Munidopsis pycnopoda Baba, 2005

Osawa, Masayuki, Chan, Tin-Yam & Yang, Chien-Hui, 2023, New records of the squat lobster genus Munidopsis Whiteaves, 1874 (Crustacea, Decapoda, Munidopsidae) from the deep sea off Taiwan, ZooKeys 1166, pp. 271-286 : 271

Munidopsis pycnopoda Baba, 2005

Figs 3 , 4

Munidopsis pycnopoda Baba, 2005: 176, fig. 84 (type locality: Mozambique Channel, 14°20'S, 45°09'E, 3485 m), 279 (key), 293 (synonymy)- Macpherson 2007: 96. Baba et al. 2008: 156 (complement).

Material examined.

Taiwan: 2 ovigerous ♀♀ (pcl 12.2, 12.3 mm), east off Taiwan, station CP5292, 23°58.16'- 23°55.25'N, 122°22.39'- 122°21.60'E, 3575-3590 m, French beam trawl, 10 Aug. 2022 (NTOU A01453 ) .

Diagnosis.

Carapace (excluding rostrum) slightly longer than wide; dorsal surface with numerous transverse ridges and pair of distinct epigastric spines; front margin oblique; outer orbital angle with prominent spine (antennal spine); lateral margin slightly convex, with 7 spines, first anterolateral, second to fifth spines and sixth and seventh spines on anterior and branchial margins, respectively, second spine strongest. Rostrum 0.4 length of remaining carapace, slightly shorter than basal width, narrowly triangular; dorsal surface with median carina. Sternite 3 subquadrate in general outline; sternite 4 narrowed and elongated anteriorly, anterior margin narrower than posterior margin of sternite 3. Pleon entirely unarmed; tergites 2 and 3 each with 2 elevated, blunt transverse ridges; posteromedian lobe of tergite 6 nearly transverse, straight; telson composed of 8 plates. Ocular peduncle short, faintly movable dorsoventrally, with 2 distinct eye-spines, mesiodorsal spine stronger than lateral spine. Article 1 of antennular peduncle with distolateral and distodorsal spines, distolateral spine larger. Antennal peduncle overreaching tip of mesiodorsal eye-spine by full length of article 4; article 1 with distomesial spine reaching midlength of article 2; article 2 with distolateral spine reaching midlength of article 3. Mxp3 merus with 5-7 small teeth on ventral margin, dorsal margin with small distal spine. P1 short, approximately as long as postorbital carapace, covered with short ridges on surfaces; chela 2.1 times as long as wide, without spines; fixed finger with short denticulate carina on distolateral margin; dactylus slightly shorter than palm, distinctly narrower than fixed finger. P2-4 moderately long, P2 overreaching tip of P1 by full length of P2 dactylus; meri each with row of distinct, irregular sized spines on dorsal margin, ventrolateral margins each with row of small spines and somewhat elevated, short ridges; propodi nearly equal in height from proximal to distal, dorsolateral and dorsomesial margins each crenulated by row of short ridges, dorsomesial margin usually with 1 or 2 distinct spines on proximal half; dactyli 0.5-0.6 length of propodi, ventral margins nearly straight, each with 12-14 teeth. Epipods present on P1, absent from P2-4.

Description.

Ridges on carapace and P1-4 each bearing row of minute granules and very short plumose setae. Coarse, short to moderately long setae on surfaces of P1-4.

Carapace (Fig. 3A ) excluding rostrum slightly longer than wide. Dorsal surface moderately arched from side to side, with pair of epigastric spines; anterior half with arcuate ridges; posterior half with longer transverse ridges, posteriormost ridge uninterrupted, elevated, preceded by shallow groove; cervical grooves distinct. Front margin oblique, slightly concave behind ocular peduncle. Orbit slightly excavated, outer orbital angle with prominent spine (antennal spine). Lateral margin slightly convex, with 7 spines; first spine anterolateral, small (abnormally absent on left side in ovigerous female, pcl 12.3 mm); second to fifth spines and sixth and seventh spines on anterior and branchial margins, respectively, second spine strongest, directly behind end of anterior cervical groove. Rostrum (Fig. 3A, B ) 0.4 length of remaining carapace, slightly shorter than basal width, narrowly triangular, horizontal or slightly upcurved distally; dorsal surface with median carina extending to epigastric region; lateral margin ridged, minutely crenulated distally; ventral surface flattish.

