Structural diversification of the gustatory organs during metamorphosis in the alpine newt Triturus alpestris.

Gustatory organs of the taste bud type occur in the epithelial lining of the oropharyngeal cavity of alpine newt larvae. They resemble the taste buds of bony fish, both in appearance (as revealed by scanning electron microscopy) and in detailed internal structure (seen on transmission electron micropscopy). During metamorphosis, at stage 55 of development, the secondary tongue (i.e. the soft tongue) is well formed and the anlages of taste discs are clearly apparent. Somewhat later, taste discs also appear in the epithelial lining outside the tongue, paralleling the disappearance of the taste buds. Well-developed taste discs of the newt differ from taste buds mainly by their structurally diversified set of 'associate cells' (mucous, wing and glial cells), which have no synaptic contact with nerve fibres. These cells accompany the neurosensory cellular components of the taste disc, i.e. the taste receptor cells and basal cells. This indicates that gustatory organs in metamorphosed newts, regardless of their small dimensions, fulfil the criteria established for taste discs previously defined in other Caudata and Anura species. Therefore, in the development of the newt there are two subsequent types of gustatory organs and two generations of the tongue: primary, in the larvae, and secondary, in metamorphosed animals.

Pectoral fin development in the Baikalian viviparous golomyankas (Comephoridae; Cottoidei), with a remark on eggs and embryos of Comephorus baicalensis (Pallas).

Measurements of pectoral fin (PF) growth in relation to standard body length (SL) for Comephorus dybowskii (SL: 14-126 mm) and C. baicalensis (SL: 22-173 mm) were made and compared with corresponding data obtained for 13 other Baikalian cottoid species (sculpins). The allometry for the PF/SL relationships (Y = a + bX) is clearly biphasic. Expressed in percentages, these values for the larval period of C. dybowskii [Yp = -28.886 + (2.419X)] are much higher than for C. baicalensis [Yp = -11.904 + (1.233X)]. The postnatal period of development of the golomyanka up to 30-35 mm SL is considered to be the larval stage. In the postlarval period, growth of pectoral fin and the body in C. dybowskii are directly proportional [Yp' = 48.92 + (-0.009X)] whereas in C. baicalensis they rise slightly [Yp' = 30.966 + (0.0505X)]. Absence of the air bladder characterizes all Baikalian cottoid species, including the golomyankas. Various species of the golomyanka differ in the ways of obtaining neutral buoyancy. It is supposed that large pectoral fins guarantee behavioural buoyancy in small species such as C. dybowskii, whereas in C. baicalensis, obtaining much larger body size but lower PFp/SL index, the buoyancy is gained mainly due to the accumulation of large amount of lipids. This paper also documents the ovary and advanced embryos of C. baicalensis.

Morphometry of gill respiratory area in the Baikalian deep-water sculpins Abyssocottus korotneffi and Cottinella boulengeri (Abyssocottidae, Cottoidei).

Abyssocottus korotneffi and Cottinella boulengeri are the deepest-living bottom species among freshwater teleosts. Both species have gill arches with nodulous gill-rakers equipped with sharp denticles. The gill-slit behind the fourth arch is reduced considerably and the hemibranch corresponding to this slit is absent, though some miniature structures resembling reduced filaments were occasionally observed there. The respiratory components of the gill apparatus in both species considered are much reduced, especially in A. korotneffi, because of the moderate number of relatively short gill filaments and the small number of respiratory lamella on them. The allometric relationship between the gill respiratory surface area (GRSA) and body mass (Y = aWb ) is expressed by Y = 328.55 W0.724 for A. korotneffi (7-22 g) and by Y = 333.15 W0.902 for C. boulengeri (3-24 g). In adult A. korotneffi, the GRSA index calculated per body weight unit is about 35% lower than that in C. boulengeri, but is 70% higher compared with the bathypelagic golomyanka Comephorus dybowskii previously examined. The data seem to correspond with the difference in biological activity of these species. J. Morphol. 233:105-112, 1997. © 1997 Wiley-Liss, Inc.

Gill structure and morphometry of its respiratory components in the Baikalian golomyankas (Comephoridae; Cottoidei; Pisces).

All four pairs of gill arches in Comephorus baicalensis and C. dybowskii (Comephoridae) are well developed. In contrast to other Baikalian cottoids (Cottidae, Abyssocottidae), the slit behind the fourth arch is well preserved and two hemibranchs are present on this arch in the golomyankas. These anatomical details are considered to contradict the opinion that Comephoridae may be derived from other Baikalian Cottoidei. The arches in golomyankas are elongated and equipped with very strong spinous gill-rakers. The external sides of the upper and lower jaws are covered with numerous spinelike denticles, the apices of which are bent toward the mouth cavity. The denticles and the spinous gill-rakers are considered to be a specific adaptation in sluggish golomyankas for precise grasping of zooplankton of different sizes, as well as fish larvae. Respiratory components of the gill apparatus in the golomyankas are reduced considerably because of short gill filaments and the sparce distribution of small respiratory lamella on them. The allometry for the relationships between gill respiratory surface area (GRSA) and body mass (Y = aWb ) in both golomyankas is biphasic: in juvenile immature C. baicalensis Yj = 199.013 W1.057 and in mature animals Ym = 322.354 W0.731 . In C. dybowskii the values for immature and mature animals are Yj = 95.736 W1.190 and Ym = 199.609W0.707 , respectively. In the sluggish bathypelagic golomyankas (Comephorus) the GRSA per body weight unit is 5-6 times smaller than that found in more active secondarily pelagic Baikalian sculpins (Cottocomephorus) examined previously. © 1996 Wiley-Liss, Inc.