RAFFLES BULLETIN OF ZOOLOGY 2016
Taxonomy & Systematics
RAFFLES BULLETIN OF ZOOLOGY 64: 257–268

Date of publication: 19 August 2016
http://zoobank.org/urn:lsid:zoobank.org:pub:88473619-8A6C-4951-AD3C-89C14653CAC3On the identities of Parasesarma carolinense (Rathbun, 1907) andParasesarma sigillatum (Tweedie, 1950), with description of a new
species from Taiwan (Crustacea: Brachyura: Sesarmidae)
Peter K. L. Ng1*, Peter J. F. Davie2 & Jheng-Jhang Li3
Abstract. The intertidal sesarmid crab Sesarma sigillata Tweedie, 1950, described from Cocos-Keeling Islands in
the Indian Ocean has long been in the synonymy of Sesarma (Parasesarma) carolinensis Rathbun, 1907, from theCaroline Islands in the western Pacific. Examination of the types of the taxa, as well as a good series of specimensfrom Cocos-Keeling Islands shows that both are distinct species of Parasesarma De Man, 1895. In addition, a new
species, P. corallicum, which is allied to P. carolinense and P. sigillatum is described from Taiwan.
Key words. Taxonomy, Parasesarma carolinense, Parasesarma sigillatum, new species, Indian Ocean, Pacific
Ocean, Taiwan

For the descriptions, only the first known member of thegroup, P. carolinense, is described in full and is thenused as a baseline for diagnosing the other two species.
Specimens examined are deposited in National Museumof Marine Biology and Aquarium (Crustacea Decapoda)(NMMBCD), Pingtung, Taiwan R.O.C.; National Museumof Natural Science (NMNS), Taichung, Taiwan R.O.C.;
Zoological Reference Collection (ZRC), of the Lee Kong
Chian Natural History Museum (previously Raffles Museumof Biodiversity Research), National University of Singapore;
The Natural History Museum (NHM), London; U.S.
National Museum of Natural History (USNM), Smithsonian
Institution, Washington D.C.; and the Queensland Museum(QM), Brisbane.

INTRODUCTION
Sesarma (Parasesarma) carolinensis was described by
Rathbun (1907) on the basis of one male obtained fromthe Caroline Islands in the west Pacific. This poorly known
species has been retained in Parasesarma De Man, 1895, by
most authors (e.g., Serène, 1968; Ng et al., 2008). Tweedie(1950: 131, fig. 3a–e) described Sesarma sigillata from the
Cocos Keeling Islands in the eastern Indian Ocean, but Serène(1968: 108) synonymised it under S. carolinensis without
comment, presumably because of their very similar carapace
form. The male first gonopod structure, so important in
helping to discriminate Parasesarma species, has not beenpreviously described for S. carolinensis.

TAXONOMY

In this paper, we clarify the identities of Sesarma carolinensis
Rathbun, 1907, and S. sigillata Tweedie, 1950, on the basisof the types, and fresh material of the latter species. Bothtaxa are here recognised as valid. Since S. carolinensis is sopoorly known, we herewith take the opportunity to redescribe
it in detail. We also describe a new species from Taiwan, P.
corallicum n. sp., which is allied to the two described species.

Family Sesarmidae Dana, 1851
Parasesarma De Man, 1895
Type species. Cancer quadratus Fabricius, 1798; subsequent
designation by Rathbun (1918).

Measurements (in millimetres) are of the maximum carapace
width and length, respectively. The abbreviations G1 and G2
are used for the male first and second gonopods, respectively.

