RAFFLES BULLETIN OF ZOOLOGY 2016
Taxonomy & Systematics
RAFFLES BULLETIN OF ZOOLOGY 64: 229–241

Date of publication: 12 August 2016
http://zoobank.org/urn:lsid:zoobank.org:pub:6314F826-732A-427C-9049-D8489D2F7C5A

Orthotheres baoyu, a new species of pea crab (Crustacea: Brachyura:
Pinnotheridae) associated with abalones from Tungsha Island, Taiwan;
with notes on the genus
Peter K. L. Ng1* & Ping-Ho Ho2
Abstract. The pinnotherid genus Orthotheres Sakai, 1969, is re-diagnosed on the basis of the type species, O.
turboe Sakai, 1969, and two allied species, O. haliotidis Geiger & Martin, 1999, and a new species, O. baoyu, fromthe South China Sea. The genus is characterised by its transversely ovate female carapace with the front visible
from dorsal view, a long third maxilliped ischiomerus which is completely fused, the third maxilliped propodus
is elongate and extends beyond the articulation with the dactylus, which is inserted subterminally on it, shortambulatory legs, which have a distinctly hooked dactylus, and the dactylus of the second and third legs in which
the ventral surface is prominently excavated. The generic affinities of the other species now referred to Orthotheres
are also discussed at length. The new species is described, figured and compare with congeners.
Key words. Crustacea, Brachyura, Pinnotheridae, Orthotheres, taxonomy, revision, new species, South China Sea

INTRODUCTION

the diagnostic characters of the genus. The genus is also
reviewed.

Orthotheres Sakai, 1969, is a genus of relatively large
pinnotherid crabs normally associated with gastropods (seeSchmitt et al., 1973; Geiger & Martin, 1999; for reviews),
currently containing eight species globally (Ng et al., 2008).
However, its composition has been debated by several
authors, and the genus is almost certainly heterogeneous(Campos, 1989; Ahyong & Ng, 2007). Part of the problem
has been knowledge of its type species, O. turboe Sakai, 1969
(from Japan), which was only briefly described and figured.
The primary characters that define members of this genus(in addition to its host) are the subovate carpus of the third
maxilliped, and the subcylindrical propodus which is elongate
and its dorso-distal margin extends beyond the articulation
with the dactylus which is inserted subterminally on it.

The terminology used follows Manning (1993) and Ahyong& Ng (2007). The following abbreviations are used: MXP3
= third maxilliped; G1 = male first gonopod; G2 = malesecond gonopod; P2–P5 = pereiopods 2–5 (ambulatory
legs 1–4), respectively. Specimens examined are depositedin the U.S. National Museum of Natural History (USNM),
Smithsonian Institution, Washington D.C.; and Queensland
Museum (QM), Brisbane; National Taiwan Ocean University(NTOU), Keelung.
TAXONOMYFamily Pinnotheridae De Haan, 1833
Genus Orthotheres Sakai, 1969

The authors recently obtained a species clearly referable
to Orthotheres from a large abalone in the South China
Sea. While it is superficially similar to O. haliotidis Geiger& Martin, 1999, from Australia, it differs in a number ofcarapace, third maxilliped, cheliped and ambulatory leg
characters. This new species, here named O. baoyu n. sp.,is described and figured. Opportunity was taken to reexamine and re-describe the types of O. turboe and clarify

Orthotheres Sakai, 1969: 275.
Type species. Orthotheres turboe Sakai, 1969, by original
designation.
Diagnosis. Female carapace transversely ovate, distinctly
wider than long, frontal margin slightly extending beyond
orbits, just visible from dorsal view; male carapace rounded,slightly wider than long, with distinct front; MXP3 positioned
obliquely in buccal cavity, ischium and merus completely
fused, elongate, carpus of palp subovate, articulating onsubventral margin, propodus elongate, subcylindrical, dorsodistal margin extends beyond articulation with dactylus,
dactylus inserted subterminally on propodus; P2–P5 short,bilaterally symmetrical, P5 shortest, dactylus short, distinctly

1
Lee Kong Chian Natural History Museum, National University of Singapore, 2Conservatory Drive, Singapore 117377, Republic of Singapore; Email: nhmngkl@
nus.edu.sg (*corresponding author)

Department of Environmental Biology and Fisheries Science, National Taiwan Ocean
University, 2 Pei-Ning Rd., Keelung 202, Taiwan, R.O.C.

