Parapolycope spiralis, Tanaka, Hayato & Tsukagoshi, Akira, 2010

Tanaka, Hayato & Tsukagoshi, Akira, 2010, Two new interstitial species of the genus Parapolycope (Crustacea: Ostracoda) from central Japan, Zootaxa 2500, pp. 39-57 : 48-56

Parapolycope spiralis sp. nov.

( Figs 8–14 )

Type series. Holotype: adult male (SUM-CO-1781), right valve length 0.37 mm, height 0.26 mm, left valve length 0.36 mm, height 0.26 mm, appendages are mounted on slide and valves are preserved in a cardboard cell slide, the Miho Spit, Shizuoka City ( Fig. 1 B), Shizuoka Prefecture (35°01'13"N, 138°31'20"E) in various depths (about 30–50 cm), on May 3rd, 2008. Paratypes: six adult males (SUM-CO-1782, SUM-CO-1783, SUM-CO-1790, SUM-CO-1791, SUM-CO-1794, SUM-CO-1868) and eight adult females (SUM-CO-1784, SUM-CO-1785, SUM-CO-1786, SUM-CO-1787, SUM-CO-1788, SUM-CO-1789, SUM-CO-1792, SUM- CO-1793), same data as holotype; two females (SUM-CO-1788, SUM-CO-1789), same locality, on October 7th, 2007.

Etymology. Latin “spira” meaning “spiral”, referring to the spiral structure of both, male copulatory duct and female spermatheca in this new species.

Occurrences. The Miho Spit (Shizuoka Prefecture, type locality, coarse sand), Ishizuhama Beach (Shizuoka Prefecture, 34°50'50"N, 138°19'53"E, medium sand, on July 22nd, 2006), Koyuruginohama Beach (Kanagawa Prefecture, 35°18'20"N, 139°18'56"E, coarse sand, on October 14th, 2006). All specimens were collected from interstitial pore water.

Dimensions. see Table 2.

Length (mm) Height (mm)

Mean Observed range N Mean Observed range N Male Right valve 0.36 0.35–0.37 4 0.26 0.25–0.26 4

Left valve 0.36 0.35–0.36 4 0.26 0.25–0.26 4 Female Right valve 0.36 0.35–0.37 4 0.25 0.25–0.26 4

Left valve 0.36 0.35–0.37 4 0.25 0.25–0.26 4 Diagnosis. Carapace slightly elliptical in lateral view. Carapace surface smooth. Length of male right valve 0.35–0.37 mm and left valve 0.35–0.36 mm, of female right valve 0.35–0.37 mm and left valve 0.35– 0.37 mm. Anterior margin with 22 wide serrations on right valve and 19 wide serrations on left valve decreasing in size to ventral in both valves. Adductor muscle scars consisting of three imprints. Male upper lip well developed. Copulatory organ bearing one extending spiral tube in male and one spiral spermatheca in female. Number of furcal claws three on left and four on right lamella in male. Each lamella with four claws in female.

Description of adult male. Carapace ( Figs 8 A–E, 9, 10). Oval in lateral view. Anterior margin with 22 wide serrations of right valve and 19 wide serrations of left valve decreasing in size to ventral in both valves. Marginal infold of each valve well developed along anterodorsal to posteroventral margin. Along inner margin of right valve, anterodorsal bar and groove, posteroventral groove, and 1 socket (part of hinge structure) at dorsal end. Along inner margin of left valve, anterodorsal bar, posteroventral bar, and 1 knob (part of hinge structure) at dorsal end. External surface smooth at low magnifications, but has minute shallow posterior pits visible with SEM. Adductor muscle scars ellipse, consisting of three closely scars.

Frontal organ. Absent.

Antennula ( Fig. 11 C, D). Uniramus, four articulated podomeres. First podomere quadrate, with two tufts of setulae on anterior margin and lateral surface, respectively. Second podomere about twice as long as first podomere, with one long setulous seta and cluster of long setae on anterior margin. Third podomere about two–thirds length of second podomere, with one short seta at anterodistal end and five posterodistal setae consisting of one seta with large disk-shaped sucker, one long and one short seta curving at tip furnished with a row of short setulae, and two slender setae of subequal length, respectively. Fourth podomere very small with two very long and three long slender setae at distal end.

