal-fin spine, sexual dimorphism in body colour and median-fin development, greater body depth); (3) Dentatherina is in Phallostethidae; (4) Atherinidae (Atherinomorinae (Craterocephalinae, Atherininae)) is diagnosed by three characters (lacrimal notch, ventral postcleithrum between first and second pleural ribs, pelvic ventral spine); (5) Atherinidae and Phallostethidae form the Atherinoidea clade diagnosed by seven characters (e.g. interopercle dorsal process absent, dorsal wings of urohyal absent, ventral postcleithrum laminar, pelvic medial plate extended to anterior end, presence of anal plate). Bedotia, Rhodes , and melanotaeniines are shown to be derived within atheriniforms rather than the plesiomorphic sister groups to a paraphyletic 'atherinoid' group. We also demonstrate that groups traditionally placed in Atherinidae (Menidiinae, Atherininae, Atherioninae, etc.) comprise a paraphyletic assemblage.     

New and previously described species of Dactylogyridae (Monogenoidea) from the gills of Panamanian freshwater fishes (Teleostei)

During an investigation of the diversity of metazoan parasites of 7 freshwater fish species from 3 localities in central Panama, the following gill dactylogyrid (Monogenoidea) species were found: Aphanoblastella chagresii n. sp. from Pimelodella chagresi (Heptapteridae); Aphanoblastella travassosi (Price, 1938) Kritsky, Mendoza-Franco, and Scholz, 2000 from Rhamdia quelen (Heptapteridae); Diaphorocleidus petrosusi n. sp. from Brycon petrosus (Characidae); Gussevia asota Kritsky, Thatcher, and Boeger, 1989, from Astronotus ocellatus (Cichlidae); Sciadicleithrum panamensis n. sp. from Aequidens coeruleopunctatus (Cichlidae); Urocleidoides flegomai n. sp. from Piabucina panamensis (Lebiasinidae); and Urocleidoides similuncus n. sp. from Poecilia gillii (Poeciliidae). Consideration of the comparative morphology and distribution of these parasites along with the evolutionary history of the host fishes suggests that diversification may be associated with geotectonic events that provided isolation of the Central American fauna with the uplift of the Panamanian Isthmus during early Pliocene (3 mya).     

Phylogenetic analysis and taxonomy of the poecilioid fishes (Teleostei: Cyprinodontiformes)

Evidence from morphology is used to infer the phylogeny of the superfamily Poecilioidea using other cyprinodontoid fishes as outgroups. The three equally most parsimonious trees resulting from the phylogenetic analysis support the monophyly of the families Anablepidae and Poeciliidae with respect to each other, but the previous taxonomy within the Poeciliinae is not consistent with the resultant phylogenetic trees. The Poeciliidae is recognized with three subfamilies: the Aplocheilichthyinae containing solely Aplocheilichthys spilauchen , the Procatopodinae containing Fluviphylax (Fluviphylacini) and the African lamp-eyed killifishes (Procatopodini), and the Poeciliinae. The inferred hierarchical relationships of included suprageneric taxa are: ((Oxyzygonectinae, Anablepinae) (Aplocheilichthyinae ((Fluviphylacini, Procatopodini) (Alfarini (Priapellini (Gambusini (Heterandrini (Cnesterodontini (Girardini, Poeciliini))))))))). The tribe Alfarini is resurrected and a new tribe, the Priapellini, is described. Tomeurus gracilis is not the most basal poeciliine, and facultative viviparity in Tomeurus is not a plesiomorphic intermediate condition of viviparity retained from the common ancestor of poeciliines. Facultative viviparity in Tomeurus is the result of an evolutionary loss of obligate viviparity. Tomeurus gracilis is recognized as a member of the tribe Cnesterodontini. Lamprichthys tanganicus and Micropanchax pelagicus are not sister taxa, and the pelagic lacustrine habits of these two species are inferred to have evolved independently. Based on the principles of vicariance biogeography, the origin of the Poecilioidea is inferred to have occurred before the separation of Africa and South America.     

