Redekea abyssalis, Tanaka & Yoo & Pham & Karanovic, 2021

Tanaka, Hayato, Yoo, Hyunsu, Pham, Huyen Thi Minh & Karanovic, Ivana, 2021, Two new xylophile cytheroid ostracods (Crustacea) from Kuril-Kamchatka Trench, with remarks on the systematics and phylogeny of the family Keysercytheridae, Limnocytheridae, and Paradoxostomatidae, Arthropod Systematics & amp; Phylogeny 79, pp. 171-188 : 171

Redekea abyssalis sp. nov. Figs 8 , 9 , 10

Material examined.

Holotype: adult male ( SMF 57056 ), LV; L 0.32 mm, H 0.16 mm: RV; L 0.31 mm, H 0.17 mm. Dissected, soft parts mounted on two glass slides and valves on a cardboard cell slide . Paratypes: 1 adult male ( SMF 57057 ); dissected, soft parts mounted on a glass slide and valves on a cardboard cell slide : 2 female ( SMF 57058 , 57059); dissected, soft parts mounted on a glass slide and valves on a cardboard cell slide .

Type locality.

Kuril-Kamchatka Trench region, the sampling station SO 250_9 of KuramBio II expedition (RV Sonne, 250th Expedition), trawled from 43°48.43'N, 151°44.35'E, 5134 m to 43°47.64'N 151°44.51'E, 5101 m by AGT on 19th August, 2016. Holotype ( SMF 57056) and 2 paratypes ( SMF 57058, 57059) were obtained by washing a body of Limnoria sp.

Diagnosis.

Shell sub-triangular in lateral view. LV; L 0.32 mm, H 0.16 mm: RV; L 0.31 mm, H 0.17 mm. Greatest H situated just behind middle L. External surface of carapace covered with shallow pits except central and mid-ventral areas of valves; pits size increasing from marginal to near central area of valves. Sensilla long existing non-collar pores surrounded with sieve pores. Hp: ejaculatory duct short and curved; hook-like process elongated conical shape; distal lobe sub-triangular.

Description of adult male

(based on holotype SMF 57056). Carapace (Figs 7 , 8A-D ) sub-triangular in lateral view. LV; L 0.32 mm, H 0.16 mm: RV; L 0.31 mm, H 0.17 mm. Greatest H situated just behind middle L. Dorsal margin arched; RV more steeply arched than LV. Anterior margin rounded; RV narrower than LV. Ventral margin of both valve weakly concave situated in front of middle L. Posterior margin rounded. External surface covered with shallow pits except central and mid-ventral areas of valves; pits size increasing from marginal to near central area of valves (Fig. 8A, B ). Sensilla long existing non-collar pores surrounded with sieve pores (Fig. 8C ): circular shaped sieve pores in anterior and posterior areas, approximate diameter 4 μm; elliptical shaped sieve pores in other areas, approximate length major axis 10-20 μm and minor axis 4-9 μm. Inner calcified lamella broadly developed in both valves (Figs 7 , 8D ). Four adductor muscle scars form a vertical row (Fig. 7 ). Hingement lophodont (Figs 7 , 8D ). A1 (Fig. 9A ) six podomeres [four and five podomeres divided by suture, same as defined 4a and 4b by Smith and Tsukagoshi (2005) and Boxshall et al. (2010)]. First podomere bare. Second podomere three-fifths as long as first podomere with one postero-distal seta. Third podomere two-fifths as long as first podomere with one short antero-distal seta. Fourth to sixth podomeres same length as third podomere. Fourth podomere with one short antero-distal seta and one long postero-distal seta. Fifth podomere with three long antero-distal setae and one long postero-distal seta. Sixth podomere with two long distal setae and one long blunt tipped distal seta. A2 (Fig. 9B ) five podomeres. First podomere (basis) parallelogram-shaped, with one long two-annulated exopodite (spinneret seta) on antero-distal end. Second (first endopodal) podomere half lengths as first podomere, with one long setulous postero-distal seta. Third and fourth podomeres fused. Third (second endopodal) podomere half lengths as first podomere, with one short antero-middle seta, one short antero-distal seta, and two short postero-distal setae. Fourth (third endopodal) podomere same length as first podomere, with one stout setulous postero-distal seta. Fifth (fourth endopodal) podomere one-fourth as long as first podomere, with one stout distal claw with a row of spines on posterior margin. Md (Fig. 9C ) coxa with one slender dorsal seta. Coxal endite consisting of eight teeth. Palp consisting of three podomeres. First podomere (basis), with one short seta on ventral margin and two short dorso-distal setae. Second podomere with two short ventro-distal setae and one lateral distal seta. Third podomere, with two slender setae on ventral margin, one slender distal seta, and one stout distal claw curved distally with a row of setae on ventral margin. Mxl (Fig. 9D ) branchial plate (exopodite) strongly reduced, consisting with 1 seta. Basal podomere with one palp (endopodite) and three endites. Palp consisting of one podomere, with three simple distal setae. Endites: dorsal one with one simple and one spatula-like distal setae; middle one with one simple and one spatula-like distal setae; ventral one with two simple distal setae. L5 (Fig. 9E ) four articulated podomeres. First podomere with one antero-lateral seta, one antero-distal seta, and one dorso-lateral seta. Second podomere one-fourth as long as first podomere, with one antero-distal seta. Third podomere one-eighth as long as first podomere, bare. Fourth podomere one-fourth as long as first podomere, with one stout sclerotized distal claw with a few spines on antero-distal margin. L6 (Fig. 9F ) four articulated podomeres. First podomere with one antero-lateral seta, one antero-distal seta, and one plumose dorso-lateral seta. Second podomere half as long as first podomere, with one thick antero-distal seta. Third podomere one-sixth as long as first podomere, bare. Fourth podomere one-third as long as first podomere, with one stout sclerotized distal claw with a few spines on antero-distal margin. L7 (Fig. 9G ) four articulated podomeres. First podomere with one antero-lateral spine, one antero-distal seta, and one dorso-lateral seta. Second podomere four-fifths as long as first podomere, with one thick antero-distal seta. Third podomere one-fifth as long as first podomere, bare. Fourth podomere three-fifths as long as first podomere, with one long stout sclerotized distal claw with a few spines on antero-distal margin. Brush-shaped organ absent. Oral cone (Fig. 10A ) subtriangular in lateral view, with six teeth on apex and one rake-like organ with three teeth. Hp and posterior body (Fig. 10B ) symmetrical. Ejaculatory duct short and curved. Hook-like process elongated conical shape. Distal lobe subtriangular. Posterior body left and right sides bearing two furcal setae.

