Ng: New pea crab from Placuna shells in Singapore
Taxonomy & Systematics
RAFFLES BULLETIN OF ZOOLOGY 66: 474–485

Date of publication: 23 August 2018
http://zoobank.org/urn:lsid:zoobank.org:pub:CA0B7FC1-AC46-4D45-8B7E-3397E1DBBDAA

Arcotheres placunicola, a new species of pea crab (Crustacea:
Brachyura: Pinnotheridae) from the window-pane shell, Placuna
ephippium Philipsson, 1788 (Placunidae) in Singapore
Peter K. L. Ng
Abstract. A new species of pea crab Arcotheres Manning, 1993 (Pinnotheridae), is described from the windowpane shell, Placuna ephippium (Philipsson, 1788) (Placunidae) in Singapore. The species had previously been
incorrectly identified as Arcotheres similis (Bürger, 1895) but with the redescription of the types by Ahyong &Ng (2007), this is now known to be a very different taxon. Arcotheres placunicola n. sp. is superficially similar
to A. palaensis (Bürger, 1895) and A. guinotae Campos, 2001, but can easily be distinguished by the structures of
the third maxilliped, as well as proportions of the chelae and ambulatory legs. The only other species known tolive exclusively in placunid shells, A. placunae (Hornell & Southwell, 1909) from India, is markedly different in
the form of the carapace and ambulatory leg structures.
Key words. Pinnotheroidea, symbiosis, Placunidae, taxonomy, new species, Southeast Asia

INTRODUCTION

found in the mytilid mussel Modiolus philippinarum (Hanley,
1843) instead (Ahyong & Ng, 2007; unpublished data). Its
relationship with A. palaensis Bürger, 1895, the type speciesof the genus, is now being revised as a complex of species,
all living in Arcidae and related taxa.

Three species of pinnotherid crabs are known to be associatedwith the Indo-West Pacific window-pane shells of thefamily Placunidae Rafinesque, 1815: Arcotheres palaensis(Bürger, 1895) (Bürger, 1895; Ahyong & Ng, 2007), A.
placunae (Hornell & Southwell, 1909) (Hornell & Southwell,1909; Trivedi et al., 2018b), and A. similis (Bürger, 1895)(Gordon, 1936) (see also Schmitt et al., 1973). Of these,
only A. placunae is known to be an obligate symbiont with
Placuna. Arcotheres palaensis and A. similis have also beenreported from a wide variety of bivalve hosts (Bürger, 1895;
Gordon, 1936; Chuang, 1961; Schmitt et al., 1973; Ahyong& Ng, 2007).

Over the last three years, the author has obtained a large seriesof specimens of Arcotheres from Placuna in Singapore. The
window-pane shell in Singapore is not Placuna placenta but
a similar species, P. ephippium (Philipsson, 1788), instead,and is now also regarded as the senior synonym of Placunasella (Gmelin, 1791) (Huber, 2010).
In this paper, the Arcotheres from Placuna ephippium in
Singapore is examined and confirmed to be an undescribed
species. It has not been found in any other bivalves as yet.
Arcotheres placunicola n. sp. is described, figured andcompared to its closest congener, A. placunae, from India.

Gordon (1936) was the first to record A. similis frominside Placuna placenta (Linnaeus, 1758) (as “Placenta
placenta”) from Singapore. In clarifying the identities ofthe extant material of Bürger (1895), Ahyong & Ng (2007:
207–208) selected a lectotype of A. similis (Bürger, 1895),
and commented that the material of Gordon (1936) identified
as this taxon almost certainly belonged to an undescribed
species instead. True A. similis has a different carapace
shape and frontal margin, proportionately shorter ambulatory
legs with a distinct structure of the dactylus and is almost
certainly a synonym of A. modiolicola Bürger, 1895, as
well as A. spinidactylus (Gordon, 1936), and are invariably

MATERIAL AND METHODSThe terminology used follows that by Manning (1993) and
Davie et al. (2015). The following abbreviations are used:
MXP3 = third maxilliped; P2–P5 = pereiopods 2–5 (first
to fourth ambulatory legs), respectively; Gl = male firstgonopod; G2 = male second gonopod. The measurements
provided (in millimetres) are of the maximum carapace
width and length, respectively.
Specimens examined are deposited in the Zoological
Reference Collection of the Lee Kong Chian Natural History
Museum, National University of Singapore (ZRC); andAustralian Museum, Sydney (AM).

