Bicosta
- Bicosta minor (Reynolds) (ref. ID; 7107)
Syn; Bicosta minor Leadbeater, 1978, p.511 (ref. ID; 7107); Salpingoeca minor Reynolds, 1976, p.13, fig.11 (ref. ID; 7107); Salpingoeca virgata Parke & Leadbeater, 1977, p.4 (ref. ID; 7107)
- Bicosta spinifera (Throndsen) (ref. ID; 7107)
Syn; Bicosta spinifera Leadbeater, 1978, p.511 (ref. ID; 7107); Salpingoeca spinifera Throndsen, 1970, p.87, fig.1A (ref. ID; 7107)
Bicosta minor (Reynolds) (ref. ID; 7107)
Synonym
Bicosta minor Leadbeater, 1978, p.511 (ref. ID; 7107); Salpingoeca minor Reynolds, 1976, p.13, fig.11 (ref. ID; 7107); Salpingoeca virgata Parke & Leadbeater, 1977, p.4 (ref. ID; 7107)
Descriptions
The lorica, 26-41 um in length (mean 31 um), is composed of seven costal strips arranged as two longitudinal costae and a posterior spine. There are transverse costa. Each longitudinal costa contains three successive costal strips and the uppermost costal strip attenuates to a pointed tip and acts as a spine anteriorly. The two anterior spines are almost equal in length and range between 9.5-17.5 um in length (mean 12.7 um). The lorica chamber, 9.3-13.1 um in length (mean 10.9 um), is made up to the posterior pairs of costal strips that form the two longitudinal costae. These costae are either not twisted or twisted. The spiral rises from lower left to upper right or "dextrorsum externe visus", and the costae cross at the level of the posterior costal strip to form the lorica chamber. In the two successive costal strips forming the lorica chamber, the anterior one, 4.8-6.6 um in length (mean 5.4 um), is usually a little shorter than the posterior one, 5.3-7.1 um in length (mean 6.1 um). The posterior spine is almost straight or simply curved and attenuates to a pointed end. The posterior spine, 7.7-13.6 um in length (mean 10.0 um), is shorter than the anterior ones. (ref. ID; 7107)
Notes
The presence of a certain twisting of the longitudinal costae has been regarded as an important specific characteristic of Bicosta spinifera, and B. minor has been attributed to a non-twisted species (Manton et al. 1980). In Osaka Bay, however, the longitudinal costae of some small organisms which were referable to B. minor were twisted like those of B. spinifera. There was not essential difference in the size ranges of the anterior spines among B. minor and B. spinifera. On the other hand, in sizes of the lorica chamber, the small twisted organisms are identical with B. minor, but B. spinifera is a little larger than B. minor. This trend is very apparent in lengths of the posterior spines. In conclusion, the dimensional ranges of the small twisted organisms correspond of those of B. minor, and not to B. spinifera. The small twisted organisms have straight or simply curved posterior spines which are shorter than its two equally long anterior spines. These characteristics are similar to those of the typical B. minor. The posterior spine of B. spinifera is characteristic S-shaped at its distal end and substantially longer than either of its two unequally long anterior spines. Furthermore, the twisting modes are different in the small twisted organisms and B. spinifera. In B. spinifera, the longitudinal costae twist in the direction from lower right to upper left and cross at the level of the anterior longitudinal costal strips that form the lorica chamber. In the small twisted organisms, however, the spiral rises from lower left to upper right and the longitudinal costae cross at the level of the posterior costal strips of the lorica chamber. The intersection point itself moves from the apical end to the posterior end of the posterior costal strip of the lorica chamber. Photographs in Pl. I illustrate the variation of the mode of the twist from non-twisted to twisted states; i.e., a clearly non-twisted lorica, a lorica with a narrow posterior end of the lorica chamber, a lorica twisted only at the posterior end of the lorica chamber and a clearly twisted lorica. The small twisted organisms and untwisted B. minor share common and/or continuous morphological and morphometrical characteristics. On the other hand, clear differences between the small twisted organisms and B. spinifera are observed in the twisted direction and the crossing levels of the costae. At this stage, we include the small twisted organisms within the specific category of B. minor, instead of establishing a separate taxon.