Remarks. Parasesarma De Man, 1895, is one of the largest
genera in the Sesarmidae, with 38 recognised species (Nget al., 2008; Rahayu & Ng, 2009, 2010; Davie & Pabriks,
2010; Naderloo & Schubart, 2010; Rahayu & Li, 2013).
Parasesarma carolinense and P. sigillatum belong to agroup of species that have relatively short ambulatory legs,with the meri transversely broad; and the meri and propodiof the second leg less than three times as long as wide (cf.
Rahayu & Ng, 2009); and are unique in having the distal
margin of their cheliped merus expanded into a lamelliform
structure with distinct spination. A third species from Taiwan,
P. corallicum n. sp., is recognised here. The three species
also share the following features: small adult size (mature

Lee Kong Chian Natural History Museum, National University of Singapore,Kent
Ridge, Singapore. Email: peterng@nus.edu.sg (*corresponding author)
1*

Queensland Museum, PO Box 3300, South Brisbane, Queensland, Australia. Email:Peter.Davie@qm.qld.gov.au
2

Department of Marine Biotechnology and Resources, National Sun Yat-sen University,
70 Lienhai Rd., Kaohsiung 80424, Taiwan. Email: epigrapsus@yahoo.com.tw
3© National University of Singapore
ISSN 2345-7600 (electronic) | ISSN 0217-2445 (print)257

Ng et al.: On the taxonomy of Parasesarma carolinense and allied new species

Fig. 1. Colour in life. A–D, Parasesarma sigillatum, Cocos-Keeling Islands; E–H, Parasesarma corallicum n. sp., Taiwan. A, male, notpreserved; B, female (8.7 × 6.4 mm) (QM-W28343); C, D, male (9.4 × 6.9 mm) (QM-W28342); E, F, male, Hsiangchiaowan, Taiwan(10.3 × 7.6 mm) (NMMBCD 4698); G, Holotype, same data (9.5 × 7.0 mm) (NMMBCD 4697); H, Wanlitung, Taiwan (8.0 × 5.7 mm)(NMNS-7548-002).

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at carapace widths of 7–8 mm); a trapezoidal carapace inwhich the lateral margins are strongly convergent towards
the posterior carapace margin; the dorsal pectinate ridges
on the palm are short; the inner surface of the chela has atransverse granulated ridge; the dorsal margin of the dactylusof the cheliped has about 16 triangular tubercles; and thetips of the fingers are excavated on the inner face. The two
species freshly collected for this study (P. sigillatum and P.
corallicum n. sp.) also do not appear to be dependent onmangrove habitats, as is typical of most Parasesarma species.
They occur, instead, in relatively exposed supralittoral
habitats on coral atolls, usually under debris or among rocks.
The habitat of P. carolinense in the Caroline Islands is notknown, but we believe it is likely to be similar.

very shallow median concavity; confluent with supraorbital
margin (Fig. 2A–C). Supraorbital margin entire, posteriorly
oblique, convex along anterior half, posterior half gently
sinuous (Fig. 2A, B). External orbital tooth triangular,
directed obliquely outwards, representing point of greatest
carapace width; antero- and posterolateral margins notdemarcated, without trace of tooth or indentation, lateral
margins straight, converging to meet weakly convex posterior
carapace margin (Fig. 2A, B). Eyes with large cornea, notreaching to external orbital tooth (Fig. 2A, B). Antennal
and antennular basal segments adjacent, not separated by
septum; basal antennular segment large; antennal flagellum
relatively long, entering orbit.
Third maxilliped with ischium relatively short, subrectangularin shape, with shallow median sulcus, left one relatively
shorter than right one (see Remarks) (Figs. 2E; 6A); merus
subovate, with distinct submedian ridge; inner margin of
merus-ischium with stiff setae; exopod slender, tip reaching
about half length of outer margin of merus, flagellum long(Figs. 2D, E; 6A).

Parasesarma carolinense (Rathbun, 1907)(Figs. 2; 5A–C; 6A–F)
Sesarma (Parasesarma) carolinensis Rathbun, 1907: 34, pl. 5 fig.
2, 2a; pl. 9 fig. 1; Tesch, 1917: 141; Serène, 1968: 108.
Parasesarma carolinense – Ng et al., 2008: 222 (list, part).