Lee Kong Chian Natural History Museum, Faculty of Science, National University ofSingapore, 2 Conservatory Drive, Singapore 117377, Republic of Singapore; Email:peterng@nus.edu.sg© National University of Singapore
ISSN 2345-7600 (electronic) | ISSN 0217-2445 (print)

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TAXONOMY

Ng, 31 March 2017; 1 male (with Sacculina) (4.8 × 4.5 mm)(ZRC 2017.1016), off Changi beach, adjacent to National
Service Recreational Country Club, coll. H. H. Tan et al., 26
May 2017; 4 females, 1 juvenile female (ZRC 2017.1011),
1 male, 2 females (AM), off Changi beach, next to Carpark7, near ferry terminal, 1.374223°N 104.006827°E, coll. S.
K. Tan et al., 25 July 2017; 1 male (with rhizocephalan),
3 females (ZRC 2017.1261), intertidal area, off Changi
beach, next to Carpark 7, near ferry terminal, 1.374223°N
104.006827°E, coll. S. K. Tan et al., 26 June 2017; 1
female (ZRC 2017.1265), Telok Paku, beach, in “Placunasella”, coll. 8 April 1965. All specimens collected frominside Placuna ephippium (Philipsson, 1788) (Placunidae)
in shallow intertidal areas in Singapore.

Family Pinnotheridae De Haan, 1833
Arcotheres Manning, 1993
Type species. Pinnotheres palaensis Bürger, 1895,
subsequent designation by Manning, 1993.
Remarks. Arcotheres Manning, 1993, currently contains 27
species from the Indo-West Pacific, all of which are associatedwith bivalves (Ng et al., 2008, 2017; Trivedi et al., 2018a).
The identities of many of these species, however, remain
unclear, and the genus will need to be revised in the future(Ahyong & Ng, 2007; Ng et al., 2017).

Comparative material. Arcotheres placunae (Hornell &Southwell, 1909): Neotype female (11.0 × 8.1 mm) (ZRC
2017.1293), muddy shore, in Placuna placenta (Linnaeus,
1758) (Bivalvia: Ostreoida: Placunidae), Balapur Bay, Beyt
Dwarka, Gulf of Kachchh, Gujarat, India, 22°27′08″N
69°08′09″E, coll. J. Trivedi, 6 January 2015; 1 male (7.0 ×
5.8 mm) (ZRC 2017.1065), same data as neotype; 1 ovigerous
female (11.5 × 7.9 mm), 9 females (largest 13.0 × 9.7 mm,
smallest 9.2 × 6.9 mm) (ZRC 2017.1008), Korangi Creek,
Karachi, 24.784°N 67.103°E, Pakistan, in Placuna sp., coll.
4 November 1998–25 October 1999. Arcotheres tivelae(Gordon, 1936): 1 ovigerous female (ZRC 2006.0051),
Persian Gulf, Homozgan Province, Iram coll. H. H. Sahafi,
25 March 2004; 1 male (5.7 × 5.1 mm), 6 females (largest
9.1 × 8.0 mm), 1 ovigerous female (11.2 × 9.8 mm) (ZRC
2009.0831), from Amiantis umbonella, Bandar Abbas, Iran,
Persian Gulf, coll. H. Saeedi, January 2009; 2 males, 2
females (ZRC 2011.155), Oman Sea, Iran, coll. E. Kamrani,
2011; 1 female (ZRC 2016.0162), Qeshm Island, Iran, coll.
M. Safaie, May 2010.

