Zootaxa 2289: 33–47 (2009)
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Copyright © 2009 · Magnolia Press
ISSN 1175-5326 (print edition)
Article
ZOOTAXA
ISSN 1175-5334 (online edition)
Aphanodactylidae, a new family of thoracotreme crabs (Crustacea: Brachyura)
symbiotic with polychaete worms
SHANE T. AHYONG1 & PETER K. L. NG2
1
Marine Biodiversity and Biosecurity, National Institute of Water and Atmospheric Research, Private Bag 14901, Kilbirnie,
Wellington, New Zealand. E-mail: s.ahyong@niwa.co.nz
2
Tropical Marine Science Institute and Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore
119260, Republic of Singapore. E-mail: dbsngkl@nus.edu.sg
Abstract
The pea crabs of the family Pinnotheridae De Haan, 1833, have traditionally been recognised on the basis of their
simplified external morphology, modified third maxillipeds, and general habit of living in association with invertebrate
hosts, usually bivalve molluscs. Recent morphological and molecular studies of Pinnotheridae show that it is not a
natural group as traditionally conceived. The subfamily Asthenognathinae Stimpson, 1858, actually belongs in the
Varunidae H. Milne Edwards, 1853, and the subfamily Tritodynamiinae Števčić, 2005, is part of the Macrophthalmidae
Dana, 1851. However, several ‘pinnotherid’ genera that are superficially similar to asthenognathines and allied to
Aphanodactylus Tesch, 1918, appear to form a discrete group, but lack the chief synapomorphy of Pinnotheridae,
namely, the highly modified maxilliped 3. Moreover, Aphanodactylus and allies do not share synapomorphies with of
any presently recognised thoracotreme family. A new family, Aphanodactylidae, is therefore established for
Aphanodactylus, Gandoa Kammerer, 2006, Uruma Naruse, Fujita & Ng, 2009, and a new genus and species described
herein, Gustavus mecognathus. Aphanodactylids (where known) are symbiotic with terebellid polychaete worms and
share short, stout, ambulatory legs with one or more spines lining the flexor margins of the ischiomeri of at least some of
the ambulatory legs; a row of distal flexor spines on the ambulatory propodi opposing a claw-like dactylus; very short
ambulatory dactyli that are less than half the respective propodus length; and marked sexual dimorphism in which the
female is distinctly wider than the male. The phylogenetic position of Aphanodactylidae remains to be determined but
the morphology of the third maxillipeds and the position of the male gonopore suggests that it may belong in the
Pinnotheroidea, to which it is tentatively assigned. Each genus of the Aphanodactylidae is diagnosed and illustrated, and
a key to the genera provided.
Keywords: Decapoda, Brachyura, Thoracotremata, Pinnotheroidea, Aphanodactylidae, Pinnotheridae, symbiosis,
Polychaeta, Terebellidae
Introduction
The crabs of the family Pinnotheridae De Haan, 1833, have long been recognised as symbionts, usually living
within the mantle chamber of bivalve molluscs or with polychaete worms. Most pinnotherids possess a
relatively poorly calcified carapace with indistinct regions, have a highly modified maxilliped 3 and a
simplified habitus, particularly with regards to the general lack of surface ornamentation. Among crabs
traditionally regarded as pinnotherids were a group of genera that have long been placed in the subfamily
Asthenognathinae Stimpson, 1858. Unlike most pinnotherids, which have a highly modified maxilliped 3,
asthenognathines are atypical in having the ischium and merus as distinct segments, with the ischium larger
than the merus, and the palp consisting of the carpus, propodus and dactylus clearly demarcated and not
enlarged.
