Eumunida balteipes, Osawa & Higashiji, 2019

Osawa, Masayuki & Higashiji, Takuo, 2019, Two large squat lobsters of the superfamily Chirostyloidea (Crustacea: Decapoda: Anomura) from the Ryukyu Islands, southwestern Japan, with description of a new species of the genus Eumunida Smith, 1883, Zootaxa 4555 (3), pp. 319-330 : 322-328

Eumunida balteipes n. sp.

( Figs. 3–6 )

Type material. Holotype: RUMF-ZC-5358, male (pcl 24.0 mm), 2.3 km northeast of Kume Island, Ryukyu Islands, Japan, sluice gate of deep sea water, 612 m, Okinawa Prefectural Deep Sea Water Research Center ( Maja , Kumejima , Okinawa), 2 February 2009 . Paratypes: RUMF-ZC-5359, 1 male (pcl 21.3 mm), 1 female (pcl 24.9 mm), same locality as in holotype, 11 January 2011 .

Description. Carapace ( Figs. 3A , 4A ) approximately as wide as long (exclusive of rostrum), widest between posterior second branchial spines; dorsal surface covered with minute setae. Rostrum ( Fig. 4A, E ) sharply spiniform, about half length of postorbital carapace; mesial supraocular spine 0.6–0.7 length of rostrum; lateral supraocular spine reaching beyond half length of mesial supraocular spine. Lateral orbital angle acute. Gastric region well defined, moderately convex; 3 small hepatic spines present, first spine largest, proximal to base of outer supraocular spine. Anterior and posterior cervical groove distinctly marked. Transverse ridges each with row of short plumose setae on anterior margin; anterior branchial region nearly smooth, with some short squamiform striae; 7 main transverse ridges behind cervical groove; first interrupted, with irregular row of some short striae on each lateral side, second ridge separated into 3 parts (holotype) or nearly complete (paratypes), other ridges complete or nearly complete; 1 shorter stria inserted laterally between sixth and seventh transverse ridges. Lateral margins moderately convex, armed with 6 spines decreasing in size posteriorly, 2 spines anterior to posterior cervical groove; first (anterolateral) spine strong, more than half length of outer supraocular spine, reaching or slightly overreaching sinus between supraocular spines, longer than second marginal spine.

Pterygostomian flap with slender spine on anterior margin ( Fig. 4E ).

Thoracic sternum ( Figs. 3C , 4C ) medially concave anteriorly. Sternite 3 ( Fig. 4C ) anteriorly with pair of triangular or bluntly angled teeth, separated by U-shaped median notch. Sternite 4 ( Fig. 4C ) with pair of prominent anterolateral spines and transverse rows of setiferous, short ridges.

Abdominal somite 1 ( Figs. 3B, C , 4B ) with 1 main transverse ridge posteriorly on tergum, surface anterior to main transverse ridge with short striae. Somite 2 ( Figs. 3B , 4B ) with 2 main transverse ridges and 3 – 5 rows of short and long striae between main ridges on tergite; dorsolateral stria separating tergite and pleuron entire; each pleuron with short, arcuate and transverse striae, anterior margin bearing prominent spine. Somite 3 ( Fig. 3B ) with 2 main transverse ridges and 2–4 rows of short and long striae between main ridges on tergite; dorsolateral stria separating tergite and pleuron entire; each pleuron with 2 long, somewhat arcuate striae and 1 short arcuate stria posteriorly. Somite 4 with 2 main transverse ridges and 1 row of interrupted striae between main ridges on tergite, posterior main transverse ridge extending to pleura; each pleuron with long stria along posterior margin. Somite 5 with 2 main transverse ridges and pair of short submedian striae between main ridges on tergite; each pleuron with 2 long striae. Somite 6 ( Figs. 3C , 4D ) with 7 pairs of arcuate and transverse striae, posteromedian pair of striae smallest; shallow posterolateral notch present; posterior margin faintly undulate. Telson ( Figs. 3C , 4D ) much wider than long, with deep, slit-like incision on lateral margin, divided into 2 parts by transverse suture; anterior part with short squamiform striae on either side of midline; posterior part further divided in 2 parts by median suture, posterior margin with distinct median notch.

Eye ( Figs. 3C , 4A, E ) short, cornea dilated, reaching or slightly overreaching tip of lateral supraocular spine when anteriorly directing position.

Antennule without distinctive features.