Arcotheres placunicola n. sp.
(Figs. 1–6)
Pinnotheres similis – Tesch, 1918: 254 (list); Gordon, 1936:
172, fig. 3 (Singapore); Silas & Alagarswami, 1967: 1210
(list) (not Pinnotheres similis Bürger, 1895).
Material examined. Holotype: ovigerous female (11.2 × 8.6mm) (ZRC 2017.1009), off Changi beach, next to Carpark7, near ferry terminal, 1.374223°N 104.006827°E, coll. S.
K. Tan et al., 7 June 2016. Paratypes: 5 males (5.6 × 4.7mm, 4.7 × 4.1 mm, 4.0 × 3.7 mm, 3.9 × 3.6 mm, 3.6 × 3.4mm), 4 ovigerous females (10.4 × 8.3 mm, 8.7 × 7.5 mm,
7.5 × 6.1 mm, 7.0 × 5.5 mm), 1 female (8.8 × 6.9 mm),
3 females (with rhizocephalans) (8.6 × 6.3 mm, 8.6 × 7.1mm, 9.0 × 6.9 mm), 2 juvenile females (3.6 × 2.9 mm, 6.2
× 5.1 mm) (ZRC 2017.1010), same data as holotype; 14
males (largest 5.1 × 4.4 mm, smallest 2.4 × 2.3 mm), 2
males (with rhizocephalans) (5.7 × 4.7 mm, 5.5 × 5.0 mm),
16 ovigerous females (largest 10.3 × 8.7 mm, smallest 7.7
× 6.3 mm), 1 ovigerous female (10.1 × 8.0 mm), 10 nonovigerous females (largest 10.3 × 7.8 mm, smallest 5.4 ×
4.5 mm), 2 females (with rhizocephalan) (6.3 × 4.9 mm,
7.8 × 5.8 mm), 1 juvenile female (3.8 × 3.7 mm) (ZRC
2017.1012), off Changi beach, next to Carpark 7, near
ferry terminal, 1.374223°N 104.006827°E, coll. S. K. Tan
et al., 8 June 2016; 1 male (4.2 × 3.8 mm), 2 ovigerous
females (7.2 × 6.1 mm, 7.5 × 6.2 mm) (ZRC 2012.0432),
off Changi beach, next to Carpark 7, near ferry terminal,
1.374223°N 104.006827°E, coll. P. K. L. Ng et al., 5 July
2012; 4 ovigerous females (largest 9.1 × 7.4 mm, smallest
6.5 × 5.4 mm), 3 non-ovigerous females (largest 8.9 × 6.9mm, smallest 8.1 × 6.7 mm), 2 females (with rhizocephalan)(8.2 × 7.3 mm, 11.2 × 9.1 mm) (ZRC 2017.1013), off Changi
beach, next to Carpark 7, near ferry terminal, 1.374223°N
104.006827°E, coll. P. K. L. Ng & P. Y. C. Ng, June 2016;
2 males (2.2 × 2.2 mm, 2.4 × 2.4 mm) (ZRC 2017.1014),
Tanah Merah Ferry Terminal Beach, near Changi Point,coll. S. K. Tan et al., 17 November 2016; 1 male (withrhizocephalan) (5.6 × 5.1 mm), 3 ovigerous females (7.3 × 5.9mm, 8.0 × 6.1 mm, 9.5 × 7.2 mm), 1 non-ovigerous female(with rhizocephalan) (9.0 × 7.4 mm) (ZRC 2017.1015),
off Changi beach, next to Carpark 7, near ferry terminal,
1.374223°N 104.006827°E, coll. P. K. L. Ng & P. Y. C.