2© National University of Singapore
ISSN 2345-7600 (electronic) | ISSN 0217-2445 (print)229

Ng & Ho: a new species of Orthotheres from Taiwan
A second group contains the American species: O. barbatus,
O. serrei, O. strombi and O. unguifalcula, all of which havefemale carapaces that are also distinctly wider than long andthe front strongly deflexed such that it is not visible fromdorsal view (cf. Rathbun, 1918: pl. 19 figs. 1–4, 9, 11, pl. 20
figs. 1, 2; Campos, 1989: fig. 2). The mesial margin of the
MXP3 ischiomerus of these species is also deeply concave,and the MXP3 propodus is clearly short and subovate or
subconical rather than elongate, with the dactylus inserted
terminally (cf. Rathbun, 1905: unnumbered second figure;
Rathbun, 1909: 69, unnumbered figure; Rathbun, 1918: figs.
41, 44a, 45; Campos, 1989: figs. 1b, 3a). The MXP3 palp of
O. unguifalcula figured by Glassell (1936: pl. 21 fig. 2) isinaccurate and it actually has three rather than two articles(see Campos, 1989: fig. 3a). The MXP3 ischiomerus of O.
barbatus figured by Rathbun (1918: fig. 44a) is rather short
but appears to be damaged. The ambulatory dactyli of all
four species are also gently curved and not strongly hooked(cf. Rathbun, 1918: pl. 19 figs. 1–4, 8–11, pl. 20 figs. 1, 2;
Campos, 1989: fig. 2).

hooked, P3 and P4 dactylus with ventral surface prominently
excavated; male abdomen with 6 free somites and telson.
Remarks. Ng et al. (2008: 250) recognised eight species
in Orthotheres Sakai, 1969 (see also Ahyong & Ng, 2007).
Five of these species occur in the western Pacific: O.
glaber (Bürger, 1895) (= Pinnotheres impressus Bürger,1895) [Philippines]; O. haliotidis Geiger & Martin, 1999
[Australia]; O. laevis (Bürger, 1895) [Philippines]; O.
longipes (Bürger, 1895)[Philippines]; and O. turboe Sakai,
1969 [Japan and Palau]; with four others in the Americas:
O. barbatus (Desbonne, in Desbonne & Schramm, 1867)[West Indies]; O. serrei (Rathbun, 1909) [Puerto Rico];O. strombi (Rathbun, 1905) [Florida]; and O. unguifalcula(Glassell, 1936) [Mexico]. Campos (1989), however, hadearlier removed O. laevis and O. longipes from the genus
and referred them back to Pinnotheres, commenting that “…
unlike Orthotheres, the female’s carapace of these species
are not appreciably broader than long, and the dactylus of
the walking legs are not uniformly very short and sharply
hooked.” (Campos, 1989: 1125). He also suggested that
Pinnotheres glaber (Bürger, 1895) and Pinnotheres impressus
Bürger, 1895, were close to O. laevis and O. longipes. Ahyong& Ng (2007) argued that because of the unusual structure of
the MXP3 palp, it seemed best to retain Pinnotheres laevis
and Pinnotheres longipes, as well as Pinnotheres glaber(which they regarded as a senior synonym of Pinnotheres
impressus) in Orthotheres for the time being. Campos (1989)
is certainly correct in his assertion that Orthotheres is notmonophyletic.

There is a third group for the remaining West Pacific species.
As re-described and figured by Ahyong & Ng (2007: fig.
24), O. glaber (= O. impressus) differs markedly from other
Orthotheres in having a rounded carapace, the female frontal
margin is visible from dorsal view, and the ambulatory legs
(notably the dactyli) are asymmetrical, and while curved,
are not prominently hooked. The carapace shape and P2–P5
characters are more typical of species of Arcotheres Manning,
1993, but the form of the palp is clearly different. Orthotheres
laevis and O. longipes also share the same set of characters
as O. glaber; and all three species probably belong to theirown group (cf. Bürger, 1895: pl. 9 figs. 23–25, 31; pl. 10
figs. 21–24; Ahyong & Ng, 2007: fig. 3E, F). The MXP3
dactylus is inserted subterminally in O. glaber (Ahyong &Ng, 2007: fig. 24C, F); but appear to be more terminal in
position for O. laevis and O. longipes (cf. Bürger, 1895:
pl. 10 figs. 22, 24).