Sternal plastron (Fig. 3C ) slightly wider than long. Sternite 3 subquadrate; anterior margin with small denticles, subdivided into 2 lobes by shallow median notch; small protuberance present below median notch. Sternite 4 narrowed and elongated anteriorly; anterior margin narrower than posterior margin of sternite 3; ventral surface concave, with median groove anteriorly.

Pleon (Fig. 3D, E ) entirely unarmed. Tergites 2 and 3 each with 2 blunt transverse ridges, anterior ridge strongly elevated, posterior ridge preceded by shallow groove. Tergite 4 with blunt transverse ridge anteriorly and obsolete ridge posteriorly on each side. Tergites 5 and 6 each with obsolete ridge anteriorly on each side; posteromedian lobe of tergite 6 nearly transverse, straight, lateral lobes weakly produced. Telson (Fig. 3E ) distinctly wider than long, composed of 8 plates.

Ocular peduncles (Fig. 3A, B, F ) short, faintly movable dorsoventrally; 2 or 3 eye-spines present, mesiodorsal spine strong and directed forward, lateral spine small, mesioventral spine tiny or absent. Cornea relatively narrow, maximum width distinctly less than width of rostrum at midlength, not pigmented.

Article 1 of antennular peduncle (Fig. 3F ) with distolateral and distodorsal spines, distolateral spine larger; ventrodistal margin with small spine mesially; ventral surface with small denticles on anterior half.

Antennal peduncle (Fig. 3A, F ) overreaching tip of mesiodorsal eye-spine by full length of article 4. Article 1 with distomesial spine reaching midlength of article 2, distolateral spine small. Article 2 with small distomesial spine ventrally, distolateral spine reaching midlength of article 3. Article 3 with small distomesial spine dorsally, distolateral margin granular. Article 4 unarmed.

Mxp3 merus (Fig. 3G ) with 5-7 small teeth on ventral margin, proximal 1 or 2 teeth stronger; dorsal margin with small distal spine; carpus unarmed.

P1 (Fig. 4A, B ) short, approximately as long as postorbital carapace, overreaching tip of rostrum by almost full length of chela, covered with short, transverse or scaly ridges on surfaces. Merus reaching nearly midlength of rostrum, with 5 distal spines (3 dorsal, 1 ventromesial, 1 ventrolateral); dorsal surface with irregular row of small spines on midline. Carpus nearly as long as wide, dorsal surface flattish, dorsodistal margin with 1 or 2 spines, mesial spine reduced in size or replaced by blunt tubercle; dorsomesial margin with row of 3 or 4 spines, distal most spine largest; laterodistal margin with small spine or unarmed; ventral surface smooth. Chela 2.1 times as long as wide. Palm slightly longer than wide, unarmed; dorsal surface somewhat convex from side to side. Fingers distally spooned; occlusal margins each distally with row of small denticles; fixed finger with short denticulate carina on somewhat inflated distolateral margin. Dactylus slightly shorter than palm, distinctly narrower than fixed finger.