Antennal peduncle ( Fig. 4E, F ) moderately slender. Article 1 with short distolateral spine. Article 2 with distolateral spine reaching proximal 0.3 of antennal acicle. Article 3 with long distomesial spine, overreaching distal margin of fourth segment and falling slightly short of tip of antennal scale. Article 4 with tiny dorsolateral distal spine and long ventrodistal spine distinctly exceeding distal margin of fifth segment. Article 5 with 3 distal spines (dorsolateral, ventrolateral and ventromesial), dorsolateral spine longest. Antennal scale spiniform, slender, distinctly overreaching distal margin of fourth article.

Maxilliped 3 (Mxp3, Fig. 3C ) moderately slender. Ischium with crista dentata bearing 12–14 slender corneous spines. Merus ( Fig. 4G ) with small spine on flexor margin slightly distal to midlength, extensor margin unarmed. Carpus unarmed. Distal article of exopod reaching midlength of merus.

Chelipeds (P1; Figs. 3A, D , 5 A–D) subcylindrical, subequal in length, 3.6–4.3 times as long as carapace exclusive of rostrum. Ischium with moderately large, ventromesial distal spine; ventral surface with short squamiform ridges. Merus squamate, 1.6–2.0 times as long as carapace exclusive of rostrum, armed with 3 rows of strong spines (dorsolateral, dorsomesial, and ventromesial), ventromesial row composed of large and small spines regularly alternated (spines bearing short plumose setae at bases); ventral surface without row of spines, but 1 prominent distolateral spine present. Carpus 1.5–1.6 times as long as broad, squamate, with 3 distal spines (dorsomesial, mesial, and ventromesial). Palm 1.0–1.2 times as long as dactylus, not massive; dorsal surface with numerous, small squamiform ridges and row of larger ridges along dorsomesial margin (larger ridges on proximal two thirds unarmed, or with 2 or 3 small, tuberculate or acute spines); ventral surface with small and large squamiform ridges, moderately small setal pad located at level of base of fingers; ventromesial margin with row of 3 or 4 spines. Fingers almost smooth, with sparse stiff setae on surfaces, not distinctly gaping, each terminating in small corneous spine (in fixed finger, terminal spine accompanied ventrally with small sharply pointed calcareous tooth); dorsal surface of dactylus and ventral surface of fixed finger each with blunt longitudinal ridge along midline; opposable margin of fixed finger minutely denticulate, with 3–5 widely spaced small triangular teeth, that of dactylus minutely denticulate, proximal denticles composed of larger blunt teeth.

Ambulatory legs (P2–4; Figs. 3E , 6 A–G) slender, with sparse, short and moderately long stiff setae on margins. Second pereopod (P2, Fig. 6 A–E) with ischium bearing 1 small, extensor distal spine. Merus equal in length to or slightly longer than propodus, 7.5–8.4 times as long as high, squamate, with extensor row of prominent spines decreasing in size proximally and 1 strong flexor distal spine; ventromesial margin with row of small spines. Carpus with extensor margin bearing row of prominent spines decreasing in size proximally; lateral surface with blunt longitudinal ridge adjacently along extensor margin and some squamiform ridges on flexor side. Propodus 8.5–11.2 times longer than high, flattish laterally, nearly smooth on surfaces, unarmed on extensor margin; lateral and mesial surfaces each with shallow longitudinal sulcus on midline; flexor margin with 7–9 corneous spines; distoventral margin with pair of subequal-sized corneous spines. Dactylus 0.3 length of propodus, nearly smooth on surfaces; flexor margin with 8 or 9 corneous spines decreasing in size proximally; surfaces with sparse, short stiff setae. Third pereopod (P3, Fig. 6F ) generally similar to P 2 in ornamentation; merus slightly shorter than or equal in length to P2 merus, 5.4–6.2 times as long as high, ventromesial margin unarmed; propodus approximately equal in length to P2 propodus, with 7–9 corneous spines on flexor margin and 2 corneous spines on distoventral margin; dactylus with 8 or 9 corneous spines on flexor margin. Fourth pereopod (P4, Fig. 6G ) with ischium bearing 2 or 3 small spines on extensor margin; merus 0.6–0.9 length of P2 merus and 0.7–0.8 length of P3 merus, 4.2–5.5 times as long as high, ventromesial margin unarmed; extensor margin with row of prominent spines in distal 0.7, followed by 2 rows of much smaller spines; lateral surface with row of small but prominent spines on proximal 0.6 to almost entire of midline; propodus approximately equal in length to P2 propodus, with 6 or 7 corneous spines on flexor margin and 2 corneous spines on distoventral margin; dactylus with 8 or 9 corneous spines on flexor margin.