Orthotheres turboe (type species of the genus), O. haliotidis
and O. baoyu n. sp. form a tight group that should berecognised as Orthotheres s. str. Members of this genus arecharacterised by possessing a carapace which is transversely
ovate and much wider than long, the females have a distinct
front that is not prominently deflexed and is still visible
from dorsal view; the MXP3 ischiomerus is subrectangular
to subovate with the mesial margin gently concave; the
MXP3 has a subcylindrical and elongate propodus withits dorso-distal margin extending beyond the articulation
with the dactylus which is inserted subterminally on it; theambulatory dactylus is strongly curved (almost at right angles)
and prominently hook-like (Figs. 3A, B, D–H, J–M; 6A–K;
9); and the dactylus of P3 and P4 is relatively shorter andbroader, with the ventral surface prominently concave (Figs.
3E, G; 6J; 9E). The concave ventral surfaces of the P3 andP4 dactyli are more pronounced in female specimens. The
dactylus on the other legs is flattened laterally, but there
is not prominent concavity on the ventral surface. In O.
haliotidis and O. baoyu n. sp., the MXP3 dactylus insertion
on the cylindrical propodus is clearly subterminal (Figs.
2B, C, G; 5B–E; 8D–F). The condition in O. turboe is thesame (Sakai, 1969: fig. 19a) although his figure is not very
precise. The problem is that in these species, the carpus of
the palp is not inserted at the margin of the ischiomerus but
actually submarginally on the inner surface (Sakai, 1969:
fig. 19a). As such, it is not easy to draw the palp accurately
with the surfaces flat.

While Orthotheres s. str. can be defined relatively easily;
the other two groups of species previously referred to thisgenus will need to referred to new genera in the future.
Specimens of these species are now being examined, andnew genera will need to be established for them once thisstudy is complete.
Orthotheres turboe Sakai, 1969
(Figs. 1–3)
Orthotheres turboe Sakai, 1969: 275, pl. 2 figs. 1, 2; text fig. 19a;
Sakai, 1976: 574, text figs. 314a–c; Miyake, 1983: 242 (list);
Miyake, 1998: 242 (list); Ng et al., 2008: 250 (list).

Material examined. Holotype: ovigerous female (12.7 ×9.1mm) (USNM 125889), in stomach of Turbo argyrotomus
Linnaeus, 1758 (Turbinidae), Yoron Island, Amami Islands,
Ryukyu Islands, Japan, coll. K. Sakai & H. Yamada, late1960s. Paratype: 1 male (4.8 × 4.5 mm) (USNM 126231),
same data as holotype.

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Fig. 1. Orthotheres turboe Sakai, 1969. A, paratype male (4.8 × 4.5 mm) (USNM 126231), Ryukyus, Japan; B, C, holotype ovigerous
female (12.7 × 9.1 mm) (USNM 125889), Ryukyus, Japan. A, B, overall habitus; C, frontal view of cephalothorax.

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Ng & Ho: a new species of Orthotheres from Taiwan

Fig. 2. Orthotheres turboe Sakai, 1969. A–E, holotype ovigerous female (12.7 × 9.1mm) (USNM 125889), Ryukyus, Japan; F–L, paratypemale (4.8 × 4.5 mm) (USNM 126231), Ryukyus, Japan. A, F, dorsal view of carapace; B, left MXP3; C, G, lateral view of MXP3 dactylus
and propodus (lateral view, setae not drawn) [dotted line at base of ischiomerus shows breakage line]; D, female abdominal somite 6 andtelson; E, female thoracic sternites 1 and 2; H, male abdomen; I, left G1 (ventral view); J, left G1 (dorsal view); K, distal part of left G1(ventral view); L, left G2. Scale bars = 2.0 mm [A, D]; 1.0 mm [B, E, F]; 0.5 mm [C, G–J, L]; 0.1 mm [K].