Accepted by P. Castro: 21 Oct. 2009; published: 13 Nov. 2009
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Tesch (1918) recognized eight genera in Asthenognathinae: Aphanodactylus Tesch, 1918; Asthenognathus
Stimpson, 1858; Chasmocarcinops Alcock, 1900; Hapalonotus Rathbun, 1897; Mortensenella Rathbun,
1909; Opisthopus Rathbun, 1893; Tritodynamia Ortmann, 1894; and Voeltzkowia Lenz, 1905. The
classification of Asthenognathinae, however, has changed considerably since 1918 following more detailed
studies of the morphology of these crabs. Opisthopus is a pinnotherine (see Schmitt et al. 1973);
Chasmocarcinops a chasmocarcinid (see Schmitt et al. 1973; Ng et al. 2008); Mortensenella a camptandriid
(see Harminto & Ng 1991); Hapalonotus a pilumnid (see Chia & Ng 1999); and Tritodynamia a
macrophthalmid (subfamily Tritodynamiinae Štev č i ć , 2005) (Štev č i ć 2005; Ng et al. 2008). Most
significantly, Asthenognathus, the type and only remaining genus in the subfamily Asthenognathinae
Stimpson, 1858, is actually a varunid (see Cuesta et al. 2005; Ng et al. 2008). Asthenognathus shares
numerous features with other varunids including the form of the thoracic sternum, male gonopore structure,
male abdomen, gonopods and general structure of the pereopods (Ng et al. 2008). Although, taxonomic
problems remain to be resolved within Asthenognathus and Tritodynamia, both being particularly speciose,
Asthenognathinae sensu stricto nevertheless has varunid affinities; and as discussed, the other genera and
species previously placed therein have been relatively easily reassigned to other families. That is, except for
Aphanodactylus, Gandoa Kammerer, 2006 (replacement name for Voeltzkowia), the recently recognised
Uruma Naruse, Fujita & Ng, 2009, and a new genus and species established below. Members of these genera
(where known) are associated with terebellid polychaete worms and united by several distinct features: short,
stout, ambulatory legs with one or more spines lining the flexor margins of the ischiomerus of at least some of
the legs; a row of distal, flexor spines on the ambulatory propodus opposing a claw-like dactylus (to be
confirmed in Gandoa); very short ambulatory dactylus that is less than half the respective propodus length;
and marked sexual dimorphism in which the female is distinctly wider than the male (to be confirmed in
Gandoa and Uruma). These genera form a discrete group but do not share synapomorphies of any presently
recognised thoracotreme family. We therefore recognise a new family herein to accommodate these genera
and species.
Materials and methods
Specimen measurements are given as carapace length (cl) and carapace width (cw), measured in millimetres
(mm). The abbreviations P2–P5, G1 and G2 are used for pereopods 2–5, male first and second gonopods,
respectively. Specimens are deposited in the Bernice P. Bishop Museum (BPBM), Honolulu, Hawaii; Natural
History Museum and Institute, Chiba (CBM), Japan; Muséum national d’Histoire naturelle (MNHN), Paris,
France; The Naturalis (formerly Rijksmuseum van Naturrlijke Historie, RMNH), Leiden, The Netherlands;
Ryukyu University Museum (RUMF), Fujukan, Okinawa, Japan; and Zoological Reference Collection (ZRC)
of the Raffles Museum of Biodiversity Research, National University of Singapore.
Systematics
Pinnotheroidea De Haan, 1833
Aphanodactylidae n. fam.
Diagnosis. Carapace strongly sexually dimorphic (where both are known); female carapace transversely ovate
to rectangular; male carapace narrower than that of female, ovate to subquadrate; surface glabrous or finely
setose; smooth or punctate; regions poorly defined. Front deflected ventrally, faintly sinuous to bilobed in
dorsal view. Orbital margins entire, well defined, infraorbital margin terminating mesially as angular tooth or
rounded corner. Antennules folding transversely or obliquely. Antennae not excluded from orbit. Cornea
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pigmented. Maxilliped 3 ischium longer than merus, subquadrate or triangular; merus subquadrate; palp
articulating at distolateral margin of merus, segments articulating end-to-end, decreasing in size distally;
exopod with flagellum. Chelipeds equal; segments unarmed; surfaces smooth, finely to sparsely setose.
Ambulatory legs relatively short, stout, P3 longest, P5 shortest, dorsal to other pereopods; P3–4 merus with
row of spines or teeth on flexor margin; propodus distoflexor angle with 1 or more spines opposing dactylus.
Dactyli short, claw-like, apices corneous. Female gonopore (vulva) on sternite 6, between suture 5/6 and 6/7.
Male gonopore (genital papilla) emerging near anterior margin of sternite 8, distinctly mesial to coxa 8.
Abdomen of female with all somites and telson distinct, mobile; males with somites and telson mobile or with
somites 4–6 fused. Male abdomen narrowly triangular or linguiform.
Included genera. Aphanodactylus Tesch, 1918 [type genus], Gandoa Kammerer, 2006, Gustavus n. gen.,
and Uruma Naruse, Fujita & Ng, 2009.
Remarks. Members of the Aphanodactylidae n. fam. all have a rather uniform appearance: transversely
rectangular or ovate carapace in females, narrower carapace in males; unornamented carapace surfaces with
very little evidence of regionalisation; short, stout pereopods 2–4 with short, claw-like dactyli opposing spines
on the distal propodal margins. These features of Aphanodactylidae are reminiscent of many Pinnotheridae
sensu lato and are essentially the basis of earlier classifications placing aphanodactylids there. Some features
remain to be confirmed for some genera; male Gandoa and female Uruma are, unfortunately, not yet known.