Molecular phylogeny of the gobioid fishes (Teleostei: Perciformes: Gobioidei)

The phylogeny of groups within Gobioidei is examined with molecular sequence data. Gobioidei is a speciose, morphologically diverse group of teleost fishes, most of which are small, benthic, and marine. Efforts to hypothesize relationships among the gobioid groups have been hampered by the prevalence of reductive evolution among goby species; such reduction can make identification of informative morphological characters particularly difficult. Gobies have been variously grouped into two to nine families, several with included subfamilies, but most existing taxonomies are not phylogenetic and few cladistic hypotheses of relationships among goby groups have been advanced. In this study, representatives of eight of the nine gobioid familes (Eleotridae, Odontobutidae, Xenisthmidae, Gobiidae, Kraemeriidae, Schindleriidae, Microdesmidae, and Ptereleotridae), selected to sample broadly from the range of goby diversity, were examined. Complete sequence from the mitochondrial ND1, ND2, and COI genes (3573 bp) was used in a cladistic parsimony analysis to hypothesize relationships among the gobioid groups. A single most parsimonious topology was obtained, with decay indices indicating strong support for most nodes. Major phylogenetic conclusions include that Xenisthmidae is part of Eleotridae, and Eleotridae is paraphyletic with respect to a clade composed of Gobiidae, Microdesmidae, Ptereleotridae, Kraemeriidae, and Schindleriidae. Within this five-family clade, two clades are recovered. One includes Gobionellinae, which is paraphyletic with respect to Kraemeriidae, Sicydiinae, Oxudercinae, and Amblyopinae. The other contains Gobiinae, also paraphyletic, and including Microdesmidae, Ptereleotridae, and Schindleriidae. Previous morphological evidence for goby groupings is discussed; the phylogenetic hypothesis indicates that the morphological reduction observed in many goby species has been derived several times independently.     

Phylogeny and biogeography of cichlid fishes (Teleostei: Perciformes: Cichlidae)

Family level molecular phylogenetic analyses of cichlid fishes have generally suffered from a limited number of characters and/or poor taxonomic sampling across one or more major geographic assemblage, and therefore have not provided a robust test of early intrafamilial diversification. Herein we use both nuclear and mitochondrial nucleotide characters and direct optimization to reconstruct a phylogeny for cichlid fishes. Representatives of major cichlid lineages across all geographic assemblages are included, as well as nearly twice the number of characters as any prior family‐level study. In a strict consensus of 81 equally most‐parsimonious hypotheses, based on the simultaneous analysis of 2222 aligned nucleotide characters from two mitochondrial and two nuclear genes, four major subfamilial lineages are recovered with strong support. Etroplinae, endemic to Madagascar (Paretroplus) and southern Asia (Etroplus), is recovered as the sister taxon to the remainder of Cichlidae. Although the South Asian cichlids are monophyletic, the Malagasy plus South Asian lineages are not. The remaining Malagasy lineage, Ptychochrominae, is monophyletic and is recovered as the sister group to a clade comprising the African and Neotropical cichlids. The African (Pseudocrenilabrinae) and Neotropical (Cichlinae) lineages are each monophyletic in this reconstruction. The use of multiple molecular markers, from both mitochondrial and nuclear genes, results in a phylogeny that in general exhibits strong support, notably for early diversification events within Cichlidae. Results further indicate that Labroidei is not monophyletic, and that the sister group to Cichlidae may comprise a large and diverse assemblage of percomorph lineages. This hypothesis may at least partly explain why morphological studies that have attempted to place Cichlidae within Percomorpha, or that have tested cichlid monophyly using only “labroid” lineages, have met with only limited success. © The Willi Hennig Society 2004.     

Ultrastructure of the epidermis of adult and embryonic Paravortex species (Turbellaria,Eulecithophora)

The epidermis and associated structures of adult and embryonic Paravortex cardii and Paravortex karlingi, internal parasites of Cerastoderma edule, have been examined using scanning and transmission electron microscopy. The cellular epidermis of adult Paravortex bears cilia and microvilli which differ in number and distribution between P. karlingi and P. cardii. Cellular organelles include mitochondria, lipid bodies, Golgi bodies, and ultrarhabdites. Epidermal nuclei are located in the proximal portion of the cells. The development of the tegument of embryo Paravortex has been described and a possible origin for the embryo capsule is suggested. These findings are discussed in relation to the phylogenetic status of the Turbellaria in relation to other Platyhelminthes and in the functional adaptation of the epidermis for a parasitic mode of life.Abbreviations bb- basal bodies - bl- basal lamella - c- cilia - cp- capsule - dc- dark cells - e- embryos - ep- epidermis - g- Golgi bodies - int- interdigitation (of cells) - l- lipid - lf- lamellar fold - mc- migrating cell - mf- membranous folds - mt- mitochondria - mv- microvilli - n- nucleus - nb- neoblasts - p- projections of epidermis - par- parenchyma of mother - pr- primary rootlet - rc- rhabditogen cells - sr- secondary rootlet - ur- ultrarhabdites - vt- vitelline material     