Diagnosis. Female: Carapace transversely ovate, wider thanlong, width to length ratio 1.39; dorsal surface smooth,glabrous, distinctly convex; front projecting slightly
anteriorly beyond orbits, entire, margin distinctly sinuouswith prominent median concavity (Figs. 1B; 2A). Eyes small,just visible in dorsal view; mobile, completely filling orbit(Fig. 2A). MXP3 outer surface with scattered short setae;
dactylus elongate, inserted distinctly before base of propodus;
propodus about 2 times length of dactylus, cylindrical, as
long as subovate carpus; carpus inserted on inner surface
of ischiomerus, just below distal margin; ischiomerus long,articles completely fused, anteromesial angle of merus
angular to weakly angularfrom lateral view; exopod relatively
stout, ca. 1/2 length of ischiomerus, flagellum 2–segmented(Fig. 2B, C). Anterior thoracic sternum wide sternites 1, 2
completely fused (Fig. 2E). Chela long; mesioventral margin
distinctly setose; outer surfaces of palm, fingers (except for
distal and marginal parts) almost smooth; ventral parts of
inner surface with numerous setae which do not obscuresurface; fingers ca. half length of palm; dactylus occlusal
margin with large subproximal tooth, with 3 or 4 denticles
behind it; pollex occlusal margin with 1 subproximal tooth,with 2 or 3 denticles behind it (Fig. 3C). Ambulatory legs
short, left and right sides symmetrical; P2–P4 merus relatively
long; P5 propodus elongate; no natatory setae present;
relative lengths of meri P2<P3=P4>P5; dactylus short withprominently hooked tip, ventral margin lined with short setae;
P3 and P4 dactylus relatively shorter, broader, dorsal margin232

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Fig. 3. Orthotheres turboe Sakai, 1969. A–H, holotype ovigerous female (12.7 × 9.1mm) (USNM 125889), Ryukyus, Japan; I–M, paratypemale (4.8 × 4.5 mm) (USNM 126231), Ryukyus, Japan. A, right P4; B, right P5; C, outer view of right female chela; D, left P3; E, ventral
view showing concave surface of left P3 dactylus; F, left P4; G, ventral view showing concave surface of left P4 dactylus; H, left P5; I,
outer view of right male chela; J–M, right P2–P5, respectively. Scale bars = 1.0 mm [A–H]; 0.5 mm [I–M].

carinate, ventral surface forming gently but prominently
concave surface (Fig. 3A, B, D–H). Abdomen wide, extending
to buccal region, covering bases of ambulatory legs; telson
deeply recessed into distal margin of somite 6 with gently
sinuous distal margin (Fig. 2D).

sternum relatively wide sternites 1, 2 fused, with shallow
concave suture (towards buccal cavity) separating fromsternite 3; sternites 3, 4 fused, with very shallow groove
separating them; sternoabdominal cavity reaching to justbefore suture between sternites 3/4. Chela relatively stout,
shorter than in female; occlusal margin of fingers with distinct
subproximal tooth and 3 or 4 denticles behind it (Fig. 2I).
Ambulatory legs short, left and right sides symmetrical; P5
propodus short; no natatory setae present; relative lengths ofmeri P2=P3=P4>P5; dactylus short with prominently hooked
tip, ventral margin lined with short setae; P3 and P4 dactylus

Male: Carapace circular, slightly wider than long, width tolength ratio 1.07; dorsal surface smooth, gently convex; front
distinctly projecting anteriorly, margin prominently sinuous(Figs. 1A, 2F). Eyes distinctly visible in dorsal view (Figs.
1A; 2F). MXP3 as in female (Fig. 2G). Anterior thoracic233