Aphanodactylids, however, differ significantly from all known Pinnotheridae in lacking the chief
synapomorphy of pinnotherids, namely, the highly modified maxilliped 3. In pinnotherids the merus of
maxilliped 3 is either considerably larger than, or fused with the ischium, forming a single unit (e.g., Ahyong
& Ng 2007: fig. 1C); and the dactylus usually articulates proximally to the distal end of the propodus, and
may be considerably enlarged or significantly reduced. Conversely, the maxilliped 3 of aphanodactylids is of
the more typical, plesiomorphic thoracotreme form: the merus is smaller than the ischium and the palp is not
enlarged. They resemble those found in a number of thoracotremes such as ocypodoids, and are what might be
expected in stem-lineage Pinnotheroidea. Comparisons of the position of the male gonopores of
aphanodactylids with specimens of other thoracotreme families revealed another noteworthy pattern. The
position of the male gonopore in aphanodactylids, being distant from the base of coxa 8, closely resembles the
condition of other pinnotherids (e.g., Nepinnotheres, Arcotheres and Viridotheres) as well as ocypodoids such
as members of the Macrophthalmidae and Ocypodidae (see also Guinot 1979). As such, the overall
pinnotherid-like habitus of aphanodactylids suggests that they are close to pinnotherids, though the
plesiomorphic form of maxilliped 3 excludes them from placement within Pinnotheridae. Aphanodactylidae is
therefore tentatively assigned to Pinnotheroidea, alongside Pinnotheridae. If our alignment of
Aphanodactylidae with Pinnotheridae is correct, then the ocypodoid-like maxilliped 3 and male gonopore
position might point towards some type of ocypodoid ancestry for Pinnotheroidea. Molecular investigations
of the phylogenetic position of Aphanodactylidae and Pinnotheridae are currently underway by several
investigators, although a close relationship between pinnotherids and ocypodoids has already been suggested
by Wetzer et al. (2009) and to a lesser extent by Palacios-Theil et al. (2009).
All known members of the Aphanodactylidae, for which hosts are recorded, are associated with tube
building polychaete worms (Terebellidae). The unusual distal propodal spines of the ambulatory legs, which
oppose the dactyli forming a subcheliform structure, and teeth present on the flexor margins of some of the
legs, possibly assists the crabs in holding onto the tube walls or the surface of their polychaete hosts. The four
aphanodactylid genera can be distinguished by the key below.
Key to genera of the Aphanodactylidae
1.
-
Maxilliped 3 merus triangular, inner distal angle produced to rounded lobe. Male abdomen with somites 4–6 fused .
......................................................................................................................................................................... Gustavus
Maxilliped 3 merus subquadrate, inner distal angle angular. Male abdomen with all somites free ............................. 2
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2.
3.
-
P2–5 meri length about 1.5 times propodus and carpus length combined. P5 merus shorter than half length of P4
merus....................................................................................................................................................................Uruma
P2–5 meri as long as or slightly longer than propodus and carpus length combined. P5 merus exceeding half length
of P4 merus ................................................................................................................................................................... 3
Carapace of females transversely subquadrate; surface distinctly punctate. ..................................................... Gandoa
Carapace of females transversely ovate; surface smooth, with few scattered pits .............................. .Aphanodactylus
Aphanodactylus Tesch, 1918
Aphanodactylus Tesch, 1918: 283 [type species: A. sibogae Tesch, 1918, by monotypy].
