Munidopsis lignicola, Komai & Tsuchida & Fujiwara, 2025

Munidopsis lignicola sp. nov.

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

( Figs. 5–9 View FIGURE 5 View FIGURE 6 View FIGURE 7 View FIGURE 8 View FIGURE 9 )

Type material. All 41 specimens were collected from a single sunken wood piece, picked up by using the manipulator of KM-ROV. Holotype: JAMSTEC 105598, male (cl 9.2 mm), KM20-10 C, KM-ROV, dive #122, Shoho Seamount, Nishi-Shichito Ridge, 32°20.97´N, 138°39.38´E, 1901 m, 26 November 2020. GoogleMaps

Paratypes: JAMSTEC 105590, 1 male (cl 6.8 mm), DNA voucher; JAMSTEC 105591, 1 juvenile (cl 6.0 mm), DNA voucher; JAMSTEC 105592, 1 juvenile (cl 4.7 mm), DNA voucher; JAMSTEC 105595, 1 male (cl 5.3 mm), 3 females (cl 5.6, 6.7, 7.5 mm); JAMSTEC 105597, 1 ovigerous female (cl 7.8 mm), DNA voucher; JAMSTEC 112448, Onboard ID KM#122 -CR-9-2, 6 males (cl 6.9–7.1 mm), 4 females (cl 5.5–6.1 mm) .

Other material examined. JAMSTEC 105593, 1 juvenile (cl 3.1 mm) ; JAMSTEC 105594, 1 juvenile (cl 2.7 mm) ; JAMSTEC 112449, 20 juveniles (cl 2.6–4.9 mm) .

Description. Carapace ( Figs. 5 View FIGURE 5 , 6A, B View FIGURE 6 ) 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, nearly straight; 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 in distal 0.3; ventral surface flat. Frontal margins strongly oblique, each with moderately small antennal spine lateral to base of ocular peduncle, followed by concavity ending in small anterolateral spine. Gastric region moderately elevated, bearing 3–5 transverse ridges medially and few arcuate ridges laterally behind pair of small epigastric spines. Anterior branchial regions bearing few, less prominent, short transverse ridges, each lateral margin with moderately strong anterior spine (stronger than anterolateral spine) followed by 1 much smaller spine and 1 or 2 granules. Posterior branchial regions with tiny spine at anterolateral corner and transverse, setose striae, extending to cardiac regions. Shallowly concave posterior margin preceded by prominent, raised, ciliated submarginal rim of nearly uniform width. Lateral plate with oblique striae, projecting anteriorly in triangular projection terminating in tiny spine.

Thoracic sternum ( Fig. 6D View FIGURE 6 ) slightly longer than wide, maximum width at sternites 6 and 7. Sternite 3 narrow, 2.2 times wider than long, deeply depressed medially, 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 3.0 times that of sternite 3, twice wider than long; anterolateral margins gently concave; no striae on surface. Sternites 5–7 without striae.

Pleon ( Figs. 5 View FIGURE 5 , 6A View FIGURE 6 ) unarmed. Pleomere 1 tergum slightly smooth. 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 with shallow, obliquely transverse groove on posterior part, medially interrupted. Pleomere 6 with shallow groove delimiting posteromedian lobe; posterior margin slightly trilobate, lateral lobes rounded, slightly exceeding beyond median lobe, median lobe distinctly wider than posterior lobes, posterior margin very slightly convex. Telson ( Fig. 6E View FIGURE 6 ) subtrapezoidal, 1.3 times as wide as long, composed of 10 plates; lateral margin nearly straight, without dense setae even in males; posterior margins of posterolateral plates gently convex.

Eyes ( Fig. 6F View FIGURE 6 ) moderate in size; well exposed. Cornea ovate, cupped within broad-based, width distinctly narrower than rostrum at midlength; fixed ocular peduncle produced into prominent dorsomesial eye-spine; dorsomesial eye-spine horizontal in lateral view, or slightly directed laterally in dorsal view; lateral eye-spine much smaller than dorsomesial eye-spine, located at lateral base of cornea, directed anterolaterally at low angle. No other spines on ocular peduncle.

Antennular peduncle basal article ( Fig. 6G View FIGURE 6 ) with crested dorsal margin, extended into slender dorsolateral spine; slightly longer ventrolateral spine located slightly mesially to dorsolateral spine; inflated lateral face with irregular, minute spinules or granules; ventromesial distal margin minutely granulate.

Antennal peduncle ( Fig. 6A, F, H View FIGURE 6 ) article 1 with ventromesial distal margin produced into acute, triangular process, distolateral margin also with small spine. Article 2 with strong distolateral spine; distomesial margin produced, with small spine. Article 3 surface smooth; distolateral and distomesial margins each with 1 small spine. Article 4 cup-shaped, with acute, stout dorsolateral tooth; surface almost smooth.

