Heteromysoides taramensis, Shimomura & Fujita, 2020

Shimomura, Michitaka & Fujita, Yoshihisa, 2020, Heteromysoides taramensis, a new species of mysid (Mysida: Mysidae) from an anchialine cave on Tarama Island, Ryukyu Islands, southwestern Japan, Zootaxa 4895 (1), pp. 135-145 : 137-144

publication ID	https://doi.org/ 10.11646/zootaxa.4895.1.8
publication LSID	lsid:zoobank.org:pub:FEC647E6-FEFF-4259-8A94-4B0CBEF899B1
DOI	https://doi.org/10.5281/zenodo.4323800
persistent identifier	https://treatment.plazi.org/id/0873FD12-FF99-FF8A-95E5-DB5F47E5FB6D
treatment provided by	Plazi
scientific name	Heteromysoides taramensis
status	sp. nov.

Treatment

Heteromysoides taramensis sp. nov.

[New Japanese Name: Tarama-me-ami]

Figs. 2–6 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6

Material examined. During the field work, only adult females (ovigerous and non-ovigerous) were found at the study site. Holotype: ovig. female (TL 3.7 mm) ( SMBL-V0585 ) . Paratypes: 1 ovig. female (TL 3.7 mm, dissected) ( SMBL-V0586 ) ; 1 ovig. female (TL 3.3 mm, dissected) ( SMBL-V0587 ) ; 1 non-ovig. female (TL 3.0 mm, dissected) ( SMBL-V0588 ) ; 1 ovig. female (TL 3.2 mm) ( SMBL-V0589 ) , 1 ovig. female (TL 3.2 mm) ( SMBL-V0590 ) , 1 ovig. female (TL 3.0 mm) ( SMBL-V0591 ) , 1 non-ovig. female (TL 3.0 mm) ( SMBL-V0592 ) , an anchialine cave “Shuga-ga (24°40'15.7"N, 124°42'25.7"E)” of Tarama Island , Ryukyu Islands, Japan, 12 October 2019, coll. Y. Fujita. GoogleMaps

Description. Carapace ( Fig. 2A, B View FIGURE 2 ) produced anteriorly with subtriangular rostrum, covering basal part of eyestalks; anterolateral corner rounded; posterior margin emarginated; cervical sulcus distinct at anterior two-fifths; last thoracic somite slightly exposed dorsally.

Eyes ( Fig. 2A, B View FIGURE 2 ) subquadrate in dorsal aspect, without spiniform process, separated from each other, extending 0.7 of first segment of antennular peduncle; cornea developed, comprise of small tube-like ommatidia situated in anterolateral part.

Antennula ( Fig. 2B, C View FIGURE 2 ) with first segment of peduncle longer than wide, with dorsal projection bearing 4 short plumose setae and 1 long simple seta; distolateral corner of first segment prolonged anteriorly, tipped with 3 short plumose setae; second segment shortest, with 1 long plumose seta laterally and 1 long plumose and 1 short simple setae medially, and with dorsal projection bearing 3 short plumose setae; third segment as long as first segment, with 3 long plumose setae medially, and with dorsal projection bearing 4 short plumose setae.

Antenna ( Fig. 2B, D View FIGURE 2 ) with scale elongated elliptical, setose all around, extending to distal margin of antennular peduncle; antennal scale 3 times as long as wide; medial margin more convex than lateral margin; distal suture marked off at distal one-eleventh; outer margin slightly concave; inner margin convex. Antennal peduncle as long as antennular peduncle; second segment twice as long as wide, as long as third segment; sympod with distomesial corner produced into blunt tooth.

Labrum ( Fig. 2E View FIGURE 2 ) subrhomboidal, 1.1 times as long as wide, with frontal margin rounded, and with many fine setae on posterior margin.

Mandibles ( Fig. 2F, G View FIGURE 2 ) with large molar portion, inner posterior margin with brush of fine setae; lacinia mobilis and spine row well-developed; first segment of palp without setae; second segment expanded, with 1 setulate seta on outer margin, 5 setulate setae on inner margin, and with 1 or 2 setulate setae distally; third segment 0.4 times as long as second segment, with some setulate and 1 pectinate setae.

Maxillula ( Fig. 3A View FIGURE 3 ) precoxal lobe as wide as basal lobe, with 10 setae on margin; basal lobe with 10 setulate setae distally, 3 plumose setae subapically.

Maxilla ( Fig. 3B View FIGURE 3 ) exopod with 4 plumose setae on margin; basis 24 plumose setae medially; first article of endopod with 4 plumose setae medially; second article with many plumose setae and fine setae on margin; bilobulate basal endites each with 7 and 5 denticulate setae distally, respectively; coxal endite with 7 plumose setae distally.

