Munidopsis juxtapallida, Komai & Tsuchida & Fujiwara, 2025

Munidopsis juxtapallida sp. nov.

[New Japanese name: Shoho-shinkai-koshiori-ebi]

( Figs. 1–5 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 )

Type material. Holotype: JAMSTEC 105596, female (cl 13.3 mm), KM20-10 C, KM-ROV dive #122, Shoho Seamount, Nishi-Shichito Ridge, 32°20.97´N, 138°39.38´E, 1901 m, associated with sunken wood, 26 November 2020, DNA voucher. GoogleMaps

Description. Carapace ( Figs. 1A View FIGURE 1 , 2A, B View FIGURE 2 ), exclusive of rostrum, 1.2 times longer than broad, moderately arched transversely; anterior and posterior cervical grooves apparent, transverse depression in anterior part of cardiac region. Rostrum narrowly triangular, far exceeding ocular peduncles by more than half length, slightly upturned; dorsal surface nearly smooth, with low but distinct median carina becoming obsolescent at base of rostrum; lateral margins without conspicuous teeth or spines, but with minute denticles of microscopic size; ventral surface flat. Frontal margins strongly oblique, each with small antennal spine lateral to ocular peduncle followed by shallow concavity ending in small anterolateral spine. Gastric region moderately elevated, bearing short, squamiform, setose striae behind pair of small epigastric spines. Anterior branchial regions bearing less prominent ciliated striae, each lateral margin with moderately strong spine (second anterolateral spine), slightly stronger than anterolateral spine, directed anteriorly and followed by 1 much smaller spine and few striae. Posterior branchial regions with tiny spine at anterolateral corner and transversely developed setose rugae, extending to cardiac regions. Shallowly concave posterior margin preceded by prominent, raised, ciliated submarginal rim of nearly uniform width. Lateral plate with oblique rugae, projecting anteriorly in triangular projection terminating in minute spine.

Thoracic sternum ( Figs. 1B View FIGURE 1 , 2D View FIGURE 2 ) almost as long as wide, maximum width at sternites 6 and 7. Sternite 3 narrow, 2.0 times wider than long, deeply depressed, anterior margin with shallow V-shaped median notch flanked by 2 small triangular lobes, anterolateral margins somewhat produced laterally. Sternite 4 narrowly extending anteriorly; surface depressed in midline, smooth; greatest width 3.4 that of sternite 3, and twice wider than long; anterolateral margins gently concave; no striae on surface. Sternites 5–7 without striae.

Pleon ( Fig. 1A, B View FIGURE 1 ) unarmed. Pleomere 1 tergum slightly punctate. Pleomeres 2 and 3 each with 2 transverse ridges separated by deep transverse groove; each pleuron with depression anteriorly. Pleomere 4 with deep, rather wide transverse groove separating tergum into 2 ridges; pleuron with shallow depression anteriorly. Pleomeres 5 and 6 without distinct ridges or rugae, but with sparse short setae on surface; posterior margin of pleomere 6 trilobate, lateral lobes rounded, slightly exceeding beyond median lobe, median lobe distinctly wider than posterior lobes, posterior margin very slightly convex ( Fig. 2D View FIGURE 2 ). Telson ( Fig. 2D View FIGURE 2 ) subtrapezoidal, 1.4 times as wide as long, composed of 10 plates; posterior margins of posterolateral plates gently convex.

Eyes ( Fig. 2A, B, E View FIGURE 2 ) moderate in size; well exposed. Cornea ovate, cupped within broad-based, slightly movable ocular peduncle produced into dorsomesial eye spine; eye spine horizontal in lateral view, or directed dorsolaterally at low angle. No other spines on ocular peduncle.

Antennular peduncle basal article ( Fig. 2F View FIGURE 2 ) with crested dorsal margin, extended into slender dorsolateral spine; much longer ventrolateral spine located mesially to dorsolateral spine; inflated lateral face with irregular, minute spinules or granules; ventromesial distal margin minutely granulate.

Antennal peduncle ( Fig. 2A, B, E, G View FIGURE 2 ) article 1 with ventromesial distal margin produced into acute, triangular process; distolateral margin also with small spine. Article 2 with distolateral spine; distomesial margin produced but unarmed. Article 3 surface rugose; distal margin granulate. Article 4 cup-shaped, with blunt, stout dorsolateral spine; surface weakly rugose.