Diagnosis. Carapace wide, ovate, males 1.4–1.5 times wider than long, females 1.6–1.9 times wider than
long; lateral margins cristate or subcristate, but not continuous to external orbital end; surface smooth,
glabrous, with few scattered pits. Front narrow, deflexed broadly triangular in frontal view; straight to weakly
sinuous in dorsal view. Orbit transverse; margins entire, unarmed; infraorbital margin mesially terminating in
acute angle; supraorbital margin demarcated from antennular fossa by even curve; infraorbital and
supraorbital margins not extending laterally beyond cornea or continuing laterally beyond orbit proper. Eyes
short, mobile, fully occupying orbit. Antennules articulating transversely to slightly obliquely. Epistome
short, medially sunken. Maxilliped 3 ischium longer than merus, both subquadrate. Thoracic sternites 1 and 2
completely fused, broadly angular anteriorly; sternites 2/3 demarcated by shallow groove; sternites 3/4 fused,
laterally unarmed; sternites 4–8 demarcated by narrow grooves, those demarcating sternites 4–7 incomplete
medially; without longitudinal groove. Cheliped merus and carpus unarmed, with sparse plumose setae. P2–5
similar in shape, P3 longest; meri about twice as long as high, as long as or slightly longer than respective
carpi and propodi combined; with plumose setae on flexor and extensor margins; meri with or without teeth
along flexor margin. P4 markedly shorter than preceding leg, dorsal to others. P2–5 with short spines on
distoflexor angle of propodi opposing dactyli; dactyli very short, claw-like. Male abdomen simple, triangular;
telson and all somites free; widest at somite 1; thoracic sternite 8 exposed when abdomen closed. Female
abdomen with telson and all somites freely articulating, widest at somite 4. Vulva ovate, maximum width not
exceeding half width of sternite 6. G1 simple, slender, broadly curved. G2 small, about 1/3 length of G1,
slender, apex blunt.
Included species. Aphanodactylus edmondsoni Rathbun, 1932, A. sibogae Tesch, 1918, A. loimiae
Konishi & Noda, 1999, A. panglao Ng & Naruse, 2009.
Material examined. Aphanodactylus edmondsoni Rathbun, 1932: BPBM 3576, holotype female (cl. 9.5
mm, cw. 16.1 mm), Oahu, Hawaiian Is., coll. C. H. Edmondson, 27 November 1931; BPBM 3577, 1 male (cl.
8.0 mm, cw. 11.6 mm), Oahu, Waimanalo, Hawaii, coll. C. H. Edmondson, 27 November 1931; ZRC
2000.0542, 1 male (cl. 8.2 mm, cw. 11.5 mm), 1 female (cl. 10.2 mm, cw. 16.9 mm), Oahu, Hawaiian Is.,
1930s, coll. C. H. Edmondson. — Aphanodactylus loimiae Konishi & Noda, 1999: CBM 5341, 1 male (cl. 7.4
mm, cw. 10.3 mm), 1 ovigerous female (cl. 8.6 mm, cw. 13.9 mm), Kyan, Kuroshima I., Yaeyama Is.,
Ryukyus, 10 m deep, coral reef, in tube of Loimia ingens (Terebellidae), 10 October 1999, coll. K. Nomura on
SCUBA; CBM 5443, 1 ovigerous female (cl. 9.1 mm, cw. 15.3 mm), Ahra Beach, Kume-jima I., Okinawa Is.,
Ryukyus, 10 m deep, coral reef, inhabiting tube of Loimia ingens, 15 June 1995, coll. K. Nomura on SCUBA.
— Aphanodactylus panglao Ng & Naruse, 2009: NMCR, holotype ovigerous female (cl. 5.0 mm, cw. 8.8
mm) Napaling, Panglao I., Bohol Sea, Philippines, stn. B8, 3 m deep, 9°37.1′ N, 123°46.1′ E, by subtidal
brushing of coral rock and debris, 7 June 2004, coll. Panglao Marine Biodiversity Project; ZRC, paratype
male (cl. 3.1 mm, cw. 4.2 mm) (ZRC), Panglao I., Bohol Sea, Philippines, associated with an unidentified
terebellid worm, early 2000s, coll. J. Hinterkircher. — Aphanodactylus sibogae Tesch, 1918: RMNH 2162,
syntype female (cl. 5.4 mm, cw. 8.8 mm), east of Dangar Besar, Sapeh Bay, north coast of Sumbawa, Lesser
Sunda Is., Indonesia, up to 36 m depth, SIBOGA Expedition st. 313, 14–16 February 1900; ZRC, 1 male (cl.
5.3 mm, cw. 7.8 mm), Sekotong, West Lombok, Indonesia, 16 May 2007, coll. D. L. Rahayu.
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FIGURE 1. Aphanodactylus loimiae, male, cl. 7.4 mm, cw. 10.3 mm (CBM 5341). A, habitus. B, cephalothorax,
anterior view. C, right maxilliped 3. D, right chela. E, right P5. F, thoracic sternum. G, left thoracic sternites 7–8, coxae,
and genital papilla. H–I, left G1, abdominal and thoracic sternal views, respectively. J–L, left G2, mesial, sternal and
abdominal views, respectively. M, abdomen. Scales: A, D, F, M = 3.0 mm; B, C, E, G = 1.5 mm; H, I = 1.0 mm; J–L =
0.5 mm.