First thoracopod ( Fig. 3C View FIGURE 3 ) short and robust: basis with 1 plumose seta distolaterally and medially, respectively; preischium trapezoidal, with 5 short and 4 long plumose setae medially; ischium as long as preischium, with 6 short and 2 long plumose setae medially; merus 1.2 times as long as ischium, with 1 plumose seta distolaterally, 13 plumose setae medially and 4 long plumose setae ventrally; carpopropodus as long as merus, with 2 plumose setae distolaterally and 4 plumose setae medially; dactylus shortest, 0.6 times as long as carpopropodus, with 11 plumose setae and 1 long simple seta distally. Endite of basis developed, with 8 plumose setae medially and dorsally, respectively, and with many fine setae on lateral margin.

Second thoracopod ( Fig. 3 View FIGURE 3 D–G) basis with 1 plumose seta medially, endopod relatively slender: preischium shorter than basis, with 1 plumose seta medially; ischium 1.7 times as long as preischium, with 5 plumose setae medially; merus longest, 1.4 times as long as ischium, with 2 plumose setae medially; carpopropodus 0.6 times as long as merus, 1.5 times as long as wide with 7 plumose setae medially, and 3 plumose and 2 simple setae laterally; dactylus 0.9 times as long as carpopropodus, 1.8 times as long as wide, with 13 barbed and 8 long, simple setae.

Third thoracopod ( Fig. 3 View FIGURE 3 H–J) basis with 2 plumose and 1 simple setae medially, and with 1 plumose seta laterally, endopod longer than endopod of second thoracopod: preischium trapezoidal, 0.7 times as long as basis, without setae; ischium 1.9 times as long as preischium, with 4 setae medially; merus as long as ischium, with 2 simple setae medially and 3 setae laterally; carpopropodus divided into 3 subsegments, as long as merus, with 3 simple and 3 pectinate setae ventrally, and 6 simple setae laterally; dactylus shortest, 0.1 times as long as carpopropodus, with 3 simple setae distally.

Fourth thoracopod ( Fig. 4A View FIGURE 4 ) basis with 2 plumose setae medially and laterally, respectively, endopod similar to third thoracopod: preischium trapezoidal, without setae; ischium 2.3 times as long as preischium, with 2 setae medially and 1 seta laterally; merus 1.1 times as long as ischium, with 2 setae medially, 2 setae distolaterally and 1 seta ventrally; carpopropodus divided into 3 subsegments with several setae at each segment, 1.2 times as long as merus; dactylus shortest, with 2 short and 1 long simple setae apically.

Fifth thoracopod ( Fig. 4B View FIGURE 4 ) basis with 2 plumose setae medially and laterally, respectively, endopod longer than one of third thoracopod: preischium trapezoidal, without setae; ischium longest, with 1 simple seta medially and laterally, respectively; merus 0.9 times as long as ischium, with 7 setae medially and 1 seta laterally; carpopropodus divided into 4 subsegments with several setae at each segment, 0.8 times as long as merus; dactylus shortest, with 3 setae apically.

Sixth thoracopod ( Fig. 4C View FIGURE 4 ) basis with 5 plumose setae, endopod shorter than one of fifth thoracopod: preischium subtriangular, without setae; ischium longest, with 2 setae medially; merus 0.6 times as long as ischium, with 8 setae medially and 2 setae distolaterally; carpopropodus divided into 4 subsegments with several setae at each segment; dactylus shortest, with 3 setae apically.

Seventh thoracopod ( Fig. 5A View FIGURE 5 ) basis with 3 plumose setae, endopod longer than one of sixth thoracopod: preischium subtriangular, without setae; ischium longest, with 1 simple seta distomedially and distolaterally, respectively; merus 0.7 times as long as ischium, with 7 setae medially and 2 setae distolaterally; carpopropodus divided into 4 subsegments with several setae at each segment; dactylus shortest, with 3 setae apically.

Eighth thoracopod ( Fig. 5B View FIGURE 5 ) basis elongated, with 1 plumose seta medially, endopod longest among all thoracopods: preischium subrectangular, without setae; ischium longest, with 1 simple seta medially; merus 0.7 times as long as ischium, with 6 simple setae medially and 2 simple setae distolaterally; carpopropodus divided into 4 subsegments several setae at each segment; dactylus shortest, with 5 simple setae apically.

Exopods of second to eighth thoracopods ( Figs. 3D, H View FIGURE 3 ; 4 View FIGURE 4 A–C; 5A, B) similar in shape, with 8 or 9-segmented flagellum; basal plate with rounded outer corner.

Marsupium ( Fig. 5A, B View FIGURE 5 ) composed of 2 pairs of well-developed oostegites on seventh and eighth thoracopods.

Abdomen ( Fig. 2A View FIGURE 2 ) with smooth somites lacking spines, folds, or ventral processes; first 3 somites decreasing in length posteriorly; third, fourth and fifth somites subequal in length; sixth somite 1.6 times as long as fifth somite.

All pleopods ( Fig. 6 View FIGURE 6 A–E) reduced to unsegmented lobes, not modified. First pleopod as long as second pleopod; second to fifth pleopods increasing in length posteriorly; fifth pleopod 1.5 times as long as fourth pleopod.