Material examined. Holotype: male (9.2 × 7.0 mm) (USNM
32861), Kusaie, Carolines, coll. 9 February 1900.

Chelipeds relatively stout in adult male, symmetrical (Fig.
2A). Merus short, inner distal part prominently carinate,forming large lamelliform structure; distal margin oflamelliform structure appears serrated, with short sharp teeth,
inner margin with denticles; outer margin uneven or with low
granules; outer surface with dorsal striation; inner surface
gently concave, smooth, with 2 rows of setae (Fig. 2A, F,
G). Carpus with inner angle not produced, rounded; outermargin and surface striated (Fig. 2F, G). Upper surface ofpalm with 2 obliquely transverse pectinate crests, primary(distalmost) crest with row of 14 or 15 tall pectinate teeth,
tip of each tooth gently curved, secondary crest with 16
or 17 relatively lower pectinate teeth (Fig. 2F, I). Outersurface of palm with striations and punctations; inner surfaceof palm with short oblique granulated crest on upper part(Fig. 2H). Fingers short, subequal to length of palm; cuttingedge of pollex with large, rounded teeth on distal half, teethon proximal part relatively lower, tip excavated, spatulate;dactylus with rounded tooth on subproximal part of cutting
margin, rest of margin with small teeth, tip excavated,
spatulate; dorsal surface of dactylus with 15 or 16 triangulartubercles, gradually sloping distally, becoming lower, eachtubercle with a strong proximal transverse ridge (Fig. 2F–I).

Diagnosis. Carapace 1.31 times broader than long; lobes offrontal margin separated by broad, very shallow concavity(Fig. 2A–C); upper surface of cheliped palm with 2 transverse
pectinate crests, primary (distalmost) consisting of row of
14 or 15 tall pectinate teeth, tip of each tooth gently curved,
secondary crest with 16 or 17 relatively lower pectinate
teeth (Fig. 2F, I); inner surface of palm with short obliquelytransverse granulated ridge on upper half (Fig. 2G); dorsal
surface of dactylus with 15 or 16 triangular tubercles, eachdactylar tubercle with distinct transverse ridge (Fig. 2F, G,I); inner distal margin of lamelliform process of merus linedwith sharp triangular teeth (Fig. 2F, G); ambulatory legs short,stout; merus of third leg 2.0 times as long as wide; upper
margin of merus with subdistal spine; propodus of third leg
2.7 times as long as wide; dactylus of third and fourth legs
0.7 and 0.8 times length of propodus, respectively (Figs. 2A;
5A–C); male telson triangular with strongly convex lateral
margins, ca. 1.5 times length of pleonal somite 6 (Fig. 6B);
G1 relatively slender, straight; apical process bent to form
an angle of about 80º from the vertical, chitinous distal partlong (Fig. 6C–F).

Ambulatory legs short, stout, laterally flattened; second andthird pairs longest (Fig. 2A). Merus with low transverse
striae on upper surface, meri of second and third legs 2.2
and 2.0 times as long as wide, respectively; upper marginof merus with subdistal spine (Figs. 2A; 5A–C). Carpus
with 2 accessory carinae on outer surface. Propodus of
third leg ca. 2.7 times as long as wide with low carina on
inferior proximal portion of outer surface, dorsal and ventral
margins with short stiff setae (Figs. 2A; 5A–C). Dactylus of
third and fourth legs 0.7 and 0.8 times length of propodus,
respectively, tip gently curved distally, terminating in acutecalcareous tip, dorsal and ventral margins with short stiff
setae (Figs. 2A; 5B, C).

