Eumunida nikko, Komai, Tomoyuki & Tsuchida, Shinji, 2014

Komai, Tomoyuki & Tsuchida, Shinji, 2014, Deep-Sea decapod crustaceans (Caridea, Polychelida, Anomura and Brachyura) collected from the Nikko Seamounts, Mariana Arc, using a remotely operated vehicle “ Hyper-Dolphin ”, Zootaxa 3764 (3), pp. 279-316 : 295-300

Eumunida nikko n. sp.

( Figs. 13–17 )

Material examined. Holotype: RV “Natsushima”, NT10-13 cruise, ROV “Hyper-Dolphin”, dive #1165, Northeast Nikko Seamount, 23°06.787’N, 142°21.936’E, 564 m, 31 July 2010, slurp gun, 1 male (cl 22.8 mm), NSMT-Cr 22720 (formerly JAMSTEC 081527).

Description. Carapace ( Figs. 13 , 14 A) (exclusive of rostrum) approximately as long as wide. Rostrum sharply spiniform, about 0.4 of carapace length; inner supraocular spine about 0.7 length of rostrum; outer supraocular spine reaching slightly beyond half length of inner supraocular spine. Gastric region well defined, moderately convex; 3 small hepatic spines present, subequal in size, first spine proximal to base of outer supraocular spine. Anterior and posterior cervical groove distinctly marked. Transverse ridges as illustrated, with dense short setae on anterior margins; anterior branchial region nearly smooth, with some short squamiform striae; 7 transverse ridges behind cervical groove, none interrupted medially; first stria divided into 3 short striae, other striae complete; 1 short lateral stria inserted between sixth and last transverse ridges. Lateral margins convex, armed with 6 spines decreasing in size posteriorly, 2 spines anterior to posterior cervical groove; greatest width measured between fifth lateral spines; first (anterolateral) spine strong, more than half length of outer supraocular spine, and reaching sinus between supraocular spines, slightly longer than second marginal spine. Strong anterior spine on pterygostomial margin ( Fig. 14 D).

Thoracic sternum medially concave. Third sternite ( Fig. 14 B) anteriorly with pair of triangular teeth, separated by U-shaped median notch. Fourth sternite ( Fig. 14 B) with pair of prominent anterolateral spines and transverse rows of setiferous, short ridges.

First pleomere with 2 transverse striae on tergum, anterior stria interrupted medially. Second pleomere as illustrated ( Fig. 14 C); 2 main transverse ridges and 4 alternating striae on tergum (2 stria between main ridges interrupted); dorsolateral stria separating tergum and pleuron entire; each pleuron bearing some short arcuate striae, anterior margin bearing prominent spine-like tooth. Third pleomere with 2 main transverse ridges and 3 alternating transverse striae on tergum; pleuron with 2 arcuate striae. Fourth pleomere with 4 transverse striae on tergum, third stria extending to pleura, posteriormost one interrupted. Fifth pleomere with 3 transverse striae on tergum, only third stria extending onto pleura, each pleuron with 1 short stria adjacent to posterior margin. Sixth pleomere with some paired arcuate or squamiform striae; shallow posterolateral notch present. Telson much wider than long, with deep, slit-like incision on lateral margin, divided into 2 parts by transverse suture; anterior part with some squamiform striae on either side of midline; posterior part further divided in 2 parts by median suture, posterior margin with distinct median notch.

Eye ( Fig. 14 A) short, cornea moderately dilated, not reaching end of outer supraocular spine.

Antennule without distinctive features.

Antennal peduncle ( Fig. 14 D, E) moderately slender. First segment with short distolateral spine clearly visible in dorsal view. Second segment with distolateral spine reaching proximal 0.3 of antennal acicle. Third segment with long distomesial spine, overreaching distal margin of fourth segment and extending as far as tip of scaphocerite. Fourth segment about twice as long as broad, with tiny dorsodistal spine and long ventrodistal spine distinctly exceeding distal margin of fifth segment. Fifth segment with 3 distal spines (dorsolateral, ventrolateral and ventromesial), dorsolateral spine longest; unarmed at base. Acicle spiniform, slender, extending well beyond distal margin of fourth segment.

