Callistocythere intermedia, Ha, Tran Manh & Tsukagoshi, Akira, 2015

Ha, Tran Manh & Tsukagoshi, Akira, 2015, First records of interstitial leptocytherids (Crustacea, Ostracoda): two new species and a redescription of Callistocythere ventricostata Ruan & Hao, 1988 collected from the Okinawa Islands, southern Japan, Zootaxa 4006 (1), pp. 83-102 : 85-89

Callistocythere intermedia sp. nov.

( Figs 2–5 )

Type locality. Interstitial environments on the northwest coast of Sesoko Beach ( Fig. 1 C), the Okinawa Islands, Japan, 26°39'4.10"N, 127°51'27.00"E on 16 May 2002 and 30 June 2014.

Type series. All specimens were collected from type locality on 16 May 2002 and 30 June 2014. Holotype: male (SUM-CO-2342). Paratypes: 4 males (SUM-CO-2343; SUM-CO-2344; SUM-CO-2345; SUM-CO-2346), and 3 females (SUM-CO-2347; SUM-CO-2348; SUM-CO-2349).

Etymology. After Latin intermedia , indicating the intermediate adaptation process from surface to interstitial environments of this new species.

Diagnosis. Carapace outline sub-quadrangular and somewhat cylindrical in lateral view and surface covered with coarse reticulations, and numerous shallow, large fossae. Small pits densely distributed along anterior, posterior and ventral margins. Strong sub-peripheral parallel ridges along anterior and posterior margins. Hingement modified entomodont and median element forming smooth bar in right valve and smooth groove in left valve. In male, copulatory organ with rounded quadrangular capsule. Distal lobe transparent and tongue-shaped with blunt tip, 3 clasping apparatus of different shapes, copulatory duct very complicated and coiling 8–9 times in capsule.

Description. Carapace ( Figs. 2–3 ). Carapace outline sub-quadrangular with greatest height at anterior third and somewhat cylindrical in lateral view. Anterior margin rounded downward, posterior margin truncated above, rounded below, dorsal margin slightly arched at middle, ventral margin sinuate and slightly concave at middle. Sexual dimorphism distinct; female form more elongate and higher than male form. Right and left valves slightly asymmetrical in lateral outline. Carapace thick, surface covered with distinct coarse reticulations and numerous shallow, large fossae. Fine pits densely distributed along anterior and posterior margins. Two strong, sub-peripheral parallel ridges running along anterior and posterior margins from dorsal to ventral area. Vestibulum developed along anterior and posterior margins. Marginal pore canals single and poly-furcated in anterior zone, single in ventral zone and bifurcated in posterior zone. Four adductor muscle scars somewhat slanting. Larger elongated frontal scar located in front of adductor scars. Two divided rounded mandibula scars in front of lowest adductor scar. Fulcral point rounded. Hingement modified entomodont; in right valve composed of 1 prominent oblong anterior serrated tooth, 1 sub-quadrangular posterior tooth, median element forming smooth bar; in left valve, 1 enlarged tooth at anterior termination, 4 medium-sized (1 bilobed tooth) and 1 small teeth, and 1 large socket at posterior termination, median element forming smooth groove. Snap structure existing in middle ventral inside, right valve bearing large rounded knob interlocking with corresponding socket of left valve.

Antennula ( Fig. 4 A). Five articulated podomeres, length ratios from proximal to distal 20:14:5:8:6. First podomere stout trapezoidal, without seta. Second podomere rectangular, covered by numerous fine setulae along anterior distal margin, bearing 2 bunches of fine setulae on one third from anterior proximal and anterior distal end, respectively, and 1 medium-length setulous seta at posterior distal end. Third podomere short, sub-quadrangular, covered by numerous fine setulae on anterior margin, with 1 long stout setulous seta at anterior distal corner. Fourth podomere consisting of two fused podomeres, and adorned with numerous setulae along anterior margin, bearing 1 long simple slender seta, 1 serrated stout claw and 1 medium-length setulous seta on anterior edge, 2 long simple, slender setae and one serrated stout claw at anterior distal end, 1 medium-length setulous seta at center, and 1 very long, simple slender seta at posterior distal end. Fifth podomere slender, equipped with two long slender setae, 1 aesthetasc, and 1 strong terminal claw with serrations arranged in 1 row along anterior margin at tip.