Diagnosis. Female: Carapace subcircular, distinctly wider
than long; dorsal and lateral surfaces smooth, glabrous; front
usually projecting anteriorly beyond orbits, entire, margin
slightly convex; anterior quarter of anterolateral margin gently
sloping posteriorly, forming angle with rest of convex margin,(Figs. 1A, 2A). Eyes small, not visible in dorsal view; mobile,completely filling orbit (Figs. 1A–C, 2A). MXP3 outer surface
with scattered short setae; ischiomerus completely fused,subrhomboidal, length about 2.5 times maximum width,
inner margin angular at widest point; carpus short; propodus
about 3 times as long as high, cylindrical, distinctly longer
than carpus; dactylus subspatuliform, inserted at medianpoint of propodus, tip not reaching propodal apex; exopod
relatively slender, about one-third length of ischiomerus,
flagellum 2-segmented (Fig. 3K, L). Chela slender, dactylus
about half palm length; palm slender, proximal part narrower
than distal part; outer surfaces of palm, fingers (except for
distal part) almost smooth, with only scattered short setae;
dactylus occlusal margin with large subproximal tooth; pollex
occlusal margin with 1 low proximal tooth, 1 submedian
tooth (Figs. 1D, 3J). Ambulatory legs dorsally, ventrally
unarmed; outer surface covered with scattered very shortsetae or glabrous; ventral margins of propodus and dactyus
more setose; relative lengths of meri P4>P3>P5>P2; left
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Fig. 1. Arcotheres placunicola n. sp., holotype ovigerous female (11.2 × 8.6 mm) (ZRC 2017.1009), Changi, Singapore. A, overall habitus;B, ventral view of cephalothorax; C, frontal view of cephalothorax; D, outer view of left chela.

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Fig. 2. Arcotheres placunicola n. sp. A, paratype ovigerous female (10.4 × 8.3 mm) (ZRC 2017.1010); B, paratype male (5.6 × 4.7 mm)(ZRC 2017.1010); C, paratype young male (2.4 × 2.4 mm) (ZRC 2017.1014); D, paratype male (4.7 × 4.1 mm) (ZRC 2017.1010). A–C,
overall habitus; D, male anterior thoracic sternum. All specimens from Changi, Singapore.

477

Ng: New pea crab from Placuna shells in Singapore(sometimes right) P4 distinctly longer than right side;P2 and P3 dactyli short, subequal; P4 dactylus elongate,
falciform; P5 dactylus longest, distal half covered with shortsetae, inner margin of distal part with 2 rows of up to 11
spinules each (Fig. 3A–D’, E–H”). Pleon extending to buccal
region, covering bases of walking legs; telson recessed into
distal margin of somite 6 (Fig. 1B). Male: Carapace almost
circular, slightly wider than long; dorsal surface covered with
scattered short setae or smooth; front distinctly projecting
anteriorly, margin gently sinuous (Fig. 2B, C). Eyes distinctly
visible in dorsal view (Fig. 2B, C). MXP3 as in female
but ischiomerus proportionately shorter (Fig. 4D). Anterior
thoracic sternum wide, sternites 1, 2 fused, partially sunken
into buccal cavity; suture between sternites 2 and 3 shallow;
sternites 3, 4 completely fused, separated only by shallow
grooves; sterno-pleonal cavity reaching to junction between
sternites 3 and 4 (Fig. 2D). Chela relatively stouter, shorter
than in female, tip of fingers longer (Fig. 4A). Ambulatory
legs dorsally, ventrally unarmed; outer surface covered withshort setae; carpus and propodus with long natatory setae; left
and right meri equal, relative lengths of meri P4>P3>P2>P5;
dactyli of P2–P4 progressively longer; left (sometimes right)
P4 dactylus slightly longer, more slender than right side; P4
and 5 dactyli subequal to that of P3, completely covered withshort setae (Fig. 4E–L’). Pleon slender, triangular, widest
at somite 3, lateral margins of somite 4 distinctly concave,
tapering distally to telson; telson semicircular with convex
lateral margins, as long as wide (Fig. 4B, C). G1 long, tip
gently curved upwards; margins lined with long setae (Fig.
4M, N, Q). G2 short, with flattened tip; exopod present ascurved structure (Fig. 4O, P).

