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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Stephanoeca

  1. Stephanoeca elegans (Norris) Throndsen (ref. ID; 7368)
  2. Stephanoeca supracostata Hara, 1996 (ref. ID; 7368 original paper)

Stephanoeca supracostata Hara, 1996 (ref. ID; 7368 original paper)

Diagnosis

Cells solitary. Protoplast when dried 2.4-7.9 um x 1.7-3.6 um, flagellum ca. 9-um long surrounded by a collar. Lorica obpyriform with waist, consists of anterior and posterior lorica chambers, 9-18 um in length. Diameter of the lorica is maximum (4.5-10.0 um) at the level of second transverse costa, ca. 3.1-6.5 um at the first transverse costa, and 2.2-4.4 um at the waist. The anterior chamber is constructed of regularly arranged 12-18 longitudinal costae, each of which is composed of two costal strips, and three transverse costae which are located at the anterior end of the chamber, near the middle level of the second longitudinal costal strips, and the posterior end of the chamber, respectively. Posterior chamber is constructed of 7-20 longitudinal costae, each of which is composed of one costal strip, and a transverse costa which is located at the anterior end of the chamber. Protoplast is located at the posterior chamber. A waist exists at the boundary of the anterior and the posterior chambers. All the costal strips are narrow rods. Reproduction is tectiform. (ref. ID; 7368)

Remarks

Stephanoeca supracostata n. sp. is closely related to Stephanoeca elegans (Norris) Throndsen. The original type of S. elegans (Norris) Throndsen sensu stricto has no transverse costa between the anterior end and the waist, while all specimens collected from the Taiwanese waters possess an additional transverse costa at the two-thirds level from the anterior end of the anterior lorica chamber where the maximum diameter of the lorica is located. Stephanoeca elegans sensu stricto has been reported from temperate Atlantic and northwest Pacific coastal, Mediterranean and Japanese waters (Leadbeater 1972, 1973; Norris 1965; Throndsen 1974) (present study), whereas S. supracostata n. sp is distributed in Japanese and Taiwanese waters. A cell possessing an additional transverse costa between the anterior end and the waist has been reported as S. elegans based on the specimen from California (Thomsen et al. 1991). Cells of S. elegans and S. supracostata n. sp. coexisted in water samples collected from Osaka Bay in Japan. This makes these Japanese samples the most suitable for examining the morphological differences of these two species. The total length of lorica and the diameter of the first transverse costa of the two species overlap. The diameter of the waist of S. elegans, however, is slightly larger than that of S. supracostata n. sp. The clear waist of the lorica in S. supracostata n. sp., at the level of the posterior transverse costae, occurs because there is a greater degree of overlap of the transverse costal strips in the posterior transverse costa than in the second transverse costa. Except for the existence or absence of the additional transverse costa, the most conspicuous morphological difference in the populations collected from Osaka Bay is the number of longitudinal costae: 20-25 in S. elegans vs. 14-18 in S. supracostata n. sp. No intermediate form between these two morphological types has been observed from this locality (i.e. Osaka Bay), thus indicating that two species identified were not artifacts of same continuous morphological variation in S. elegans, but were genetically distinct. Except for the number of the longitudinal costae; morphological, dimensional, and numerical characteristics of S. elegans collected from Japan coincided well with the type material. The type specimen of S. elegans has 18 longitudinal costae (Norris 1965), while the specimens collected from Osaka Bay possessed 20-25 longitudinal costae. The numerical variation in longitudinal costae in this species has been reported by Leadbeater as 16-18 from Norway (Leadbeader 1972) and as 13-15 from Jugoslavia (Leadbeater 1973). It appears clear that S. elegans has a very wide range of variation in the number of the longitudinal costae, from 13 to 25. The posterior two (the third and the fourth) transverse costae of S. supracostata n. sp. are located at the waist of the lorica. The third transverse costa binds the posterior ends of the second longitudinal costal strips to construct the anterior lorica chamber. The anterior ends of the third longitudinal costal strips are connected by the fourth transverse costa. The second and third longitudinal costal strips are not well matched, and usually do not connect with each other. The longitudinal costae are not continuous from the top to the bottom of the lorica but are separated into two parts at the waist. The anterior and the posterior chambers are connected by linkage between some of the posterior ends of the second longitudinal costal strips with the fourth transverse costa; and some of the anterior ends of the third longitudinal costal strips link to the third transverse costa. Because the anterior and posterior chambers may not be firmly connected, separations between them are occasionally observed. This independence of the lorica chambers in S. supracostata n. sp. suggests different construction and function of these lorica chambers for the protoplast. The posterior lorica chamber may protect the protoplast from direct attachment of outside solids. The anterior chamber surrounding the feeding organelles, a flagellum, and a collar, may control water current produced by the flagellum and sieve food particles of suitable sizes. One cell collected from Osaka Bay and stored at room temperature for 1 day was found to possess a long (ca. 30 um) slender tentacle developed from the distal end of a posterior labial peduncle. Many cells of S. supracostata n. sp. are observed to attach to substrates, such as detritus. The exceptionally long posterior tentacle observed in the free-floating cells of S. supracostata n. sp. are probably used for the purpose of attachment. (ref. ID; 7368)

Etymology

The specific name is derived from the Latin supracostata referring to the additional transverse costa above the waist. (ref. ID; 7368)

Distribution

Coastal waters of Japan and Taiwan. (ref. ID; 7368)

Type specimen

Collected from Nan-Wan, Taiwan (December 1992), deposited in the Herbarium of Miyazaki International College, Miyazaki, Japan, No. 19214. (ref. ID; 7368)