Ultrastructure of prostomial photoreceptors in four marine polychaete species (annelida)

The photoreceptors of four polychaete species were investigated by transmission electron microscopy: Eteone longa and Anaitides mucosa (Phyllodocidae), Scolelepis squamata (Spionidae), and Heteromastus filiformis (Capitellidae). Four different types of light-sensitive organs could be distinguished: 1) a simple, unpigmented rhabdomeric type; 2) a simple ocellus composed of a sensory and a pigmented cell; 3) complex eyes with a lens consisting of secretory granules; 4) a simple, unpigmented type with modified cilia. In spite of its simpler organization the fourth type is listed last, because its function as a photoreceptor seems dubious. The first type (unpigmented rhabdomeric receptor) occurs in all four species investigated. It is the only type of photoreceptor in Heteromastus. Additionally, the two phyllodocids Eteone and Anaitides possess another kind of receptor (type 4) in close proximity to the type 1 receptor. Simple ocelli (type 2) are found in Scolelepis. A pair of complex eyes (type 3) is present in both Eteone and Anaitides, but they show important differences in the two species. First, the eyes in Eteone exhibit ciliary rudiments within the sensory processes, but such rudiments are absent in the eyes of Anaitides. Secondly, the sensory cells in Anaitides possess pigment granules, whereas in Eteone they do not. Thirdly, the lens in Eteone is composed of secretion granules of equal electron density, whereas in Anaitides the lens granules show increased electron density centrally. Lens material appears to be secreted from a single corneal cell in Eteone, and from several corneal cells in Anaitides. In both species these corneal cells are located distally outside the lens.     

New osteological and morphological data of four species of Aphaniops (Teleostei; Aphaniidae)

Aphaniops dispar, widespread around the Arabian Peninsula, was recently separated in four species (A. dispar, A. hormuzensis, A. kruppi, A. stoliczkanus) by molecular results and colour patterns, but the morphological differences are small and call for more studies. Here we report differences in skeleton and median fin osteology of these species. In addition, we introduce the term 'modified caudal vertebra' to describe caudal vertebrae that are not directly associated with caudal ray support but are visibly modified from a 'usual' caudal vertebra. Aphaniops hormuzensis, an endemic species to southern Iran, has a significantly higher number of modified caudal vertebrae compared to the more widespread A. stoliczkanus and A. dispar, and also to A. kruppi. This is a surprising result as the caudal skeleton and related structures of the posterior caudal vertebral column have yielded successful results in separating between families or genera, but there are only a few studies that have examined these structures for their role in species diagnosis. Our study also highlights that state-of-the-art methods in X-raying and improved staining procedures assist in the discrimination of superficially similar species.     

Length–weight relationships for four Aphanius species of Iran (Teleostei: Cyprinodontidae)

Length–weight parameters are presented for four endemic tooth‐carps of the genus Aphanius from Iran.     

Karyotype analysis in three species of the genus Chirostoma (Atheriniformes: Atherinidae)

Karyotype analyses of three Chirostoma species, C. estor, C. patzcuaro, and C. jordani from Mexico, are presented. C. estor and C. jordani have both a diploid number of 2N = 48 and a fundamental number of NF = 68, but different karyotype formulae. The co-occurrence of these karyotypes with morphometric and allozymatic primitive features so far reported suggests that the ancestral karyotype of the genus Chirostoma was similar to the one shown by these species. The divergent karyotype of C. patzcuaro (2N = 44 and NF = 44) could be related to its endemism and to the relatively small size of its populations. Received: February 7, 2001 / Revised: September 7, 2001 / Accepted: October 11, 2001