Antenna ( Fig. 4 B). Four articulated podomeres, the ratios of length 40:16:38:5. First podomere stout, possessing 2 bunches of setulae on lateral center and anterior distal margin and very long, stout two segmented (but almost fused) exopodite (= spinneret seta) at anterior distal end. Second podomere short sub-quadrangular bearing bunch of fine setulae at antero-proximal end and one long setulous seta postero-distally. Third podomere oblong, covered with fine setulae from proximal to two-third along anterior margin, 2 simple slender setae at anterior medially, 1 aesthetasc, 2 medium-length setulous setae at posterior medially, 1 simple, slender and 1 stout, setulous seta at postero-distal corner. Fourth podomere very small and bearing two strong sub-equal length terminal claws.

Mandibula ( Fig. 4 C). Five articulated podomeres. Coxa stout and bearing developed teeth and aesthetasc-like setae at ventral end. Basis sub-trapezoidal with 2 simple setae on middle of ventral margin, and exopodite as one large plumose seta on dorsal margin. First podomere of endopodite with 2 medium-length setulous setae on middle of distal margin and 2 long, stout plumose setae (annulated at distal half) at ventro-distal corner (lower ventrodistal one only setulous along ventral margin). Second podomere of endopodite sub-pentagonal, bearing 1 long simple and 2 medium-length, annulated setulous setae on middle of dorsal margin, 1 long, annulated setulous seta at anterior distal end, 1 medium-length simple seta and 1 long stout plumose seta (annulated at distal half) at anterior ventral corner. Third podomere of endopodite very small, sub-quadrangular, equipped with 1 annulated setulous seta and 3 simple setae at distal end.

Maxillula ( Fig. 4 D). Thin branchial plate with 16 feather-like setae. Basal podomere bearing palp (endopodite) and 3 endites. Palp consisting of 2 podomeres, proximal podomere with 1 simple, 1 setulous and 1 claw-like setae at dorsal distal end; distal podomere with 1 setulous, and 2 simple setae distally. Dorsal most endite (endite 1) bearing 1 setulous and 2 simple setae, middle and ventral endites (endite 2 and 3) bearing 3 simple setae, respectively.

Fifth limb ( Fig. 4 E). Four articulated podomeres, length ratios from proximal to distal 29:18:11:10. First podomere bearing 1 setulous seta on middle of anterior margin, 2 setulous setae at anterior distal end, and one setulous seta on posterior proximal margin. Second podomere covered with setulae along anterior margin and distal end, and possessing 1 setulous seta at anterior distal end. Third podomere covered with setulae along anterior margin and distal end. Fourth podomere covered with setulae along anterior margin and distal end, and bearing 1 strong terminal claw with serrations arranged in 1 row along anterior margin at tip.

Sixth limb ( Fig. 4 F). Four articulated podomeres, length ratios from proximal to distal 15:11:9:6. First podomere bearing 1 setulous seta on middle of anterior margin, 1 setulous setae anterior distally and 1 setulous seta at posterior proximal corner. Second podomere covered by short setulae along anterior margin and distal end and possessing 1 setulous seta at anterior distal end. Third podomere covered by short setulae along anterior margin and distal end. Fourth podomere covered by short setulae along anterior margin and distal end, and bearing 1 strong terminal claw with serrations arranged in 1 row along anterior margin at tip.

Seventh limb ( Fig. 4 G). Four articulated podomeres, length ratios from proximal to distal 12:11:4:5. First podomere bearing 1 setulous seta on middle of anterior margin, 1 setulous setae at anterior distal end, and 1 setulous seta at posterior proximal corner. Second podomere covered with setulae along anterior margin and distal end, and possessing 1 setulous seta at anterior distal end. Third podomere covered with setulae along anterior margin and distal end. Fourth podomere covered with setulae along anterior margin and distal end, and bearing 1 strong terminal claw with serrations arranged in 1 row along anterior margin at tip.

