There are four species of Eleotris found in Japan: E. oxycsephala TEMMINCK & SCHLEGEL, E. melanosoma BLEEKER, E. acanthopomus BLEEKER and E. fusca BLOCH & SCHNEIDER. Specimens of these four species and E. mauritianus BENNETT and E. sandwicensis VAILLANT & SALTVAGE which resemble them were compared in detail. The specimens counted and observed in this study are listed in table 1. Besides these, BLEEKER'S specimens from Rijksmuseum van Natuurli jke Historie were examined, and they are listed in table 14 with the results of the observation dealt with separately from the results of the observation in this study. The fin counts and the characteristics of scales which show certain degrees of difference are shown in tables 2-9. The characteristics of the gill rakers are clearly distinguishable among the species. The shapes of the outer gill rakers on the 1st arch of E. oxycephala are very distinct, being short pedestals covered with spines (fig. 14), while the outer gill rakers of others are rods with spines on their inner side (fig. 15). The number of outer gill rakers, the ratio between the length of the portion without gill rakers in the ceratobranchial against its length and the position of outer gill rakers in relation to inner gill rakers are different among the species (figs. 16-17, table 10-12). Together with these, the sizes of the membranes between the 1st gill arch and the pharynx are also different among them (figs. 18-21). The difference between E. melanosoma and E. acanthopomus which is not distinguishable on the scale counts is very conspicuous here. The patterns of pit organs on the head are the most distinguishable characteristics (figs. 1-12 and 22-25). The pit organs of E. oxycephala are very different from those of other species, having longitudinal rows of pit organs from the chin to the lower margin of the preopercle (fig. 9), instead of having transverse lines (fig. 10). And also E. oxycephala has a longitudinal line of pit organs immediately behind the eye (line 13 in fig. 5), instead of a transverse line (line 8 in figs. 6 and 7, and line 10 in fig. 8). E. melanosoma differs from the others in having more prominent lines of pit organs (fig. 23). The characteristic patterns of pit organs in the infraocular region of each species are shown in figures 5-8. In E. oxycephala, lines 3, 4 and 5 do not cross line 11 (fig. 5); in E. melanosoma, only line 5 does not cross line 13 (fig. 6); in E. acanthopomus, E. mauritianus and E. sandwicensis line 3 and 5 do not cross line 13 (fig. 7); in E.. fusca lines 3, 5 and 7 do not cross line 15 (fig. 8). Anomalous arrangements of pit organs are not found on both sides of any specimen examined except on a specimen of E. fusca which has seven lines instead of eight. The transverse lines of pit organs along the preopercle differ, too, among the species as shown in table 13. Pit organs on the opercle are of two types (figs. 11-12): the one in which line 1 and line 2 do, not meet is that of E. oxycephala, E. acanthopmus, E. mauritianus and E. sandwicensis; the other in which line 1 and line 2 meet and line 2 does not cross line 1 is that of E. melanosoma and E. fusca. The anal papilla of the female of E. oxycephala is also different from that of the others in that it has fringes on the posteriormargin (fig. 26), while the others have no fringes (fig. 27). E. oxycephala is different from the others in coloration, too, having two dark lines backward and downward from the eye, while the others have three, although it is often difficult to observe these lines. In most of the specimens of E. melanosoma these lines could not be seen. The clear difference in the characteristics of gill rakers and pit organs separating E. mauritianus and E. sandwicensis
Scapulae of 84 species of gobiid fishes were stained with alizarin red and examined. They were classified into four types as follows. Enclosing scapula type: The scapula completely encloses the scapula foramen (figs. 1-3). Forked scapula type: The scapula surrounds the scapula foramen incompletely and the lower margin is broken by the foramen (fig. 4). Blotched scapula type: The scapula is not broken at the lower margin by the scapula foramen which is outside of the scapula. No scapula type: The scapula does not appear when stained with alizarin red. In certain cases two of the four types were found among matured individuals of the same species and sometimes even in the right and left scapulae of the same specimen were different. These conditions were observed in Odontobutis obscure, Gobius niger, Quisquilius naraharai and Zonogobius semidoliatus. Scapulae of Lubricogobius exiguus TANAKA and Mugilogobius abei (JORDAN & SNYDER) shown in the figures 8 and 19-22 of my previous paper, are thought to be included in such a special group.The blotched scapula was found in two specimens of Pandaka pygmaea HERRE preserved in alcohol, so it seems probable that all Pandaka pygmaea have the blotched scapula. Among 150 species, including the results of my previous paper, 12 species are of the enclosing scapula type, 66 species (45 species in my previous paper except Lubricogobius exiguus and 21 species in the present study) belong to the forked scapula type, 1 species (Pandaka pygmaea in my previous paper) is of the blotched scapula type, and 64 species (18 species in my previous paper and 47 species in the present study) belong to the no scapula type. Besides the above mentioned species, there are 6 species of the special group in which two types of scapula were found. In 1 species, the enclosing scapula type and the forked scapula type are found; in 4 species (Lubricogobius exiguus in my previous paper and 3 species in the present study) the forked scapula type and the blotched scapula type are found ; in 1 species (Mugilogobius abei in my previous paper) the blotched scapula type and the no scapula type are found. However, if more specimens of the same species are examined, it is possible that the number of the species to be included in the special group will increase. The results of the present study further confirm the conclusion of my previous paper that the characteristics of the scapula provide a useful means of distinguishing the genera of gobiid fishes. But as I have not examined other characteristics. I do not refer to the classification of the genera of gobiid fishes.
The histological observations on the barbels of Rita rita (HAM.) are reported. The maxillary barbel has epidermis and dermis surrounding a cartilaginous axis. The stratified epidermis embodies mucous cells, club cells and taste buds. The basement membrane lies in between epidermis and dermis except at the places of dermal papillae. The dermis is made up of connective tissue fibres and encloses nerve bundles and blood vessels. The mandibular barbel has an identical structure. The mucous cells and club cells increase in number and size in the basal region of nasal barbel. The club cells appear first at the beginning of the flap.Only the lower half of the flap, facing the narial aperture, lacks in taste buds.
The barbels of a marine catfish, Arius thalassinus (RUPP.) have been studied. Each barbel is composed of epidermis, dermis and a central rod of cartilage. The epidermis has a stratified epithelium. It contains abundant cutaneous taste buds and a few, small club cells. The mucous cells are not seen. The dermis incloses blood vessels and nerves. The axial, supporting, skeletal rod is cartilaginous in nature. The barbels are of stiff, and flexible type. The various histological constituents have been explicitly discussed.