Bull. Natl. Mus. Nat. Sci., Ser. A, Suppl. 5, pp. 83–99, February 21, 2011

Two New Species of the Genus Microprosthema Stimpson,
1860 (Stenopodidea: Spongicolidae),from the Ryukyu Islands
Tomomi Saito1 and Junji Okuno2
1

Port of Nagoya Public Aquarium, Minato-ku, Nagoya 455–0033, Japan
E-mail: t-saito@nagoyaminato.or.jp
2
Coastal Branch of Natural History Museum and Institute,
Chiba, 123 Yoshio, Katsuura, Chiba 299–5242, Japan
E-mail: okuno@chiba-muse.or.jp

Abstract Two new species of the spongicolid genus Microprosthema Stimpson, 1860, are described. The first, Microprosthema fujitai sp. nov., is described on the basis of material collectedfrom Okinawa Island, the Ryukyu Islands, southern Japan. The second, M. lubricum sp. nov., is described from the Kerama Islands, the Ryukyu Islands, and the Society Islands, French Polynesia.
This work increases the number of the species in Microprosthema to 12, and of those known fromthe Indo-West Pacific to five. Microprosthema fujitai is distinguished from its congeners by having
fewer spines on the carapace, the absence of a median carina on the posterior part of the thirdpleonal somite, the possession of lateral spines on the sixth pleonal somite, and the presence of agroove on the third pereopod carpus. Microprosthema lubricum is unique in the reduced armamentof the body and thoracic appendages and the lack of an epipod on the fourth pereopod.
Key words : Decapoda, Stenopodidea, Spongicolidae, Microprosthema, new species, Ryukyu Islands, Japan, Society Islands, French Polynesia.

The spongicolid genus Microprosthema
Stimpson, 1860, contains 10 described species
distributed in tropical shallow waters in the world(Table 1). All species are small-sized, living
latently in coral or rocky reefs. Although the
Indo-West Pacific marine biota is generally higher in diversity than other marine biogeographicalregions (Briggs, 1995), there are only three previously described species of Microprosthema fromthis region: M. validum Stimpson, 1860; M.
scabricaudatum (Richters, 1880) and M. plumicorne (Richters, 1880), suggesting that more
species await discovery. In this study, we describe
two new species of the genus, M. fujitai and M.
lubricum, on the basis of material primarily fromthe Ryukyu Islands. A single specimen of M.
lubricum from the Society Island, French Polynesia, in the southwestern Pacific, is also included.
The postorbital carapace length is abbreviatedas cl in the text. Counts of teeth on the lateral

margins of the antennal scale and the uropods include the terminal tooth. The specimens examined in this study are deposited in Natural History Museum and Institute, Chiba (CBM); Coastal
Branch of Natural History Museum and Institute,
Chiba (CMNH); Florida Museum of Natural History, Gainesville (FMNH); National Museum of
Nature and Science, Tokyo (NSMT); National
Museum of Natural History, Smithsonian Institution (USNM) and Kitakyusyu Museum of Natural History and Human History (KMNH), where
the specimens of Zoological Laboratory, Facultyof Agriculture, Kyusyu University (ZLKU) havebeen transferred.
The following specimens were examined forcomparison.
Microprosthema emmiltum Goy, 1987: holotype, female (cl 5.2 mm), USNM 231363, Isla
Santa Maria, Galapagos Islands; paratype, female (cl 3.8 mm), USNM 231364, same locality

T. Saito and J. Okuno

84
Table 1.

Geographical ranges of the known species of Microprosthema Stimpson, 1860.

SpeciesGeographical Range

Reference

Microprosthema emmiltum Goy, 1987
Microprosthema fujitai sp. nov.
Microprosthema granatense Criales, 1997
Microprosthema inornatum Manningand Chace, 1990
Microprosthema jareckii Martin, 2002
Microprosthema looensis Goy
and Felder, 1988
Microprosthema lubricum sp. nov.