Male copulatory organ ( Fig. 5 ). General shape of capsule rounded quadrangle, right and left hemipenes almost symmetrical. Distal lobe transparent and thumb-like shape with blunt tip, 3 clasping apparatus of different shapes; proximal most one long tongue-shaped, second one L-shaped with blunt tip and the distal most one short triangular shape with blunt tip. Copulatory duct very long and complicated, coiling 8–9 times inside the capsule.

Dimension. See Table 1 .

Species name Sex Valve Length (µm) Height (µm) RV 3 417–433 427 3 169–196 181

Abbreviations: F, female; M, male; LV, left valve; RV, right valve; N, examined individual number.

Remarks. Callistocythere intermedia sp. nov. inhabits the interstitial environment around the shoreline in areas dominated by coarse sand (particles from 1.4–1.9 mm in size) to a depth of 10 cm below the surface of the sediment. This species resembles Callistocythere subjaponica Hanai, 1957 ( C. littoralis group) in shape and carapace ornamentation, but this new species can be distinguished by the densely arranged small pits along the anterior and posterior margins and its much smaller carapace. In terms of hinge structure, the intermediate element of the hingement and the single enlarged anterior terminal tooth of the medium element of the left valve suggest some affinity with the Callistocythere japonica group. No brush-shaped organ has been observed in any of the examined specimens.

Figures

FIGURE 1. Maps showing the location of the study area. A, map of Japan; B, map of the Okinawa Islands; C, sampling site of this study (Sesoko Beach).

FIGURE 2. Callistocythere intermedia sp. nov. Internal view of male carapace. A, left valve; B, right valve (holotype, SUM-CO- 2342). Scale: 50 µm.

FIGURE 3. Carapace of Callistocythere intermedia sp. nov. (SEM images). A, B, external lateral view of male right and left valves, respectively (holotype, SUM-CO- 2342); C, D, external lateral view of female right and left valves, respectively (paratype, SUM-CO- 2347); E, F, internal lateral view of male left and right valves, respectively (paratype, SUM-CO- 2342); G, H, internal lateral view of female left and right valves, respectively (paratype, SUM-CO- 2348); I, complete female carapace in ventral view (paratype, SUM-CO- 2349); J, complete male carapace in dorsal view (paratype, SUM-CO- 2344); K, L, posterior and anterior socket of hingement on female left valve, respectively (paratype, SUM-CO- 2348); M, N, posterior and anterior teeth of hingement on female right valve, respectively (paratype, SUM-CO- 2348). Scale: 50 µm (A – J) and 10 µm (K – N).

FIGURE 4. Callistocythere intermedia sp. nov. A, antennula; B, antenna; C, mandibula; D, maxillula with distal parts figured at higher maginification; E, branchial plate of maxillula; F, fifth limb; G, sixth limb; H, seventh limb. A, male (paratype, SUM- CO- 2345); B, C, D, F, G, H, male (holotype, SUM-CO- 2342); E, male (paratype, SUM-CO- 2348). Scale: 20 µm for A, B, C, E, F, G, H and 10 µm for D.

FIGURE 5. Male copulatory organ of Callistocythere intermedia sp. nov. Abbreviations: ca, clasping apparatus; cd, copulatory duct; dl, distal lobe. (holotype, SUM-CO- 2342). Scale: 20 µm.

Tables

TABLE 1. Dimensions of the valves of two new species and Callistocythere ventricostata Ruan & Hao, 1988 of the family Leptocytheridae.

Callistocythere intermedia sp. nov. M	LV RV	N 4 4	Range 374–389 375–391	Mean 382 382	N 4 4	Range 200–213 200–215	Mean 205 208
F Callistocythere ryukyuensis sp. nov. M	LV RV LV	5 5 7	377–425 379–431 300–321	402 404 311	5 5 7	207–246 206–240 147–163	225 222 157
F	RV LV RV	7 3 3	299–325 310–311 310–312	311 311 311	7 3 3	149–164 158–164 159–163	158 162 161
Callistocythere ventricostata Ruan & Hao, M 1988 F	LV RV LV	2 2 3	410–422 407–415 414–434	416 411 422	2 2 3	166–178 175–185 173–200	172 180 138