Eumunida subsolanus, Baba & Wicksten, 2019

Baba, Keiji & Wicksten, Mary K., 2019, Chirostyloidean squat lobsters (Crustacea: Decapoda: Anomura) from the Galapagos Islands, Zootaxa 4564 (2), pp. 391-421 : 393-396

Eumunida subsolanus n. sp.

( Figs. 2–4 , 17A )

Type material. CDF NA064-018-01-03-A, holotype, female (CL 6.0 mm), ROV Dive H1435, East Wolf Seamount, 1°13.952'N, 91°6.82937'W, 305 m, 27 June 2015.

Description. Carapace: Broader than long (0.9 × as long as broad). Dorsal surface with distinct transverse ridges: 6 ridges on anterior half; first 3 placed between 3 hepatic spines, first interrupted into 3 scale-like ridges, second medially interrupted, preceded by short median ridge, third short and transverse, placed between last hepatic spines, fourth interrupted into several short ridges, fifth anteriorly convex, last transverse; 7 transverse ridges on posterior half; first preceded by cervical groove (anteriorly convex median ridge flanked by similar lateral ridges and by shorter interrupted striae between first and second ridges), second and third interrupted, fourth and fifth uninterrupted, remainder interrupted; several striae between lateral portions of sixth and seventh ridges; anterior branchial region with several small scale-like ridges. Lateral margins convex, with 9 spines: 3 spines anterior to posterior cervical groove (first anterolateral, strongest, directed slightly ventrally, far falling short of hiatus between mesial and lateral supraocular spines; third small) and 6 posteriorly diminishing spines on posterior branchial margin. Rostral spine deflected slightly ventrally but distally slightly upturned, length 0.5 × postorbital carapace length, mesial supraocular spine reaching distal quarter of rostral spine, lateral supraocular spine terminating in midlength of mesial supraocular spine. Pterygostomian flap smooth on surface, anteriorly produced to strong spine.

Sternal plastron: 1.2 × longer than broad, lateral extremities divergent posteriorly to sternite 6, sternite 7 slightly broader than sternite 6. Sternite 3 anterior margin with 2 short submedian processes each ending in small spine. Sternite 4 with strong, anteriorly directed spine on each side.

Abdomen: With 3 transverse ridges on tergites 2–3, 2 obsolescent ridges on tergites 4–5, 5 interrupted ridges on tergite 6. Pleuron of somite 2 with 4 short transverse ridges arranged longitudinally. Telson 0.6 × as long as broad; posterior lobe slightly narrower and 1.6 × longer than anterior lobe, posterior margin distinctly emarginate.

Eye: Globular. Cornea inflated, as long as remaining eyestalk, reaching tip of lateral supraocular spine, breadth 0.7 × distance between hiatuses formed by lateral and mesial supraocular spines.

Antenna: Article 1 with small lateral spine; article 2 with distolateral spine reaching midlength of article 4; antennal acicle overreaching article 4; article 3 with distomesial spine somewhat overreaching article 4; article 4 with small distolateral and strong distomesial spine; article 5 with 3 small distal spines (2 mesial, 1 lateral).

Mxp: Mxp 3 basis lacking denticles on mesial ridge; ischium with 15 proximally diminishing denticles on crista dentata; merus 1.7 × longer than ischium, flexor margin with small spine distal to midlength.

P1: 4.5 × carapace length, obsolescently squamate, with sparse setae. Merus 2.0 × longer than carapace; 4 rows of spines (1 dorsal, 1 ventral, 1 lateral and 1 mesial), mesial and ventral spines well developed. Carpus with 3 distal spines (1 mesial, 1 ventromesial and 1 midventral). Palm 8.1 × as long as broad, 3.7 × longer than carpus, with row of 11 small dorsal spines along mesial margin and another row of larger ventral spines along mesial margin; small round setal pad on ventral surface. Fingers with nearly straight opposable margins; distally incurved and crossing when closed, fixed finger with bifurcate tip; movable finger 0.7 × length of palm.

P2–4: With sparse setae, lateral faces weakly squamate. Meri successively shorter posteriorly (P3 merus 0.8 × length of P2 merus, P4 merus 0.9 × length of P3 merus), slightly narrower on P2 than on P3 and P4; length-breadth ratio, 6.0 on P2, 4.0 on P3, 3.5 on P4; merus-propodus length ratio, 1.11 on P2, 0.86 on P3, 0.77 on P4; dorsal crests with 11, 10, 6 spines on P2, P3, P4 respectively; lateral surface with row of 4 spines somewhat dorsal to midline on P4, spineless on P2 and P3; ventrolateral margin with distal spine smaller than dorsodistal spine; ventromesial margin with distal spine on P2, no spine on P3 and P4; P2 merus 0.8 × postorbital carapace length. Carpi subequal; carpus-propodus length ratio, 0.3 on P2–4; extensor margin with 4 proximally diminishing spines on P2–4. Propodi subequal on P2 and P4, slightly longer on P3 than on P2 and P4; length-breadth ratio, 7.2 on P2, 7.0 on P3, 6.7 on P4; flexor margin with pair of terminal spines preceded by 11, 10, 8 movable spines on P2, P3 and P4 respectively; propodus-dactylus length ratio, 2.2 on P2, 2.0 on P3 and P4. Dactyli 1.4 (P2), 1.7 (P3), 1.6 (P4) × longer than carpi; dactylus-propodus length ratio, 0.45 on P2, 0.49 on P3, 0.50 on P4; distally ending in strong, incurved spine, flexor margin with 9 obliquely directed small spines.