proportionately shorter (Fig. 4Q versus Fig. 4M). Whilefemale ambulatory leg asymmetry is pronounced in speciesof Arcotheres, the condition for males is not well known.
The left and right male P2–P5 of A. placunicola are almost
symmetrical except for the P4 dactylus, which on one side, isslightly longer and more slender than the other (Fig. 4G, K).
Remarks. Arcotheres placunicola n. sp. is morphologicallyquite different from A. placunae (Hornell & Southwell,1909) from India and Pakistan (Hornell & Southwell, 1909;
Trivedi et al., 2018b), even though both species are livingin the same host genus. Arcotheres placunae is not wellknown and there have been suggestions that the originaldescription and figures are not accurate and that it may beconspecific with A. tivelae (Gordon, 1936) (see Naderloo& Türkay, 2012; Naderloo et al., 2015). There is no doubt,
however, that they are separate taxa (see Naderloo, 2017).
The original types of A. placunae are lost but Trivedi et al.
(2018b) redescribed and figured the species at length fromtopotypic material, selected a neotype and its taxonomy is
now clear. Most obvious is the fact that the adult female
carapace of A. placunae is dorso-ventrally flattened such thatthe dorsal surface is only gently convex, with the frontal
margin and anterior part of the anterolateral margin on thesame plane (Fig. 7A–C). Arcotheres placunicola, on the other
hand, has the dorsal carapace surface prominently convex,
the front is protruding more anteriorly with the anterior
part of the anterolateral margin gently sloping posteriorly(Figs. 1A, 2A). In addition, the male and female chelae ofA. placunicola are more slender, with the proximal partnarrower than the distal part (Figs. 1D, 3J, 4A) (versus
chelae stouter with the proximal and distal parts subequalin height in A. placunae; Trivedi et al., 2018b: fig. 8J); thefemale ambulatory meri are distinctly longer (Figs. 1A, 2A,
3A–H) (versus ambulatory meri proportionately shorter in
A. placunae; Figs. 7A–C, 8A–H; Trivedi et al., 2018b: fig.
4); the inner margin of the distal part of the P5 dactylus has
a shorter rows, each with only a maximum of 11 spinules(versus the same margin has a longer row with up to 20
spinules in A. placunae; Fig. 8D’, H’, H”; Trivedi et al.,2018b: fig. 4H’, L’); the male pleon is less triangular in shapewith the lateral margin of somite 4 more concave (Fig. 4B,C) (versus pleon clearly triangular in A. placunae; Trivedi
et al., 2018b: fig. 3B); and the tip of the G1 is upcurved(Fig. 4M, N, Q) (versus tip laterally directed in A. placunae;
Trivedi et al., 2018b: fig. 3D).

Colour. The colour is very variable. Females can be paleyellow to orange (Figs. 5D, 6C, D, G, H) or dirty white withbrown patterns (Figs. 5A, B, E, 6A, B, F); while males area more uniform brown to greenish-brown (Fig. 5A, C, F).
Variation. The good series of females and males of A.
placunicola allows a good understanding of variation in
the species. Female specimens are remarkably consistentin the diagnostic characters described here. The female
front is usually distinct, being produced anteriorly (e.g.,
Figs. 1A, 6A, C), although in a few specimens, it is lessdistinct, being almost level with the anterolateral margins(Figs. 2A, 6G). The series of males is especially importantas they are rarely collected for the genus. Smaller males ofA. placunicola (carapace width ca. 3 mm and less, e.g., ZRC
2017.1014) have a carapace which appears more quadrate,with the anterolateral margin more angular and the front
more produced (Fig. 2C), and the pleonal somite 6 andtelson are also relatively wider and almost subrectangularin shape (Fig. 4C). In males exceeding 4.5 mm in carapace
width (e.g., ZRC 2017.1010), the carapace is overall morerounded with the front less pronounced (Fig. 2B) and themale pleonal somite 6 and telson are more elongate with thetelson semicircular (Fig. 4B versus Fig. 4C). The natatory
setae on the ambulatory legs are also less pronounced in thesmaller males. The G1 structures, however, remain almost
identical, although the upcurved tip in smaller males is