P2-4 (Fig. 4C-H ) moderately long, somewhat compressed laterally; P2 overreaching tip of P1 by full length of P2 dactylus. Meri decreasing in size posteriorly, P3 0.9 length of P2, P4 0.8 length of P3; dorsal margins bluntly crested, each with row of irregularly sized spines, terminal spine on each P3 and P4 strongest; lateral surfaces with short, transverse or arcuate ridges; ventrolateral margins each with row of small spines and somewhat elevated, short ridges, terminal spine on each P2 and P3 strongest. Carpi each with 4 or 5 spines on dorsal crest; lateral surfaces each with elevated, longitudinal ridge subparalleling dorsal crest. Propodi about 5.6 times as long as high, nearly equal in height from proximal to distal; dorsal surface flattish, dorsolateral margin crenulated by row of short ridges, dorsomesial margin also crenulated and with 1 or 2 (P2 and P3) and 0 or 1 (P4) distinct spines on proximal half; lateral surfaces with sparse, short ridges; ventral surfaces with 0 or 1 corneous spine on distal one-third; distoventral margins each with 2 corneous spines. Dactyli 0.5-0.6 length of propodi, moderately slender; ventral margins nearly straight, each with 12-14 proximally diminishing teeth, each tooth bearing short bristle-like setae; terminal claws short, curved.

Epipods present on P1, absent from P2-4.

Coloration.

Body and appendages entirely white.

Distribution.

Previously only known from the Mozambique Channel at depths of 3450-3485 m ( Baba et al. 2008). The present material collected from off Taiwan at depths of 3575-3590 m represents the first record M. pycnopoda from the Pacific Ocean and greatly extends the geographic range of this species (Fig. 5 ).

Remarks.

Baba (2005) originally described M. pycnopoda based on three specimens from the Mozambique Channel, with a note of intraspecific variation. The two specimens examined from off Taiwan agree well with the type specimens in the diagnostic characters, but they differ in having the carapace with stronger arcuate ridges on the gastric region and with two spines, instead of one spine, on the posterior branchial margin, the anterior margin of the thoracic sternite 3 being bilobed instead of nearly transverse, the thoracic sternite 4 being less elongate anteriorly, and the lateral eye-spine being stronger. Macpherson (2007) also pointed out the same difference in the shape of the thoracic sternite 3 in his topotypic material. Moreover, in one of the two Taiwanese specimens examined (ovigerous female, pcl 12.3 mm) there is a small spine laterally on each protogastric region of the carapace; this spine is not described or illustrated in the type material of M. pycnopoda .

As discussed by Baba (2005), M. pycnopoda is morphologically close to M. lignaria Williams & Baba, 1989 from the eastern Pacific off Oregon, but it is distinguishable from the latter species by the wider base of the rostrum, the P2-4 meri with more strongly upstanding spines on the dorsal margins, and the P2-4 dactyli being distally thicker and with straight, rather than somewhat arched, ventral margins.

Figures

Figure 3. Munidopsis pycnopoda Baba, 2005, ovigerous female (pcl 12.3 mm), east off Taiwan, station CP 5292, NTOU A 01453 A carapace, eyes, and antennal peduncles, dorsal view (setae partially drawn on left side) B rostrum and eye, right lateral view C anterior part of sternal plastron, ventral view (setae drawn only on right side) D pleomeres 1 - 4, dorsal view (setae drawn only on left side of pleomere 2) E telson and posterior margin of pleomere 6, external view (setae not drawn) F left eye, article 1 of antennular peduncle, and antennal peduncle, ventral view (setae not drawn) G left Mxp 3, merus, lateral view (setae not drawn). Scale bars: 1.0 mm.

Figure 4. Munidopsis pycnopoda Baba, 2005, ovigerous female (pcl 12.3 mm), east off Taiwan, station CP 5292, NTOU A 01453 A left P 1, carpus and chela, dorsal view (setae partially drawn on palm) B left P 1, fixed finger, lateral view C left P 2, merus, lateral view (setae not drawn) D left P 3, merus and carpus, lateral view (setae not drawn) E left P 3, propodus and dactylus, lateral view (setae partially drawn) F left P 3, distal part of propodus, ventral view G left P 3, ventral margin of dactylus, lateral view H right P 4, merus, lateral view (setae not drawn). Scale bars: 1.0 mm.

Figure 5. Global geographic distributions of Munidopsis albatrossae Pequegnat & Pequegnat, 1973 (red) and M. pycnopoda Baba, 2005 (blue). Dotted line symbols are records based only on ROV images. Shaded symbols refer to new records in this work.