Munidopsis nautilus Rodríguez-Flores & Seid & Rouse & Giribet 2023, sp. nov.

Munidopsis nautilus sp. nov. (Fig. 16 a–j, Supplementary Fig. S4.) Zoobank: urn:lsid:zoobank.org:act:ADD10D8C-8E69-48E1-B0AD-EDB9 D13FD62B Material examined Holotype. ECUADOR: off Galapagos Islands, leg. E/V Nautilus, ROV Hercules, ROV Hercules dive H1433, Stn NA063-016, ROV Hercules dive H 1433, 20.vi. 2015, 0.73720°N, 85.89091°W, 2600 m: 1 ov. F 11.0 mm (MCZ IZ-70119). Etymology Named after the Exploration Vessel Nautilus from which the exploration of the Galapagos Rift region was conducted, yielding these specimens. The name is a substantive in apposition. Diagnosis Carapace dorsally smooth, pair of epigastric scales, cervical grooves weakly distinct. Rostrum narrowly triangular, lateral margins subparallel, unarmed. Frontal margins concave. Orbit excavated, outer orbital angle with a spine. Anterolateral angle armed with a small spine. Branchial margin armed with spines. Abdominal somites unarmed. Telson divided into 9 plates. Sternite 3 anterolaterally blunt, anterior margin nearly straight with a median notch, sternite 4 widely triangular. Eyes unarmed, immovable, epistomial spine present. Article 1 of antennule with well-developed dorsolateral and distolateral spines. Article 1 of antenna with distomesial and distolateral spines. Mxp3 merus rectangular in lateral view, with dorsal carina. P1 moderately slender, with some spines, ventral pad in palm, fixed finger without denticulate carina on distolateral margin. P2–4 slender, unarmed; meri and propodi cylindrical, dactyli stout, curving, flexor margin with teeth along all margins decreasing proximally. Epipods absent from all pereopods. Description Carapace 1.2× longer than broad, widest posteriorly; weakly convex from side to side. Dorsal surface smooth, covered in small scales, each with a few short setae and some thick long setae; pair of epigastric produced and elevated scales. Regions not delineated, anterior and posterior cervical grooves weakly distinct. Mid-dorsal ridge medially interrupted. Posterior margin unarmed, angular, emarginated medially. Rostrum narrowly triangular, dorsally flattened, slightly directed downwards, 0.2× as long as remaining carapace length, 1.7× longer than broad, lateral margins serrated anteriorly. Frontal margin concave behind ocular peduncle, outer orbital angle produced into a spine above antennal peduncle, outer orbital spine strong, much larger (twice as large) than anterolateral spine. Lateral margins straight; anterolateral spine small; branchial margins armed with spines. Pterygostomian flap surface irregular, anterior margin acute. Sternum Slightly longer than broad, maximum width at sternite 7. Sternite 3 broad, 3.2× wider than long, anterolateral angle blunt, anterior margin nearly straight with a median notch. Sternite 4 narrowly elongated anteriorly; surface flattened, smooth; greatest width 2.9× that of sternite 3 and 1.8× wider than long. Abdomen Unarmed; tergite 2 with anterior transverse ridge, lateral partsof dorsal surfaces smooth; tergites 3–6 lacking ridges; tergite 6 with weakly produced posterolateral lobes and nearly transverse posteromedian margin. Telson composed of 9 plates; 1.2× as wide as long. Eye Eye immovable; flattened peduncle recovering all cornea surfaces, laterally and ventrally spinose, projected on dorsal surface in an acute triangular medial spine, exceeding midlength of rostrum, with serrated lateral margins; epistomial spine absent. Antennule Article 1 of peduncle with well-developed dorsolateral and small distolateral spines, distodorsal spine lateral margin strongly concave; distomesial margin dentate. Antenna Peduncle clearly exceeding eye. Article 1 with distomesial and distolateral spines. Article 2 with well-developed distolateral and distomesial spines, distal surface with dorsal carina. Article 3 with distomesial angle unarmed, distolateral spine well-developed, distal surface with denticles, dorsal surface carinated. Article 4 unarmed. Flagellum thick, longer than carapace. Mxp3 Ischium as long as merus measured on extensor margin, with distal flexor and extensor spines. Crista dentata finely denticulate. Merus with 2 spines along flexor margin, proximal strong, distal small; extensor margin unarmed, dorsal surface carinated. Dactylus and carpus unarmed; propodus dorsal surface armed with a longitudinal carina. P1 Slender, with few scales and long setae, 2.2× longer than carapace. Merus 1.9× carpus length, with row of welldeveloped spines on mesial margin and some distal stout spines, extensor margin serrated with few spines including strong distal spine. Carpus 1.5× longer than broad, with row of well-developed spines on mesial margin and some distal stout spines. Palm armed with distal spine mesial margin, slightly longer than carpus, pad of setae on ventral surface, 1.7× longer than broad. Fingers unarmed, 1.2× longer than palm, opposing margins straight, not gaping, spooned, fixed finger without denticulate carina on distolateral margin. Cheliped pad oval on ventral side of fixed finger. P2–4 Slender, covered in setose scales, cylindrical in crosssection, slightly decreasing in size posteriorly. P2 merus slender, 2.0× carapace length, 6.5× longer than high and 1.2× length of P2 propodus. P3 meri longer than P2 and P4 (P3 merus 1.2× length of P2 merus, P4 merus 0.8× length of P3 merus); extensor margin of P2–4 meri with spines along entire border, distal ending in thick spine in P2–3; flexor margin serrated, distal spine strong; carpi unarmed, lateral side smooth; P2–4 propodi 7.5–9.0× as long as high, cylindrical in cross-section, extensor margin unarmed, flexor margin armed with 0–3 spines, distal spine strong; dactyli highly setose, 0.38–0.4× length of propodi; distal claw short, moderately curved; flexor margin distally curved, with 11–12 teeth at distal half margin, ultimate tooth at midlength between penultimate tooth and dactylar angle. Epipods Absent from all pereopods. Colouration Unknown. Distribution Off Galapagos, at 2600-m depth. Genetic data COI and 28S rRNA. Remarks The new species is morphologically similar to M. lentigo from the East Pacific Rise (Williams and Van Dover 1983). We have found the following morphological differences between both species: • The new species presents produced epigastric scales whereas these epigastric scales are absent or weakly marked in M. lentigo. • The spines on the branchial margin of the carapace are smaller than the outer orbital spine in the new species than in M. lentigo. • The rostrum is narrowly triangular in the new species, whereas this is more strap-like in M. lentigo. Unfortunately, we only have one specimen of the new species, therefore we cannot discuss intraspecific variation. However, Munidopsis lentigo and the new species are highly divergent genetically, with a genetic distance between 12 and 13% for COI.Published as part of Rodríguez-Flores, Paula C., Seid, Charlotte A., Rouse, Greg W. & Giribet, Gonzalo, 2023, Cosmopolitan abyssal lineages? A systematic study of East Pacific deep-sea squat lobsters (Decapoda: Galatheoidea: Munidopsidae), pp. 14-60 in Invertebrate Systematics 37 (1) on pages 43-45, DOI: 10.1071/is22030, http://zenodo.org/record/753473