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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Saroeca

Saroeca Thomsen, 1979 emend. Hara & Takahashi, 1987 (ref. ID; 7106 redescribed paper)

Choanoflagellida: Family Acanthoecidae (ref. ID; 7106)

[ref. ID; 7106]
Diagnosis; Cell is solitary, with a flagellum surrounded by a collar of tentacles. Lorica is conical, with a small number of long, attenuating costal strips diverging anteriorly, and stipitate posteriorly. One or two transverse costae, the anterior one connects with the anterior longitudinal costal strips at the point where they are widest. (ref. ID; 7106)
  1. Saroeca attenuata Thomsen, 1979 (ref. ID; 7106)
  2. Saroeca paucicostata Hara & Takahashi, 1987 (ref. ID; 7106 original paper)

Saroeca paucicostata Hara & Takahashi, 1987 (ref. ID; 7106 original paper)

Descriptions

Cell is solitary and planktonic. The protoplast is 3-6 um long and 1.5-3 um wide after desication. The flagellum is 5-14 um long and is surrounded by a ring of tentacles. The lorica is 17.5-29.5 um long and comprises anterior spines (5-10 um in length), a lorica chamber (5-8 um in length) and a posterior spine (7-12 um in length). There are commonly four, occasionally three or five, longitudinal costae, each formed by two successive costal strips that converge at the posterior end of the lorica chamber. The anterior sigmoidal costal strips are exceptionally long and slender and 7.5-12.5 um long. The anterior three fourths of the costal strips project beyond the lorica chamber to form the anterior spines. The posterior longitudinal costal strips are simply curved and 4-6 um in length. There are two transverse costae. The anterior one, 2.5-4.0 um in length, is composed of 6-10 costal strips and crosses the anterior longitudinal costal strips at the proximal one fourth of the strips, where they are widest. The junctions are mostly "T"-shaped. The posterior transverse costa, 1.5-2.5 um in diameter, is composed of 4-6 costal strips and crosses at the junctions of the anterior and the posterior longitudinal costal strips. The posterior spine is sigmoidal, 7-12 um in length, and projects from the posterior end of the lorica chamber. (ref. ID; 7106)

Notes

The present species is obviously closely related to Saroeca attenuata described by Thomsen (1979) as can be seen from the general form of the lorica, the small number of the longitudinal costae and, especially, the very long anterior longitudinal costal strips and the level at which the anterior transverse costa crosses the longitudinal costae, i.e. they connect with the anterior longitudinal costal strips at their widest point (Thomsen 1979, Pl.I,6-8 in the present study). These characteristics separate these two species from the other species of Acanthoecidae and make it reasonable to include these two species in a same genus. There are, however, some significant differences between the present species and S. attenuata. First, in this species there are two transverse costae, one connects the first longitudinal costal strips at the widest point and the other is located at the connection between the first and the second longitudinal costal strips (Pl.I,6-8). By contrast, in S. attenuata, there is only one transverse costa that connects the longitudinal costae at the widest point of the first longitudinal costal strips. Second, in the present species, each of the longitudinal costae are formed by two successive costal strips that do not join (pl.I,7) or join (pl.I,6-8) each other before terminating posteriorly. By contrast, three or four costal strips form the longitudinal costae of S. attenuata and the longitudinal costae always join each other before they terminate posteriorly (Thomsen 1979). The characteristics mentioned above seem to exclude the present species from the previous generic category of Saroeca, as well as differentiate the present species from S. attenuata. The genus Saroeca has been initially defined as the genus in which the longitudinal costae join each other before terminating and only one transverse costa exists (Thomsen 1979). However, the essential similarity between S. paucicostata and S. attenuata does not allow us to classify these two species in separate genera. Instead, we intend to emend the generic diagnosis of Saroeca. The small number, 3 to 5, of longitudinal costae in the present species (Pl.I,6-8), from which the specific name has been derived, also distinguishes it from S. attenuata with 6 to 8 longitudinal costae. Variation of the absolute lorica size among the present specimens rule out simple interpretation of a direct influence on size by temperature. The Saroeca attenuata specimens reported from West Greenland (fig.95 in Thomsen 1982) has only five longitudinal costae, each of which is formed by two costal strips and two transverse costae. These characteristics indicate that his specimens should be identified as S. paucicostata rather than S. attenuata. (ref. ID; 7106)

Etymology

The specific name derives from the Latin paucicostata, "having a small number of costae". (ref. ID; 7106)

Iconotype

Pl.I,6 depicts a cell collected on 14 October 1980 from water at 22.7 degrees C. (ref. ID; 7106)