Antenna ( Fig. 11 F, G). Typically biramous with exopodite and endopodite consisting of nine and three podomeres, respectively. Exopodite: first podomere less than half the length of basal podomere; second to eighth podomeres small, each with one very long seta; ninth podomere also very small, with one long seta at proximal and one long, one medium, one very short setae at distal end. Endopodite: first podomere almost same length to first podomere of exopodite; second podomere about two–thirds length of first podomere, with three setae along dorsal margin consisting of two very short, one short and six setae at distal end consisting of one short, two medium, three long. Third podomere about two–thirds the length of second podomere, with one strong hook-shaped seta extending backward, and two distal long setae.

Mandibula ( Fig. 12 A, B). Coxal endite with four teeth and two setae ( Fig. 12 B). Basis with three plumose setae on ventral margin. Exopodite one stout plumose seta. Endopodite consisting of two podomeres. First podomere with two plumose seta on ventral margin near proximal end and two long setulous setae on dorsal margin near distal end. Second podomere very small, bearing one setulous seta on ventral margin and one claw-like distal seta.

Maxillula ( Fig. 12 C). Precoxal endite with six short setulous setae of different lengths. Coxal endite with two short plumose setae on medial surface near ventral margin and four plumose setae on ventral margin.

Basis and first podomere of endopodite fused. Basis with setulae on dorsal margin, and one short and two long plumose setae on ventral margin. First podomere of endopodite with one long seta at dorsodistal end and two long setae on ventral margin. Second podomere small, with four setae consisting of two long with setulae and two long stout with some rigid setulae located bilaterally at about one–thirds from proximal ends of setae. Exopodite consisting of two podomeres. First podomere of exopodite, with tufts of setae on dorsal margin. Second podomere with tuft of setae on dorsal margin. Ventral margin with three slender long setae and one slender very long setae; ventrodistal end with two slender very long setae and one slender long seta.

Fifth limb ( Fig. 12 D). Coxa bearing branchial plate (epipodite) with 12 long plumose setae, and two short setulous setae on dorsal margin. Basis and endopodite fused. Basis with three plumose setae on dorsal margin, one slender plumose seta on ventral margin. Endopodite with two plumose and two short slender setae on distal margin. Exopodite with one stout setulous seta at distal end.

Furca ( Fig. 13 A). Left lamella with three claws. Right lamella with four strong claws. One long projection on the right lamella rising upward to dorsally.

Male copulatory organ ( Fig. 13 A). Arising from outer surface of body at left side of last trunk segment and bearing very long spiral tube.

Upper lip ( Fig. 11 A). Chitinous hook sharp and distal part conical. Distal part hemispheric with rough surface.

Description of adult female. Carapace ( Figs. 8 F–J), mandibula, maxillula, and fifth limbs similar to those of adult male.

Antennula ( Fig. 11 E). Uniramus with four articulated podomeres. First and second podomeres almost same structure as male. Third podomere about one–third length of second podomere with one short seta at anterodistal end and two setae at posterodistal end. Fourth podomere small, with five long setae.

Antenna ( Fig. 11 H). Only endopodite different from that of adult male. Endopodite consisting of three podomeres. First podomere bare. Second podomere widened distally, with one seta at anterodistal end and six setae at posterodistal end. Third podomere about one–third in length of second podomere, with two long setae at distal end.

Furca ( Fig. 13 B). Each lamella with four strong claws increasing in size towards distal ends.

Female copulatory organ ( Fig. 13 B). Spermatheca spiral.

Upper lip ( Fig. 11 B). Sub-semicircular.