Maxilliped 3 ( Fig. 2H View FIGURE 2 ) basis with 3 corneous-tipped denticles on ventromesial margin, in line with crista dentata on ischium. Ischium bearing crista dentata consisting of finely uniform, evenly spaced corneous spines; produced anteroventral angle blunt. Merus with 3 small spines on lower margin; upper margin broadly arched, with small distal spine. Carpus, propodus, and dactyl folded on merus-ischium and approximately as long as those 2 articles together, dense setation on dorsal surface of each, and distally on flexor surface of propodus and dactylus.

Epipod present only on pereopod 1 (cheliped).

Chelipeds (pereopods 1) ( Figs. 1A, B View FIGURE 1 , 3A, B View FIGURE 3 ) moderately stout, subequal in length, approximately 1.8 length of carapace. Ischium dorsodistal margin produced into small spine; surfaces ornamented with short transverse or squamiform ridges bearing short stiff setae. Merus widened distally, also ornamented with short transverse or squamiform ridges bearing stiff setae on surfaces; dorsal margin with row of 3 small spines; distal margin minutely denticulate, with 1 small spine mesially; ventrolateral distal angle produced, with 1 minute spine. Carpus short, approximately as long as wide, ornamented with squamiform ridges on surfaces (strongest on dorsal surface); dorsodistal margin with 3 tiny spines including 1 at articular knob to palm. Chela 0.8 times as long as carapace; palm 1.2 times as long as wide, parallel-sided, surfaces with scattered tufts of short setae, mesial face with some squamiform ridges; fingers spooned at tips, occlusal margins closely fitting, entirely crenulate; no crest on distolateral margin of fixed finger; dactylus 1.4 times as long as palm.

Ambulatory legs (pereopods 2–4) ( Figs. 1A, B View FIGURE 1 , 3C–F View FIGURE 3 ) moderately long, generally similar in structure, armature and setation, corresponding articles of respective legs approximately equal in length except for meri, being successively shorter posteriorly; setation generally sparse, arising from margins of short ridges.

Pereopod 2 ( Fig. 3C, D View FIGURE 3 ) not reaching tip of cheliped. Ischium with tiny dorsodistal spine. Merus ornamented with squamiform ridges on surfaces, margins of those ridges sometimes minutely multidenticulate; dorsal margin with row of 7 small spines, including 1 on dorsodistal margin; ventrolateral distal angle with 1 small spine. Carpus short, extensor ridge produced distally into small spine, followed by smaller spines or denticles, distolateral margin with 1 additional spine inferior to base of extensor distal spine; lateral face with faintly tuberculate longitudinal ridge, produced flexor distal margin spinulose. Propodus extensor surface nearly flat, outer and inner margins bluntly ridged, spineless; lateral face with squamiform ridges, flexor distal angle produced into tiny spine; mesial face longitudinally sulcate; ventrolateral distal angle with 1 corneous spinule. Dactylus 0.8 times as long as propodus, slightly curved, terminating in small, curved corneous claw; surfaces with scattered tufts of thin setae, particularly numerous on extensor surface; flexor margin with row of 13 triangular, corneous-tipped teeth, diminishing in size proximally, each bearing slender corneous spinules or spiniform setae.

Pereopod 3 ( Fig. 3E View FIGURE 3 ) ischium with dorsodistal denticle. Merus with row of 7 small spines, including 1 on dorsodistal margin; ventrolateral distal angle with 1 tiny spine. Dactylus with row of 14 triangular teeth, each bearing corneous spinule or spiniform setae.

Pereopod 4 ( Fig. 3D View FIGURE 3 ) ischium with short transverse ridge on dorsal surface. Merus dorsodistal margin unarmed, dorsal surface without true spines but with denticles formed by edges of squamiform ridges; ventrolateral angle without spine. Dactylus with row of 13 triangular teeth each bearing spiniform setae or corneous spinules, and 1 minute corneous spinule at end of tooth row.

