Munidopsis militaris n. sp.

(Figs. 1–3)

Material examined. Holotype: 1 ovigerous female (PCL 14.9 mm), Carlsberg Ridge, Northwest Indian Ocean, 57°34.2’E, 9°46.8’N, depth 2016 m, Greyish yellow calcareous ooze and solidified foraminifera sand, Stat. 28I- (CR)-S033-TVG18, coll. television grab, R/V Zhu Kezhen, 9 May 2013.

Diagnosis. Carapace excluding rostrum distinctly longer than broad, dorsal surface with transverse, interrupted ridges; lateral margins armed with 6 spines; frontal margins oblique, antennal spines well developed. Gastric regions elevated, armed with pair of epigastric spines. Rostrum triangular, unarmed. Sternite 3 divided into 2 parts by longitudinal groove, marginally serrated. Abdominal tergites smooth, unarmed. Eyestalk immovable, armed with both mesial eyespine and lateral eyespine. Antennular peduncle with strong ventrolateral spine and dorsolateral spine on distal margin. Third maxilliped ischium with well-developed crista dentata, merus armed with small disto-extensor spine. Pereopod 1 merus triangular in cross section, with 2 longitudinal rows of spines (dorsal and ventromesial), and 4 spines on distal margins; chela with mesial and lateral margins each armed with row of spines, fixed finger with well-developed denticulate carina on distolateral margin. Pereopods 2–4 meri, carpi and propodi each armed with row of spines on extensor margin, dactyli flexor margin straight, with 8 or 9 movable corneous spines. Pereopods without epipod.

Description. Carapace (Fig. 1 A) (excluding rostrum) distinctly longer than broad. Frontal margins oblique, antennal spines well developed. Lateral margins approximately parallel, bearing short, sparse setae, each armed with 6 spines, including 1 anterolateral spine, 4 spines on anterior branchial margin (decreasing in size posteriorly), and 1 small spine at base of posterior cervical groove; spine at base of anterior cervical groove strongest; posterior branchial margins with oblique ridges. Posterior margin slightly concave, unarmed. Dorsal surface covered with transverse, interrupted ridges, bearing long setae anteriorly on gastric and hepatic regions; cervical grooves deep; regions well defined. Gastric region strongly elevated, armed with 2 epigastric spines, flanked by several sharp tubercles or short scale-like ridges. Cardiac region well delineated, with 2 transverse, straight, elevated ridges. Rostrum subtriangular, approximately 0.3 remaining carapace length, 1.2 times broader than long (base at level of antennal spine base); dorsal surface evenly and longitudinally carinate, covered with small tubercles bearing stiff setae; distal one-third of lateral margins weakly serrated. Pterygostomial (Fig. 1 B) flaps with oblique rugae on lateral surface, anterior end acute as small spine.

Sternal plastron (Fig. 1 C) slightly broader than long, widening posteriorly. Sternite 3 slightly broader than anterior margin of sternite 4, divided into two parts by longitudinal median groove; anterior margins deeply concave, distinctly denticulate. Sternite 4 pear-shaped, anterior part longitudinally grooved, narrowly elongated and bent upward; posterior part broad, ventral surface depressed and covered with short rugae bearing setae anteriorly. Sternites 5–7 each with elevated, transverse ridges on ventral surface, bearing simple setae.

Abdominal tergites (Fig. 1 A) smooth and unarmed; tergites 2–4 each with 2 transverse ridges bearing stiff setae anteriorly, posterior ridge in tergite 4 relatively low and interrupted; tergite 6 with straight posterior margin.

Telson (Fig. 1 D) composed of 10 distinct plates.

Eyestalk immovable. Peduncle short, nearly invisible in dorsal view, broader than cornea. Mesial eyespine relatively long, anterolaterally directed, reaching to distal 0.46 of rostrum. Lateral eyespine relatively short. Cornea oval-shaped, globular, broader than long.

Antennular peduncle (Fig. 1 E) with basal article longer than broad; distal margin minutely denticulate, bearing strong ventrolateral spine and dorsolateral spine; lateral face distinctly inflate, forming oblique groove extending from base of dorsolateral spine to central part of ventral surface, groove covered with short rugae; mesial margin straight, proximomesial margin protruding into triangular lobe.

Antennal peduncle (Fig. 1 E) reaching to level of mesial eyespine terminal, bearing setae on lateral and mesial margins. Article 1 short and immovable, with strong distomesial and distolateral spines. Article 2 armed with strong distolateral spine, distomesial margin spinulose. Article 3 subrectangular, ventrodistal margin minutely denticulate; Article 4 short.

Third maxilliped (Fig. 2 A, B) slender. Ischium approximately as long as merus length, disto-extensor corner acutely produced; crista dentata (Fig. 2 B) well-developed, extending onto basis. Merus with extensor margin slightly convex, armed with small disto-extensor spine; flexor margin bearing 4 or 5 small denticles; ventral surface covered with short rugae. Carpus with extensor margin slightly rugose. Propodus with distoflexor margin convex. Dactylus short. Dactylus flexor margin, propodus distoflexor margin and carpus dorsal distoflexor margin densely covered in long setae.