Maxilliped 3 ( Fig. 7A View FIGURE 7 ) basis with 5–7 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; weakly produced distoventral angle blunt; ventral margin sharply carinate. Merus ( Fig. 3A View FIGURE 3 ) with 4 small spines on lower margin; upper margin broadly arched, with small distal spine. Carpus, propodus, and dactyl folded on merus-ischium, approximately as long as those 2 articles together; dense setation on dorsal surface of each, distally on flexor surface of propodus and dactylus.

Chelipeds (pereopods 1) ( Figs. 5 View FIGURE 5 , 7B–D View FIGURE 7 ) short, stout, subequal in length, approximately 1.4 length of carapace, excluding rostrum. Ischium dorsodistal margin with small spine followed by few minute denticles; surfaces almost smooth. Merus widened distally, ornamented with rather obsolescent, short transverse ridges and sparse setae on surfaces; dorsal margin with row of 5 small spines, including dorsodistal spine; distal margin with 1 small spine adjacent to distomesial lobe angle; ventrolateral distal angle produced into spine; ventromesial distal angle also with spine. Carpus short, approximately as long as wide, surfaces almost smooth, with sparse setae; dorsodistal margin with 3 small spines including 1 on articular knob to palm. Chela 0.5 times as long as carapace; palm 1.1 times as long as wide, parallel-sided, surfaces with scattered tufts of short to long setae; fingers deeply spooned, occlusal margins closely fitting on dorsal side, leaving deep concavity on ventral side, crenulate on entire dorsal side to distal half of ventral side; distolateral margin of fixed finger produced into tuberculate crest; dactylus subequal in length to palm.

Ambulatory legs (pereopods 2–4) ( Figs. 5 View FIGURE 5 , 8A–D View FIGURE 8 ) moderately long, generally similar in structure, armature and setation, corresponding articles of respective legs approximately equal in length except for meri which successively shorter posteriorly. Setation generally sparse, arising from margins of short ridges.

Pereopod 2 ( Fig. 8A, B View FIGURE 8 ) overreaching tip of cheliped by length of dactylus. Ischium without spine or spinule on dorsal surface. Merus ornamented with short transverse ridges on surfaces, margins of those ridges sometimes minutely multidenticulate or spinulose; dorsal margin with row of 7 or 8 small spines increasing in size distally, including 1 on dorsodistal margin; ventrolateral distal angle with 1 small spine. Carpus short, extensor ridge produced distally into small spine, followed by 2 smaller spines, distolateral margin with 1 small additional spine inferior to base of extensor distal spine; lateral face with distinct longitudinal ridge, produced flexor distal margin spinulose. Propodus extensor surface nearly flat, with sparse long setae, outer and inner margins bluntly ridged; lateral face nearly smooth, flexor distal margin with pair of slender movable spines flanking base of dactylus; mesial face nearly flat. Dactylus 0.7 times as long as propodus, nearly straight, terminating in small, curved corneous claw; surfaces with scattered tufts of thin setae; flexor margin with row of 9 or 10 triangular teeth, diminishing in size and becoming obtuse proximally, each bearing slender corneous spinules or spiniform setae also diminishing in size proximally.

Pereopod 3 ( Fig. 8C View FIGURE 8 ) merus with row of 6 or 7 small spines, including 1 on dorsodistal margin; ventrolateral distal angle with 1 tiny spine. Dactylus with row of 10 or 11 triangular teeth, each bearing spiniform seta or corneous spinule.

Pereopod 4 ( Fig. 8D View FIGURE 8 ) merus dorsodistal margin with small spine, dorsal surface unarmed; ventrolateral angle without spines. Dactylus with row of 9 or 10 triangular teeth each bearing spiniform setae or corneous spinules, and 1 minute corneous spinule proximal to end of tooth row.

Pereopod 5 chelate. Merus outer face rugose, sharply edged ventrolateral margin with few blunt denticle. Carpus outer surface with 2 longitudinal ridges. Chela with brush-like setae.

Epipod present only on pereopod 1 (cheliped).

Male pleopods 1 and 2 modified into gonopods.

Uropod ( Fig.6E View FIGURE 6 ) with protopod bearing small spine on distomedial lobe. Exopod lateral margin slightly convex, with row of movable spinules extending onto distolateral margin; outer lateral surface with movable spinules arranged in 2 longitudinal rows. 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 whitish; corneas light yellow ( Fig. 9 View FIGURE 9 ).

Size. Largest male cl 9.2 mm; largest female (ovigerous) cl 7.8 mm.

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

Habitat. All the specimens inhabited a piece of sunken wood ( Fig. 9 View FIGURE 9 ).

