Hexapinus latipes (De Haan, 1835 )

Rahayu, Dwi Listyo & Ng, Peter K. L., 2014, New genera and new species of Hexapodidae (Crustacea, Brachyura) from the Indo-West Pacific and east Atlantic, Raffles Bulletin of Zoology 62, pp. 396-483 : 409-414

publication ID	https://doi.org/ 10.5281/zenodo.5353945
publication LSID	lsid:zoobank.org:pub:4CF42744-861A-4635-9703-E6639CEBFAA9
persistent identifier	https://treatment.plazi.org/id/03EB87DA-3B36-E344-FC7A-FA15FB1F9A70
treatment provided by	Tatiana
scientific name	Hexapinus latipes (De Haan, 1835 )
status

Treatment

Hexapinus latipes (De Haan, 1835) View in CoL

( Figs. 10–13 View Fig View Fig View Fig View Fig )

Hexapus latipes De Haan, 1835 View in CoL : pl. D.

Hexapus sexpes View in CoL – De Haan, 1835: 35, 63, pl. 11, fig. 5; Odawara, 1965: 47, fig. a–d; Takeda, 1979: 153. (not Cancer sexpes Fabricius, 1798 )

Hexapus (Hexapus) sexpes View in CoL – Sakai, 1976: 554 (part), pl. 196, fig. 1. (not Cancer sexpes Fabricius, 1798 )

Hexapinus latipes View in CoL – Manning & Holthuis, 1981: 170; Yamaguchi & Baba, 1993: 434, fig. 154; Ng et al., 2008: 86.

Material examined. Lectotype: female (10.0 × 6.7 mm) ( RMNH 31783 About RMNH d), Japan. Others: Japan: 1 female (10.2 × 7.6 mm) (NSMT-Cr 5694), Kushimoto, Kii Peninsula, Wakayama Prefecture, 33 ° 27.2'N 135 ° 45.4'E – 33 ° 27.2'N 135 ° 45.6'E, 19–27 m, dredge, coll. M. Takeda, 17 July 1978; 1 female (30.4 × 17.9 mm) ( KPM NH 7123 ), Enoshima Island , T. Sakai Collection; 1 female (28.7 × 16.7 mm) ( KPM NH 7460 ) Minabe, Wakayama, T. Sakai Collection; 1 female (30.4 × 17.5 mm) ( KPM NH 6331 ), Mikawa-Ishiki, Aichi Prefecture, T. Sakai Collection. GoogleMaps

Diagnosis. Carapace subquadrate, about 1.2–1.3 times as broad as long, dorsal surface pitted, region indistinct. Anterolateral margin arcuate, posterolateral margin sinuous with 1 protuberance; posterolateral corner with angled prominence over base of posterior pereopods; lateral margin of carapace wall produced medially. Orbit distinct, transverse; eye small, slightly movable. Pterygostomial region with row of oblique striae. Third maxillipeds broad; ischium of third maxillipeds longer than merus, strongly expanded distally, with rounded mesial margin, merus broader than long; exopod relatively broad, flagellum well developed. Chelipeds stout, unequal; major chela with very slightly gaping fingers when closed, large tooth at cutting edge of dactylus; minor chela with same ornamentation as major chela, fingers not gaping when closed. P2–P4 short, stout; P3 longest. Female thoracic sternum relatively broad; thoracic sternal groove very short, extends obliquely from sternoabdominal cavity; sternoabdominal cavity reaches distal part of sternite 4.

Description. Carapace subquadrate, about 1.3 times as broad as long, dorsal surface pitted, region indistinct, median H-shaped depression shallow; some granules present on dorsolateral margins, only scattered granules on posterior margin ( Figs. 10A View Fig , 11A View Fig , 12A View Fig , 13A View Fig ). Anterolateral margin arcuate, posterolateral margin sinuous with 1 protuberance; posterolateral corner with angled prominence over base of posterior pereopods; lateral margin of carapace wall produced medially. Front deflexed, obscurely divided into 2 lobes, not projecting beyond lower edge of orbits ( Fig. 10C View Fig ). Orbit distinct, transverse; eye small, slightly movable, cornea small, as wide as peduncle ( Figs. 10C View Fig , 12C View Fig ). Pterygostomial region with row of oblique, broken or entire, striae, oblique row of setae under row of striae adjacent of Milne Edwards’ opening. Third maxillipeds ( Fig. 13C–E View Fig ) broad; ischium of third maxillipeds 1.2 times as broad as long, longer than merus, strongly expanded distally, with rounded mesial margin, merus broader than long, carpus, propodus and dactylus cylindrical; dactylus longer than propodus, combined length of dactylus, propodus and carpus shorter than that of merus and ischium; exopod relatively broad, about 0.5 times width of ischium, flagellum well developed.