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Remarks. Aphanodactylus is the best known and largest genus of the aphanodactylids, and appears to be
closest to Gandoa (see Remarks under the account of Gandoa). Four described species are presently known,
all from the western Pacific and associated with terebellid polychaete worms. The taxonomy of these
Aphanodactylus species has been treated and discussed in detail by Konishi & Noda (1999), Ng & Naruse
(2009) and Ng et al. (in press). A male and female of A. loimiae are illustrated here to represent the genus
(Figs. 1, 2).
FIGURE 2. Aphanodactylus loimiae, ovigerous female, cl. 8.6 mm, cw. 13.9 mm (CBM 5341). A, habitus. B,
cephalothorax, anterior view. C, thoracic sternum. D, right chela. E, right P4. Scales A, C, D = 3.0 mm; B, E = 1.5 mm.
Gandoa Kammerer, 2006
Voeltzkowia Lenz, 1905: 364 [type species: V. zanzibarensis Lenz, 1905, by monotypy].
Gandoa Kammerer, 2006: 270 [replacement name of Voeltzkowia Lenz, 1905, preoccupied by Voeltzkowia Boettger,
1893 (Reptilia)].
Diagnosis. Carapace wide, subrectangular, females 1.6 times wider than long; surface distinctly punctate.
Front narrow, deflexed triangular in frontal view; broadly convex in dorsal view. Orbit transverse, normal;
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orbital margins entire, unarmed; infraorbital margin mesially terminating in rounded angle; supraorbital
margin demarcated from antennular fossa by even curve; infraorbital and supraorbital margins continuing
laterally beyond orbit proper to form narrow, tapered slit. Eyes short, fully occupying orbit. Maxilliped 3
ischium longer than merus, merus subcircular; ischium subquadrate, widening distally, anterointernal angle
acute. Cheliped merus and carpus unarmed, with sparse setae. P2–5 similar in shape, setose, P3 longest; meri
about twice as long as high, about as long respective carpi and propodi combined; dactyli very short, clawlike. P4 markedly shorter than preceding leg, dorsal to others. Female abdomen with telson and all somites
freely articulating, widest at somite 4.
Included species. G. zanzibarensis (Lenz, 1905) (Fig. 3), G. brevipes (H. Milne Edwards, 1853).
Material examined. Gandoa brevipes (H. Milne Edwards, 1853): MNHN B-10616, lectotype female (cl.
5.1 mm, cw. about 8.5 mm, carapace soft), Mayotte, Comoro Is., coll. Cloué.
FIGURE 3. Gandoa zanzibarensis (Lenz, 1905), female holotype. A, habitus. B, cephalothorax, frontal view. C, left
maxilliped 3. D, abdomen. (After Lenz 1905: pl. 47 figs. 9–9c).
Remarks. As has been discussed at length by Ng & Naruse (2009), Pinnixia brevipes H. Milne Edwards,
1853, from Mayotte, western Indian Ocean, is best placed in Gandoa. Gandoa is currently poorly understood,
being known only from Lenz’s (1905) account of the female holotype of G. zanzibarensis, and from the dried
female holotype of G. brevipes. As can be deduced from comparison of the accounts of Aphanodactylus and
Gandoa, very little actually distinguishes the two genera. The most important distinctions between
Aphanodactylus and Gandoa appear to be the ovoid versus subrectangular carapace in females, the almost
smooth versus distinctly punctate carapace surface, and the lateral continuation of the upper and lower orbital
margins beyond the orbit proper in the latter. The upper and lower orbital margins in Aphanodactylus may or
may not extend beyond the orbit proper, and thus appear to overlap with or approach the condition in Gandoa.
The slight carapace shape differences between female Gandoa and Aphanodactylus, and differences in surface
punctation are rather minor distinctions, raising the possibility that Gandoa might ultimately prove to be
synonymous with Aphanodactylus (see Ng & Naruse 2009). These authors concluded, however, that until
species of Gandoa can be more fully evaluated, and males are discovered and described, it is best to recognize
Gandoa as a distinct genus. Moreover, the Gandoa-Aphanodactylus distinction correlates biogeographically,
with both species of Gandoa occurring in the western Indian Ocean, and the four species of Aphanodactylus
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in the western Pacific. Thus, we follow Ng & Naruse (2009) in recognizing the two genera as separate
pending further study.
Gustavus n. gen.
Type species. Gustavus mecognathus n. sp., by present designation.