Description. Carapace trapezoidal, 1.31 times broader thanlong; dorsal surfaces relatively smooth, glabrous; regions
poorly defined, separated by shallow grooves except for
deeper H-shaped median gastric groove; lateral parts of
dorsal carapace surface with distinct oblique striae; posterior
surface with short transverse striae; lateral margins withnumerous tufts of short setae (Fig. 2A, B). Postfrontal
region distinct, low, rounded, not cristate, separated into 4lobes by narrow, distinct longitudinal grooves; median lobes
approximately same width as lateral lobes (Fig. 2A–C). Front
truncate, distinctly deflexed downwards, margin weakly
bilobed from dorsal view with lobes separated by broad,259

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Fig. 2. Parasesarma carolinense (Rathbun, 1914), holotype male (9.2 × 7.0 mm) (USNM 32861), Caroline Islands. A, overall habitus; B,
dorsal view of carapace; C, frontal view of cephalothorax; D, anterior thoracic sternum and pleon; E, third maxillipeds; F, dorsal view ofleft cheliped; G, dorsal view of right cheliped; H, outer view of left chela; I, dactylar tubercles of left chela.

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Surface of thoracic sternites 1–4 smooth; sternites 1–3
completely fused, without trace of sutures; separated fromsternite 4 by deep suture (Fig. 2D). Male sternopleonalcavity reaching suture between sternites 3, 4. Male pleon
relatively broad, all somites free; telson triangular withstrongly convex lateral margins, ca. 1.5 times length ofpleonal somite 6; somite 6 almost twice as wide as long,lateral margins strongly convex; somites 3–5 progressively
more trapezoidal; somites 1, 2 very narrow longitudinally;reaching coxa of fourth ambulatory leg, sternite 8 completely
covered (Fig. 6B).

Islands, coll. P.J.F. Davie & P.K.L. Ng, 24 March 2011;
2 males (largest 10.5 × 7.9 mm), 4 females (largest 11.4
× 8.1 mm) (QM-W28345), stn CK3, Tanjong Puji, West
Island, Cocos-Keeling Islands, 12°11.589’S, 96°51.549’E,
coll. P.J.F. Davie & P.K.L. Ng, 20 March 2011.
Diagnosis. Carapace 1.35–1.44 times broader than long;
frontal margin bilobed, separated by broad, very shallow
concavity (Fig. 3A–C); upper surface of cheliped palm
with 2 transverse pectinate crests, primary (distalmost) crestwith row of 15–18 tall pectinate teeth, tip of each tooth
gently curved, secondary crest with 9 or 10 relatively lower
pectinate teeth, followed by patch of 12–15 scattered low,
more rounded pectinate tubercles on median part of palm
(Figs. 3H; 7A); inner surface of palm with low, obliquelytransverse, submedian granulated ridge (Fig. 3I); dorsal
surface of dactylus with 16–18 triangular tubercles, eachdactylar tubercle with distinct transverse ridge (Fig. 3E,
F, H, I); inner distal margin of inner lamelliform process
of merus lined with sharp triangular teeth (Fig. 3E, F, I);
ambulatory legs short, stout; merus of third leg 2.0 times aslong as wide; upper margin of merus with subdistal spine;
propodus of third leg 2.8 times as long as wide; dactylus of
third and fourth legs 0.8 and 1.0 times length of propodus,
respectively (Figs. 3A; 5D–G); male telson semicircular, ca.
1.2 times length of pleonal somite 6 (Fig. 6H); G1 relatively
slender, straight; apical process bent at 90° from the vertical,
chitinous distal part long, aperture terminal (Fig. 6I–L).

G1 relatively slender, straight; apical process bent to form
an angle of about 80° from the vertical, chitinous distal
part long, aperture terminal (Fig. 6C–F). G2 short, about athird length of G1.
Colour in life. Not known.
Habitat. Not known.
Remarks. The left third maxilliped (Fig. 6A) appears to
be abberant, with the ischium relatively short. On the rightthird maxilliped, the ischium is proportionately longer (Fig.
2E). The right third maxilliped structure of P. carolinense
agrees well with those of P. sigillatum and P. corallicum(Fig. 6G, N), respectively.
The species is known only from the holotype specimen.
Comparisons with P. sigillatum and P. corallicum n. sp.
are provided in the Discussion.

