Undulacandona colymba, Smith & Kamiya, 2015

Smith, Robin James & Kamiya, Takahiro, 2015, Four new species of the subfamily Candoninae (Crustacea, Ostracoda) from freshwater habitats in Japan, European Journal of Taxonomy 136, pp. 1-34 : 25-31

Undulacandona colymba sp. nov.

urn:lsid:zoobank.org:act:04046FDB-2E5C-4590-95EE-D74E97DE5837

Figs 14–17

Diagnosis

Lateral view of carapace elongate with straight, almost level hinge. Male with anterior and posterior margins approximately equally rounded. Female with anterior margin more inflated than posterior one, with dorsal-posterior margin straight to slightly concave. Dorsal view with posterior and anterior ends compressed and pointed. Surface of carapace with fine longitudinal striations in both sexes. Antennule with six segments, first two of which partially fused forming one segment. Male antenna with well developed sexual bristles, t2 terminating in large, rounded structure. Female antenna with claw G2 as long as G1. Seta h2 on seventh limb claw-like and relatively long, almost four times longer than seta h1. Hp with medial lobe (h) curved and hook shaped, outer lobe (a) much larger than medial lobe, with wide base, widening distally to form flattened lobe with rounded distal end and with thin projection on apical outer side.

Etymology

From the Greek kolymbis, meaning a “diving bird”, such as a grebe; the shape of the outer lobe (a) of the hemipenis is reminiscent of the head of a diving bird.

Type material

Holotype

♂ ( LBM 1430006279 ), dissected with appendages sealed in a glass slide and valves stored dry in a micropalaeontological cavity slide. Collected from the type locality on 25 Sep. 2011.

Allotype

♀ ( LBM 1430006280 ), dissected with appendages sealed in a glass slide and valves stored dry in a micropalaeontological cavity slide. Collected from the type locality on 25 Sep. 2011.

Paratypes

1 ♂, dead when collected but with appendages ( LBM 1430006281), 1 ♀ ( LBM 1430006282), both dissected with appendages sealed in glass slides and valves stored dry in micropalaeontological cavity slides. 1 ♂ right valve ( LBM 1430006283) and 1 whole ♀ carapace ( LBM 1430006284), both stored dry in micropalaeontological cavity slides. All collected from the type locality on 25 Sep. 2011.

Type locality

Groundwater below agricultural land in Tsunosato, Kohoku-cho, Nagahama City, Shiga Prefecture, Japan, 35º26’57.0” N, 136º11’58.6 E ”, approximately 440 meters from Lake Biwa and 80 meters from a small satellite lake (Nodanuma) (locality 7 on Fig. 1 ). Access to the groundwater is via hand pumps used for obtaining water for small-scale agriculture.

Other material examined

3 ♀♀, 1 ♀ right valve, all from the type locality collected on 25 Sep. 2011.

Description

Carapace length 755–778 µm, height 322–365 µm ( Figs 14 , 15 A–E). Lateral view of carapace elongate with straight, level dorsal margin in central region, sloping down either side to anterior and posterior margins. Both anterior and posterior margins slightly unevenly curved, with maximum curvature below mid-height. Ventral margin straight to slightly sinuous. Posterior margin of male more inflated than that of female. Left valve overlaps right valve along ventral margin, and free margins in antero-dorsal and postero-dorsal regions; anterior and posterior margins with very little overlap. Dorsal view spindlelike, with pointed anterior and posterior ends. Internally, with more or less equally wide calcified inner lamella both anteriorly and posteriorly. Surface of valves covered with fine striations, more prominent in female compared with male. Colour whitish to translucent.

Antennule ( Fig. 15F ) with six segments, first two of which partially fused together, with possible articulation between them. Dorsal margin of first segment with one robust seta at apical end. Second segment with two long setae on apical ventral corner. Third segment with one apical-dorsal seta. Fourth segment elongate with one apical seta. Fifth segment elongate with two long and one shorter apical setae. Final segment small and elongate with long ya aesthetasc, two long and one short apical setae.

Antenna ( Fig. 15G ) exopodite consisting of rounded base with three very short setae. Y aesthetasc long and slender. Male with divided second endopodal segment, with two male bristles, t2 and t3 ( Fig. 15I ). Male bristle t2 very thick and stout, approximately reaching to end of final segment, terminating with large, thin, flattened disc structure. Male bristle t3 stout, but thinner than t2, curved, slightly exceeding base of final segment, and with finely indented end. Male t4 seta tiny. z1 and z2 both large claws, subequal in length to claw G2. G3 seta protruding to about end of final segment. Gm small and slender, about half-length of claw GM.

Female antenna with claw G2 equal in length to G1 and G3 ( Fig. 15H ). Claw Gm slender and about half length of claw GM ( Fig. 15K ). One specimen with one antenna with claw GM (outer-most one) shorter than Gm ( Fig. 15J ). Seta z3 absent.

Mandibular palp ( Fig. 16 A–B) first segment with reduced setulous S2 seta and short, slender alpha seta, together with long setulous S1 seta and one long seta on inner edge. Second segment with group of three long setae, together with slender beta seta and one slightly offset long seta (3+1+beta) on inner edge, and two setae on outer distal corner. Third segment with three sub-apical setae on outer edge and three stout setae and one short seta arranged along apical edge; outer-most one gamma seta. Final segment with two long, stout setae towards apical outer edge, and three apical, slender, shorter setae on inner edge. Number of setae on branchial plate not observed. Mandibular coxa typical of subfamily, with approximately 7 teeth ( Fig. 16C ).

