Munidopsis chunii Balss, 1913

De Matos-Pita, Susana S. & Ramil, Fran, 2014, Squat lobsters (Crustacea: Anomura) from Mauritanian waters (West Africa), with the description of a new species of Munidopsis, Zootaxa 3765 (5), pp. 418-434 : 421-427

Munidopsis chunii Balss, 1913

( Figs. 1–5 )

Munidopsis chuni Balss, 1913: 224 .

Munidopsis chunii .— Baba et al. 2008: 137 (compilation)

Material examined. MAURIT 1107, Stn L59, 1215– 1282 m, 6 males 8.8–12.7 mm, 2 females 7.8–10.1 mm, 5 ovigerous females 8.0– 11.4 mm; Stn L60, 1512– 1530 m, 6 males 6.4–11.4 mm, 1 female 9.4 mm, 1 ovigerous female 8.1–10.3 mm; Stn L66, 1243– 1317 m, 2 males 5.4–6.4 mm, 3 females 6.4–6.7 mm; Stn L68, 1136– 1146 m, 31 males 7.6–12.4 mm, 24 ovigerous females 8.6–15.3 mm. MAURIT 0 811, Stn L33, 1331– 1347 m, 1 male 8.5 mm, 1 female 6.4 mm; Stn L38, 1010– 1124 m, 6 males 10.9–13.5 mm, 3 ovigerous females 11.3–13.3 mm.

MAURIT 1011, Stn L40, 1214– 1275 m, 3 males 7.7–8.2 mm, 1 female 8.3 mm, 6 ovigerous females 8.6–11.0 mm.

Description. The following description is based on a male (11.8 mm) from MAURIT 1107 Stn L68, for variations of this species, unless otherwise specified, see below.

General: Carapace and legs covered with tuberculate transverse striae supporting bases of setae; setae scarce and short in the carapace, denser and somewhat long and plumose in the legs ( Fig. 1 b).

Carapace: Carapace longer than broad, with lateral margins somewhat diverging posteriorly. Dorsal surface with the different regions demarcated. Epigastric region with 2 transversal spines, each one followed apart by a minutely denticulate transverse striae at each side of the middle line; middle line from posterior to the base of the rostrum until protogastric region, with a weak longitudinal carina that is furnished with 3 or 4 separated and very short minutely tuberculate transverse striae (sometimes this carina can not be well appreciated). Mesogastric region with one median spine that arises from short minutely tuberculated transverse stria. Metagastric region with a median spine that arises from the anterior of 2 medium size minutely denticulated transverse striae that are curved anteriorly following the cervical sinus. Cardiac region with a median spine on a transversal ridge, the crest of this ridge is minutely denticulated. Frontal margin unarmed; weakly carinated at the base of the rostrum and minutely denticulated just behind antennal peduncle. Lateral margins with 2 prominent spines, the biggest one on the anterolateral margin over a conspicuous mamelon, the other one located on the anterobranchial region, over a smaller and rounded prominence too ( Fig. 2 e). Posterior margin with a minutely denticulated carina. All carapace spines are anteriorly directed ( Fig. 1 c). Pterygostomian flap surface with spaced minutely tuberculate transverse striae; ending anteriorly in 4–7 small and irregular teeth.

Rostrum: Spiniform and running slightly upwards; about 1/2 (1/ 3 in females) length of the carapace; lateral margins furnished with denticles that are bigger and placed more apart each other in the base while they are smaller and closely placed distally; dorsally furnished with some short minutely tuberculate transverse striae, no carina neither dorsally nor lateral ( Fig. 2 e).

Sternum: Sternite 3 rectangular with rounded corners, about 4 times wider than high, anterior margin with a wide median concavity that is flanked laterally by 3–5 irregular denticles, this denticles are followed laterally by a small and rounded perforation in which the third maxilliped is articulated ( Fig. 2 b). Sternite 4 about 2.5 times as broad as the preceding one, narrowing anteriorly and with a rounded hollow on each side in which the P1 is articulated ( Fig. 2 b).