Ng & Ho: a new species of Orthotheres from Taiwan
ischiomerus, flagellum 2–segmented (Fig. 5B, D). Anterior
thoracic sternum wide sternites 1, 2 completely fused. Chelalong; mesioventral margin distinctly setose; outer surfaces ofpalm, fingers (except for distal and marginal parts) almost
smooth; ventral parts of inner surface with numerous setae
which do not obscure surface; fingers ca. half length of palm;
dactylus occlusal margin with large triangular subproximal
tooth, with 4 or 5 denticles behind it; pollex occlusal margin
with 1 subproximal tooth, with 3 or 4 denticles behindit (Fig. 6M). Ambulatory legs short, left and right sides
symmetrical; P2–P4 merus relatively long; P5 propodus
elongate; no natatory setae present; relative lengths of meriP2<P3=P4>P5; dactylus short with prominently hooked tip,
ventral margin lined with short setae; P3 and P4 dactylus
relatively shorter, broader, dorsal margin carinate, ventral
surface gently but prominently concave surface (Fig. 6E–K).
Abdomen wide, extending to buccal region, covering basesof ambulatory legs; telson deeply recessed into distal marginof somite 6 with gently sinuous distal margin (Fig. 5G, H).

with ventral surface gently concave (Fig. 3J–M). Abdomen
relatively wider; telson semicircular (Fig. 2H). G1 relatively
stout, distal third gently curved outwards, tip with distinct
dorsal opening (Fig. 2I–K). G2 short, with subspatuliform
tip; exopod stout, almost as long as endopod (Fig. 2L).
Remarks. Sakai (1969: 277) stated that a female (presumably
the holotype) was 13.0 by 8.5 mm while a male specimen
was 5.1 by 5.0 mm. The present holotype female measures
12.7 × 9.1 mm and the paratype male is 4.8 × 4.5 mm. The
holotype female and paratype specimens examined agree withthose he figured (Sakai, 1969: pl. 2 figs. 1, 2). The MXP3of the species, as figured by Sakai (1969) is misleading. It
was clearly drawn in situ from the inner surface, with thestructure still attached to the specimen and probably also
at an angle, making it appear longer; and the propodus anddactylus very short (Sakai, 1969: fig. 19a). The MXP3 isactually less elongate, and the propodus and dactylus much
longer (Fig. 2B).
For comparisons with O. haliotidis and O. baoyu n. sp., seeremarks for the latter species.

Male: Carapace circular, slightly wider than long, width tolength ratio 1.10; dorsal surface smooth, gently convex; front
distinctly projecting anteriorly, margin gently sinuous (Fig.
4A). Eyes distinctly visible in dorsal view (Fig. 4A). MXP3 asin female. Anterior thoracic sternum relatively wide sternites
1, 2 fused, with shallow concave suture (towards buccal
cavity) separating from sternite 3; sternites 3, 4 fused, withvery shallow groove separating them; sternopleonal cavity
reaching to just before suture between sternites 3/4. Chelarelatively stout, shorter than in female; occlusal margin of
fingers with subproximal tooth (larger in dactylus) and 4 or
5 denticles behind it (Fig. 6L). Ambulatory legs short, left
and right sides symmetrical; P5 propodus long; no natatory
setae present; relative lengths of meri P2=P3=P4>P5; dactylus
short with prominently hooked tip, ventral margin lined withshort setae; P3 and P4 dactylus with ventral surface gently
concave (Fig. 6A–D). Abdomen relatively narrower; telson
semicircular (Fig. 5F). G1 relatively stout, distal third gently
distinctly bent outwards, tip without distinct large opening(Fig. 5I–L). G2 short, with rounded tip; exopod stout, shorter
than endopod (Fig. 3M).

Orthotheres haliotidis Geiger & Martin, 1999
(Figs. 4–6)
Pinnixa faba – Haswell, 1882: 113; Grant & McCulloch, 1906:
6, 23; Schmitt et al., 1973: 108 (list); Davie, 2002: 431 (list).
[not Pinnixa faba (Dana, 1851)].
Orthotheres haliotidis Geiger & Martin, 1999: 273, figs. 1–7; Ng
et al., 2008: 250 (list); Ahyong & Brown, 2003: 10.