Merus of third maxilliped ( Fig. 14 F) with small spine on flexor margin distal to midlength, extensor margin with minute distal spine. Ischium with crista dentata bearing 11 (right) or 13 (left) slender corneous spines.

Chelipeds ( Figs. 13 , 15 ) subcylindrical, subequal in length, about 3.5 times as long as carapace (excluding rostrum). Ischium with small ventromesial distal spine. Merus squamate, about 1.7 times as long as carapace, armed with 3 rows of spines (dorsolateral, dorsal, and dorsomesial); dorsomesial row composed of large and small spines regularly alternated; ventral surface without row of spines, but 1 prominent distolateral spine present. Carpus squamate dorsally, almost smooth ventrally, with 2 distal spines (dorsomesial and ventral) ( Fig. 15 C, E). Palm 1.2 times as long as dactylus, not massive, entirely squamate (dorsal surface with more numerous squamiform ridges than ventral surface), armed with only 1 row of spines (ventromesial, consisting of 4 small spines, visible in dorsal view), and some stiff setae; ventral surface with tiny setal pad located at level of base of fingers ( Fig. 15 E, F). Fingers not gapping, furnished with tufts of stiff setae; opposable margin of fixed finger minutely denticulate, with widely spaced small triangular teeth, that of dactylus minutely denticulate, with few small blunt teeth proximally.

Ambulatory legs (second to fourth pereopods) ( Fig. 16 ) squamate on meri and carpi, smooth on propodi and dactyli, furnished with sparse, long stiff setae. Second pereopod ( Fig. 16 A) with ischium bearing 1 small extensor distal spine. Merus 1.1 times longer than propodus, with extensor row of prominent spines decreasing in size proximally and 1 strong flexor distal spine. Carpus with extensor margin bearing row of prominent spines decreasing in size proximally; lateral surface with weak median ridge and few squamiform ridges inferior to median ridge. Propodus unarmed on extensor margin; lateral surface with shallow longitudinal sulcus on midline; flexor margin armed with 9 corneous spinules and 1 distal movable spine. Dactylus ( Fig. 16 B) about 0.4 length of propodus, with 9 corneous flexor spines decreasing in size proximally; surfaces and margins with sparse stiff setae.

Third pereopod ( Fig. 16 C) similar to second pereopod, but merus slightly shorter, propodus subequal in length; propodus with 1 flexor distal and 8 flexor marginal spinules. Fourth pereopod ( Fig. 16 D) shorter than preceding pereopods; ischium with 3 spinules on extensor margin; merus about 0.8 length of second pereopod; extensor margin with row of prominent spines in distal 0.7, followed by 2 rows of minute spinules; lateral surface with row of prominent spines on distal 0.7 of midline.

Coloration in life. Dorsal surface of body and appendages generally vivid orange. Distal halves of rostrum and supraocular spines, and almost entire of branchial spines on carapace white. Thoracic sternum white, with large orange spot medially. Cheliped with fingers whitish on distal halves; merus with white spots at bases of dorsal spines, mesial spines white in distal halves. Ambulatory legs with dactyli pale orange; distal halves and proximal parts of propodi white; distal parts of meri whitish. See Fig. 17 .

Distribution. Known only from the type locality, Northeast Nikko Seamount, 564 m.

Ecology. The holotype was found on rocks nearby colonies of primnoid soft corals.

Remarks. The genus Eumunida comprises of 29 species: three from the Atlantic Ocean, three from the Indian Ocean, and 24 from the West to Central Pacific (Baba et al. 2008; Baba & Lin 2008). Eumunida nikko n. sp. appears closest to E. sternomaculata de Saint Laurent & Macpherson, 1990a, known from New Caledonia. Shared characters are: a pair of prominent spines on the anterior margin of the fourth thoracic sternite (corresponding to the subgenus Eumunida de Saint Laurent & Poupin, 1996); the carapace with complete striae on the posterior part and two spines anterior to the lateral end of the posterior cervical groove, and the first lateral marginal spine is more than half length of the outer supraocular spine and reaches at most to the hiatus between the supraocular spines; a ventral setal pad on the palm of the cheliped; and the absence of the ventral row of spines on the merus of the cheliped. The new species is distinguished from E. sternomaculata by the lack of a dorsomesial row of spines on the cheliped palm, the possession of two, rather than three distal spines on the cheliped carpus, and the presence of two non-spiniform teeth on the anterior margin of the third thoracic sternite. In E. sternomaculata , the palm of cheliped is armed with a dorsomesial row of small spines; the third thoracic sternite bears two sharp spines on the anterior margin (de Saint Laurent & Macpherson 1990a; de Saint Laurent & Poupin 1996).