Diagnosis. Carapace wide, ovate to subpentagonal, males 1.4 times wider than long, females 1.8 times wider
than long; lateral margins cristate but not continuous to external orbital end; surface finely pubescent,
especially towards anterior half. Front narrow, deflexed medially, prominently triangular in frontal view;
medially emarginate in dorsal view. Orbit transverse, normal; orbital margins entire, unarmed; infraorbital
margin mesially terminating in rounded angle; supraorbital margin demarcated from antennular fossa by acute
tooth; infraorbital and supraorbital margins not continuing laterally beyond orbit proper. Eyes short, mobile,
fully occupying orbit. Antennules articulating obliquely. Epistome short, medially sunken. Maxilliped 3
covering buccal cavern; ischium slender, triangular, markedly longer than merus, inner distal angle produced
mesially to form rounded lobe; merus rounded-subquadrate. Thoracic sternites 1 and 2 completely fused,
broadly rounded anteriorly; sternites 2/3 demarcated by shallow groove; sternites 3/4 fused, laterally
unarmed; sternites 4–8 demarcated by narrow grooves, those demarcating sternites 4–7 medially incomplete;
without longitudinal groove. Cheliped merus and carpus unarmed, covered with short, fine, black-brown setae
and some longer plumose setae on merus and carpus. P2–5 similar in shape, P3 longest; meri 3 or more times
as long as high, slightly longer than carpus and propodus combined; covered with short, fine, black setae,
especially on carpus and propodus, and longer plumose setae on merus to coxa. P5 markedly shorter than
preceding leg, dorsal to others. P4 and 5 ischia and meri with prominent spines of flexor margins. P2–5 with
short spines on distoflexor angle of propodi opposing dactyli; dactyli very short, claw-like. Male abdomen
broad, linguiform, somites 4–6 fused; widest at somite 3; thoracic sternite 8 exposed when abdomen closed.
Female abdomen with telson and all somites freely articulating, widest at somite 4. Vulva large, ovate, almost
as wide as sternite 6. G1 simple, slender, strongly bent mesially at distal quarter. G2 small, about ¼ length of
G1, slender, apex blunt.
Etymology. Named for Gustav Paulay, who collected the type material of G. mecognathus. Gender
masculine.
Included species. Monotypic.
Gustavus mecognathus n. gen., n. sp.
(Figs. 4, 5, 7A)
Material examined. ZRC, male holotype (cl. 6.1 mm, cw. 8.8 mm), female paratype (cl. 8.0 mm, cw. 13.9
mm), SW Cocos Barrier, Guam, near small pass on large terebellid worm, G. Paulay, 20 March 2000.
Description. Female: Carapace ovate, distinctly broader than long, width to length ratio 1.8; dorsal
surface smooth, regions poorly demarcated, scattered shallow pits; surface finely pubescent on surface and
margins; lower lateral margins with dense plumose setae. Front deflexed, medially emarginate in dorsal view,
triangular in anterior view, inner orbital margin rounded in dorsal view. Orbital margins entire, slightly
narrowed laterally; eye filling orbit, cornea simple; infraorbital margin terminating mesially as rounded angle,
supraorbital margin terminating mesially in slender, ventrally directed tooth. Anterolateral margin entire,
convex laterally, cristate, continuing onto posterolateral margin but not supraorbital margin. Epistome very
short, medially sunken. Antennule folding obliquely, filling fossa. Antennae with stout basal antennal article,
not reaching distolateral angle of carapace; antenna not excluded from orbit.
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FIGURE 4. Gustavus mecognathus n. gen., n. sp., male holotype, cl. 6.1 mm, cw. 8.8 mm (ZRC). A, habitus. B,
cephalothorax, anterior view. C, right maxilliped 3. D, right chela. E–H, right P2–P5. I, thoracic sternum. J, abdomen. K,
right G1, abdominal view. L, right G2, abdominal view. Scales: A = 2.9 mm; B, K–L = 1.0 mm; C = 0.7 mm; D–J = 2.0
mm.
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FIGURE 5. Gustavus mecognathus n. gen., n. sp., female paratype, cl. 8.0 mm, cw. 13.9 mm (ZRC). A, habitus. B,
cephalothorax, anterior view. C, right maxilliped 3. D, left chela. E–H, right P2–P5. I, thoracic sternum. J, abdomen.
Scales: A = 2.9 mm; B, C = 1.0 mm; D–I = 2.0 mm; J = 4.0 mm.