Material examined. 2 ovigerous females (12.7 × 8.8 mm,
12.3 × 7.9 mm) (AM P3155), in Haliotis asinina, Masthead
Island, 23°32’S 151°44’E, Queensland, Australia, coll. A.R.
McCulloch & E. Le G. Troughton, no date; 1 ovigerous
female (14.0 × 9.9 mm) (AM P64672), North West Island,
Capricorn Group, 23°18’S 151°42’E, Queensland, Australia,
coll. M. Ward, December 1929; 1 ovigerous female (10.0 ×
7.0 mm) (AM P72222), Heron Island, 23°26’S 151°55’E,
Queensland, Australia, coll. J. Bishop, no date; 1 male
(7.4 × 6.7 mm), 1 ovigerous female (11.4 × 7.9 mm) (AMP72223), in branchial cavity of Haliotis asinina, Heron Island,
23°26’S 151°55’E, Queensland, Australia, coll. M.L. Kok,
8 April 1963; 1 male (6.3 × 6.1 mm), 1 ovigerous female(13.7 × 9.3 mm) (QM), almost certainly from Queensland,no other data.

Remarks. The present specimens agree well with thedescription and figures of Geiger & Martin (1999) whose
specimens were from Queensland and Western Australia(see also Ahyong & Brown, 2003). The MXP3 ischiomerus
depicted by Geiger & Martin (1999) appears to be dimorphic
although the authors did not discuss it. The inner distolateral
margin of the ischiomerus of the male paratype was shownas almost straight and sloping, with the edge angular (Geiger& Martin, 1999: figs. 3A, 4A, B) whereas that of the female
holotype was figured as evenly convex with the edge
rounded (Geiger & Martin, 1999: fig. 4C). The conditionof the male paratype agrees well with those observed forthe present series of specimens for both sexes, and there isno dimorphism observed. It is possible the female holotype
figured by Geiger & Martin (1999: fig. 4C) is anomalousin this character or the structure was figured at an angle.
Geiger & Martin (1999: fig. 3) shows a gently curved G1
with a relatively short distal part although Geiger & Martin

Diagnosis. Female: Carapace transversely ovate, wider thanlong, width to length ratio 1.41–1.55; dorsal surface smooth,glabrous, distinctly convex; front projecting slightly anteriorly
beyond orbits, entire, margin gently sinuous with shallow
median concavity (Fig. 4B; 5A). Eyes small, just visible indorsal view; mobile, completely filling orbit (Fig. 5A). MXP3
outer surface with numerous short setae; dactylus elongate,
inserted distinctly before base of propodus; propodus about
2 times length of dactylus, cylindrical, as long as subovate
carpus; carpus inserted on inner surface of ischiomerus, justbelow distal margin; ischiomerus long, articles completely
fused, anteromesial angle of merus distinctly angular fromlateral view; exopod relatively stout, ca. 2/3 length of234

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Fig. 4. Orthotheres haliotidis Geiger & Martin, 1999. A, male (7.4 × 6.7 mm) (AM P72223); B, C, ovigerous female (12.7 × 8.8 mm)(AM P3155). A, B, overall habitus; C, frontal view of cephalothorax.

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Fig. 5. Orthotheres haliotidis Geiger & Martin, 1999. A–C, G, ovigerous female (12.7 × 8.8 mm) (AM P3155); D, E, H, ovigerous female(12.3 × 7.9 mm) (AM P3155); F, I–M, male (7.4 × 6.7 mm) (AM P72223). A, dorsal view of carapace; B, left MXP3 (setae not drawn);
C, left MXP3 palp (lateral view, setae not drawn); D, left MXP3 (setae not drawn); E, left MXP3 palp (lateral view, setae not drawn);
F, male abdomen; G, H, female abdominal somite 6 and telson; I, left G1 (ventral view); J, distal part of left G1 (ventral view, setae notdrawn); K, left G1 (dorsal view, setae not drawn); L, distal part of left G1 (dorsal view, setae not drawn); M, left G2 (ventral view). Scalebars = 1.0 mm [A, F, G, H], 0.2 mm [B–E, I–M].

Orthotheres baoyu n. sp.
(Figs. 7–9)

(1999: fig. 7) indicates a G1 more like the present one (Fig.
5I, K), with the distal part more elongated and curved atright angles. The median part of the G1 looks as if it has a
low indentation (cf. Geiger & Martin 1999: fig. 7B) but thisappears to be an artifact of the SEM process.

