Munidopsis longispinosa Cubelio, Tsuchida & Watanabe, 2007

Munidopsis longispinosa Cubelio, Tsuchida & Watanabe, 2007 View in CoL

Figs 5 View Figure 5 , 6 View Figure 6

Munidopsis longispinosa Cubelio, Tsuchida & Watanabe, 2007 c: 5 View in CoL , figs 3 b, 5 (type locality: Hatoma Knoll, Okinawa Trough).

Munidopsis verrilli Dong and Li 2015: 94, figs 3, 6, 8 C (not Munidopsis verrilli Benedict, 1902). View in CoL View Cited Treatment

Material examined.

Southern East China Sea – Okinawa Trough, Tangyin hydrothermal vent field • 1 male ( 26.4 mm); 25°04'N, 122°34'E; 1219 m depth; 7 May 2014; collected by television grab, R/V Kexue; GenBank no.: PX 111642 ; MBM 287955 View Materials GoogleMaps . Northeastern South China Sea – Site F cold seep field ; 22°7'N, 119°17'E; 1160 m depth; collected by Faxian ROV of R/V Kexue • 1 female ( 20.8 mm); 16 Mar. 2014; MBM 189174 View Materials GoogleMaps • 1 female ( 14.3 mm), 4 males ( 9.2–23.1 mm), 6 ovigerous females (15.6–29.0 mm); 3 Jun 2020; GenBank no.: PX 111640 ; MBM 287956 View Materials GoogleMaps • 5 males ( 15.1–32.1 mm); 9 Jun 2021; GenBank no.: PX 111641 ; MBM 287957 View Materials GoogleMaps • 1 male ( 17.2 mm); Jun 2021; MBM 287958 View Materials GoogleMaps .

Description.

Carapace: distinctly longer than broad (excluding rostrum). Frontal margins oblique, antennal spine well developed. Lateral margins subparallel, sparsely setose; anterolateral spine relatively short, anteriorly directed; anterior branchial margin with 3 (rarely 4) spines; posterior branchial margin with spine at end of posterior cervical groove. Posterior margin slightly concave, with elevated submarginal ridge. Dorsal surface with regions moderately defined, covered with short, transverse rugae; rugae longer and more strongly elevated on posterior branchial region, bearing short setae particularly dense on lateral branchial region; cervical groove deep. Gastric region strongly elevated, with pair of epigastric spines. Cardiac region with deep, transverse median groove, posterior cardiac region slightly elevated. Intestinal region weakly delineated. Rostrum narrowly triangular, nearly horizontal, ~ 0.2 remaining carapace length, 1.7 × longer than broad; dorsal surface smoothly carinate. Pterygostomial flaps with oblique rugae on surface, anterior end blunt.

Sternum: approximately as long as broad, widening posteriorly. Sternite 3 1.7 × broader than long, divided into 2 parts by longitudinal median groove; anterior margin with median notch, bearing small lateral tooth. Sternite 4 distinctly broader than long; anterolateral margin denticulate; anterior part narrow, with longitudinal median groove; ventral surface depressed medially and with some short rugae. Sternites 5–7 separated by transverse ridges, with interrupted longitudinal median groove.

Pleon: tergites smooth, unarmed. Tergites 2–4 each with 2 transverse ridges bearing dense setae anteriorly, posterior ridge on tergite 4 relatively low and medially interrupted. Tergite 5 smooth, without distinct groove and ridge. Tergite 6 with straight posteromedian margin. Telson composed of 10 distinct plates.

Eye: eyestalk immovable. Peduncle short, broader than cornea. Mesial eyespine elongated, anteriorly or anterolaterally directed, reaching to distal 0.4 of rostrum. Lateral eyespine short, sometimes with affiliated smaller spines. Cornea globular.

Antennule: article 1 longer than broad; distal margin with strong ventrolateral spine and relatively small dorsolateral spine; lateral surface slightly inflated, with oblique groove extending from base of dorsolateral distal spine to median part of ventral surface; mesial margin straight.