Coloration: Pale orange yellow, lateral portions of carapace pale orange red.

Etymology. From the Latin subsolanus (= eastern), alluding to the occurrence of the species in the eastern Pacific Ocean.

Remarks. The specimen is presumably in the process of molting because the integument is more rigid than usual and the transverse ridges on the abdomen are not clearly visible.

Eumunida subsolanus n. sp. belongs to the subgenus Eumunida de Saint Laurent & Poupin, 1996 , diagnosed by a pair of spines on the anterolateral margins of sternite 4. The combination of the following characters links the species to E. similior Baba, 1990 from Madagascar, E. depressa de Saint Laurent & Poupin, 1996 from Japan and E. treguieri de Saint Laurent & Poupin, 1996 from French Polynesia: the carapace lateral margin bears three spines anterior to the posterior cervical groove, the dorsal surface has at least some uninterrupted transverse ridges on the posterior half; and the P1 palm has a small ventral pad. Eumunida subsolanus is closer to E. similior in having the posterior portions of the abdominal tergites 2–4 (behind the third major transverse ridge) each smooth rather than bearing an additional stria as in E. depressa and E. treguieri . Eumunida subsolanus , however, is distinguished from E. depressa and E. treguieri by the following features: the carapace lateral margin bears six instead of five spines on the posterior branchial region; the P2 merus dorsally bears fewer spines (7 versus 11), and ventromesially, only one distal spine instead of a row of 7 spines (the P3–4 meri are unarmed on the ventromesial margin in both species). The P1 palm bears 2 rows (dorsal and ventromesial) of spines in E. subsolanus , whereas the dorsal row is absent in E. similior . However, this character is problematic: Puillandre et al. (2011) found that the presence or absence of spines on the P1 palm and merus as well as the relative size of eyes, which had been used to discriminate among E. karubar , E. parva and E. smithii (See de Saint Laurent & Poupin 1996) , were not supported by DNA barcoding (and synonymized the former two with the latter as a consequence).

Eumunida subsolanus differs from E. depressa and E. treguieri in having six instead of four spines on the posterior branchial margin, in addition to the absence of striae behind the third major transverse ridge on the abdominal tergites 2–4. Pereopods 2–4 in the new species are broader relative to length instead of narrow compared to the other two species. In addition, the dactyli are longer, the dactylus-propodus length ratio being 0.45–0.50 vs. 0.29–0.33 (propodus-dactylus length ratio, 2.0–2.2 vs. 3.0–3.5). However, the sole specimen of E. subsolanus is much smaller than the known specimens of the related species and it seems not unlikely that this difference is size related. Unfortunately, it remains difficult to ascertain allometric variation given that a range of sizes from small to large not available for any of the known species. In small species, such as E. ampliata de Saint Laurent & Poupin, 1996 and E. smithii Henderson, 1885 , the dactyli are relatively long (de Saint Laurent & Poupin 1996) as in this new species, and in the other small specimen (CL 6 mm) of E. chani Baba & Lin, 2008 from Taiwan, the dactylus-propodus length ratio is 0.37–0.40.

Distribution. East Wolf Seamount, Galapagos Islands at 305 m depth.

Figures

FIGURE 2. Eumunida subsolanus n. sp., holotype, female (CL 6.0 mm), CDF NA064-018-01-03-A. A, carapace and abdomen extended, tailfan omitted, dorsal. B, same, lateral. C, sternal plastron. D, telson. E, left antenna, ventral. F, left Mxp3, ventral. G, same, lateral. Scales = 1 mm.

FIGURE 3. Eumunida subsolanus n. sp., holotype, female (CL 6.0 mm), CDF NA064-018-01-03-A, left P1. A, dorsal. B, ventral. C, mesial. D, lateral. E, mesial spines of merus, ventral. F, distal part of fingers, dorsal. Scales = 1 mm.

FIGURE 4. Eumunida subsolanus n. sp., holotype, female (CL 6.0 mm), CDF NA064-018-01-03-A. A, left P2, lateral. B, same, distal part, setae omitted. C, left P3, lateral. D, same, distal part. E, left P4, lateral. F, same, distal part. Scales = 1 mm.

FIGURE 17. A, Eumunida subsolanus n. sp., holotype, female (CL 6.0 mm), CDF NA064-018-01-03-A. B, Heteroptychus nautilus n. sp., holotype, ovigerous female (CL 5.2 mm), CDF NA064-009-01-01-A. C, Uroptychus bellus Faxon, 1893, male (CL 4.5 mm), with Antipatharia, CDF NA064-130-01-01-A. D, Uroptychus occidentalis Faxon, 1893, two specimens on Chrysogorgia sp., CDF NA064-013-01-01-A. E, same, right ovigerous female (CL 11.4 mm), left specimen not available for study, CDF NA064-013-01-01-A.