Unique morphologies of Encheliophis vermiops (Carapidae) with revised diagnosis of the genus

Encheliophis vermiops was first briefly described in 1990 on the basis of three specimens. This study validates this species and provides previously unrecorded useful characters to realise the identification: (1) the forward orientation of the palatine teeth, (2) the enlarged teeth of the third basibranchial, (3) the particularly well-developed pharyngeal apparatus, (4) the unpigmented band along the base of anal fin and (5) the insertion of the primary sonic muscle on the parasphenoid. Moreover, the particular morphology of Encheliophis vermiops forces us to reconsider the diagnosis of the genus.     

Sperm dimorphism and spermatozeugmata in the commensal bivalve Pseudopythina macrophthalmensis (Galeommatoidea, Kelliidae)

The bivalve Pseudopythina macrophthalmensis (Galeommatoidea) is a commensal with the crab Macrophthalmus convexus (Ocypodidae) in Okinawa Prefecture, Japan. It is a protandric hermaphrodite which incubates the 65-μm large ova in the suprabranchial cavity. The species produces two types of sperm, which were studied with the electron microscope. The euspermatozoon has an elongate 2.8-μm-long, pointed acrosome, a slender 12- to 13-μm-long nucleus and a middlepiece containing several closely packed mitochondria arranged as a 5.5- to 6.0-μm-long sheath around the basis of the flagellum. The paraspermato- zoon is vermiform, 220-μm-long and up to 5-μm-broad. Anteriorly there is a ca 7-μm-long bullet-shaped acrosome followed by a subcylindrical 3.0- to 4.7-μm-long nucleus. Adjacent to the nucleus occurs a bundle of 26–42 40-μm-long flagella. The cytoplasm is packed with spherical lipid droplets and ovoid granules of unknown composition. Sperm of both types aggregate to form spermatozeugmata, which were found in the posterior mantle cavity or in paired seminal receptacles. Within the receptacles the euspermatozoa dissociate themselves from the spermatozeugma and become attached to the epithelial lining of the receptacle whereas the paraspermatozoa presumably disintegrate. The possible significance of the two types of sperm is discussed in the light of their presumed functions in gastropods. Accepted: 9 November 2000     

Sex, seminal receptacles, and sperm ultrastructure in the commensal bivalve Montacuta phascolionis (Veneroida; Galeommatacea)

It is argued that the paired structures in adult Montacuta phascolionis previously claimed to be testes are seminal receptacles. The receptacles in 3.0mm long females are filled with sperm cells or spermatids. A 2.0-mm long specimen had a well-developed testes exhibiting ripe sperm. It is concluded that the species is a protandrous hermaphrodite and that the previously described dwarf males are rather complemental males. The ultrastructure of the sperm cells is described and compared with that of the sperm of related species.     

A comparative study of sperm postspawning destruction in flatfishes Hippoglossoides (Cleisthenes) herzensteini and Hippoglossoides dubius (Teleostei, Pleuronectidae)

Ultrastructural aspects of sperm destruction patterns were offered as additional cytological parameters for evaluation of the genus affinity of flatfishes Hippoglossoides dubius and Cleisthenes herzensteini. At the beginning of spermatozoan destruction, cell membrane in both species was found swollen, besides, discontinuity of membranes was observed, and membraneous parts were seen separating from sparmatozoa. We observed the ability of separated membraneous parts to aggregate to twisting conglomerates that wind round the objects of destruction. In H. dubius the membraneous conglomerates wound round spermatozoa, and after that such spermatozoa were phagocyted by follicular cells. In C. herzensteini, the membraneous conglomerates grasped the particles of destructed spermatozoa: the formed residual bodies were collected in the gonad lumen but not phagocyted by follicular cells. The expressiveness of the differences found in the pattern of sperm destruction is so considerable that, in the authors' opinion, these data are to supplement a list of criteria making reasonable reconsideration of the taxonomic status of C. herzensteini: its belonging to the genus Hippoglossoides, and establishing of the genus Cleisthenes as an independent rank.     

Revision of the bathyal fish genusHomostolus (Ophidiiformes,Ophidiidae)

The ophidiid fish genusHomostolus is revised on the basis of 44 specimens. Meristic and morphometric characters strongly indicate that the genus as presently known contains a single species,Homostolus acer Smith et Radcliffe, 1913, withHomostolus japonicus Matsubara, 1943, reduced to synonymy. Geographical variations found in certain meristic characters indicate thatH. acer expanded its range from Philippine waters into both northern and southern waters. The species is distributed on deep-sea floors from the Pacific Ocean off central Japan, to the Indian Ocean off northern Western Australia, and to the Tasman Sea off New South Wales, at bathyal depths from about 400 to 700 m.     