Antenna: peduncle thick, nearly reaching to level of midlength of rostrum. Article 1 with strong distomesial spine reaching distal margin of article 2 and short distolateral spines reaching midlength of article 2. Article 2 armed with short distolateral spine reaching midlength of article 3. Article 3 subrectangular, unarmed. Article 4 short.

Mxp 3: ischium slightly shorter than merus; disto-flexor corner with acute spine; crista dentata well-developed. Merus with extensor margin convex, armed with strong disto-extensor spine; flexor margin with 3 small teeth; lateral surface with sparse short rugae. Carpus with few short rugae on lateral surface. Propodus short, flexor margins convex.

P 1: subequal, moderately stout, ~ 1.7 × longer than pcl, covered with numerous stiff setae on surfaces and margins. Ischium ~ 0.6 merus length, dorsodistal margin with acute spine; ventrodistal margin produced, with strong subterminal spine; surfaces covered with short rugae. Merus ~ 1 / 2 of pcl, with short, transverse rugae on surfaces; distal margin with strong dorsal, dorsomesial, ventromesial and ventrolateral spines: dorsal spine followed by row of spines along midline of dorsal surface, ventromesial spine followed by 2 strong median spines; mesial surface smooth. Carpus half of merus length, longer than broad; surfaces with short rugae; distal margin with dorsal, dorsomesial, dorsolateral and lateral spines, dorsomesial spine strongest, followed by 1 or 2 spines along dorsomesial margin. Chela compressed dorsoventrally, palm ~ 0.6 merus length, 1.1 × longer than broad, with short rugae on surfaces; lateral margin slightly convex; mesial margin armed with 3 (rarely 1 or 2) spines. Dactylus 1.4 × palm length, with tufts of short setae on margins and surfaces; occlusal margins weakly serrated and distally spooned, with low triangular process on distal third of fixed finger.

P 2–4: slender; margins and surfaces bearing dense long, stiff setae, lateral surface with short scale-like rugae. P 2 ~ 1.9 × pcl, reaching base of P 1 dactylus. Meri subequal in width on P 2–4, decreasing in length posteriorly; P 2 merus 0.7 × pcl and 4.8 × longer than broad, P 3 and P 4 meri ~ 0.9 and 0.8 length of P 2 merus, respectively; extensor margin armed with row of spines decreasing in size proximally; flexor margin rugose, with strong distal spine. Carpi subequal in length on P 2–4, ~ 0.4 P 2 merus length; extensor margin ridged, with strong distal spine; lateral surface with low, submarginal ridge along extensor margin, ending in short distal spine; flexor margin with acute distal spine. Propodi subequal in width on P 2–4; P 2 propodus subequal or slightly longer than P 3 and P 4 propodi, 0.8 P 2 merus length, and 6.5 × longer than broad; extensor margin unarmed; flexor margin distally with pair of small but distinct corneous spines. Dactyli ~ 1 / 2 propodus length; extensor proximally straight, distal claw strongly curving; flexor margin straight, with 14 or 15 movable corneous spines on distal 0.8 length, each spine of distal half margin present on low, broad triangular tooth, ultimate spine closer to penultimate spine than to distal claw.

P 1 –4 without epipods.

Coloration.

Entirely whitish.

Habitat.

Chemosynthetic environments: cold seeps and hydrothermal vents.

Distribution.

Northeastern South China Sea and Okinawa Trough, southern East China Sea; depth 1160–1481 m.

Genetics.

The genetic distance between M. longispinosa and M. verrilli from southern California is 12.8 % – 14.6 %. No genetic distances between specimens of M. longispinosa from the Okinawa Trough and the Site F site (Table 2 View Table 2 ).

Remarks.