Chelipeds stout, unequal ( Fig. 11C View Fig ). Major chela with very slightly gaping fingers when closed, large tooth at cutting edge of dactylus; dactylus with scattered tubercles on upper outer surface proximally, tufts of setae on upper margin proximally; inner surface near upper margin with longitudinal ridge; palm slightly wider than long, surface covered with tubercles; lower margin with long and dense setae medially, fixed finger smooth; carpus without setae on upper outer surface, setose on upper inner surface, inner angle blunt, unarmed, outer face covered by tubercles; merus short, upper outer surface covered with tubercles, fringe of setae dorsomesially. Minor chela with same ornamentation as major chela, fingers not gaping when closed.

P2–P4 ( Figs. 10A View Fig , 11A View Fig ) short, stout; P3 longest. P2 most slender, dactylus upcurved, fringe of setae on upper and lower margins, slightly longer than propodus, outer surface of propodus with tubercles obscured by tufts of short setae, lower margin with long setae, strong spines distally, carpus longer than propodus, outer surface with tubercles on upper half covered by short setae, short setae on lower margin, merus almost twice length of carpus, outer surface with tubercles and short setae, upper and lower margins with tufts of dense short setae. P3 stouter, longer than P2; P4 stouter than P3. Ornamentation of P3 and P4 similar to P2 but with longer, denser setation; merus of P4 about 2 times as long as broad.

Female thoracic sternum relatively broad ( Figs. 10B View Fig , 11B View Fig , 12B View Fig ), sternites 1 and 2 fused, separated from sternite 3 by distinct ridge; sternite 3 separated from sternite 4 by ridge laterally, thoracic sternal groove very short, extends obliquely from sternoabdominal cavity ( Fig. 13B View Fig ); sternites 4–7 well developed, separated by distinct sutures; sternite 8 exposed, triangular, half length of female abdominal somite 1, sternoabdominal cavity reaches distal part of sternite 4. Juvenile female abdomen relatively narrow ( Figs. 10B View Fig , 13G View Fig ); somites 1 and 2 free; somites 3–5 separated by shallow grooves, lateral margin sinuous; somite 6 slightly shorter than somites 3–5, lateral margin sinuous; adult female abdomen relatively broad ( Figs. 12B View Fig , 13F View Fig ) with 6 somites free and rounded telson.

G1 not known.

Colour. Not known.

Remarks. The lectotype of H. latipes is a small dried specimen (10.0 × 6.7 mm, RMNH 31783d) and not in very good condition ( Fig. 10 View Fig ). It has been listed as a male by Manning & Holthuis (1981: 170), and in every respect, it does look like a male. The abdomen is relatively narrow and triangular (De Haan, 1835: pl. 11, fig. 5; Figs. 10B View Fig ), and somites 3–5 even appear to be fused. However, a close examination of the abdomen shows that the sutures between somites 3–5 are still discernible albeit rather shallow. The short and stout abdomen, while superficially resembling the male abdomens of Hexapus and Mariaplax , new genus, differ in that in these genera, male abdominal somites 3–5 are completely fused without any trace of sutures (e.g., Figs. 5F View Fig , 25F View Fig ). Another specimen from Japan examined which is about the same size (10.2 × 7.6 mm, NSMT-Cr 5694) ( Fig. 11A View Fig ) also resembles the holotype and has the same abdominal structure ( Fig. 13G View Fig ). However, when the abdomen is detached, it is clear that it is actually a juvenile female, with the pleopods already evident. Like the holotype specimen, the abdominal somites 3–5 also have shallow but distinct sutures ( Fig. 13G View Fig ). We are therefore certain that the holotype specimen of Hexapinus latipes , which is smaller than the NSMT juvenile female, is also a female. We have observed the same situation in Hexapinus simplex , new species, in which both male and female specimens are known. Juvenile females of this species possess abdomens that resemble those of males except they are relatively shorter and stouter, and the sutures between abdominal somites 3–5 are still visible ( Fig. 21D View Fig ). True males of Hexapinus simplex , even when juvenile (5.4 × 3.4 mm, ZRC 2013.1689), have elongate abdomens, with somites 3–5 completely fused ( Fig. 21E, F View Fig ). We believe when males of Hexapinus latipes are found, the male abdomens will also be more elongate and slender. Odawara (1965) briefly describes and illustrates a male (28.0 × 17.0 mm) and a female (33.0 × 19.5 mm) of what he identifies as “ Hexapus sexpes ” ( Odawara, 1965: 48, text fig. a–d) from Japan. His figures leave little doubt in our mind that his species is what we now call Hexapinus latipes . Odawara’s (1965: 48 fig. d) of the male ventral surface shows a male abdomen that appears to be relatively elongate, especially somite 6, and agrees in general with what is here defined for the genus. Unfortunately, we have not been able to locate these specimens; they are not in NSMT or KPM.