Variations. The dorsomesial margin of the P1 palm is unarmed (paratype male, pcl 21.3 mm, RUMF-ZC- 5359), two acute spines (paratype female, pcl 24.9 mm, RUMF-ZC-5359), or three tuberculate spines (holotype, pcl 24.0 mm, RUMF-ZC-5358). The length of the P1 and proportions of articles of the P1–4 (length/height ratios) somewhat vary in the type specimens as shown above.

Color ( Fig. 3A ). Carapace, abdomen, and Pl orange in general. Abdomen reddish orange along posterior margin of tergite of each somite; lateral parts of somites 4 and 5 and mostly entire parts of somite 6 white. Telson and uropods also white with margins reddish orange. Ocular, antennular, antennal peduncles and Mxp3 reddish orange; cornea black. Pl reddish orange on proximal and distal one thirds of merus, distal part of palm, and median parts of fixed finger and dactylus; proximal and distal one thirds of fixed finger and dactylus white. P2 – 4 reddish orange with white bands on median part and distal margin of each merus, proximal one fourth of each carpus, and proximal one sixth and distal one third of each propodus (distal white band of propodus bearing pale orange stripe along midline); dactylus white along ventral margins. Spines on carapace and P1–4 white on distal parts, bases of spines on P1 – 4 reddish orange.

Habitat. The specimens of the present new species have been sometimes collected from the strainer at the exit of the deep-sea sluice gate in the Okinawa Prefectural Deep Sea Water Research Center; seven individuals were found in January 2008 ( Shiroma et al. 2009).

Ecology in aquarium. The Okinawa Churaumi Aquarium has kept the present new species with the display plate named “ Eumunida pacifica ” as an icon of deep sea creatures over about ten years, although the living individuals for exhibition were replaced several times by others newly obtained from the field (the type locality of the new species, off Kume Island) when existing specimens died. The longest period for which a specimen has been kept is about seven years at water temperatures of 9–12°C. The handling and feeding techniques for E. balteipes n. sp. are not so difficult compared to those of other deep-sea crustaceans such as Heterocarpus laevigatus Spence Bate, 1888 [ Caridea : Pandalidae ] and Linuparus trigonus (von Siebold, 1824) [Achelata: Palinuridae ], which were collected around Okinawa Island and have also been reared in the aquarium. Eumunida balteipes n. sp. is carnivorous and was fed pieces of krill and soft parts of small bivalves twice a week. The squat lobsters are usually motionless except during feeding time when they become active. When more than two individuals are kept in same aquarium, they often fight heavily as some pereopods are detached from the body. This suggests that individual of E. balteipes n. sp. keeps a certain distance between from other individuals in the field.

Distribution. Kume Island, Ryukyu Islands, southwestern Japan; 612 m.

Etymology. The specific name is a combination of the Latin, balteus (= band) and pes (= leg), in reference to the banded color pattern of the pereopods.

Remarks. Eumunida balteipes n. sp. closely resembles E. sternomaculata de Saint Laurent & Macpherson, 1990 known from New Caledonia, in the following morphological characters: a pair of prominent spines on the anterior margin of thoracic sternite 4 (corresponding to the subgenus Eumunida Smith, 1883 ); the carapace with complete transverse ridges on the posterior part, two spines anterior to the lateral end of the posterior cervical groove, and the first lateral marginal (anterolateral) spine being more than half the length of the lateral supraocular spine and reaching at most to the hiatus between the supraocular spines; and the Pl with a ventral setal pad on the palm and three distal spines on the carpus but lacking a ventral row of spines on the merus. However, the armature of thoracic sternite 3 and the P1 palm distinguishes the two species. The anterior median margin of the thoracic sternite 3 has two angular teeth in E. balteipes n. sp., instead of two sharp spines in E. sternomaculata . The dorsomesial margin of the P1 palm is unarmed or with two or three small acute or tuberculate spines in E. balteipes n. sp. (in the holotype, three tuberculate spines), but the spines are greater in number, ranging from four to seven in E. sternomaculata (in the holotype, six or seven spines; cf. de Saint Laurent & Macpherson 1990). Additionally, the abdominal somite 2 may have more numerous striae between two main transverse ridges on the tergite in E. balteipes n. sp. than E. sternomaculata (cf. de Saint Laurent & Macpherson 1990: figs. 6b, 7f).