Colour in life. Dorsal surfaces of carapace and ambulatory
legs dirty white with large and small uneven patches of darkbrown to grey (Fig. 1A–C). Chelae light orange, although
ventral half darker, with dorsal parts sometimes appearing
paler (Fig. 1A–D).

Parasesarma sigillatum (Tweedie, 1950)(Figs. 1A–D; 3; 5D–G; 6G–M; 7A)
Sesarma sigillata Tweedie, 1950: 131, fig. 3a–e.
Sesarma (Parasesarma) sigillatum – Serène, 1968: 108.
Parasesarma carolinense – Ng et al., 2008: 222 (list, part) (notSesarma (Parasesarma) carolinensis Rathbun, 1907).

Habitat. Parasesarma sigillatum inhabits supralittoral orupper intertidal zones. It prefers a sandy substrate with somemud, and with grass growing nearby. The crabs were foundhiding under flotsam, pieces of wood and small rocks. An
allied species, Parasesarma cf. lenzii (De Man, 1895) cansometimes be found with it, although this species prefers
muddier and wetter substrates.

Material examined. Lectotype (here designated): male (10.7
× 7.6 mm) (NHM 1950.4.17.4), Cocos-Keeling Islands, coll.
C.A. Gibson-Hill, 1941. Paralectotype: 1 female (10.4 × 7.5mm) (NHM 1950.4.17.5), same data as lectotype. Others:
24 males (largest 11.1 × 7.8 mm), 20 females (largest 11.0
× 7.8 mm) (1 ovigerous) (ZRC 1965.8.2.260–269), CocosKeeling Islands, coll. C.A. Gibson-Hill, 1941; 1 female (9.9
× 7.0 mm) (ZRC), Cocos-Keeling Islands, coll. P.K.L. Ng& P.J.F. Davie, 21 March 2011; 1 male (9.1 × 6.7 mm), 1
juvenile male, 6 females (largest 8.6 × 6.3 mm) (ZRC), stn
CK 26, lagoon side of airport near Meterological Station,
West Island, Cocos-Keeling Islands, coll. P.K.L. Ng & P.J.F.
Davie, 24 March 2011; 2 males (9.4 × 6.9 mm, 9.0 × 6.7mm) (QM-W28342), stn CK16, lagoon side of airport near
Meterological Station, West Island, Cocos-Keeling Islands,coll. P.J.F. Davie & P.K.L. Ng, 22 March 2011; 3 males(largest 7.8 × 5.9 mm), 16 females (largest 8.7 × 6.4 mm)(QM-W28343), same data QM-W28342; 2 males (largest 9.2
× 6.9 mm) (QM-W28344), stn CK26, lagoon side of airport
near Meterological Station, West Island, Cocos-Keeling

Remarks. Tweedie (1950: 131) stated that one male andone female were “cotypes”, but noted that he also had
43 additional specimens. This means that only the two
specimens in the NHM (labelled as cotypes) are syntypes,
with the remaining material in ZRC not types. The NHM
male is here designated the lectotype of Sesarma sigillata
Tweedie, 1950. There are, however, 44 specimens in a bottle
in the ZRC (24 males, 20 females), not 43, suggesting that
Tweedie miscounted. The two NHM specimens are in very
poor condition: all the chelipeds and ambulatory legs aredetached; and their carapaces are very delicate, with that of
the female already medially broken. However, they agree with
the ZRC specimens in all aspects, including the structure of
the G1. Both G1s of the lectotype male are intact and stillon the specimen, and the G1 figured by Tweedie (1950:
fig. 3d) must have therefore come from one of the males in
the ZRC. It was probably from the male in ZRC which has
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Fig. 3. Parasesarma sigillatum (Tweedie, 1950). A–H, male (9.5 × 6.8 mm) (ZRC 1965.8.2.269), Cocos-Keeling Island; I, lectotype
male (10.7 × 7.6 mm) (NHM 1950.4.17.4), Cocos-Keeling Island. A, overall habitus; B, dorsal view of carapace; C, frontal view of
cephalothorax; D, anterior thoracic sternum and pleon; E, dorsal view of left cheliped; F, dorsal view of right cheliped; G, outer view ofright chela; H, dactylar tubercles of right chela; I, inner view of left chela.