Cubelio et al. (2007 c) described M. longispinosa based only on the male holotype collected from the hydrothermal-vent field of the Hatoma Knoll in the Okinawa Trough. Our specimens share several key morphological features with the holotype, including the presence of a pair of epigastric spines and five lateral marginal spines of the carapace, and elongated mesial eyespine. However, the original description and figures lacked details on the spination of the P 1 merus and carpus. In addition, the holotype was described to have small accessory spines (tubercles) near the epigastric spines, a row of flexor spines on the P 2–4 meri, and unarmed flexor margins on the P 2–4 propodi ( Cubelio et al. 2007 c); these characters contrast with our material. Actually, judging from the figures provided by Cubelio et al. (2007 c), the holotype seems to lack the accessory gastric spines (tubercles) and the flexor spines on the P 2 merus. In our specimens, tuberculate rugae may occur on the gastric region and the flexor margins of the P 2–4 meri, but they never form distinct spines. The distal pair of corneous spines on the flexor margin of the P 2–4 propodi are exceptionally small and easily overlooked. The holotype and other Hatoma Knoll material are unavailable for further morphological and genetic comparison, but given the general morphological similarity and the close proximity of the Tangyin hydrothermal field to the Hatoma Knoll, we still assign our specimens to M. longispinosa . The observed morphological differences from the holotype are likely attributable to intraspecific variation and insufficient original description.

The specimens of M. longispinosa from the Site F seep were previously misidentified as M. verrilli ( Dong and Li 2015) because they both have a pair of epigastric spines only on the carapace dorsal surface, a row of five spines on the carapace lateral margin, unarmed rostrum, mesial and lateral eyespines, and P 2 not reaching the distal end of P 1. Munidopsis longispinosa can be readily distinguished from M. verrilli in the following characters: the mesial eyespine is slender and reaches distal ~ 0.4–0.5 of the rostrum, the lateral cardiac regions of the carapace are ill-defined, the P 1 merus has two rows of spines (median spines are absent on the mesial surface), the P 1 carpus has four spines on the distal margin (an additional spine is present on the distolateral margin), and the flexor margin of P 2–4 propodi has a pair of distal corneous spines only. In M. verrilli , the mesial eyespine is short and only reaches the proximal 0.3–0.4 of the rostrum, the lateral cardiac regions of the carapace are elevated, the P 1 merus has three rows of spines (distinct median spines are present on the mesial surface), the P 1 carpus has three spines on the distal margin (a spine is absent on the distolateral margin), and the flexor margin of P 2–4 propodi has three corneous spines including the distal pair. Other minor differences of M. longispinosa from M. verrilli include thicker, stiffer setae on the P 1, three (rarely one or two) instead of usually two spines on the mesial margin of the P 1 palm, and small instead of strong spines on the extensor margin of the P 2–4 carpi.

Dong and Li (2015) pointed out that the Site F material was different from M. verrilli in having six spines on the carapace lateral margin, including the anterolateral spine. However, the number of the spines seems variable: the fourth lateral spine may bear an accessory spine, giving the appearance of six. The shape of the rostrum is likewise variable in M. longispinosa , ranging from short and broadly triangular to slender and narrow (somewhat spiniform).

Munidopsis longispinosa is also similar to M. asiatica from the Sea of Okhotsk, which was proposed as a junior synonym of M. similis by Rodríguez-Flores et al. (2023). Munidopsis longispinosa is different from the latter in having ill-defined lateral cardiac regions of the carapace, two rows of spines on the P 1 merus and relatively smaller spines on the extensor margin of P 2–4 carpi ( Smith 1885; Marin 2020; Rodríguez-Flores et al. 2023). Additionally, both M. asiatica and M. similis seem to have three distal spines on the P 1 carpus judging from the photos of the specimens ( Marin 2020; Rodríguez-Flores et al. 2023). The armature on the flexor margin of the P 2–4 propodi is unclear in M. similis but it was illustrated distally unarmed in M. asiatica ( Marin 2020) , a character rather unusual in Munidopsis species.

Munidopsis longispinosa therefore appears endemic to the chemosynthetic habitats in two regions: the Site F cold seep in the northern South China Sea and the hydrothermal fields in the Okinawa Trough, southern East China Sea.