Gathering all specimens of Bicosta minor that we took from Osaka Bay, total lengths of loricae ranged from 26 to 41 um (mean 31 um). The size distribution of specimens of B. minor, collected in different seasons, rules out any simple interpretation in terms of direct influence by temperature. Manton et al. (1980) reached the same conclusion from data collected in geographically separate localities. The ratios of the anterior and posterior spine lengths to the lorica chamber length were constant among the organisms of B. minor with differently sized loricae, which were collected from water at various temperatures. In general, anterior spines were longer than the lorica chamber by a factor of approximately 1.2. The posterior spine was shorter than the lorica chamber by a factor of 0.9. Extremely long or short anterior and/or posterior spines were also observed occasionally. The size is apparently uniform over different temperatures. This seems to suggest that the population of Bicosta minor in Osaka Bay is of a single biotype with respect to size. According to Manton et al. (1980) who used material collected from several localities of the world, the most typical range of whole lorica length of B. minor was between 20-30 um. As the lorica length which was used by Manton et al. (1980) was meant the shortest distance from tip to tip of the anterior and posterior spines, the length calculated by their method was smaller than the value calculated by our method by the factor 0.83 in minimum for Bicosta minor. The range reported by Manton et al. (1980) (20-30 um), however, is smaller than that of our materials (26-41 um), even if the bias of the value may be calibrated. The range of the whole lorica length, based on the specimens collected from the type locality in the Norwegian water, is 30-45 um (Reynolds 1976), and then larger than our specimens. The specimens in Osaka Bay are intermediate in size range between those reported by Reynolds (1976) and Manton et al. (1980). In addition to size, the existence of twisted organisms in our material indicated that the population of B. minor in Osaka Bay may be included in a separate biotype to the other population in other localities. There is an obvious discontinuity in whole lorica length between Bicosta spinifera and B. minor. These two species have the same or the continuous range in the anterior spine length and the lorica chamber length. The obvious discontinuity in the whole lorica length, therefore, is ascribed to different length of the posterior spines, which is short in B. minor and long in B. spinifera. Direct evidence on replication of the lorica is, unfortunately, scarce, but the organisms shown in Plate I illustrate the possible stages of replication in Bicosta minor so far encountered in this studies. It should be noted that the development of the lorica interpreted here has been pieced together from observation of shadowcast whole mounts under the electron microscope. Arrowheads in the photo 8 in Pl. I indicate the two nascent costal strips, one as thick as the complete one but the other thinner, and neither liberated to the exterior, are still present within the cytoplasmic area. From their curved shape, we hypothesize that these two costal strips may be the strips that will be forming the lorica chamber. Because of the short and curved morphology, and the fact that the ends are obliquely cut and bent backwards, we can guess that these two new costal strips represented are the two anterior costal strips that will form the lorica chamber. Since the three (or four) new costal strips shown in photo 10 in Pl. I are short and slightly curved, they will be the anterior two and the posterior one (or two) costal strips of the lorica chamber. Besides these strips forming the lorica chamber, photo 11 in Pl. I depicts two long attenuated costal strips with pointed ends, which project backward from the posterior end of the lorica chamber of the mother cell. This pair of long costal strips will be of two anterior spines of the new cell. All the several costal strips for the whole lorica have already been completely formed in the region previously shared by the mother cell. It is now obvious that the order of formation of costal strips is predetermined for these species. The anterior costal strips of the lorica chamber are formed first, followed by the posterior costal strips of the lorica chamber, then anterior spines and finally the posterior spine costal strip. The preceding formation of the costal strips of the lorica chamber over the formation of spine strips was suggested also by Manton et al. (1980) for Bicosta spinifera, the species most closely related to B. minor.