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Fig. 4. Parasesarma corallicum n. sp., holotype male (9.5 × 7.0 mm) (NMMBCD 4697), Taiwan. A, overall habitus; B, dorsal view ofcarapace; C, frontal view of cephalothorax; D, anterior thoracic sternum and sternopleonal cavity; E, dorsal view of left cheliped; F, dorsal
view of right cheliped; G, outer view of right chela; H, dactylar tubercles of right chela; I, inner view of left chela.

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Fig. 5. Left ambulatory legs. A–C, Parasesarma carolinense (Rathbun, 1914), holotype male (9.2 × 7.0 mm) (USNM 32861), Caroline
Islands; D–G, Parasesarma sigillatum (Tweedie, 1950), male (9.5 × 6.8 mm) (ZRC 1965.8.2.269), Cocos-Keeling Island; H–K, Parasesarma
corallicum n. sp., holotype male (9.5 × 7.0 mm) (NMMBCD 4697), Taiwan. A, D, H, first ambulatory leg; B, E, I, second ambulatoryleg; C, F, J, third ambulatory leg; G, K, fourth ambulatory leg. Legs of all species to scale.

Parasesarma corallicum sp. nov.
(Figs. 1E–H; 4; 5H–K; 6N–T; 7B)

its own catalogue number (ZRC 1965.8.2.260) and a notein Tweedie’s handwriting that it was photographed; thisspecimen no longer has an pleon or gonopods suggesting
they may have been removed for figuring and not returnedto the bottle.

Material examined. Holotype: male (9.5 × 7.0 mm)(NMMBCD 4697), Hsiangchiaowan, Kenting, Pingtung,southern Taiwan, coll. J.-J. Li, 10 August 2015. Paratypes:
1 male (10.0 × 7.3 mm) (ZRC), same data as holotype; 1male (10.3 × 7.6 mm), 1 female (8.0 × 5.8 mm) (NMMBCD
4698), Hsiangchiaowan, Kenting, Pingtung, southern Taiwan,coll. J.-J. Li, 21 August 2015; 2 males (8.1 × 5.7 mm, 6.3
× 4.7 mm), 1 female (6.9 × 4.7 mm) (ZRC), Wanlitung,Kenting, Pingtung, southern Taiwan, coll. J.-J. Li, 5 July
2014; 1 male (9.1 × 6.1 mm) (NMMBCD 4699), Wanlitung,Kenting, Pingtung, southern Taiwan, coll. J.-J. Li, 20 July

There is a label with the NHM material that states that thisspecies is conspecific with “Sesarma carolinense”, suggestingthat Serène may have examined the material before hesynonymized S. carolinense with S. sigillata.
The differences between P. carolinense s. str. and P.
corallicum n. sp. are outlined in the Discussion.

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Fig. 6. A–F, Parasesarma carolinense (Rathbun, 1914), holotype male (9.2 × 7.0 mm) (USNM 32861), Caroline Islands; G–M, Parasesarma
sigillatum (Tweedie, 1950), male (9.5 × 6.8 mm) (ZRC 1965.8.2.269), Cocos-Keeling Island; N–T, Parasesarma corallicum n. sp., holotype
male (9.5 × 7.0 mm) (NMMBCD 4697), Taiwan. A, G, N, left third maxilliped; B, H, male pleon; O, male pleon (somites 1 and 3 broken);
C, P, ventral view of left G1; D, Q, dorsal view of left G1; E, ventral view of right G1; F, distal chitinous part of right G1 (ventral view);
I, ventral view of right G1; J, dorsal view of right G1; K, distal chitinous part of right G1 (ventral view); L, distal chitinous part of rightG1 (dorsal view); M, right G2; R, distal chitinous part of left G1 (ventral view); S, distal chitinous part of left G1 (dorsal view); T, left
G2. Setae for all structures denuded. Scale bars = 0.5 mm [A–E, G–J, M–Q, T]; 0.1 mm [F, K, L, R, S].