Pereopod 1 (P1, chelipeds) (Fig. 2 C–E) subequal, 1.7 times as long as PCL, densely covered in stiff setae on surface and margins, mostly from base of rugae, spines and tubercles. Ischium short, about 0.6 merus length, armed with distinct dorsodistal and laterodistal spines; ventrodistal margin anteriorly produced, with strong subterminal spine; surfaces covered with short rugae. Merus about 0.7 PCL, approximately triangular in cross section, forming 3 longitudinal carinae; dorsal and ventromesial carinae each armed with row of spines (strongest on distal margin, successively decreasing in size), ventrolateral carina unarmed but with strong spine on distal margin; mesial surface slightly convex, armed with distomesial spine; lateral and ventral surfaces flat, unarmed; short rugae present on carinae and surfaces, some rugae elevated as acute tubercles. Carpus short, approximately 0.4 merus length, dorsal surface armed with 2 rows of spines, with distal spines situated on dorsodistal margin; dorsomesial margin armed with strong subterminal spine; ventrodistal margin produced into triangular lobe, with small terminal spine; short rugae present on surfaces. Chela relatively compressed, approximately as long as merus (including fixed finger), 2.8 times longer than broad; lateral margin of palm (excluding fixed finger) armed with row of 5 strong spines, accompanied with 1 or 2 spines on ventral or dorsal side; mesial margin armed with row of 3 or 4 strong spines; short rugae present on surfaces and margins bearing tufts of setae. Fingers 0.9 palm length, opposable margins distally spooned and serrated; occlusal margins nearly straight, with proximal triangular process on fixed finger; lateral margin of fixed finger spinose, with well-developed denticulate carina distally.

Pereopods 2–4 (P2–4, ambulatory legs 1–3) (Fig. 3 A–D) slender; each segment bearing long, stiff setae densely on margins and surfaces, lateral surfaces with short scale-like rugae. P2 approximately 2.3 times PCL, slightly overreaching distal end of cheliped. Meri slender, triangular in cross section; P2 merus approximately 0.9 PCL (P3 merus 0.9 P2 merus length, P4 merus 0.8 P2 merus length), 7.5 times as long as broad (P3 6.7 times, P4 5.8 times); extensor margin armed with row of spines, distal spine longest; flexor margin rugose, with strong distoflexor spine. Carpi each with 2 longitudinal carinae on dorsal surface; lateral carina rugose, tuberculate, and either unarmed (P4) or armed with small median spine (P2 and P3); mesial carina armed with row of strong spines, distal spine somewhat laterally situated and smaller than penultimate spine; flexor margin armed with strong distoflexor spine, and small affiliated spines on P2. Propodi slender, P2 propodus 0.8 merus length (P3 propodus 0.9 merus length, P4 propodus approximately as long as merus); extensor surface nearly flat, with 2 indistinct longitudinal carinae, mesial carina armed with row of spines (distal spine situated at distal one-fourth (P2) or onethird (P3 and P4)), lateral carina slightly rugose, either unarmed (P4) or armed with 2 small spines (P2 and P3); flexor margin rugose, with pair of distal corneous spines, and additional corneous spine on midline proximal to distal pair. Dactyli (Fig. 3 D) 0.4–0.5 propodi length, slightly curving distally; extensor margin rugose, proximally straight; flexor margin straight, with 8 or 9 movable corneous spines (increasing in size distally) each based on triangular tooth.

Pereopods without epipod.

Coloration. Entirely whitish.

Habitat. Free living on greyish yellow calcareous ooze and solidified foraminifera sand at 2016 m.

Distribution. Carlsberg Ridge, Northwest Indian Ocean Ridge.

Etymology. The specific name is the Latin word militaris, “of war”, alluding to the extraordinarily armed pereopods.

Remarks. The new species belongs to a group of species that have a pair of epigastric spines, mesial and lateral eye-spines, abdominal tergites unarmed, 5 or 6 spines (including the anterolateral spine) on the lateral margin of the carapace, and denticulate carina on the distolateral margin of the P1 fixed finger. The most closely related species are M. lignaria Williams & Baba, 1989, M. nitida (A. Milne Edwards, 1880), M. pycnopoda Baba, 2005, M. verrilli Benedict, 1902 and M. vicina Faxon, 1893. Munidopsis militaris n. sp. can be distinguished from these relatives by having the palm armed with a row of strong spines on the lateral margin and the P2–4 propodus armed with row(s) of slender spines on the dorsal carinae. By contrast, the other five species have the palm unarmed on the lateral margin, and the P2–4 propodus unarmed (M. nitida and M. verrilli), or only armed with 1 (M. pycnopoda) or 2 (M. lignaria and M. vicina) spines on the proximal half. The new species further differs from M. lignaria, M. nitida, M. pycnopoda and M. vicina in having pereopods without an epipod, whereas the latter four have an epipod on the P1.

The unusual character of the armed lateral margin of the palm relates M. militaris n. sp. to another Indian Ocean species M. laurentae Macpherson & Segonzac, 2005 from the South Africa. The latter species, however, has many small and moderate-sized spines on the gastric region, and the carapace posterior margin preceded by a row of spines; whereas the new species has only two epigastric spines, and the carapace posterior margin unarmed.

The new species is also similar to M. centrina Alcock & Anderson, 1894, from the Indian Ocean and eastern Australia (Ahyong & Poore 2004; Baba 2005) in the armature of the carapace lateral margins and the P2–4, and the absence of the epipod on the pereopods, but can be distinguished from the latter by having the relatively short eyestalks, only one pair of epigastric spines, and the armed cheliped palms; whereas in M. centrina, the eyestalks are relatively long, gastric region bears additional spines besides epigastric ones, and the cheliped palms are unarmed.