Pereopod 5 ( Fig. 1A, B View FIGURE 1 ) moderately short, slender, chelate. Merus outer face rugose, sharply edged ventrolateral margin with 2 blunt denticles. Carpus outer surface with 2 longitudinal ridges. Chela with brush-like setae.

Uropodal protopod with distinct spine on distomedial lobe. Exopod lateral margin slightly convex, with row of movable spinules extending onto distolateral margin; outer lateral surface with scattered movable spinules. Endopod lateral margin irregularly denticulate, with few movable spinules, distolateral to distal margin with closely spaced, minute spinules; submedian ridge on outer surface with individual or sets of 2 or 3 movable spinules.

Colouration in life. Body and appendages entirely whitish; cornea light yellow ( Fig. 1A, B View FIGURE 1 ).

Distribution. Known only from the type locality on Shoho Seamount, Nishi-Shichito Ridge, at a depth of 1901 m.

Habitat. The holotype was collected from the same sunken wood piece with specimens of M. lignicola sp. nov. ( Fig. 4 View FIGURE 4 ).

Remarks. Morphologically, Munidopsis juxtapallida sp. nov. closely resembles M. exuta Macpherson & Segonzac, 2005 , M. geyeri Pequegnat & Pequegnat, 1970 , M. pallida Alcock, 1894 , and M. recta Baba, 2005 . Munidopsis exuta and M. geyeri exhibit amphi-Atlantic distributions, at depths of 2860–4237 m and 1700–4151 m, respectively ( Gaytán-Caballero et al. 2022). Munidopsis pallida Alcock, 1894 is known from the Andaman Sea, Bay of Bengal and off Taiwan at depths of 2233–3299 m ( Baba 2005). Munidopsis recta is known from the Gulf of Panama and East Pacific Rise, at depths of 2216–3190 m ( Baba 2005; Jones & Macpherson 2007). Shared characters include: rostrum without lateral spines; pleon unarmed; pleomere 6 posterior margin not markedly produced; distomesial eye-spine present and lateral-eye spine absent; cheliped fixed finger without denticulate carina on distolateral part; and epipods present only on cheliped ( Baba 2005; Macpherson & Segonzac 2005; Gaytán-Caballero et al. 2022). Munidopsis juxtapallida sp. nov. differs from the aforementioned four species in the weaker second lateral spine on the anterior branchial margin of the carapace, which is directed anteriorly ( Fig. 2A View FIGURE 2 ). In contrast, in M. exuta , M. geyeri , M. pallida , and M. recta , those spines are stronger and directed anterolaterad at the angle of 45° (cf. Baba 2005; Macpherson & Segonzac 2005; Gaytán-Caballero et al. 2022). The new species further differs from M. pallida in the less prominent striae or rugae on the dorsal surface of the carapace ( Fig. 2A View FIGURE 2 versus Baba 2005: fig. 75a, b), the less curved dactyli of the pereopods ( Fig. 3D View FIGURE 3 versus Baba 2005: fig. 75h), and the telson divided into 10 plates, rather than 8 plates ( Fig. 2D View FIGURE 2 versus Baba 2005: fig. 75d). Munidopsis juxtapallida sp. nov. is distinguished from M. exuta further by the presence of well-developed antennal spines on the carapace frontal margins ( Fig. 2A View FIGURE 2 ), the weaker distolateral spine on antennal peduncle article 2 ( Fig. 2E View FIGURE 2 versus Macpherson & Segonzac 2005: fig. 5E), the stouter propodus of pereopod 2 ( Fig. 3C View FIGURE 3 versus Macpherson & Segonzac 2005: fig. 5H), and the less clearly defined posterolateral lobes of pleomere 6 ( Fig. 2D View FIGURE 2 versus Macpherson & Segonzac 2005: fig. 5C). In M. exuta , the antennal spines are usually absent ( Macpherson & Segonzac 2005: fig. 5A; Gaytán-Caballero et al. 2022: fig. 3A–G). The absence of spines on the extensor surface of the pereopod 2 propodus distinguishes M. juxtapallida sp. nov. from M. recta (Fig. versus Baba 2005: fig. 85i).