Galapagos Islands; Panama; Mexico
Ryukyu Islands, Japan
Carribean sea, Columbia
Ascension Island

Goy (1987)
This study
Criales (1997)
Manning and Chace (1990)

Guana Island, British Virgin Islands
Looe Key, Florida

Martin (2002)
Goy and Felder (1988)

Ryukyu Islands, Japan; Society Island,
French Polynesia
Caribbean Sea; Belize; Mexico; Florida

This study

MauritiusRichters (1880)

Japan; Mauritius; Marshall Islands;
Papua New Guinea

Richters (1880); Holthuis(1946); Baba et al. (1968);
Devaney and Bruce (1987);
von Martens (1872)

Microprosthema manningi
Goy and Felder, 1988
Microprosthema plumicorne(Richters, 1880)
Microprosthema scabricaudatum(Richters, 1880)
Microprosthema semilaeve(von Martens, 1872)
Microprosthema validum Stimpson, 1860

Eastern American Sea; Bahama;
Columbia
Japan; Port Jackson, Australia;
Karachi, North Arabian Sea

with holotype.
Microprosthema granatense Criales, 1997:
holotype, male (cl 3.5 mm), USNM 275993, Tayrona National Park, Granate Bay, Colombia.
Microprosthema inornatum Manning andChace, 1990: holotype, male (cl 1.8 mm), USNM
221894, Ascension Island, South Atlantic Ocean.
Microprosthema looensis Goy and Felder,
1988: holotype, ovigerous female (cl 4.3 mm),
USNM 233999, Looe Key, Florida, USA.
Microprosthema manningi Goy and Felder,
1988: holotype, male (cl 4.3 mm), USNM
233997, Carrie Bow Cay, Belize; allotype,ovigerous female (cl 5.9 mm), USNM 233998,
same locality with holotype.
Microprosthema scabricaudatum (Richters,
1880): female (cl 2.7 mm), CBM-ZC 3241,
Kumejima Island, Ryukyu Islands; 2 males (cl2.8–3.0 mm), ovigerous female (cl 3.0 mm), juv.
(cl 1.5 mm), ZLKU 11094, Amami-oshima Island.
Microprosthema semilaeve (von Martens,
1872): male (cl 4.5 mm), USNM 184533, Dry
Tortugas, Florida.
Microprosthema validum Stimpson, 1860:
male (cl 2.0 mm), ZLKU 11098, Ishigaki-jima

Goy and Felder (1988)

Stimpson (1860);
Holthuis (1946)

Island, Ryukyu Islands; male (cl 3.1 mm), 2 females (cl 2.9–3.1 mm), NSMT-Cr 8176, HongKong; CMNH-ZC 00972, Kumejima-Island,
Ryukyu Islands; male (cl 2.9 mm), CMNH-ZC
00973, Kumejima-Island, Ryukyu Islands.
Taxonomy
Microprosthema fujitai sp. nov.
[New Japanese Name: Ryukyu-sango-hime-ebi](Figs. 1–7)

Material examined. Holotype: NSMT-Cr
21265, female (cl 3.0 mm), Maeda-misaki, Okinawa Island, Ryukyu Islands, 3 m depth, 15 September 2003, coll. Y. Fujita.
Allotype: NSMT-Cr 21266, male (cl 2.0 mm),same locality as holotype, 8–6 m depth, 22 June
2003, coll. Y. Fujita.
Diagnosis. Small-sized spongicolid shrimp
with somewhat depressed body form. Rostrum
armed with 5 or 6 dorsal teeth and 1 or 2 ventral
teeth. Carapace with cervical groove, armed
posteriorly with cinctures of spines. Pleura ofsecond to fifth somites each with anterolateraland posterolateral sulci; pleuron of sixth somite
armed with 1 or 2 lateral spines. Cornea darkly

Two New Shrimps of Microprosthemapigmented. Antennal scale armed with 4 or 5 lateral teeth. Carpus of third pereopod having deep
longitudinal groove along dorsomesial margin.
Dactyli of fourth and fifth pereopods biunguiculate; propodi and carpi indistinctly subdivided.
Description of female. Rostrum (Figs. 1, 2A,B) slender, directed forward, overreaching
midlength of antennal scale, 0.63 of carapace
length, narrowly triangular in dorsal view; dorsal
margin armed with 6 large acute teeth, proximal
tooth posterior to orbital margin; ventral margin
with 1 large acute tooth subdistally, directed ventrad; lateral margin unarmed.
Carapace (Figs. 1, 2A, B) with postrostral median ridge extending to epigastric region; postorbital region armed with 3 stout spines directed
anteriorly; orbital margin concave, inferior orbital angle obsolete; antennal spine small, acuminate; pterygostomial margin produced, with several spines of various sizes; gastric region with 3
pairs of postrostral submedian spines; cervicalgroove distinct, posterior margin armed withcincture of several spines of various size, directed anteriorly; branchial region armed with scat-

