Halosbaena okinawaensis, Fujita, 2017

Fujita, Yoshihisa, 2017, Halosbaena okinawaensis, a new species of Thermosbaenacea (Crustacea) from submarine cave on Okinawa Island, Ryukyu Islands, southwestern Japan, Zootaxa 4317 (1), pp. 155-164 : 156-163

publication ID	https://doi.org/ 10.11646/zootaxa.4317.1.7
publication LSID	lsid:zoobank.org:pub:60C7D398-902A-4B86-B596-8Cfe5E2E4A32
DOI	https://doi.org/10.5281/zenodo.5999633
persistent identifier	https://treatment.plazi.org/id/03ED879F-FFE1-880C-A2FE-8E97FCC40D29
treatment provided by	Plazi
scientific name	Halosbaena okinawaensis
status	sp. nov.

Treatment

Halosbaena okinawaensis View in CoL sp. nov.

Japanese name: Okinawa-kooiebi Figs 1–5 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5

Material examined. Holotype. Adult male 2.4 mm ( KMNH IvR 500924); submarine cave located at the northern end of Okinawa, Cape Hedo; collected by Y. Fujita, 10 August, 2016.

Paratypes. 1 adult male 2.3 mm ( KMNH IvR 500925), 1 adult female 1.9 mm ( KMNH IvR 500926), 4 juveniles of 0.9 mm ( KMNH IvR 500927), 1.1 mm ( KMNH IvR 500928, 500929), 1.3 mm ( KMNH IvR 500930); collection data as for holotype.

Description of male holotype. Carapace 0.3 times as long as body length; thoracomeres 7 and 8 lacking lateral setae; pleonites 2–6 each with a pair of simple macrosetae laterally and 2 pairs of simple macrosetae ventrally; pleonite 6 with 6 simple macrosetae dorsally.

Antenna 1 ( Fig. 1 View FIGURE 1 B): peduncle segment 1 with 2 subplumose macrosetae and 2 simple macrosetae; peduncle segment 2 0.9 as long as segment 1, with 3 subplumose macrosetae and 8 simple macrosetae; peduncle segment 3 0.8 times as long as segment 2, with 2 subplumose macrosetae and 4 simple macrosetae; accessory flagellum 4- segmented; main flagellum damaged, wanting.

Antenna 2 ( Fig. 1 View FIGURE 1 C): peduncle segment 1 without setae; peduncle segment 2 1.3 times as long as segment 1, with 3 teazel macrosetae; peduncle segment 3 0.7 times as long as segment 2, with 4 teazel macrosetae; peduncle segment 4 as long as segment 3, with 5 teazel macrosetae; peduncle segment 5 and flagellum damaged, wanting.

Ocular scales ( Fig. 1 View FIGURE 1 D) mediodistal angle pointed, each with pair of simple setae dorsally.

Labrum ( Fig. 2 View FIGURE 2 A) 0.8 times as long as wide, with ciliate microsetae (type 2b) on distal margin and subdistaly on lateral margins, and with ovate microsetae (type 2a) subdistally.

Left mandible ( Fig. 1 View FIGURE 1 G): incisor with 4 cusps; molar process with many fine setae apically; lacinia mobilis with 5 cusps; setal row with 4 stout plumose macrosetae (type IB1); segment 1 of palp without setae; segment 2 with 4 plumidenticulate macrosetae; segment 3 with 4 plumidenticulate macrosetae and 1 serrulate seta.

Right mandible ( Fig. 1 View FIGURE 1 H): incisor with 5 cusps; molar process with many fine setae apically; setal row with 6 stout plumose macrosetae (type IB1); segment 1 of palp without setae; segment 2 with 4 plumidenticulate macrosetae; segment 3 with 4 plumidenticulate macrosetae and 1 serrulate seta.

Labium ( Fig. 2 View FIGURE 2 B) deeply cleft, its two lobes with rounded converging tips, covered both ventrally and along margins with many ciliate microsetae (type 2b).

Maxilla 1 ( Fig. 2 View FIGURE 2 C) differentiated into coxal endite with mediodistal armature of 12 stout plumose macrosetae (type IB1); basal endite with distal armature of 6 toothed macrosetae (type III) and 1 stout lateral seta with broad base; row of 6 short setules along medial margin. Endopod as slender 2-segmented palp: segment 1 with 1 long simple macroseta (type IIA1); segment 2 with 2 long simple macrosetae laterally, 1 long simple macroseta medially, and 2 long simple macrosetae (type IIA1) and 2 bisetulate macrosetae (type IB3(b)) apically.

Maxilla 2 ( Fig. 2 View FIGURE 2 D): coxal endite with 17 long plumose macrosetae (type IA1), 8 simple macrosetae and 2 stout plumose macrosetae (type IB1). Basal endites: endite 1 with 8 stout plumidenticulate macrosetae, 1 long plumidenticulate macroseta and 7 obscurely serrate plumidenticulate macrosetae apically; endite 2 with two transverse rows of 33 small and 15 large rake-like serrate subterminal macrosetae; endite with 96 rake-like serrate macrosetae increasing in size and dentation towards the medial margin of endite. Endopod ( Fig. 2 View FIGURE 2 D) 2-segmented; segment 1 without setae; segment 2 with 2 simple macrosetae (type IIA1) laterally and 3 simple macrosetae (type IIA1) apically.