Description of adult female

(based on paratype SMF 57058). Carapace (Fig. 8E, F ) sub-triangular in lateral view. LV; L 0.33 mm, H 0.20 mm: RV; L 0.33 mm, H 0.18 mm. L5 (Fig. 9H ) longer than that of male in appearance. Four articulated podomeres. First podomere with two antero-lateral seta, one antero-distal seta, and one dorso-lateral seta. Second podomere four-fifths as long as first podomere, with one antero-distal seta. Third podomere two-fifths as long as first podomere, bare. Fourth podomere three-fifths as long as first podomere, with one stout sclerotized distal claw with a few spines on antero-distal margin. Copulatory organ and posterior body (Fig. 10C ) female genital opening paired. Sclerotized framework of genital opening roughly circular. Genital lobe paired with each two furcal setae.

Etymology.

The species epithet ' Redekea abyssalis ' refers to the abyssal zone of the Pacific Ocean where the species was discovered.

Distribution.

Only recorded from the type locality.

DNA sequence.

The 18S rDNA sequences of two paratypes ( SMF 57057, SMF 57058) were obtained. GenBank accession numbers are MW338926 (1177 bp) for SMF 57058 and MW338927 (1685 bp) for SMF 57057.

Remarks.

To date, the genus Redekea comprised two species: the type species, R. perpusilla de Vos, 1953 and R. californica de Vos and Stock, 1956. Redekea abyssalis resembles these two species in the general carapace and appendage morphology. However, there are small, but consistent differences between the new and the other two species. First of all, R. abyssalis is larger, with valve size approximately 0.3 mm, while the other two species measure approximately 0.2 mm. Secondly, R. abyssalis sp. nov. has a slender valve outline than R. perpusilla , and broader than R. californica . Thirdly, the distal claw of the male L5 in R. abyssalis has a sharply bended tip, the bending in R. perpusilla occurs at about mid-length, while in R. californica the claw is evenly curved from the proximal end all the way to its tip. Finally, distal lobe and hook-like process of Hp in R. abyssalis is shorter and narrower than that of the other two species.

Figures

Figure 7. Redekea abyssalis sp. nov., male, holotype (SMF 57056). A RV, internal lateral view B LV, internal lateral view. Scale bar: 100 μm.

Figure 8. Scanning electron microscope images of valves of Redekea abyssalis sp. nov. A - D male, holotype (SMF 57056) E, F female, paratype (SMF 57058). A RV, posetro-ventral area, external lateral view B RV, antero-ventral area, external lateral view C RV, pore system, external view D LV, internal lateral view E RV, external lateral view F LV, internal lateral view. Scale bars: 50 μm (A - C); 100 μm (D - F).

Figure 9. Redekea abyssalis sp. nov. A - G male, holotype (SMF 57056) H female, paratype (SMF 57058). A A 1 B A 2 C Md D Mxl E L 5 F L 6 G L 7 H L 5. Scale bar: 50 μm.

Figure 10. Redekea abyssalis sp. nov. A, B male, holotype (SMF 57056) C female, paratype (SMF 57058). A Oral cone B left Hp C female copulatory organ. Scale bar: 50 μm.