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Fig. 7. Details of pectinate crests on chela. A, Parasesarma sigillatum (Tweedie, 1950), lectotype male (10.7 × 7.6 mm) (NHM 1950.4.17.4),
Cocos-Keeling Island; B, Parasesarma corallicum n. sp., holotype male (9.5 × 7.0 mm) (NMMBCD 4697), Taiwan. Arrow points todirection of dactylar finger. Scales = 0.5 mm.

2014; 1 male (8.8 × 6.4 mm), 1 female (8.8 × 6.3 mm) (QM),
Wanlitung, Kenting, Pingtung, southern Taiwan, coll. J.-J.
Li, 21 July 2014; 2 males (9.0 × 6.6 mm, 8.6 × 6.0 mm)(QM), Wanlitung, Kenting, Pingtung, southern Taiwan, 6August 2014; 1 ovigerous female (8.3 × 5.8 mm) (NMMBCD
4700), Wanlitung, Kenting, Pingtung, southern Taiwan, coll.
L.-K. Tseng, 28 July 2014; 3 male (11.3 × 7.6 mm – 8.1
× 5.6 mm), 1 female (10.7 × 7.8 mm) (NMMBCD 4701),
Hsiangchiaowan, Kenting, Pingtung, southern Taiwan, coll.
J.-J. Li, 2 Nov 2014.1 ovigerous female (7.7 × 5.3 mm)(NMNS-7548-001), Wanlitung, Kenting, Pingtung, southern
Taiwan, coll. L.-K. Tseng, 25 October 2014; 1 male (8.0 ×
5.7 mm) (NMNS-7548-002), Wanlitung, Kenting, Pingtung,southern Taiwan, coll. J.-J. Li, 3 May 2014.

uniformly coloured (Fig. 1G). Ambulatory legs whitishgrey with patches of brown (Fig. 1E–H). Chelae yellow toyellowish-brown (Fig. 1E–H).
Etymology. The name is derived from its habit of living
near coral reefs.
Habitat. The specimens of Parasesarma corallicum n.
sp. were active among sandy substrates around the highly
eroded dead coral areas in the supralittoral zone. Most of
this area is dry to moist. The crabs hide deep in numerous
crevices in the dead coral during the day, and were observed
only in the evening and at night. Parasesarma corallicum
n. sp. occurs sympatrically with Stelgistra stormi (De Man,
1895), Nanosesarma andersonii (De Man, 1895) (bothSesarmidae) and Grapsus albolineatus (Latreille, in Milbert,
1812) (Grapsidae).

Diagnosis. Carapace 1.34–1.47 times broader than long;
lobes of frontal margin separated by broad, relatively deeper
concavity (Fig. 4A–C); upper surface of cheliped palm with
2 transverse pectinate crests, primary (distal-most) crestwith row of 16 or 17 tall pectinate teeth, tip of each tooth
gently curved, secondary crest with 11 or 12 relatively
lower pectinate teeth (Figs. 4H; 7B); inner surface of palm
with low obliquely transverse submedian granulated ridge(Fig. 4I); dorsal surface of dactylus with 15 or 16 triangulartubercles, each dactylar tubercle with distinct transverse ridge(Fig. 4E, F, H); inner distal margin of lamelliform process
of merus lined with acutely triangular teeth (Fig. 4E, F);
ambulatory legs short, stout; merus of third leg 2.3 times aslong as wide; upper margin of merus with subdistal spine;
propodus of third leg 2.7 times as long as wide; dactylus of
third and fourth legs 0.8 and 0.9 times length of propodus,
respectively (Figs. 4A; 5H–K); male telson semicircular, ca.
1.2 times length of pleonal somite 6 (Fig. 6O); G1 relatively
slender, straight; apical process bent at 90º from the vertical,
chitinous distal part long, aperture terminal (Fig. 6P–S).