In Southeast Asia, Arcotheres placunicola is also superficiallysimilar to A. palaensis (Bürger, 1895) in the general carapace
shape, but can easily be separated by its proportionately longer
female P2–P5 meri (Fig. 3A–H) (versus proportionately
shorter meri in A. palaensis, cf. Ahyong & Ng, 2007: fig.
9A); the female chela is short and stout (Figs. 1D, 3J) (versus
elongate and more slender in A. palaensis, cf. Ahyong & Ng,
2007: fig. 9B); and the MXP3 dactylus is relatively shorter(Fig. 3K, L) (versus relatively longer in A. palaensis, cf.
Ahyong & Ng, 2007: fig. 9C). Significantly, the P5 dactylusof A. placunicola has a distinct row of subterminal spinules
on the ventral margin (Fig. 3H’, H”), which is absent in

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Fig. 3. Arcotheres placunicola n. sp. A, L, paratype ovigerous female (10.1 × 8.0 mm) (ZRC 2017.1012), Changi, Singapore; B–K, holotype
ovigerous female (11.2 × 8.6 mm) (ZRC 2017.1009), Changi, Singapore. A–D, left P2–P5, respectively; E–H, right P2–P5, respectively;D’, distal part of dactylus of left P5 showing stiff subdistal spinules (dorsal view, soft setae not drawn); H’, distal part of dactylus ofright P5 showing stiff subdistal spinules (ventral view, soft setae not drawn); H”, distal part of dactylus of left P5 showing stiff subdistal
spinules (dorsal view, soft setae not drawn); I, fingers of right chela (setae denuded); J, left chela and carpus; K, L, outer view of right
MXP3. Scales: A–H, J = 1.0 mm; D’, H’, H”, I, K, L = 0.5 mm.

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Fig. 4. Arcotheres placunicola n. sp. A, B, D–P, paratype male (5.6 × 4.7 mm) (ZRC 2017.1010); C, Q, paratype young male (2.4 × 2.4mm) (ZRC 2017.1014). Both specimens from Changi, Singapore. A, right chela and carpus (setae not drawn); B, C, male pleon; D, right
MXP3 (setae not drawn); E–H, right P2–P5, respectively; I–L, left P2–P5, respectively (setae not drawn); L’, distal part of P5 dactylus(dorsal view, soft setae not drawn); M, left G1 (ventral view, setae not drawn); N, left G1 (dorsal view, setae not drawn); O, left G2 (setae
not drawn); P, right G2 (mesial view showing exopod, setae not drawn). Scales: A, B, E–L = 1.0 mm; M–P = 0.5 mm; C, L’, Q = 0.25 mm.

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Fig. 5. Arcotheres placunicola n. sp. Colour in life. A–D, G, paratype specimens from ZRC 2017.1010, Changi, Singapore; E, paratype
female (8.8 × 6.9 mm) (ZRC 2017.1010), Changi, Singapore; F, paratype male (4.7 × 4.1 mm) (ZRC 2017.1010), Changi, Singapore. A,
G, in situ on Placuna ephippium Philipsson, 1788 (Placunidae).

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Fig. 6. Arcotheres placunicola n. sp. Colour in life. A, B, paratype ovigerous female (8.0 × 6.1 mm); C, paratype non-ovigerous female
with rhizocephalan (9.0 × 7.4 mm); D, paratype male with rhizocephalan (5.6 × 5.1 mm); E, F, paratype ovigerous female (7.3 × 5.9mm) (crab indicated by arrow); G, H = paratype ovigerous female (9.5 × 7.2 mm). E, in situ on Placuna ephippium Philipsson, 1788
(Placunidae). All material from ZRC 2017.1015, Changi, Singapore.

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Fig. 7. Arcotheres placunae (Hornell & Southwell, 1909), overall habitus. A, neotype ovigerous female (11.0 × 8.1 mm) (ZRC 2017.1293),
India; B, ovigerous female (9.2 × 6.9 mm) (ZRC 2017.1008), Pakistan; C, ovigerous female (11.5 × 7.9 mm) (ZRC 2017.1008), Pakistan;D, male (7.0 × 5.8 mm), (ZRC 2017.1065), India.