Abdomen: Tergites 2–4 each with 2 transverse ridges, anterior ones running laterally up to the tip of the pleuron; each ridge supports a row of small denticles in the crest on somites 2 and 3, while on somite 4 is unarmed and rounded. 2 median spines on tergites 2 and 3 arising respectively from anterior and posterior ridges; 1 spine over anterior ridge on tergite 4. Tergite 6 having posterior margin flanked by 2 conspicuous lobes with a rounded depression between the lobes ( Figs. 1 a, c). The uropod exopod margin, the lower and inner laterals of uropod endopod and free margins of the telson posterior plates, furnished with long plumose setae and with movable teeth; exposed endopod dorsal surface when uropods retracted, with very short minutely tuberculate transverse striae suporting bases of simple setae. Telson composed of 12 plates ( Fig. 1 c); lateral plate free margin (outer lateral) with bristle setae in adult males and short plumose setae in adult females.

Eye: Ocular peduncles movable and very short. Cornea rather cylindrical, rounded distally and with smooth surface ( Fig. 2 e).

Antennule: Basal article armed with three large spines: one lateral, one distolateral and one distomesial; ventrodistal margin between these last 2 spines denticulate. The tip of the lateral spine on left antennule is trifid (this trifid tip was found only in this specimen, in the rest of the specimens examined was simple) ( Figs. 2 a, e).

Antenna: Basal article immovable, with triangular outer lateral margin and with the distal margin rounded and denticulate. Article 2 with a dorsodistolateral triangular prolongation with the rounded margin denticulate, one ventrodistolateral spine and one small subterminal ventrodistomesial spine. No distinct spines on article 3, but distomesial and distolateral margins denticulate. Article 4 with the lateral expansion spinose ( Figs. 2 d, e).

Maxilliped 3: Ischium about the same lenght of merus and with 18–21 denticles on the inner mesial ridge. Merus extensor margin with one distal spine, followed by 3 or 4 weak denticles (1 more notorious, 2 weak and 1 minute) each one furnished with 1 single setae, merus flexor margin with 2 strong spines and distal margin denticulate. Carpus, propodus and dactylus unarmed ( Fig. 2 c).

Pereopod 1 (cheliped): Chelipeds subequal, about 2.5 times the carapace length (without rostrum) in males, and 2 times in females. Ischium with one dorsodistal spine and a small distomesial submarginal spine. Merus with 4 distal spines: dorsomesial, dorsolateral, ventrolateral (subterminal) and ventromesial; one dorsomesial spine on distal half (in this specimen absent on left cheliped, see variations). Carpus about twice long as broad, with 4 distal spines: dorsomesial (sometimes double, see variations), dorsolateral, ventrolateral and a subterminal ventromesial one; the ventral and ventromesial distal margins minutely denticulated. Palm about 1.5 times carpus length, cylindrical and with a notorious spine at the distal dorsal margin, where the movable finger articulates. Fingers as long as palm, somewhat depressed and with cutting edges furnished with a row of irregular sized denticles ( Fig. 2 f). Epipod absent.

Pereopods 2–4: P2 overreaching P1 carpus when extended forward, P3 and P4 diminishing in length and overreaching carpus of the preceding leg ( Fig. 1 b). Merus with 2 distal spines (dorsal and ventrolateral). Carpus with 1 distodorsal spine and the ventral margin minutely denticulate and 2 weak carinae-like composed by very short transversal striae, one following the distodorsal spine, the other one parallel laterally and less notorious on P4. Propodus elongate, smooth and unarmed. Dactylus particularly setose on the extensor margin; flexor margin armed with 10-12 teeth decreasing in size proximally; each teeth is furnished subapically with a single seta ( Fig. 2 g). Epipods absent.

