Oithona nana Giesbrecht 1893

Oithona nana Giesbrecht, 1892

Oithona nana Giesbrecht, 1892:538–546, pl. 34: figs. 10–11, 20, 24, 26, 34, 35, 42; pl. 44: figs. 2, 4, 6.—González and Bowman 1965:272, fig. 20 c-g.—Nishida et al., 1977:138–139, figs. 11, 12.

MATERIAL.— and from PN-11-60, PN-13-60, PN-18-60, PN-20-60, PN-21-60, PN-23-60, PN-25-60, PN-26-60, PN-27-60, PN-29-200, PN-30-200, PN-32-200, PN-33-200, PN-34-200, PN-35-200, PN-36-200, PN-37-200, PN-38-200, PN-43-200, PN-44-200, PN-45-200, PN-46-200, PN-49-200, PN-55-200, PN-56-200, PN-57-200, PN-58-200, PN-59-200, PN-62-200, PN-64-200, PN-65-200, PN-67-200, PN-70-200, Alpha Helix Sta 5.5, and NMNH-STRI Sta 126.

FEMALES.—Length range (30 specimens) 0.58-0.72 mm; Pr/Ur-1.1. Ri1P4 (Figure 8c) with a distinct row of 4 long spines; O. nana is the only species encountered with surface armature on RiP1–4. Ri2P4 (Figure 8c) with both setae modified; neither seta strongly curved, both with flange on distal 3/5; Ri3P4 proximal seta similar, with flange on distal 3/5. P5 elongate, with several long hairs dorsal to it on posterior margin of Ur1. Knob near genital opening armed with short, thick spine and longer seta.

MALE.—Length range (30 specimens) 0.47–0.53 mm; Pr/Ur-1.3. Flap of Cph (Figure 8e) relatively broader and shorter than in O. hebes and O. fonsecae; it reaches middle of Pg1. Pore signature significantly different; anterodorsal cluster roughly circular; posterior to this a poorly defined horizontal group of organs usually followed by 5 distinct columns. Ventral organs of columns also appear as continuation of horizontal group. Cph flap with less distinct series of columns much more closely spaced. Below horizontal group an area devoid of organs and ventral to this, a group of poorly organized organs along ventral part of Cph and flap.

Intraspecific variation in the pore signature has been observed in this species. In another specimen, on the right side, organs in the horizontal group anterior to the 5 distinct columns appear organized into a smaller 6th column (Figure 8f, g). This new column simply may have resulted from shifting in position of the organs; such shifting has been noted in O. hebes. On the right side of a 3rd specimen, a distinct gap behind a horizontal group was followed by only 4 columns; on left side gap was absent and 6 columns were present (Figure 8h, i).