A unique adhesion apparatus on the eggs of the catfishClarias gariepinus (Teleostei,Clariidae)

Eggs of the catfishClarias gariepinus were investigated for the first time using light and electron microscopy (SEM and TEM). In shape, they differ strongly from those of other teleosts, their characteristic profile resembling a fur cap. This shape is unique among the eggs of teleostean fishes. The eggs ofC. gariepinus are attached to substrata at their animal pole, which shows an annular bulge consisting of numerous tiny attaching-filaments. These filaments seem to be a part of the zona radiata externa. The micropyle, located within the center of the annular bulge, is a straight opening in the zona radiata. Different ways of egg adhesion in teleosts were compared and discussed as well as the position of the micropyle with respect to fertilization.     

Otolith crystals (in Carapidae): growth and habit

The biomineralization of otoliths results mainly from the release of soluble Ca(2+), which is in turn precipitated as CaCO(3) crystals. In some Carapidae, sagittae sections have been shown to reveal a three-dimensional asymmetry with a nucleus close to the sulcal side, an unusual position. This study seeks to understand otolith formation in Carapus boraborensis. The unusual shape of the otolith is partly explained by the distribution of the epithelium cells, and particularly the sensory epithelium. Experimental evidence shows for the first time that aragonite growth takes place along the c-axis. These aragonite needles present two different habits. On the sulcal side is found the acicular form resulting from rapid growth during a short period of time. On the anti-sulcal side, the prismatic form seen there is due to a slower growth speed over longer periods. The otolith surface was observed each hour during a period of 24h in fishes reared in similar conditions. This allowed for the first time the direct observation on the otolith surface of the deposition of the two layers (L-zone and D-zone). In C. boraborensis, the organic-rich layer (D-zone) develops during the day, whereas the CaCO(3) layer (L-zone) seems to be deposited during the night.     

Morphological evidence for the biological role of caniniform teeth in combtooth blennies (Blenniidae, Teleostei)

Combtooth blennies have recurved, fang-like caniniform teeth at the rear end of a single row of incisiform teeth. The lengths and positions of these canines were measured in the lower jaws of males of 14 species of Mediterranean Blenniidae. In four species, lower jaw canines were measured in males and females, while in one species, the upper jaw canines of both sexes were also measured. Relative (to body length) canine length in males tends to be significantly greater (10–40%) than in females. There are significant interspecific differences in relative canine length, with smaller species tending to have relatively larger teeth. No significant correlation was obtained between canine length and importance of animal prey in the diet, nor with 'hole fit' of males, which may be related with the intensity of paternal care. We suggest that canines in combtooth blennies are predominately used for predator deterrence and agonistic interactions.     

Behavior and physiology of coexistence in two species of Dascyllus (Pomacentridae,Teleostei)

Synopsis In the Gulf of Aqaba Dascyllus aruanus and D. marginatus, form distinct populations organised into harems of single males and groups of females, living permanently in Stylophora and Acropora corals. Each harem consists of 4 sexual casts: dominating males, adult females, sex-changing fish and juveniles. The sexual performance of each adult fish in such social units is controlled by the presence or absence of a dominating male. In corals occupied by mixed groups of both species, only those females spawn that belong to the same species as the dominating male. Direct observation in the sea shows that such situations are produced by indiscriminative settling mechanisms of groups of juvenile fish. Evidence is also presented, demonstrating that dispersion of coral colonies suitable for occupancy and predation by piscivorous fish can modulate such complicated reproduction.     

Inducible defence against a ciliate grazer Pseudomicrothorax dubius,in two strains of Phormidium (cyanobacteria)

Experiments were done with two strain of filamentous, mat-forming Phormidium and their ciliate grazer Pseudomicrothorax dubius, to explain why the ciliates remain hungry in an apparent surplus of food, except for the first 24 hours after feeding. Under grazing pressure, both strains of cyanobacteria showed statistically significant increases in the number of filaments terminating in an empty sheath, compared to the control. Direct observations revealed that the mechanism behind this effect was active withdrawal of the trichomes inside the sheaths when disturbed by grazers. As P. dubius is unable to ingest trichomes with such endings, we conclude that cyanobacteria are not limited to chemical means of defence against grazers but can also defend themselves by means of movement and changes in filament morphology. This is apparently the first report on behavioural defence observed in cyanobacteria.     