The above observations are also supported by the fact that H. latipes is a large species, at least for the Hexapodidae . We have adult females measuring 30.4 mm in carapace width (KPM NH 7123), and possess all the non-sexual characters of smaller specimens. We are confident they are conspecific. Manning & Holthuis (1981: 170) suggested that because of the substantial size differences observed between the reported specimens of “ Hexapus latipes ” from Japan, it seemed there are possibly two species present there. We now know that the small ones are merely juvenile females. However, these authors are not incorrect that there is more than one species of “ Hexapus latipes ” in Japan; two other species, Hexapinus simplex , new species, and Mariaplax chenae , new species, both of which have been confused with “ Hexapus latipes ” at one time or another (see discussion for these species), occur in the islands.

The figure of the third maxilliped of the type of Hexapinus latipes in the original publication (De Haan, 1835: pl. D) (present Fig. 13C View Fig ) is problematic. The figure of the entire buccal cavity with the intact third maxillipeds shows a third maxilliped that closely resembles that of our present specimens ( Fig. 13E View Fig ). However, De Haan’s figure of the right third maxilliped (De Haan, 1835: pl. D) does not look like that of the other Hexapinus species , with the merus and ischium too quadrate in shape, and the exopod too slender. In fact, it closely resembles the third maxilliped of Mariaplax species. In the RMNH is a box containing several mouthparts glued onto a card labelled as “ Hexapus latipes ” which were almost certainly extracted from the type specimen ( Fig. 10D View Fig ; see also Yamaguchi & Baba, 1993: 434). Yamaguchi & Baba (1993: fig. 154b) depicted the card but it is too small to see details; it is figured here again ( Fig. 13C View Fig ). The third maxilliped on the card is the left one ( Fig. 10D View Fig ) and is almost identical to those observed in our present material, with the merus less quadrate and the ischium clearly wider than long with the mesial margin prominently convex ( Fig. 13C View Fig ). Where the right third maxilliped has gone is not known. The specimen itself no longer has any mouthparts, with both third maxillipeds removed ( Fig. 10B View Fig ). It would therefore appear that De Haan’s original figure of the third maxilliped is simply inaccurate. It is also possible that De Haan had more than one specimen of what he called “ Hexapus latipes ”, and the right third maxilliped he figured was actually from a similar-sized Mariaplax specimen (perhaps M. chenae , which is known from Japan), but the specimen is just no longer around. Whatever be the case, there is only one extant specimen left in RMNH and it is the lectotype of the species, and we are now certain this is what Manning & Holthuis (1981) as well as ourselves are now recognising as Hexapinus latipes (De Haan, 1835) s. str.

The form of the third maxilliped is relatively constant. One slight variation observed is that the exopod of a young female (10.2 × 7.6 mm, NSMT-Cr 5694) is relatively narrower, being only slightly more than 0.4 times the width of the ischium. In other specimens, the exopod is wider, at 0.5 times the width of the ischium ( Fig. 13C, D View Fig ).

Type locality. Japan .

Distribution. Kii Peninsula, Enoshima Island, Aichi Prefecture, Japan. Subtidal, 27 m.