ACKNOWLEDGEMENTS

A. palaensis (cf. Ahyong & Ng, 2007: fig. 9A). The samedifferences apply to A. guinotae Campos, 2001, a species
closely related to and possibly synonymous with A. palaensis.

The author is most grateful to Tan Siong Kiat, curator ofmolluscs at the Lee Kong Chian Natural History Museum,for helping him obtain so many specimens as well as advice
on the taxonomy of Placuna. Thanks are also due to themany other curators in the museum for their help in field
work, as well as to Tan Heok Hui (ZRC) for most of thecolour photographs of the freshly collected specimens. The
author also thanks Quddusi Kazmi (Karachi) and Jignesh
Trivedi (Gujarat) for kindly sending comparative materialof Arcotheres placunae. The constructive comments by
Tohru Naruse, Shane Ahyong, and an anonymous referee
are gratefully acknowledged.

Bürger (1895: 373) also recorded A. palaensis from “Placunasella” in Ubay in the Philippines but this record is doubtful.
Ahyong & Ng (2007: 201) re-examined the types andselected a female specimen from Palau as the lectotype of
A. palaensis, commenting that the specimens from Ubay
belonged to A. guinotae instead. Arcotheres palaensis and
A. guinotae are very similar and are probably synonyms(unpublished data). The author has a good collection ofboth species from Singapore and Peninsular Malaysia fromthe arcid genera Anadara and Barbatia; and none havebeen found in Placuna. The condition of the Bürger (1895)
type material in any case is generally poor and some of theassociated data may not be reliable (see Ahyong & Ng, 2007:
192). As has been discussed above, however, A. placunicola
differs markedly from the lectotype of A. palaensis so theidentities of these two species is not in question.

LITERATURE CITED
Ahyong S & Brown DE (2003) Description of Durckheimia lochin. sp., with an annotated check-list of Australian Pinnotheridae(Crustacea: Decapoda: Brachyura). Zootaxa, 254: 1–20, figs.
1, 2.
Ahyong ST & Ng PKL (2007) The pinnotherid type material of
Semper (1880), Nauck (1880) and Bürger (1895) (Crustacea:
Decapoda: Brachyura. Raffles Bulletin of Zoology, Supplement
16: 191–226.
Bürger O (1895) Ein Beitrag zur Kenntnis der Pinnotherinen.
Zoologische Jahrbucher, Abtheilung fur Systematik, Geographie
und Biologie der Thiere, 8: 361–390, pls. 9, 10.
Campos E (2001) A new crab species of the genus Arcotheres
Manning, 1993, from Thailand (Crustacea, Brachyura,
Pinnotheridae). Zoosystema, 23(3): 493–497.

Prior to the study of the type material by Ahyong & Ng
(2007), the identity of A. similis was been unclear, andrecords of this species from Crassostrea sp. or Saccostrea
sp. (Ostreidae) (cf. Rathbun, 1924), and Staveila subdistorta
Récluz, 1852 (Mytilidae) and Pinna sp. (Pinnidae) (cf.
Ahyong & Brown, 2003) will all need to be re-examined
to ascertain their actual identity (see also Ward, 1967;
Davie, 2002).

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Fig. 8. Arcotheres placunae (Hornell & Southwell, 1909), ovigerous female (11.5 × 7.9 mm) (ZRC 2017.1008), Pakistan. A–D, left P2–P5,
respectively; E–H, right P2–P5, respectively; D’, distal part of dactylus of left P5 showing stiff subdistal spinules (dorsal view, setae notdrawn); H’, distal part of dactylus of left P5 showing stiff subdistal spinules (ventral view, setae not drawn); H” = distal part of dactylusof right P5 showing stiff subdistal spinules (dorsal view, setae not drawn); I, outer view of right MXP3; J, right chela and carpus. Scales:
A–H, J = 1.0 mm; D’, H’, H”, I = 0.5 mm.

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