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Maxilliped 3 ischium distinctly longer than merus, slender, triangular, distomesial angle produced to
rounded lobe extending mesially to level of mesial meral margin; merus smaller than ischium, slightly wider
than long, rounded-quadrate: palp articulating on distal margin of merus; exopod slender, overreaching base
of merus, flagellum short, not reaching distal margin of merus.
Chelipeds equal, covered with fine, short, black setae; merus triangular in cross section, with plumose
setae proximally; carpus smooth, inner angle rounded with sparse plumose setae; chela surfaces smooth, palm
about 1.4 times longer than dactylus; pollex with convex occlusal margin, crenulate proximally; dactylus
occlusal margin with low, blunt teeth proximally.
P2–5 relatively short, P3 longest, P5 shortest, dorsal to other pereopods; propodus and carpus covered
with short, fine, black-brown tomentum; merus with plumose setae along flexor and extensor margins; merus
about 3 times as long as high, slightly longer than carpus and propodus combined; dactyli short, stout, apices
corneous. P2 and 3 meri with scattered granules on flexor margin. P4 and 5 ischia and meri with stout spines
on flexor margins. P2–5 propodi with 1–3 small distoflexor spines opposing dactyli.
Male: Carapace subpentagonal, broader than long, width to length ratio 1.4; dorsal surface smooth,
regions poorly demarcated, scattered shallow pits; surface with fine, scattered setae on surface and margins;
lower lateral margins with dense, plumose setae. Front deflexed, medially emarginate in dorsal view,
triangular in anterior view, inner orbital margin angular in dorsal view. Orbital margins entire, slightly
narrowed laterally; eye filling orbit, cornea simple; infraorbital margin terminating mesially as rounded angle,
supraorbital margin terminating mesially in triangular, ventrally directed tooth. Anterolateral margin entire,
convex laterally, cristate, continuing onto posterolateral margin but not supraorbital margin. Epistome very
short, medially sunken. Antennule folding obliquely, filling fossa. Antennae with stout basal antennal article,
not reaching distolateral angle of carapace; antenna not excluded from orbit.
Maxilliped 3 covering buccal cavern when closed; ischium distinctly longer than merus, slender,
triangular, distomesial angle produced to rounded lobe extending mesially beyond level of mesial meral
margin; merus smaller than ischium, slightly wider than long, rounded-quadrate: palp articulating on distal
margin of merus; exopod slender, reaching almost to midlength of merus, flagellum short, not reaching distal
margin of merus.
Chelipeds equal, covered with fine, short, black setae; merus triangular in cross section, with plumose
setae proximally; carpus smooth, inner angle rounded with sparse plumose setae; chela surfaces smooth, palm
about 1.2 times longer than dactylus; pollex with convex occlusal margin, with blunt teeth proximally;
dactylus occlusal margin with low, blunt teeth proximally.
P2–5 relatively short, P3 longest, P5 shortest, dorsal to other pereopods; propodus and carpus covered
with short, fine, black-brown tomentum; merus with plumose setae along flexor and extensor margins; merus
about 3 times as long as high or greater, slightly longer than carpus and propodus combined; dactyli short,
stout, apices corneous. P2 and 3 merus with scattered granules on extensor margin. P4 and 5 ischia and meri
with stout spines on flexor margins. P2–5 propodi with 1–3 small distoflexor spines opposing dactyli.
Etymology. Derived from the Greek mekos for length, and gnathos for jaw, alluding to the elongate
ischium of maxilliped 3.
Remarks. Gustavus mecognathus n. gen., n. sp., is perhaps the most peculiar of the aphanodactylids in
the triangular rather than subquadrate maxilliped 3 ischium, broad male abdomen in which somites 3–5 are
fused, and in the finely pubescent body surface, with longer, plumose setae around the bases of the pereopods
and pterygostomian surfaces of the carapace. In all other aphanodactylids, the maxilliped 3 ischium is
subquadrate, the male abdomen (not known in Gandoa) is narrowly triangular with all somites and telson
freely mobile, and the carapace and most surfaces of the pereopods are glabrous. Gustavus differs from other
aphanodactylids in numerous other features including: a sharply triangular instead of broadly angular front (in
anterior view); strongly oblique articulation of the antennules (versus slightly oblique to near transverse); an
acute process demarcating the supraorbital margin from the upper antennular fossa; and a rounded rather than
angular mesial termination of the infraorbital margin.
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Gustavus mecognathus has proportionally more slender ambulatory legs than other aphanodactylids. The
ambulatory meri are about three or more times longer than high in Gustavus in comparison to about twice as
long as high in Aphanodactylus and Gandoa. The P2–4 meri in Uruma are also about three times as long as
high, though the legs are disproportionately larger in comparison to the carapace in Uruma than in Gustavus.