Remarks. There are a few doubts about the original description of the genus Parapolycope . One issue is the sheet-shaped seta (blattförmig verbreiterte Borste = leaf-shaped broadened bristle in Klie, 1936:522) of the male antennula . Klie (1936) might have mistaken the disk-shaped sucker as a sheet due to a sub-optimal microscopical magnification. The second issue is the position of male copulatory organ. For Parapolycope germanica , the type species of the genus, Klie (1936) described the right furcal lamella of the male bearing 4 claws and a shorter filamentous structure, while the left lamella shows 3 claws and a longer filament. An additional structure on the distal tip of the right lamella, which Klie (1936) interpreted as a gonoporus, led him to the conclusion that the right furcal lamella carries the copulatory organ and he therefore included this character into the generic diagnosis. However, we found that in Parapolycope spiralis sp. nov. only the LONG filamentous structure of the LEFT furcal lamella (which actually rises from the outer surface of body at the left side of the last trunk segment) can achieve a spiral structure fitting to that of the female spermatheca. Further, its hollow morphology (in contrast to the solid appearance of the SHORT filament of the RIGHT lamella) clearly shows that in this species the left furcal lamella has to be considered the one bearing the copulatory organ and not the right lamella as stated by Klie (loc.cit.). Unfortunately, Chavtur (1977) gives no detailed description of the morphology and localisation of the male copulatory organ in Parapolycope kunashiri .

Extending the comparison to a couple of Polycope species reported and partly described by Klie in the same paper ( Klie 1936), namely Polycope difficilis , P. dispar , P. frequens , P. striata , P. fragilis and P. helgolandica , it is obvious that in these species (1) males always have less furcal claws than females, (2) the two male furcal lamellae have different numbers of claws and (3) the copulatory organ is always located on the furcal lamella bearing the smaller number of claws. This is mostly, but not necessarily the left lamella – in P. helgolandica , the RIGHT lamella has both, the smaller number of claws and the copulatory organ. The fact that (1) and (2) also apply to Parapolycope spiralis sp. nov. additionally supports our doubts about Klie’s opinion on the orientation of the copulatory organ in Parapolycope germanica and we therefore consider this character of the genus description as doubtful and thus as not diagnostic. A reinvestigation of the type material of Parapolycope germanica as the genus’ type species would be desirable to dispel the doubts about Klie’s generic diagnosis of Parapolycope .

The presence of the generic character of Parapolycope , a maxillula with an exopodite shorter than the basis, justifies the designation of Parapolycope oligohalina sp. nov. to the genus, although this new species shows some morphological peculiarities compared to its congeners. These are e.g. an antennal exopodite consisting of 8 podomeres (instead of 9) and, the absence of the mandibular exopodite and of the chitinous hook on the male upper lip. The character of Parapolycope spiralisi sp. nov. is almost congruous with the generic character of Parapolyope.

Both new species can easily be distinguished from their congeners, Parapolycope germanica Klie, 1936 and Parapolycope kunashiri Chavtur, 1977 , by the shape of the male copulatory organ.

Parapolycope oligohalina sp. nov. is the smallest of these four species. However, carapace outline and appendage morphology of Parapolycope oligohalina sp. nov. are similar to Polycope noodti Hartmann, 1959 from Panama (Caribbean Sea), Polycope aidae Hartmann, 1959 from El Salvador, Polycope minutissima Hartmann, 1974 from South Africa (Indian Ocean), and Polycope minuta Hartmann, 1974 from Mozambique. Parapolycope oligohalina sp. nov. is distinguished from Polycope noodti and Polycope aidae by the morphology of their male antennula and antenna. Polycope minutissima and Polycope minuta differ from the new species by the lack of carapace surface ornamentation, the number of anteroventral teeth in the right valve, and also by a few differences that appear in the chaetotaxy of the maxillula and fifth limb.

Parapolycope oligohalina sp. nov. were collected from the interstitial habitat of a river mouth with low salinity (0.5–2.0) at low tides and almost fully marine conditions at high tide. This new species is able to swim actively in both low salinity water (1.0) and marine water (35.0) in a petri dish for about one month. This wide tolerance to salinity changes contradicts the opinion that myodocopans are exclusively fully marine organisms ( Horne et al., 2002). The occurrence of this new species in oligohaline ranges represents that myodocopans can also live in almost freshwater (lowest salinity is 0.5) environments. Since this new species has only been found in river mouths, it is likely that the species is especially adapted to the environment of high salinity changes given in estuaries.