Color. Yellow cornea and orange-red exoskeleton with a white spot covering the central distal carapace and proximal rostrum in living specimens; whitish in alcohol.

Variations. In the foregoing description the basic spinulation of carapace, abdomen and chelipeds is detailed. Nevertheless, in the 102 specimens studied, we found many variations from this basic pattern. One or more of these variations, not related to sex, age or size of the animal, can appear together in the same specimen. These variations are summarized as follows: 69 specimens show a double distal dorsomesial spine on P1 carpus ( Figs. 3 a, b, d, e, g) instead of a single spine ( Figs. 3 c, f); 53 specimens display variations in the carapace dorsal gastric, cardiac and branchial spinulation pattern. The most common variations involve the presence of one additional spine over the protogastric region and/or over the posterior ridge on the metagastric region ( Figs. 4 b, d, f, g). Additional spines can be developed from the minutely dentate transverse striae on the anterior protogastric, lateral epigastric, mesogastric, metagastric, cardiac and dorsobranchial regions ( Figs. 4 a, c, e, h); these spines can be bifid ( Fig 4 f). The metagastric spine was absent in 3 specimens ( Fig. 4 i).

The spinulation along the P1 merus dorsal and ventromesial margins in 32 of the studied specimens varies, including either the absence of the typical spines from the basic pattern or the presence of additional ones ( Figs. 3 a–g).

The spinulation over abdominal tergites 2, 3 and 4 varies in 16 specimens, usually with additional spines formed by enlargement of some of the denticles over the transverse ridges, but in 5 of them, the spine on tergite 4 is absent. One specimen lacks spines on the posterior ridge of tergite 3 and on tergite 4. Another specimen shows the posterior ridge of the abdominal tergites 2 and 3 devoid of spines.

Variations in the anterolateral and laterobranchial spinulation of the carapace were observed in four individuals, including either the absence or the presence of additional spines ( Figs. 4 d, i). One specimen shows a double distodorsal spine on right P4 merus and another exhibits an abnormal T-shaped fixed finger on right cheliped. Furthermore, we found too that the denticles on the mxp3 extensor margin are variable and related to the size of the animal. In this way, those with CL around 6 mm have two denticles ( Fig. 5 a); with CL: 8–10 mm they have two denticles ( Fig. 5 b), two denticles and one seta ( Fig. 5 c) or even three denticles ( Fig. 5 d); with CL over 10 mm they can have three denticles ( Fig. 5 f), three denticles and one seta ( Fig. 5 e) or four denticles ( Fig. 5 c); all denticles are furnished with one seta. Mxp3 flexor margin spinulation displays some variations too, involving several small spines developed from the denticulate distal margin, and also additional spines between the major ones, in this case always related with the biggest specimens ( Fig. 5 g).

Distribution. Only recorded from two areas: near Victoria, Cameroon (type locality) and along Namibia, in depths from 400 to 710 m ( Doflein & Balss 1913; Macpherson 1983). Our records extend the geographical distribution northwards to Mauritania and also increase its bathymetrical range from 710 to 1530 m deep.

Remarks. The first description of this species is only a brief diagnosis (Balss 1913). Later, Doflein & Balss (1913) provide a little more extended description of the same specimens and they add a figure of this species too. These descriptions were based only in two specimens, one male and one small female and no further description are reported in the literature. Our specimens, both males and females, agree well with the male description given by Doflein & Balss (1913), and the differences appreciated, in both males and females, can be explained after the variations above mentioned.

This species has been confused with Munidopsis bispinata Miyake & Baba, 1970 ; but the two species can be separated by the following features:

The rostrum is about 1/3–1/2 length of the carapace in M. chunii , but about 1/4–1/ 3 in M. bispinata .

The abdominal tergites 2 and 3 carry two spines, one on the anterior and one on the posterior transverse ridge in M. chunii but only a single spine on the anterior transverse ridge in M. bispinata . Both species have a single spine on abdominal tergite 4 anterior ridge.