Maxillula ( Fig. 16D ) first palp segment with three apical setae on outer corner, and one apical seta slightly offset towards inner edge. Final segment elongated, terminating with three long stout setae, and three shorter, more slender setae. Branchial plate with morphology typical of subfamily.

Male fifth limb palps ( Fig. 16 E–F) with fused terminal hooks, slightly asymmetrical. Palps slightly taper distally to long, curved hooks, each bearing two setae at base.

Female fifth limb small and stubby ( Fig. 16G ). Endite with approximately 12 setae, basis with one a-seta and c-seta. Palp very reduced, terminating with three short setae.

Sixth limb ( Fig. 16H ) very long and slender, with five segments. First and second segments with no setae. Third and fourth segments with very short f and g setae respectively. Final segment with very short h1 and h3 setae and long, slender h2 claw.

Seventh limb ( Fig. 16I ) with four segments. First segment with d1 and d2 of approximately similar length, and seta dp longer. Second segment with no setae. Third segment with small g seta. Final segment with short h1 seta, longer and claw-like h2 seta, about four times longer than h1, and a very long, reflexed h3 seta, approximately as long as the second and third segments combined.

Caudal ramus ( Fig. 17C ) short and stout and strongly curved, with wide proximal base tapering distally. Claws Ga and Gp similar in length and slightly sinuous. Seta sa tiny, seta sp short and located approximately at one-third length of ramus from distal end. Caudal ramus attachment long and branched. Hemipenis ( Fig. 17A ) basal capsule elongated, roughly triangular-shaped, widening distally. Inner lobe (b) wide and rounded, with uneven distal margin. Medial lobe (h) curved and hook shaped, tapering distally to small, finger-like projection. Outer lobe (a) much larger than medial lobe, with wide base, widening distally to form flattened lobe with rounded distal end and with thin projection on apical outer side. Bursa copulatrix (e) s-shaped, tapering distally, with small, reflexed distal projection.

Zenker organ ( Fig. 17B ) relatively small, with wide central tube. Internally with three rosettes. Posterior end plate funnel-shaped, leading to distal section of vas deferens. Anterior end plate large and bulbous.

Remarks

One female has an antenna with the claw GM (the outer-most claw) on the final segment significantly shorter than the claw Gm (the claw next to it), whereas usually claw GM is larger than Gm. This is an unusual feature for the superfamily, but because it occurred in only one antenna in one specimen, it is probably an anomaly restricted to this one specimen. In addition to Undulacandona colymba sp. nov., two female specimens of an additional undescribed species of Undulacandona were collected. Due to the lack of males, this third species of the genus is not described herein.

This is the second species to be described in the genus Undulacandona ; the first, Undulacandona spinula Smith, 2011 , was found in a well below the city of Otsu in Shiga Prefecture (locality 9 on Fig. 1 ). The new species is easily distinguished from U. spinula by the shape of the carapace and the male hemipenes. In particular, the outer and medial lobes of the hemipenes of Undulacandona colymba sp. nov. are much larger and differently shaped from those of U. spinula .

Ecology and distribution

Both species of the genus are stygobionts, collected from groundwater via wells, in the case of Undulacandona colymba sp. nov. from a well with a hand pump attached in a vegetable patch. The underlying sediments are Pleistocene to Holocene alluvial sands and gravels, which surround Lake Biwa. Undulacandona colymba sp. nov. is currently only known from the type locality in Shiga Prefecture.

Figures

Fig. 14. Undulacandona colymba sp. nov. A. External view of male right valve (LBM 1430006283). B. Right view of female carapace (LBM 1430006284). C. Dorsal view of female carapace, anterior to right (LBM 1430006284). D. Detail of external surface of male right valve (LBM 1430006283). E. Detail of external surface of female right valve (LBM 1430006284). F. Internal view of male right valve (LBM 1430006283). G. Internal view of female right valve. Scale bar: A–C, F–G = 300 µm; D–E = 87 µm.

Fig. 15. Undulacandona colymba sp. nov. A. Internal view of male left valve (LBM 1430006279). B. Internal view of male right valve (LBM 1430006283). C. Internal view of female left valve (LBM 1430006280). D. Internal view of female right valve (LBM 1430006280). E. Detail of external surface of female right valve. F. Female antennule (LBM 1430006280). G. Female antenna (LBM 1430006280). H. Detail of female antenna (LBM 1430006280). I. Detail of male antenna (LBM 1430006279). J. Detail of female’s final antennal segment (LBM 1430006280). K. Detail of female’s final antennal segment. Scale bar: A–D = 464 µm; E = 232 µm; F–G = 117 µm; H–K = 92 µm.

Fig. 16. Undulacandona colymba sp. nov. A. Female mandibular palp (LBM 1430006282). B. Alpha, beta and gamma setae of mandibular palp (LBM 1430006282). C. Female mandibular coxa (LBM 1430006282). D. Female maxillula (setae on endites not drawn) (LBM 1430006280). E–F. Left and right male fifth limb palps (LBM 1430006279). G. Female fifth limb (LBM 1430006282). H. Male sixth limb (LBM 1430006281). I. Female seventh limb (LBM 1430006280). Scale bar: A–B, D = 61 µm; C, E–I = 117 µm.

Fig. 17. Undulacandona colymba sp. nov. A. Hemipenis (LBM 1430006279). B. Zenker organ (LBM 1430006279). C. Male caudal ramus and attachment (LBM 1430006281). Scale bar = 117 µm.

Fig. 1. Map of the main islands of Japan, showing the localities mentioned in the text.