Material examined. Holotype: ovigerous female (12.7 ×
9.4 mm) (NTOU CP 20020627a), from 8.5 cm long abalone(Haliotis asinina Linnaeus, 1758; Haliotidae), Tungsha
islands, Taiwan, coll. M.-H. Chen, 27 June 2002. Paratype:
1 poorly preserved female (8.6 × 7.1 mm) (NTOUCP
20020627b), same data as holotype.

For comparisons with O. turboe and O. baoyu n. sp., seeremarks for the latter species.

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Fig. 6. Orthotheres haliotidis Geiger & Martin, 1999. A–D, ovigerous female (12.7 × 8.8 mm) (AM P3155), Queensland; L, male (6.3 ×
6.1 mm) (QM), Queensland; E–K, M, ovigerous female (13.7 × 9.3 mm) (QM), Queensland. A–D, right P2–P5, respectively; E–H, left
P2–P5, respectively; I, right P4; J, ventral view showing concave surface of right P4 dactylus; K, right P5; L, outer view of right malechela; M, outer view of left female chela. Scale bars = 1.0 mm.

Diagnosis. Female: Carapace transversely ovate, wider thanlong, width to length ratio 1.35; dorsal surface smooth,glabrous, gently convex; front projecting slightly anteriorly
beyond orbits, entire, margin gently sinuous with shallow
median concavity (Figs. 7A, B; 8A). Eyes small, just visible
in dorsal view; mobile, completely filling orbit (Figs. 7B;
8A). MXP3 outer surface with numerous short plumose
setae; dactylus elongate, inserted distinctly before baseof propodus; propodus about 2 times length of dactylus,
cylindrical, as long as subovate carpus; carpus inserted
on inner surface of ischiomerus, below distal margin;ischiomerus very long, articles completely fused, anteromesial
angle of merus rounded from lateral view, subangular fromsubmesial view; exopod relatively stout, ca. 1/2 length ofischiomerus, flagellum 2–segmented (Fig. 8D–F). Anterior
thoracic sternum wide sternites 1, 2 completely fused. Chelarelatively long; mesioventral margin distinctly setose; outersurfaces of palm, fingers (except for distal and marginal
parts) almost smooth; ventral parts of inner surface withnumerous setae which do not obscure surface; fingers ca.
half length of palm; dactylus occlusal margin with large
subproximal tooth, with no denticles behind it; pollex occlusal
margin with 1 subproximal tooth, with no denticles behindit (Fig. 8C). Ambulatory legs short, left and right sides
symmetrical; P2–P4 merus relatively long; P5 propodus
elongate; no natatory setae present; relative lengths of meri237

Ng & Ho: a new species of Orthotheres from Taiwan

Fig. 7. Orthotheres baoyu n. sp., holotype ovigerous female (12.7 × 9.4 mm) (NTOU CP 20020627). A, overall habitus; B, frontal viewof cephalothorax; C, ventral view of cephalothorax.

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Fig. 8. Orthotheres baoyu n. sp., holotype ovigerous female (12.7 × 9.4 mm) (NTOU CP 20020627). A, dorsal view of carapace; B, female
abdominal somite 6 and telson; C, outer view of right chela; D, left MXP3; E, left MXP3 (mesial view, setae not drawn); F, lateral viewof MXP3 dactylus and propodus. Scale bars = 2.0 mm [A, B]; 1.0 mm [C, E]; 0.5 mm [D, F].

with the median part gently concave (Figs. 4B; 5A; 8A). The
MXP3 are distinct for O. baoyu; it has the most prominently
elongated ischiomerus, with the anteromesial part rounded
when it is lying flat (Fig. 8D). In O. turboe and O. haliotidis,
the ischiomerus is relatively shorter (Figs. 2D, G; 5B, D)
with the anteromesial part somewhat weakly angular toangular in O. turboe (Fig. 2D, G) and distinctly angular inO. haliotidis (Fig. 5B, D; Geiger & Martin, 1999: figs. 3A,
4). In O. baoyu, only when the ischiomerus is tilted at a
30° angle does the anterointernal part appear angular (Fig.
8E), but is distinctly rounded when it is observed flat down
(Fig. 8D). The female chela of O. baoyu is distinct in that
it is proportionately the longest, and the occlusal margin
behind the large subproximal tooth on each finger is entire(Fig. 8C). In O. turboe and O. haliotidis, the female chelae
are distinctly shorter and the occlusal margin behind thelarge subproximal tooth on each finger is lined with several
denticles (Figs. 3C; 6M). The proportions of the ambulatory
legs differ. In O. turboe and O. baoyu, the merus of P2–P4
is proportionately longer (Figs. 3A, D, F; 9A–G) than in O.
haliotidis (Fig. 6F, G, I). For the P5, the propodus of O.
turboe and O. baoyu (Figs. 3B, H; 9H, I) is distinctly longer
than that of O. haliotidis (Fig. 6H, K). The female abdomen
is relatively widest in O. turboe (Fig. 2B) compared to thoseof O. haliotidis (Fig. 5G, H) and O. baoyu (Figs. 8C; 9B).