Maxilliped ( Fig. 2 View FIGURE 2 E): coxal endite with 4 pappose macrosetae; basal endite with three rows of plumidenticulate macrosetae, ventral row of 9 curved macrosetae, central row of 6 bifid macrosetae, and dorsal row of 7 stout serruulate macrosetae plus outermost modified plumidenticulate macroseta; endopod and exopod each with outer margin finely setulose; epipodite hardly developed, lobate and smooth.

Gnathopod ( Fig. 2 View FIGURE 2 F): baso-ischium longest segment, with 1 simple macroseta dorsally; merus half length of baso-ischium, with 1 teazel macroseta (type IIB3) on both dorsodistal and ventrodistal angles of segment,; carpus 0.6 times as long as merus, with 3 teazel macrosetae ventrally; propodus as long as carpus, with 1 teazel macroseta dorsodistally and 4 teazel macrosetae ventrodistally; dactylus 0.7 times as long as propodus, with 2 terminal teasel macrosetae and 2 terminal serrulate macrosetae (type IIB1).

Pereiopod 2 ( Fig. 3 View FIGURE 3 A): basis without setae; ischiomerus with 1 short simple macroseta proximally and 1 teazel macroseta (type II3 B) ventrodistally; carpus 0.7 as long as ischiomerus, with 2 teazel macrosetae (type II3 B) ventrally and 1 simple macroseta dorsodistally; propodus 1.4 times as long as carpus, with 2 teazel macrosetae (type II3 B) ventrally, and 1 short simple macroseta and 1 subplumose macroseta (type IB2) dorsodistally; dactylus 0.3 times as long as propodus, with 2 teazel macrosetae (type II3 B) ventrally and well-developed serrulate macroseta (type IIB1(b)) representing terminal “unguis”; segment 1 of exopod subtrapezoidal, widest subdistally, with 1 plumose macroseta (type IB1) dorsally; segment 2 with 3 ventral, 3 dorsal and 2 terminal plumose macrosetae (type IB1). Pereiopod 3 ( Fig. 3 View FIGURE 3 B) as long as pereiopod 2: basis without setae; ischiomerus with 1 simple macroseta proximally and 2 teazel macroseta (type II3 B) ventrodistally; carpus 0.7 times as long as ischiomerus, with 1 simple seta dorsodistally and 2 teazel macrosetae (type II3 B) ventrally; propodus as long as carpus, with 2 teazel macrosetae (type II3 B) ventrally, and 1 short simple macroseta and 1 subplumose macroseta (type IB2) dorsodistally; dactylus 0.4 times as long as propodus, with 2 teazel macrosetae (type II3 B) ventrally and well-developed serrulate macroseta (type IIB1(b)) forming terminal “unguis”; segment 1 of exopod with 1 plumose macroseta (type IB1) dorsally. Pereiopod 4 ( Fig. 3 View FIGURE 3 C) similar to pereiopod 3 in shape and chaetotaxy. Pereiopod 5 ( Fig. 3 View FIGURE 3 D): endopod similar to pereiopod 3 in shape and chaetotaxy; segment 1 of exopod 0.7 times as wide as segment 1 of exopod of pereiopod 3. Pereiopod 6 ( Fig. 4 View FIGURE 4 A): endopod similar to pereiopod 5 in shape and chaetotaxy; segment 1 of exopod 0.9 times as long and 0.8 times as wide as pereiopod 5 counterpart,; segment 2 with 2 ventral, 2 dorsal and 2 terminal plumose macrosetae (type IB1). Pereiopod 7 ( Fig. 4 View FIGURE 4 B): endopod similar to that of pereiopod 6 in shape and chaetotaxy; segment 1 of exopod smallest of all pereiopods; segment 2 with 2 ventral, 1 dorsal and 2 terminal plumose macrosetae (type IB1).

Male penial lobe ( Fig. 4 View FIGURE 4 B) 2.1 times as long as ischiomerus of pereiopod 7, slightly broadened distally,.

Pleopod 1 ( Fig. 5 View FIGURE 5 A) with 2 processes: one subtriangular with 2 subplumose macrosetae and one tapering with 1 subplumose macroseta. Pleopod 2 ( Fig. 5 View FIGURE 5 A) with 2 short subplumose setae ventrally and 2 long subplumose setae apically.

Uropod and telson damaged.