Eumunida australis de Saint Laurent & Macpherson, 1990b from the Tasman Sea, E. annulosa de Saint Laurent & Macpherson, 1990a from New Caledonia, and E. spinosa Macpherson, 2006 from New Caledonia, are also similar to E. nikko n. sp., but the presence of one or more ventral spines in addition to a ventrodistal spine on the cheliped merus immediately distinguishes the former three species from the present new species (de Saint Laurent & Macpherson 1990a, b; de Saint Laurent & Poupin 1996; Macpherson 2006).

Eumunida chani Baba & Lin, 2008 is also similar to E. nikko n. sp. in sharing most of the characters mentioned above, but the former is immediately distinguished from the present new species by the relatively narrower carapace, the absence of a setal pad on the ventral surface of the palm of cheliped and the much less spinose merus of the cheliped (cf. Baba & Lin 2008: Fig. 1 A, G, F).

Puillandre et al. (2011) discovered an undescribed species morphologically very similar to E. annulosa and E. sternomaculata , though it remains unnamed. Nevertheless, the present new species differs from the undescribed species in the lack of a distomesial marginal spine on the cheliped carpus. Puillandre et al. (2011) also remarked that the length of the anterolateral (first lateral) spine of the carapace in the undescribed species is intermediate between E. annulosa and E. sternomaculata (longer in E. sternomaculata than in E. annulosa ). The present new species is rather similar to E. sternomaculata in this regard.

From Japanese waters, the following eight species of Eumunida have been recorded ( Baba 2005; Baba et al. 2008): E. ampliata de Saint Laurent & Poupin, 1996; E. balssi Gordon, 1930 ; 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. smithii Henderson, 1885 . Eumunida nikko n. sp. is easily distinguished from these eight species by the combination of the presence of a pair of spines on the fourth thoracic sternite and the possession of two spines anterior to the posterior cervical groove on the carapace.

Etymology. Named after the Nikko Seamount, embracing the type locality of the new species. Used as a noun in apposition.

Figures

FIGURE 1. Map showing the location of the Northeast Nikko Seamount and tracking of the operation of ROV “ Hyper- Dolphin ” during the dive # 1165.

FIGURE 13. Eumunida nikko n. sp., holotype, male (pcl 22.8 mm), NSMT-Cr 22720, entire animal in dorsal view (in preservative).

FIGURE 14. Eumunida nikko n. sp., holotype, male (pcl 22.8 mm), NSMT-Cr 22720. A, carapace and eyes, dorsal view; B, third and fourth thoracic sternites, ventral view (setae omitted); C, first and second abdominal somites, dorsal view; D, left antennal peduncle, lateral view; E, same, ventral view; F, merus of left third maxilliped, lateral view (setae omitted). Scale bars: 5 mm for A, C; 2 mm for B, D – F.

FIGURE 15. Eumunida nikko n. sp., holotype, male (pcl 22.8 mm), NSMT-Cr 22720, right cheliped. A, merus, dorsal view (setae omitted); B, same, ventral view; C, carpus, ventral view; D, carpus and chela, dorsal view; E, same, ventral view; F, close up of basal part of fingers, showing detail of ventral setal pad. Scale bars: 5 mm for A – E; 2 mm for F.

FIGURE 16. Eumunida nikko n. sp., holotype, male (pcl 22.8 mm), NSMT-Cr 22720, left ambulatory legs in lateral view. A, second pereopod (setae omitted); B, same, dactylus and distal part of propodus, lateral view; C, third pereopod; D, fourth pereopod.

FIGURE 17. Eumunida nikko n. sp., holotype, male (pcl 22.8 mm), NSMT-Cr 22720, in aquarium, showing coloration in life.