P2<P3=P4>P5; dactylus short with prominently hooked tip,
ventral margin lined with short setae; P3 and P4 dactylus
relatively shorter, broader, dorsal margin carinate, ventral
surface forming gently but prominently concave surface (Fig.
9). Abdomen wide, extending to buccal region, covering basesof ambulatory legs; telson deeply recessed into distal marginof somite 6 with distinctly sinuous distal margin (Fig. 8B).
Male: not known.
Etymology. The species name is derived from the Chinesename for abalone, “bao-yu”. The name is used as a noun
in apposition.
Remarks. The three species differ in various characters.
For well-preserved female specimens, the dorsal carapace
surface of O. haliotidis (Fig. 4C) and O. turboe (Fig. 1C)
is distinctly more convex compared to that of O. baoyu n.
sp. (Fig. 7B). Although the carapace width to length ratios
do not reflect it, the carapace of O. turboe appears to be thewidest because posterolateral parts are more prominently
expanded laterally (Figs. 1B; 2A); in O. haliotidis andO. baoyu, the posterolateral areas are only gently convex(Figs. 4B; 5A; 7A; 8A). The frontal margin of O. turboe isdiagnostic in that it is distinctly sinuous, with the medianpart prominently concave (Figs. 1B; 2A). In O. haliotidis
and O. baoyu, the frontal margin is only slightly sinuous239

Ng & Ho: a new species of Orthotheres from Taiwan

Fig. 9. Orthotheres baoyu n. sp., holotype ovigerous female (12.7 × 9.4 mm) (NTOU CP 20020627), ambulatory legs. A, left P2; B, rightP2; C, left P3; D, right P3; E, ventral view showing concave surface of right P3 dactylus; F, left P4; G, right P4; H, left P5; I, right P5.
Scale bars = 1.0 mm.

ACKNOWLEDGEMENTS

In males, the carapaces do not differ substantially. However,the frontal margin of the male O. turboe (Figs. 1A; 2F) is
like that of the female, being distinctly more sinuous thanthat of O. haliotidis (Fig. 4A). There are no major differencesin the structure of the MXP3 between the sexes of the two
species (O. turboe and O. haliotidis) in which males andfemales are known (e.g., Fig. 2B, G). The male chelae of O.
turboe and O. haliotidis are also very similar in shape andproportions (Figs. 3I; 6L). For the ambulatory legs, the P5
propodus of O. turboe (Fig. 3M) is proportionately shorter
than that of O. haliotidis (Fig. 6D). The male abdomens of
the two species also differ, with that of O. turboe (Fig. 2H)
being transversely broader than that of O. haliotidis (Fig.
5F). The G1s of O. turboe and O. haliotidis are very similar,
but the distal third of O. turboe (Fig. 2I, J) is more gently
curved than that of O. haliotidis, which is more distinctly
bent (Fig. 5I, K).

We are very grateful to the late Chen Ming-Hui for passing
us his specimens of Orthotheres bayou for our study. Thanks
are also due to Peter Davie (QM) and Shane Ahyong (AM)for allowing us to examine the specimens of O. haliotidis
in their holdings; and to Rafael Lemaitre and Karen Reed
(USNM) for arranging the loan of the types of O. turboe.
Comments by Ernesto Campos, Shane Ahyong and Jose C.
Mendoza helped refine the manuscript, and are very muchappreciated.
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