Uropods ( Fig. 6F View FIGURE 6 ) extending beyond apex of apical spines of telson, setose around entire margins: endopod 3.7 times as long as wide, with large statolith, without mesial spines; exopod 1.1 times as long as endopod.

Telson ( Fig. 6F, G View FIGURE 6 ) entire, tapering posteriorly, subtriangular, 1.1 times as long as sixth somite, 1.3 times as long as maximum width, with 5 or 6 pairs of simple spines distolaterally, 1 pair of long simple spines subapically and 1 pair of short simple spines apically.

Color in life. Adult: body ( Fig. 1C, D View FIGURE 1 ) mostly transparent, with some reddish chromatophores scattered on entire body; corneas of eyes dark brown. Embryos in marsupium ( Fig. 1E View FIGURE 1 ): body pale olive-green; corneas of eyes dark brown.

Etymology. The new species is named after the type locality, Tarama Island.

Remarks. The shape of telson and arrangement of the spines on the telson link the new species to Heteromysoides nana Murano, 1998 from mangroves in Channel Island, Northern Territory, Australia ( Murano 1998), H. stenoura Hanamura & Kase, 2004 from a submarine cave on Grand Cayman, the Caribbean Sea ( Hanamura & Kase 2004), H. songkhlaensis Yolanda, Sawamoto & Lheknim, 2019 from shallow waters in the Songkhla Lagoon, southern Thailand ( Yolanda et al. 2019) and H. kumejimensis from a submarine cave on Kumejima Island, Ryukyu Islands, Japan ( Shimomura & Fujita 2020). Heteromysoides taramensis is distinguished from H. nana by following characters (those of H. nana in parentheses): telson 1.3 times as long as wide at base (1.6 times as long as wide), with 5 or 6 pairs of simple spines distolaterally, 1 pair of long spines subapically and 1 pair of short spines apically (4 pairs of simple spines distolaterally, 1 pair of long spines subapically and 1 pair of short spines apically); antennal scale extending to distal margin of third segment of antennular peduncle (not extending); and antennal sympod with distomesial corner produced into blunt tooth (acute tooth). Heteromysoides taramensis differs from H. stenoura in having the following characters (those of H. stenoura in parentheses): ocular process on the eyes absent (present); antennal scale elongated elliptical (slender); distal suture of antenna marked off at distal one-eleventh (without suture); antennal sympod with distomesial corner produced into blunt tooth (without teeth); telson 1.3 times as long as wide at base (1.8 times), with 5 or 6 pairs of simple spines distolaterally, 1 pair of long spines subapically and 1 pair of short spines apically (with 4 or 5 pairs of short simple spines laterally, 1 pair of long spines subapically and 1 pair of short spines apically), gradually narrowing (abruptly narrowing at basal one-fifth); and posterior margin of telson rounded (nearly truncate). Heteromysoides taramensis is distinguished from H. songkhlaensis by following characters (those of H. songkhlaensis in parentheses): eyes subquadrate in dorsal aspect (subglobular); antennal scale extending to distal margin of third segment of antennular peduncle (reaching middle part of third segment); endopod of second thoracopod slender (stout); and telson with 5 or 6 pairs of simple spines distolaterally, 1 pair of long spines subapically and 1 pair of short spines apically (11–19 simple spines distally, increasing in length posteriorly). Heteromysoides taramensis is distinguished from H. kumejimensis by following characters (those of H. kumejimensis in parentheses): eyes subrectangular in dorsal aspect (subglobular); antennal scale elongated elliptical (slender); distal suture of antenna marked off at distal one-eleventh (without suture); and telson 1.3 times as long as wide at base (1.7 times), with 5 or 6 pairs of simple spines distolaterally, 1 pair of long simple spines subapically and 1 pair of short simple spines apically (3 or 4 pairs of short simple spines laterally, 3 or 4 pairs of long serrate spines posterolaterally and 1 pair of short simple spines apically).

Habitat and biological implication. The anchialine cave “Shuga-ga” is located on the northern part of Tarama Island, and the entrance is about 430 m from the sea ( Fig. 1A View FIGURE 1 ). The interior of the cave where the present specimens were collected is about 15 m long from the entrance, and there is an anchialine pool ( Fig. 1B View FIGURE 1 ) in the innermost area of the cave. This pool lies in total darkness, and its breadth is about 10 m 2 (about 5 m long × 2m wide) and its greatest depth is about 40 cm at low tide. The water was almost clear, with the salinity 0.9 PSU and temperature 24.8°C in 10–12 November 2007 (see Fujita & Sunagawa 2008). The water level of the pool falls and rises with the tides.

Although there are six anchialine habitats (caves and wells) in Tarama Island, Heteromysoides taramensis sp. nov. has only been found at “Shuga-ga” cave. Other crustaceans found from this anchialine pool include: two atyids, Antecaridina lauensis (Edmondson, 1935) and Halocaridinides trigonophthalma (Fujino & Shokita 1975) ; and one gecarcinid, Tuerkayana hirtipes (Dana, 1851) ( Fujita & Sunagawa 2008; Weese et al. 2013; Fujita, personal observation in 2019).