Description of female paratype (KMNH IvR 500926). Body and appendages similar to those of male holotype; pleonite 6 ( Fig. 5 View FIGURE 5 B) with 8 simple macrosetae dorsally. Ocular scales ( Fig. 1 View FIGURE 1 E) each with 3 simple setae dorsally. Pereiopod 7 (4C): segment 2 of exopod with 1 ventral, 1 dorsal and 2 terminal plumose macrosetae (type IB1). Uropod ( Fig. 5 View FIGURE 5 B): protopod with 3 medial and 3 lateral simple macrosetae; segment 1 of exopod 1.2 times as long as protopod, with 6 cuspidate macrosetae and 4 subplumose macrosetae laterally, and with 1 cuspidate macroseta and 3 subplumose macrosetae medially; segment 2 damaged; endopod 1.6 times as long as protopod, with 4 simple macrosetae and 3 subplumose macrosetae laterally, 7 cuspidate macrosetae and 5 subplumose macrosetae medially, 4 subplumose macrosetae apically, and with 1 short simple seta and 4 long, slender subplumose setae dorsally. Telson ( Fig. 5 View FIGURE 5 B) 1.3 times as long as broad, with 1 pair of simple setae dorsally, 4 pairs of cuspidate macrosetae laterally, 1 pair of simple setae subdistally and 4 pairs of serrate macrosetae on posterior margin.

Description of the paratype juvenile (KMNH IvR 500928). Body ( Fig. 1 View FIGURE 1 A): carapace 0.4 times as long as body; pleonite 6 ( Fig. 5 View FIGURE 5 C) with 4 simple macrosetae dorsally. Ocular scales ( Fig. 1 View FIGURE 1 F) with each with 1 pair of simple setae dorsally. Pereiopod 5 ( Fig. 4 View FIGURE 4 D) shorter than those of adult male and female, but similar in chaetotaxy. Pereiopod 6 ( Fig. 4 View FIGURE 4 E): exopod and endopod both rudimentary, devoid of segmentations and setae. Pereiopod 7 absent. Uropod ( Fig. 5 View FIGURE 5 C) 1.9 times as long as telson; protopod without setae; segment 1 of exopod as long as protopod, with 5 cuspidate macrosetae and 1 subplumose macrosetae laterally, and with 1 cuspidate macroseta and 2 subplumose macrosetae medially; segment 2 0.7 times as long as segment 1, with 2 subplumose macrosetae laterally, 2 subplumose macrosetae medially and 3-4 subplumose macrosetae apically; endopod 1.5 times as long as protopod, with 3 simple macrosetae and 1 subplumose macroseta laterally, 3 cuspidate macrosetae and 4 subplumose macrosetae medially, 5 subplumose macrosetae apically, and with 1 short simple macroseta and 4 long, slender subplumose setae dorsally. Telson ( Fig. 5 View FIGURE 5 C) 1.4 times as long as broad, with 2 pairs of cuspidate macrosetae laterally, 1 pair of simple setae subdistally and 4 pairs of serrate macrosetae on posterior margin; dorsal setae wanting.

Variation. Some variations in adult specimens were recognized in the number of dorsal setae on pleonite 6, dorsal setae on eye lobes, and subplumose setae on segment 2 of exopod of pereiopods. Pleonite 6 ( Fig. 5 View FIGURE 5 B) with 3 or 4 pairs of dorsal setae. Ocular scales ( Fig. 1 View FIGURE 1 D–F) each with 2 or 3 simple setae. Pereiopods 2–5 ( Fig. 3 View FIGURE 3 ): segment 2 of exopod with 2 or 3 ventral, 2 or 3 dorsal and 2 terminal subplumose macrosetae. Pereiopod 7: segment 2 of exopod with 1 or 2 ventral, 1 dorsal and 2 terminal subplumose macrosetae.

Remarks. Halosbaena okinawaensis sp. nov. is close to H. acanthura and H. fortunata , with which it shares the eye lobes having an acute mediodistal angle. Halosbaena okinawaensis is distinguished from H. acanthura by the following features (those of H. acanthura in parentheses): segment 1 of exopod of pereiopods 2–6 subtrapezoidal (subovate); penial lobe curved (nearly straight); and telson with a pair of short simple macrosetae subdistally on dorsal surface (subdistal setae wanting). Halosbaena okinawaensis differs from H. fortunata in the following features (those of H. fortunata in parentheses): segment 1 of exopod of pereiopods 2–6 subtrapezoidal (subovate); and telson with a pair of simple macrosetae and a pair of short simple macrosetae subdistally on outer surface (subdistal setae wanting).

Habitat and biological implication. The submarine cave popularly known as “Hedo Dome” is located on the north coast of Okinawa Island, Ryukyu Island, southwestern Japan. The cave’s entrance lies at 15 m below sea level, and is 14 m wide and 3 m high. The interior of the cave is about 53 m long, and is continued by a stepwise tunnel, with some frontage road. The innermost part of the cave ends in an air pocket, and the water was very clear with the salinity about 23 ‰ and the temperature 24.5 °C. Halosbaena okinawaensis sp. nov. was collected only at the innermost part of the cave.

A rare portunid crab, Atoportunus gustavi Ng & Takeda, 2003 (Portunidae) was recently recorded from this cave ( Fujita & Mizuyama 2016). The other cave fauna inhabiting various portions of this cave, including sponges, molluscs, and decapod crustaceans, will be reported in a forthcoming paper.

Etymology. The new species is named after the type locality.