Distribution. Presently known only from the type locality, Guam.
Uruma Naruse, Fujita & Ng, 2009
(Figs. 6, 7B)
Uruma Naruse, Fujita & Ng, 2009: 60 [type species: U. ourana Naruse, Fujita & Ng, 2009, by monotypy].
FIGURE 6. Uruma ourana Naruse, Fujita & Ng, 2009, male holotype, cl. 4.2 mm, cw. 9.2 mm (RUMF-ZC-907). A,
cephalothorax, anterior view. B, right maxilliped 3. C, left P4, dorsal view. D, propodus and dactylus of left P4, ventralinner view. E, right P5, dorsal view. F, abdomen. G, right G1, abdominal view. H, right G2, thoracic sternal view. Scales:
A = 1.0 mm; B =0.8 mm; C, E = 1.5 mm, D = 1.3 mm; F = 2.0 mm; H, G = 0.5 mm. (After Naruse et al. 2009: figs. 3, 4).
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FIGURE 7. A, Gustavus mecognathus n. gen., n. sp., male holotype, cl. 6.1 mm, cw. 8.8 mm (ZRC) (lower) and female
paratype, cl. 8.0 mm, cw. 13.9 mm (ZRC) (upper) (photo: G. Paulay). B, Uruma ourana Naruse, Fujita & Ng, 2009, male
holotype, cl. 4.2 mm, cw. 9.2 mm (RUMF-ZC-907) (after Naruse et al. 2009: fig. 1).
Diagnosis. Carapace wide, trapezoidal, margins cristate, but not continuous to external orbital end, epimeral
suture just inferior to carapace proper; surface smooth, glabrous. Front narrow, deflexed medially, triangular
in frontal view. Orbit oblique, mesial part of supraorbital margin placed more posteriorly than external orbital
end; orbital margins entire, outer part granulated, infraorbital margin mesially terminating in sharp tooth;
supraorbital margin demarcated from antennular fossa by obtuse angle; supraorbital margin demarcated from
antennular fossa by acute tooth; infraorbital and supraorbital margins not continuing laterally beyond orbit
proper. Eyes short, mobile, fully occupying orbit. Epistome short, medially sunken. Maxilliped 3 covering
about 4/5 of buccal cavern. Thoracic sternites 1 and 2 completely fused, sternite 1 tooth-like, directed dorsally
at proximal end of buccal cavern; sternites 2 and 3 demarcated by deep groove; sternites 3 and 4 fused, lateral
parts marked by very shallow depressions and pits; sternites 4–8 demarcated by narrow lateral grooves at
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outside of sternal cavity, grooves ending at lateral parts of sternal cavity; sternal cavity depressed medially, no
clear longitudinal groove. Cheliped merus with large transverse and triangular lobe on subdistal part of dorsal
margin. P2–4 similar in shape, P3 longest; meri about 3 times as long as high, about 1.5 times length of
propodus and carpus length combined; carpus longer than propodus. P5 merus slightly longer than carpus and
propodus combined, about twice as long as high, just reaching proximal half of P4 merus; distal end of
ischium and proximal end of merus each with single sharp tooth on flexor margin. P2–5 all with single pair of
short, sharp claw on distoflexor angle of propodi; dactyli very short, claw-like. Male abdomen with all
somites freely articulating, first somite widest. Thoracic sternite 8 exposed when abdomen closed, somite 3 to
telson forming triangular outline. G1 straight, slender, distally tapering incurved. G2 small, about ¼ length of
G1.
Included species. Monotypic.
Material examined. Uruma ourana Naruse, Fujita & Ng, 2009: RUMF-ZC-907, holotype male, cl. 4.2
mm, cw. 9.2 mm, Oura Bay, Okinawa , Ryukyu Is., Japan, 8 m, from a tube of unidentified worm, coll. M.
Obuchi, 28 July 2007.
Remarks. Uruma ourana was recently described in detail by Naruse et al. (2009) and is presently known
only from the male holotype collected from Okinawa.
Acknowledgements
We are grateful to Gustav Paulay, Tomoyuki Komai, Tohru Naruse and Danièle Guinot for access to
specimens. STA acknowledges support from the NIWA Capability Fund, the New Zealand Foundation for
Research, Science and Technology (CO1X0502), and fellowships from the Raffles Museum of Biodiversity
Research, National University of Singapore.
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