Revision of the Indo-West pacific bathyal fish genusGlyptophidium (Ophidiiformes,Ophidiidae)

The ophidiid genusGlyptophidium is revised on the basis of 280 specimens. The seven recognized species fall into two well-defined species-groups: I.argenteum species-group withargenteum Alcock, 1889,effulgens sp. nov. andlucidum Smith et Radcliffe, 1913 is characterized i.a. by having 1 ray in each ventral fin, 1 median basibranchial tooth patch, 11 precaudal vertebrae, origin of dorsal fin above vertebrae nos. 3–4. II.macropus species-group withmacropus Alcock, 1894 (lectotype selected),longipes Norman, 1939,oceanium Smith et Radcliffe, 1913 andjaponicum Kamohara, 1936 (re-established and neotype described) is characterized i.a. by having 2 rays in each ventral fin, 2 median basibranchial tooth patches, 12–13 precaudal vertebrae, origin of dorsal fin above vertebra no. 1 or in front.     

A comparison of food capture and ingestion in juveniles of two flatfish species, Pleuronectes platessa and Limanda limanda (Teleostei: Pleuronectiformes)

Juvenile plaice, Pleuronectes platessa ( n =6, 151–197 mm SL) and dab Limanda limanda ( n =6, 119–180.5 mm SL) feeding on pieces of mussel flesh were studied by high-speed (200 fields s⁻¹) videophotography at 11) C. Prey capture cycles (involving jaw protrusion and opercular expansion) were described in both species. The capture cycle was followed by at least one cycle (similar to the capture cycle in all respects except food intake) which is believed to transport food to the oesophagus. The transport cycle (or cycles) was followed by a species-specific number of normal respiratory cycles (7 or 8 in plaice, 11 or 12 in dab) and a final single cycle when food debris was violently ejected from the opercular cavity. The respiratory cycles and ejection cycle cleansed the orobranchial/opercular cavities and gills. Differences between the species were relatively minor, but plaice captured and transported food more quickly than dab.     

Morphological and ultrastructural organization of the male genital apparatus of some Aphididae (Insecta, Homoptera)

Ultrastructural investigations on the amphigonic reproductive mechanisms in Aphidoidea (Homoptera, Sternorryncha) species, of which little is known in the literature, can provide useful information on their reproductive biology. Morphological and ultrastructural investigations were carried out on the reproductive tract and on spermatozoa from sexually mature males of five species belonging to three subfamilies of Aphidoidea. The organization of the reproductive tract and of spermatozoa appears simple and similar in the examined species. Each testis consists of three follicles containing many cysts arranged in a progressive order of maturation from the distal to the proximal tract; spermiogenesis only occurs in sexually mature males, ending with the organization of sperm bundles. Gametes are neatly arranged in each bundle and kept together by a cap showing a particular organization. The distal tract of each spermiduct is enlarged and full of gametes; close to the testis the two spermiducts merge together, except in Drepanosiphum platanoidis where the spermiducts run independently. The various tracts of each examined gland showed no peculiar differences either in the same species or among the species. Some interesting hypotheses are proposed in this work about the probable roles of the investigated structures in the reproductive mechanisms of these insects.     

Effects of jaw adductor hypertrophy on buccal expansions during feeding of air breathing catfishes (Teleostei,Clariidae)

Some species of Clariidae (air breathing catfishes) have extremely well developed (hypertrophied) jaw closing muscles that increase the maximal biting force of these species. As these enlarged jaw muscles tightly cover the suspensoria, which are firmly connected to the neurocranium, we expect diminished lateral expansions during suction for species with hypertrophied jaw muscles. In turn, this could imply a reduced suction performance for these species. Compared to Clarias gariepinus, which has relatively small jaw closers, Clariallabes longicauda shows a clear hypertrophy of the jaw adductors. A kinematic analysis of prey capture in these two species is presented here. As predicted, Clariallabes longicauda shows less lateral expansion (average abduction of the hyoids of 19.0°) than Clarias gariepinus (abduction of 31.1°). However, our data indicate that the decrease in lateral expansion capacity in the species with excessive adductor development is compensated for by a larger and faster ventral expansion of the buccal cavity by depression of the hyoid.