Remarks. Munidopsis lignicola sp. nov. is morphologically closest to Munidopsis nitida (A. Milne-Edwards, 1880) , recorded widely in the Indo-Pacific and western Atlantic oceans ( Baba 2005; Osawa et al. 2008, 2013; Baba et al. 2009; Taylor et al. 2010; Macpherson et al. 2017, 2020), in having a relatively narrow rostrum, parallel carapace lateral margins bearing 2–4 small spines on each anterior branchial margin, a pair of conspicuous epigastric spines on the carapace, mesial and lateral eye-spines on the ocular peduncle, unarmed pleomeres 2–4, pereopod 1 (cheliped) being shorter than pereopod 2, a denticulated ridge on the distolateral margin of the cheliped fixed finger, unarmed propodi of pereopods 2–5, and an epipod present on pereopod 1 (cf. Baba 2005). The two species differ in the following particulars: the cornea is relatively smaller in M. lignicola sp. nov. than M. nitida ( Fig. 6A, F View FIGURE 6 versus Baba 2005: fig. 72a–e); the ocular peduncle is armed with a lateral eye spine in M. lignicola sp. nov. ( Fig. 6F View FIGURE 6 ), whereas such a spine is absent in M. nitida (cf. Dong et al. 2019). Furthermore, Munidopsis nitida attains a much larger size as an adult than M. lignicola sp. nov. (maximal cl 24.0 mm in M. nitida versus 9.2 mm in M. lignicola sp. nov.) ( Baba 2005).

Munidopsis lignaria Williams & Baba, 1989 , M. pycnopoda Baba, 2005 , and M. giribeti Rodriguez-Flores, 2025 , are also similar to this new species; M. lignaria was also compared with M. nitida in the original description ( Williams & Baba 1989). Differentiating characters between M. lignicola and the latter three species are as follows: the lateral margins of the carapace are parallel in the new species ( Fig. 6A View FIGURE 6 ), rather than narrowing anteriorly in M. lignaria and M. pycnopoda (cf. Williams & Baba 1989: fig. 4a; Baba 2005: fig. 84a); the telson has 10 plates in M. lignicola sp. nov. ( Fig. 6E View FIGURE 6 ), eight plates instead in M. lignaria (cf. Williams & Baba 1989: fig. 2f); the propodi of the pereopods 2 and 3 are unarmed in M. lignicola sp. nov. ( Fig. 8A View FIGURE 8 ), whereas armed with two or three spines on extensor margin in M. lignaria (cf. Williams & Baba 1989: fig. 4h), M. pycnopoda (cf. Baba 2005: fig. 84a) and M. giribeti (cf. Rodríguez-Flores 2025: Fig. 10D View FIGURE 10 ); Munidopsis giribeti is characteristic in having more salient spines on the carapace and pereopods 2–4 meri and carpi (cf. Rodríguez-Flores 2025: Figs. 9A–D View FIGURE 9 , 10D View FIGURE 10 ) compared to the other related species.

Dong et al. (2019) compared their new species, M. spinifrons , with M. nitida . Munidopsis lignicola sp. nov. is readily distinguished from M. spinifrons by the lack of small spines on the rostral lateral margins ( Fig. 6A View FIGURE 6 versus Fig. 11A View FIGURE 11 ), much weaker spines on the carapace lateral margins ( Fig. 6A View FIGURE 6 versus Fig. 10 View FIGURE 10 ), the absence of a spine on the ventromesial margin of the cheliped merus ( Fig. 7C View FIGURE 7 versus Fig. 11G View FIGURE 11 ), and less developed spines on upper margins of pereopods 2 and 3 meri and carpi ( Fig. 8A, C View FIGURE 8 versus Fig. 11J View FIGURE 11 ). Furthermore, M. lignicola sp. nov. attains a much smaller size than M. spinifrons (maximal carapace length 9.2 mm versus 24.9 mm)

All 41 specimens of M. lignicola sp. n ov. inhabited on a single piece of sunken wood. These specimens varied in size and included multiple generations, from juveniles to spawning individuals. The chelae of M. lignicola sp. nov. are similar to those of M. nitida and M. lignaria , in having close fitting, crenulate distal edges on the tips of the spooned fingers, and a serrate distolateral angle on the fixed finger. The latter two species are known to be associated with sunken wood ( Williams & Turner 1986; Williams & Baba 1989), as in the present new species. Williams & Baba (1989) noted that the chelae of M. lignaria and M. nitida could be used for boring, tunneling in, or shredding wood, and the same can be said for this new species. Other congeneric species associated with sunken wood include M. andamanica MacGilchrist, 1905 , M. bispinoculata Baba, 1988 , M. hendersoniana Faxon, 1893 , M. pilosa Henderson 1885 , M. subchelata Balss, 1913 , and M. vicina Faxon, 1893 ( Wolff 1979; Baba et al. 2009). Among these, M. andamanica , M. bispinoculata , M. lignaria , M. nitida , and M. pilosa have been documented as xylophagous ( Van Dover 1988; Hoyoux et al. 2009, 2012). It is probable that M. lignicola sp. nov. is also xylophagous.

Etymology. Derived from the Latin lignum (= wood) and colo (= to inhabit), in reference to the habitat of the species.