The apical ends of the newly formed costal strips of the lorica chamber in photos 9 and 11 in Pl. I point posteriorly. The attenuated tips of the newly formed anterior spines in photos 11-13 in Pl. I also point posteriorly, while the new posterior spine points anteriorly photos 12 and 13 in Pl. I. In addition to the order of formation, the direction of the newly formed costal strips is also predetermined. As a whole, the new costal strips that are synthesized and stored in the mother protoplast are oriented in the opposite direction to the corresponding costal strips of the mother lorica.
In the previous investigations (Thomsen 1977; Leadbeater 1979), it has been observed in Acanthoecidae that the newly formed costal strips are released outside and are accumulated in the front of the mother protoplast before cell division. In B. minor, these costal strips may be neither released nor accumulated outside the mother protoplast before cell division. The water temperature in Osaka Bay ranged from 8.2 to 26.2 degrees C throughout the period investigated, and Bicosta minor was abundant and common in December and January when the water temperature ranged around 10 degrees C. They were found, though in less abundance, at all other seasons as well. This species has been found almost all over the world, wherever temperature is in a range from -1 to 26.2 degrees C (Manton et al. 1980, this study), and seems to occur at lower frequencies at temperature below 4 degrees C (Manton et al. 1980) but the most abundant at moderate temperatures. (ref. ID; 7107)
Sampling site
Surface seawater samples were collected from the Shioya Coast of Osaka Bay, which faces to the inland sea, Setonaikai. (ref. ID; 7107)
Synonym
Bicosta spinifera Leadbeater, 1978, p.511 (ref. ID; 7107); Salpingoeca spinifera Throndsen, 1970, p.87, fig.1A (ref. ID; 7107)
Descriptions
The "Y" shaped lorica, 57-66 um in length (mean 61 um), is composed of only seven costal strips, arranged as two longitudinal costae and a posterior spine. No transverse costa is present. Each longitudinal costa contains three successive costal strips and the apical costal strip, 11-19 um in length, attenuates to a pointed tip anteriorly and acts as a spine. The anterior spines are unequal in length. The lorica chamber, 13.5-17.0 um in length (mean 15.4 um), is made up of the posterior pairs of the longitudinal costae, each of them are composed of two costal strips. These longitudinal costae are twisted. The spirals rise from lower right to upper left and cross at the level of the anterior costal strips to form the lorica chamber. The costal strips of the anterior lorica chamber, 7.4-8.3 um in length, are usually a little shorter than the posterior ones, which are 7.4-10.0 um in length. The posterior spine, 18-32 um in length (mean 24.5 um) attenuates to a fine point. It is longer than the anterior spines and ends in a characteristic S-shaped distal extremity. (ref. ID; 7107)
Notes
The lorica structures of five specimens, collected from Osaka Bay on 12 May 1980 when the water temperature was 16.4 degrees C, were exactly identical with previous descriptions (e.g., Manton et al. 1980). SEM observation of the specimens from Osaka Bay reveals that the spiral of the longitudinal costae invariably rises from lower right to upper left or "sinistrorsum externe visus". The direction of twisting has not been mentioned previously, but the schematic drawing in Fig. 10 of Reynolds (1976) and the transmission electron microscopy photograph in Fig.28 of Manton et al. (1980) indicate the same direction as shown in our examination. The range of the lorica dimensions found by us corresponds to those reported by Manton et al. (1980) for the South African population (Cape, water temperature 10 degrees C) and the South Alaskan population (Homer, water temperature 10 degrees C). These are the localities with the highest water temperature recorded prior to our study. This species has been rarely ecountered outside the cold-water realm and has been thought to be absent from water at temperatures above 16 degrees C (Manton et al. 1980). Nevertheless, the material was collected from water at 16.4 degrees C in May, 1980, when the water temperature was increasing steadlily, but was absent when the water was colder in Osaka Bay. Temperature is not the only determinative environmental factor in the distributions of B. spinifera. (ref. ID; 7107)
Sampling site
Surface seawater samples were collected from the Shioya Coast of Osaka Bay, which faces to the inland sea, Setonaikai. (ref. ID; 7107)