The banded color pattern of white and reddish orange on the P1 – 4 is also similar between E. balteipes n. sp. and E. sternomaculata . Nevertheless, the new species differs from E. sternomaculata in the supraocular spines being mostly orange instead of white and the P2–4 meri each with a white or pale-colored band on the median part of the lateral surface which is absent in the latter species (cf. de Saint Laurent & Macpherson 1990: fig. 1A).

Puillandre et al. (2011) discovered an undescribed species from the Norfolk Ridge in the southwestern Pacific, which is morphologically close to E. annulosa de Saint Laurent & Macpherson, 1990 and E. sternomaculata , although it remains unnamed. The undescribed species agrees with E. sternomaculata and E. balteipes n. sp. in having three distal spines on the P1 carpus, but the distomesial spine is generally very small in the undescribed species ( Puillandre et al. 2011: 331) instead of distinct in the latter two species.

Ten species of the genus Eumunida have been recorded from Japanese waters ( Baba et al. 2008; Komai & Tsuchida 2014; present study): E. ampliata de Saint Laurent & Poupin, 1996 ; E. balssi Gordon, 1930 ; E. balteipes n. sp.; E. depressa de Saint Laurent & Poupin, 1996 ; E. dofleini Gordon, 1930 ; E. funambulus Gordon, 1930 ; E. gordonae Baba, 1976 ; E. macphersoni de Saint Laurent & Poupin, 1996 ; E. nikko Komai & Tsuchida, 2014 ; and E. pacifica Gordon, 1930 . Among the Japanese species, E. balteipes n. sp. is closest to E. nikko in the morphology and coloration which mostly agree with those of E. sternomaculata mentioned above, but is distinguished by the P1 carpus having three instead of two distal spines, the P1 palm with a larger and more developed setal pad on the ventral surface, and the supraocular spines and lateral marginal spines of the carapace being orange in general, rather than white (for the coloration of E. nikko , cf. Komai & Tsuchida 2014: fig. 17). Although the size of setal pad on the P1 palm probably changes with body size, the type specimens of E. balteipes n. sp. and E. nikko are almost same in size (pcl, 21.3–24.9 mm versus 22.8 mm), and thus it is treated as an interspecific distinction.

A new Japanese name, Shima-tsuno-koshioriebi (meaning banded, horned squat lobster in Japanese), is given for E. balteipes n. sp. based on the holotype.

Figures

FIGURE 3. Eumunida balteipes n. sp., paratype female (pcl 24.9 mm), RUMF-ZC-5359, fresh specimen (A); holotype male (pcl 24.0 mm), RUMF-ZC-5358, preserved specimen (B–E). A, entire animal, dorsal view; B, carapace, abdomen, anterior appendages, and basal parts of P1–4, dorsal view; C, same, ventral view; D, carpus and chela of left P1, dorsal view; E, right ambulatory legs, lateral view.

FIGURE 4. Eumunida balteipes n. sp., holotype male (pcl 24.0 mm), RUMF-ZC-5358. A, carapace and eyes, dorsal view (setae illustrated only on left frontal area); B, abdominal somites 1 and 2, dorsal view (setae illustrated only on left anterior margins of main ridges of somite 2); C, anterior part of thoracic sternum, ventral view (setae omitted); D, posteromedian part of abdominal somite 6 and telson, extensor view (setae omitted); E, left, anterior parts of carapace and pterygostomian flap, eye, and antennal peduncle, lateral view; F, left antennal peduncle, ventral view; G, merus of right Mxp3, lateral view (setae omitted). Scales = 5.0 mm.

FIGURE 5. Eumunida balteipes n. sp., holotype male (pcl 24.0 mm), RUMF-ZC-5358, left P1. A, ischium and merus, dorsal view (setae illustrated only on proximal spines on ventromesial margin of merus); B, same, ventral view; C, carpus and chela, dorsal view (setae omitted); D, same, ventral view. Scales = 5.0 mm.

FIGURE 6. Eumunida balteipes n. sp., holotype male (pcl 24.0 mm), RUMF-ZC-5358, left P2–4 (A–E, P2; F, P3; G, P4). A, F, G, ischium, merus, and carpus, lateral view (setae omitted); B, merus, mesial view; C, propodus and dactylus, lateral view (setae omitted); D, distal part of propodus, mesial view; E, dactylus, lateral view. Scales = 5.0 mm.