The chitinous hook of male upper lip of Parapolycope spiralis sp. nov. is more slender than that of Parapolycope germanica . The spiral shapes in both, male copulatory duct and female spermatheca in Parapolycope spiralis sp. nov. are specific characters in this new taxon. However, the male copulatory duct only forms a spiral when the dissection is carried out in the gum-chloral medium ‘Neo-Shigaral’ ( Fig. 14 ), and not in dissections in glycerine and marine water. The special shape may thus be induced by special physical or chemical properties of the mounting medium. Nevertheless, since the female spermatheca always forms a spiral, the male copulatory organ also must obtain a spiral shape during copulation. The incidental detection of the male copulatory organ forming a spiral in ‘Neo-Shigaral’ may thus be seen as evidence for its morphological ability to do so during copulation.

Figures

FIGURE 1. Map showing the location of the study area. A, Map of Shizuoka Prefecture in Japan; B, The type locality of Parapolycope spiralis sp. nov. C, The type locality of Parapolycope oligohalina sp. nov.

FIGURE 8. Parapolycope spiralis sp. nov. A and B, holotype (SUM-CO- 1781); C and D, paratype (SUM-CO- 1782); E, paratype (SUM-CO- 1783); F and G, paratype (SUM-CO- 1784); H, paratype (SUM-CO- 1785); I, paratype (SUM-CO- 1786); J, paratype (SUM-CO- 1787). A, Right external lateral view of male valve; B, Left external lateral view of male valve; C, Internal lateral view of male left valve; D, Internal lateral view of male right valve; E, Dorsal view of male carapace; F, Right external lateral view of female valve; G, Left external lateral view of female valve; H, Internal lateral view of female left valve; I, Internal lateral view of female right valve; J, Dorsal view of female carapace. Scale: 0.1 mm.

FIGURE 9. Internal lateral views of valve in Parapolycope spiralis sp. nov. A – D, paratype (SUM-CO- 1782) of male right valve; E – I, paratype (SUM-CO- 1782) of male left valve. A, Anterior marginal infold; B, Socket structure of dorsal end in hinge structure; C, Median element of hinge structure; D, Posteroventral gain of marginal infold; E, Anterior marginal infold; F, Knob structure of dorsal end in hinge structure; G, Median element of hinge structure; H, Posteroventral bar of hinge structure; I, Anteroventral marginal infold.

FIGURE 10. Parapolycope spiralis sp. nov. A and B, paratype (SUM-CO- 1794). A, Interior lateral view of male left valve; B, Interior lateral view of male right valve. Arrows indicate anterior. Scale: 0.1 mm.

FIGURE 11. Parapolycope spiralis sp. nov. A, C, D, F, and G; holotype (SUM-CO- 1781): B, E, and H; paratype (SUM- CO- 1788). A, Left lateral view of male upper lip; B, Left lateral view of female upper lip; C, Antennula of male; D, Third podomere with setae of antennula of male; E, Antennula of female; F, Antenna of male; G, Endopodite of antenna of male; H, Antenna of female except for exopodite. Scale: 0.05 mm.

FIGURE 12. Parapolycope spiralis sp. nov. A – D, holotype (SUM-CO- 1781). A, Mandibular palp of male; B, Mandibular coxa of male; C, Maxillula of male; D, Fifth limb of male. Abbreviations: ba, basis; cx, coxa; en, endopodite; ep, epipodite; ex, exopodite. Scale: 0.05 mm.

FIGURE 13. Parapolycope spiralis sp. nov. A, holotype (SUM-CO- 1781); B, paratype (SUM-CO- 1789). A, Left lateral view of posterior trunk segment, furca, and copulatory organ of male; B, Right lateral view of posterior trunk segment, furca and copulatory organ of female. Abbreviations: cd, copulatory duct; lp, long projection; fs, female spermatheca. Scale: 0.05 mm.

FIGURE 14. Parapolycope spiralis sp. nov. male. A, paratype (SUM-CO- 1868); B, holotype (SUM-CO- 1781). A, Right lateral view of posterior trunk segment, furca, and copulatory organ mounted in glycerin; B, Left lateral view of same parts mounted in the gum-chloral medium ‘ Neo-Shigaral’. Scale: 0.05 mm.