The following four species are also similar in some degree to M. juxtapallida sp. nov.: M. bracteosa Jones & Macpherson, 2007 , known from the East Pacific, near Juan de Fuca Ridge and Monterey Bay, at depths of 2441– 2891 m, M. producta Baba, 2005 , from East Pacific off Costa Rica and the Gulf of Panama, at depths of 3260–3680 m, M. scotti Jones & Macpherson, 2007 , from the Northeast Pacific, on the Juan de Fuca Ridge, at depth of 2715 m, and M. starmer Baba & de Saint Laurent, 1992 , known from the North Fiji Basin hydrothermal vent site, at depths of 2750 m. Nevertheless, Munidopsis juxtapallida sp. nov. is readily distinguished from M. producta and M. scotti by the presence of only one pair of epigastric spines on the carapace gastric region ( Fig. 2A View FIGURE 2 ) and the absence of spines on the extensor surface of the pereopod 2 propodus ( Fig. 3C View FIGURE 3 ). In M. producta and M. scotti , there are some additional spines on the carapace gastric region (cf. Baba 2005: fig. 81a; Jones & Macpherson 2007: fig.7A, B); the propodus of the pereopod 2 is armed with some spines on the extensor margin (cf. Baba 2005: fig. 81h, I; Jones & Macpherson 2007: fig. 7H). Munidopsis producta further differs from M. juxtapallida sp. nov. in the strongly upturned rostrum ( Baba 2005: fig. 81b) and the prominent posteromedian lobe of the pleomere 6 ( Baba 2005: fig. 81d). In M. juxtapallida sp. nov., the rostrum is only slightly upcurved ( Fig. 2B View FIGURE 2 ); there is no median lobe on the posterior margin of the pleomere 6 ( Fig. 2D View FIGURE 2 ).

The new species is readily distinguished from M. bracteosa by the slightly upcurved rostrum ( Fig. 2B View FIGURE 2 ), the subequal first and second anterolateral spines on the carapace ( Fig. 2A View FIGURE 2 ), the non-produced posterior margin of pleomere 6 ( Fig. 2D View FIGURE 2 ), and the nearly straight flexor margin of the dactyli of pereopods 2 and 3 ( Fig. 3C–E View FIGURE 3 ). In M. bracteosa , the rostrum is strongly upturned ( Jones & Macpherson 2007: fig. 3B); the second anterolateral spine on the carapace is much stronger than the first anterolateral spine ( Jones & Macpherson 2007: figs. 2B, 3A); the posterior margin of pleomere 6 is produced as a broad convexity; and the flexor margins of the dactyli of pereopods 2 and 3 are weakly concave ( Jones & Macpherson 2007: figs. 3H, I).

Munidopsis starmer View in CoL is rather distinctive among the allied relatives in the absence of an epipod on cheliped and the prominent posterolateral lobes on the pleomere 6 ( Baba & de Saint Laurent 1992). In the above mentioned species, including the new species, the cheliped has an epipod; the posterolateral margins of the pleomere 6 are not produced ( Baba 2005; Macpherson & Segonzac 2005; Jones & Macpherson 2007; this study).

Munidopsis subsquamosa Henderson, 1885 View in CoL , known widely from the Indo-West Pacific, including off Japan, at depths of 1789–3960 m ( Baba 2005), is also morphologically similar to M. juxtapallida , and needs to be compared with the present new species considering its occurrence in Japanese waters. Munidopsis juxtapallida sp. nov. is readily distinguished from M. subsquamosa View in CoL by the absence of extra spines on the carapace gastric region (versus additional spines are present) ( Fig. 2A View FIGURE 2 versus Baba 2005: figs. 88a, b, 89a–d, 90a, b), anteriorly directed first (anterolateral) and second spines on the anterior branchial margin (versus anterolaterally directed) ( Fig. 2A View FIGURE 2 versus Baba 2005: figs. 88a, 89a, b, 90a, b), and the nearly straight dactyli of pereopods 2–4 (versus gently arcuate) ( Fig. 3C–F View FIGURE 3 versus Baba 2005: figs. 88i, j, 89i, j, 90g –j).

Etymology. The Latin juxta (near, close) plus pallida reflects the close morphological similarity of this new species to the one originally described from the Bay of Bengal by Alcock (1894).