Remarks. The specimens of this species were consistentin all the diagnostic characters examined. One ovigerous
female (7.7 × 5.3 mm) (NMNS-7548-001), however, lacked a
subdistal spine on the merus of first and fourth left ambulatory
legs These spines were probably eroded as the crabs moved
around the coral crevices.
See discussion for comparisons with P. carolinense s. str.
and P. sigillatum.
GENERAL DISCUSSION
The three species are all very similar in general morphology.
However, the second and third ambulatory meri of P.
carolinense are relatively shorter (Figs. 2A; 5A, B) (somewhat
longer in P. sigillatum and even more so in P. corallicum n.
sp.; c.f. Figs. 3A; 4A; 5E, F, I, J); the fourth ambulatory merus
is more slender in P. carolinense (Figs. 2A; 5C) (distinctly
broader in P. sigillatum and P. corallicum; Figs. 3A; 4A;
5G, K); the fourth ambulatory dactylus is distinctly shorter

Colour in life. Dorsal surfaces of carapace light brown withpatches of white (Fig. 1E, H), with brown areas sometimes
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RAFFLES BULLETIN OF ZOOLOGY 2016
in P. carolinense (Fig. 5C) (distinctly longer in P. sigillatum
and P. corallicum, Fig. 5G, K); and the third maxilliped
merus and ischium of P. carolinense are proportionately
shorter (Figs. 2E; 6A) (relatively longer in P. sigillatum
and P. corallicum; Fig. 6G, N).

finger tips of the chelae of P. carolinense, P. sigillatum andP. corallicum closely resemble those of Stelgistra stormi (DeMan, 1895) from Indonesia, Taiwan and Japan (see Ng &Liu, 1999; Komai et al., 2004); although the latter is fromsupralittoral eroded limestone rocks and the finger tips are
more distinctly spoon-shaped.

The male telson of P. carolinense (Fig. 6B) is also
proportionately longer (ca. 1.5 times length of pleonal somite6) than those of P. sigillatum or P. corallicum (ca. 1.2 times
length of pleonal somite 6) (Fig. 6H, O). The G1s of the three
species are superficially similar; although the chitinous distal
part of the G1 in P. carolinense is slightly bent upwards at
an 80°angle to the vertical (Fig. 6C–E), while bent at rightangles in P. sigillatum and P. corallicum (Fig. 6I, J, P, Q).

ACKNOWLEDGEMENTS
The first author is grateful to Rafael Lemaitre and Karen
Reed (USNM) for allowing him to examine the type of
Sesarma carolinensis, and to Paul Clark (NHM) for sending
the types of Sesarma sigillatum. Rafael Lemaitre also kindly
helped us with checking some important details of his typespecimen. We are grateful to Tomoyuki Komai and Dwi
Listyo Rahayu for their many helpful comments to themanuscript. The second author would like to acknowledge
partial support from Australian Biological Resources Study
Grants nos. 208–72, and 207–50.

In all three species, the first oblique pectinate crest on thedorsal margin of the chela is distinct and the relatively tall
pectinate teeth are arranged in one discrete row (Fig. 2F, I,
3E, H, 4E). In P. carolinense and P. corallicum, the relatively
lower pectinate teeth on the secondary crest of granules
are also arranged in a distinct row (Figs. 2F, I, 7B). In P.
sigillatum, however, the pectinate tubercles on the secondary
crest diffuse into a patch of low pectinate tubercles towards
the median surface of the chela (Figs. 3H, 7A).

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The inner distal margin of the lamelliform process of themerus is lined with sharp teeth in all three species, but in P.
corallicum n. sp., these spines are usually more acute (Fig.
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