The antennal peduncle basal article has a small tubercular tooth and article 3 has a minute spine on the outer distal margin in M. bispinata ; these are absent in M. chunii .

The mxp3 merus extensor margin has 2–4 small denticles or setae in M. chunii but only one seta and no denticles in M. bispinata . The meral flexor margin has 2 strong spines and the distal margin is most denticulate in M. chunii , whereas in M. bispinata , there are three spines, the distal one being very minute.

The P2 carpus has one dorsal spine (the distal one) in M. chunii while it has two dorsal spines in M. bispinata .

The P2–4 dactylus flexor margin is armed with 10–12 teeth in M. chunii but only seven in M. bispinata .

Some of these features, mainly those applicable to the spinulation of the abdominal somites and mxp3 merus, can be very variable as we have explained above. In consequence, to ensure the correct identification of the species, consideration of the combination of these features is required.

The records for this species in the literature cited depths of 400 to 710 m, whereas all our specimens were captured at depths greater than 1000 m.

Figures

FIGURE 1. Munidopsis chunii Balss, 1913, MAURIT 1107 Stn L 68, male CL 11.8 mm. Entire animal a) lateral view, P 1 – 4 removed b) dorsal view c) dorsal view. Scale bar a, c, 5 mm; a, c: all setae omitted.

FIGURE 2. Munidopsis chunii Balss, 1913, MAURIT 1107 Stn L 68, male CL 11.8 mm a) right antennule peduncle, ventral view b) anterior sternum c) right mxp 3, ventral view d) right antenna peduncle, ventral view e) anterior carapace, left detailed f) right cheliped, dorsal view g) right P 2. Scale bar a – d 1 mm, e – g 5 mm; a – g: all setae omitted.

FIGURE 3. Munidopsis chunii Balss, 1913, variations on P 1 carpus and merus spinulation. MAURIT 1011 Stn L 40: a) left cheliped, dorsal view, male CL 8.3 mm b) right cheliped, dorsal view, ovigerous female CL: 8.64 mm. MAURIT 1107 Stn L 59: c) left cheliped, dorsal view, male CL 8.8 mm d) left cheliped, dorsomesial view, ovigerous female CL 10.5 mm; Stn L 60: e) left cheliped, dorsal view, male CL 11.4 mm; Stn L 68: f) left cheliped, dorsal view, male CL: 11.8 mm. MAURIT 0 811 Stn L 38: g) right cheliped, dorsal view, male CL 13.3 mm. Scale bar 1 mm; a – g: all setae omitted.

FIGURE 4. Munidopsis chunii Balss, 1913, variations on dorsal and lateral carapace spinulation. MAURIT 1107 Stn L 68: a) male CL 8.8 mm b) ovigerous female CL 9.9 mm c) male CL 9.0 mm. MAURIT 1011 Stn L 40: d) ovigerous female CL 9.0 mm. MAURIT 1107, Stn L 59: e) ovigerous female CL 10.5 mm f) male CL 8.8 mm g) female CL 7.8 mm; Stn L 60: h) male CL 7.6 mm i) ovigerous female CL 10.3 mm. Scale bar 5 mm; a – i: all setae omitted.

FIGURE 5. Munidopsis chunii Balss, 1913, variations on mxp 3 merus flexor and extensor margins. MAURIT 0 811 Stn L 33: a) left mxp 3 merus, ovigerous female CL 6.4 mm. MAURIT 1011 Stn L 40: b) left mxp 3 merus, female CL 8.3 mm c) left mxp 3 merus, female CL 8.3 mm d) right mxp 3 merus, male CL 8.9 mm. MAURIT 1107 Stn L 68: e) left mxp 3 merus, ovigerous female CL 10.5 mm f) right mxp 3 merus, ovigerous female CL 11.8 mm g) left mxp 3 merus, ovigerous female CL 12.2 mm. Scale bar 1 mm.