Diaphanoeca
Order Choanoflagellida Kent, 1880: Family Acanthoecidae Norris, 1965 (ref. ID; 5772)
- Diaphanoeca grandis Ellis, 1930 (ref. ID; 5772) reported year? (ref. ID; 3175) reported author and year? (ref. ID; 7368)
- Diaphanoeca grandis minor (ref. ID; 7368)
- Diaphanoeca sphaerica (ref. ID; 7368)
- Diaphanoeca spiralifurca Hara, 1996 (ref. ID; 7368 original paper)
Diagnosis
Cells solitary. Protoplast (dried) 4.3-8.2 um x 2.5-5.9 um, flagellum 9.3-14.1 um long surrounded by a collar. Lorica ovoid, consisting of anterior projections, lorica chamber, and pedicel. Lorica 21-40 um in length exclusive of pedicel, 6.1-11.0 um in diameter at the first transverse costa, maximum diameter (6.6-14.5 um) at the second transverse costa. Protoplast suspends between first and second transverse costae. Anterior projections, 11-13 um in number, consist of two costal strips with a bifurcated anterior tip. Lorica chamber consists of anterior and posterior chambers. The anterior chamber, located between the two transverse costae, is constructed with transverse and longitudinal costae. The first transverse costa has the same number of costal strips as the longitudinal costae and the costal strips connect the anterior end of every other longitudinal costa at both ends. Longitudinal costae, connecting to the anterior projection have three costal strips between the first and the second transverse costae and are arranged spirally from the middle of the anterior lorica chamber to the posterior. The costal strips forming the second transverse costa, which has a same number of costal strips as the longitudinal costae, connect the longitudinal costae at one end and the middle of the next transverse costal strip at the other end, and separate the anterior and posterior chambers. The second transverse costa has the maximum diameter of the lorica because of a lesser degree of overlapping of each transverse costal strip. Longitudinal costae bifurcate, arranged spirally in the posterior lorica chamber, which is tapered and forms a simple pedicel. A thin membrane lines from the anterior projections to the second transverse costa. All costal strips are narrow rods. Reproduction is tectiform. (ref. ID; 7368)
Remarks
This new species closely resembles Diaphanoeca grandis and Diaphanoeca sphaerica (Thomsen, 1982). The anterior half of the lorica is almost identical to D. grandis. Bifurcation of longitudinal costae exists in both D. sphaerica and the new species. The morphological details of the lorica that distinguish these three species are: (1) the form of the first transverse costal strips (with triangular enlargements at one end is D. sphaerica and without typical enlargement in D. grandis and D. spiralifurca n. sp.); (2) the overlapping of the first transverse costal strips (which is complete in D. grandis and D. spiralifurca n. sp. while partial in D. sphaerica); (3) the spiral arrangement of longitudinal costae (without spiral arrangement of, when existing, arising from just beneath the first transverse costa in D. grandis, while only existing at the posterior end in D. sphaerica, and in the posterior half of the lorica in D. spiralifurca n. sp.); (4) tne number of transverse costae (being more than three in D. grandis, three in D. sphaerica and two in D. spiralifurca n. sp.); and (5) the bifurcation of longitudinal costae (with no bifurcation in D. grandis, bifurcation at the posterior end in D. sphaerica, and bifurcation from the second transverse costa in D. spiralifurca n. sp.). The spiral arrangement of the longitudinal costae was also observed in the specimens of D. grandis collected from northern Japan. None of the cells identified as D. grandis collected from Osaka Bay (middle Japan; more than 40 cells) or Hawaii (6 cells) showed spiral arrangement following treatment for electron microscopy, while all 16 cells from Lake Saroma (a lagoon in Hokkaido, northern Japan) showed the spiral arrangement. However, the spiral arose from the first transverse costa, not the posterior half of the lorica, as does in D. spiralifurca n. sp. These cells were identified as D. grandis, because all of the transverse costae in these cells, including those with and without spiral arrangement of the longitudinal costae, were arranged perpendicular to the main axis of the cell, and no cells showed the bifurcation of the longitudinal costae. The spiral arrangement of the longitudinal costae is not an artifact of preparation for electron microscopy, but rather defines morphological characteristics among the three species (D. spiralifurca n. sp., D. grandis and D. sphaerica) or among the geographic variants of D. grandis.
The total lorica length without the pedicel is 21-40 um in D. spiralifurca n. sp., and is a little smaller than that of D. grandis, 24-46 um (Ellis 1929). A subspecies of D. grandis, D. grandis minor, has been described by light microscopical observation (Throndsen 1974), and is characterized by its small size, e.g. the total lorica length is 18-22 um in D. grandis minor (Throndsen, 1974). The lorica dimensions of D. spiralifurca n. sp. ranges between those of D. grandis and D. grandis minor with some overlapping. D. spiralifurca n. sp., however, is distinguished from D. grandis minor by possessing the spiral arrangement of longitudinal costae and by possessing fewer transverse costae than D. grandis minor (two vs. four).
In general, these three species have similar transverse/longitudinal costal arrangements, similar attachment between longitudinal and transverse costal strips and an anterior projection with two costal strips. In addition, similarity is also found between each of two of the three species, such as overlapping of the transverse costal strips and spiral arrangement of longitudinal costae. It is thus evident that these three species form a well-circumscribed group in the genus Diaphanoeca and are closely related to each other. The lorica lining membrane of D. spiralifurca n. sp., covering the lorica from the anterior projection to the second transverse costa, closely resembles that of D. grandis (Manton et al., 1981), but consists not only of fibrils but also of continuous membranous matrices. The fibrils are woven more or less perpendicularly in D. grandis, more randomly in D. spiralifurca n. sp. Particles under the membrane lining area, however, have no clear shadow. Because the clear shadows of the thin fibrils are visible, if a bare particle exists in the membranous area, the particle should have a clear shadow. It is, thus, likely that the particles under the membranous area lose their shadow because the membrane matrices cover them smoothly, much like as snowfall covering the rough surface of the land. The existence of the continuous membrane also can be elucidated by the different texture of the formvar matrix and differences in electron density between the area in the lorica with or without lining membrane. (ref. ID; 7368)
Etymology
The specific name is derived from the Latin spiralifurca referring to the spirally arranged fork-shaped longitudinal costae. (ref. ID; 7368)
Distribution
Costal waters of Japan and Taiwan. (ref. ID; 7368)
Type specimen
Collected from Osaka Bay, Japan (July 1980), deposited in the Herbarium of Miyazaki International College, Miyazaki, Japan, No. 4865. (ref. ID; 7368)