85

tered spines of various sizes, directed anteriorly.
Sixth thoracic sternite (Fig. 2C) with medially
jointed pair of triangular lobes, each lateral margin unarmed, ventral surface concave. Seventh
sternite with paired, broad trapezoid plates, eachdistolateral angle weakly produced, ventral surface concave, unarmed. Eighth sternite withpaired smaller trapezoid plates, each distolateralangle rounded, ventral surface concave, unarmed.
Pleonal somites (Fig. 1) not sculptured. First
pleonal somite short, divided in two sections by
distinct transverse carina; anterior section withpleuron unarmed laterally, posteroventrally ending in process supported by short transverse carina, posterior section with pleuron unarmed laterally, posteroventral margin unarmed. Second to
fifth pleura with shallow transverse sulci anterolaterally and posterolaterally; pleura unarmed laterally; ventral margins produced, terminating inlarge acute tooth, armed with a few anterior andposterior teeth. Second pleonal somite withrather distinct transverse carina, ending at middleof pleuron. Third somite longest, with transverse
carina anteriorly, ending at middle of pleuron.

Fig. 1. Microprosthema fujitai sp. nov. Holotype, female (cl 3.0 mm), NSMT-Cr 21265, Okinawa Island, theRyukyu Islands. Whole animal in lateral view.

86T. Saito and J. Okuno

Fig. 2. Microprosthema fujitai sp. nov. Holotype, female (cl 3.0 mm), NSMT-Cr 21265, Okinawa Island, theRyukyu Islands. A: carapace and cephalic appendages, lateral; B: same, dorsal; C: sixth to eighth thoracic
sternites; D: sixth pleonal somite, telson and left uropods, dorsal. Setae omitted.

Fourth and fifth somites lacking transverse carina. Sixth somite (Fig. 2D) armed with shorttransverse row of 2 strong lateral spines on eitherside; distoventral angle terminating in large
tooth, armed with an anterior accessory tooth.
Telson (Fig. 2D) oblong, slightly constricted nearbase, feebly narrowing distally, length 1.8 timesof maximum width; dorsal surface with shallow
median groove flanked by dorsolateral carinae

each bearing row of 3 strong, symmetrically situated spines, and 2 pairs of small spines proximally; lateral margins each armed 1 strong spine at
midlength; posterior margin rounded, armed with
3 small spines.
Eye (Fig. 2A, B) well developed, cornea hemispherical, darkly pigmented; eyestalk armed withseveral spines of various sizes on dorsal andfrontal regions. Antennular peduncle (Fig. 2A, B)

Two New Shrimps of Microprosthemareaching midlength of antennal scale; first segment subequal to distal two segments combined,with longitudinal, distolateral row of plumose
setae; stylocerite acute, straight; second segmentwith a few strong mesial spines and rather strong
distolateral spines; third segment armed withsmall distolateral spine; flagella slender, long, 2.1
times longer than carapace. Antenna (Fig. 2A, B)
with stout basicerite bearing 1 or 2 moderately
large spines at distolateral angle, and with a few

87strong additional spines on ventrolateral margin;
mesial margin with laminate process; antennal
scale 2.6 times longer than broad, lateral margin
nearly straight, armed with 5 teeth, dorsal surface
with 2 longitudinal carinae; carpocerite short,overreaching level of third segment of antennularpeduncle, armed with a few strong spines on
mesial and lateral margins; flagellum slender,
long, 4.8 times longer than carapace.
Mandible (Fig. 3A, B) robust; palp consistingFig. 3. Microprosthema fujitai sp. nov. Holotype, female (cl 3.0 mm), NSMT-Cr 21265, Okinawa Island, theRyukyu Islands. A: right mandible, ventral; B: same, dorsal; C: right maxillule, ventral; D: right maxilla, ventral; E: right first maxilliped, ventral; F: right second maxilliped, ventral; G: left third maxilliped, ventral; H:
left first pereopod, lateral; I: left second pereopod, lateral; J: right fourth pereopod, lateral; K: right first pleopod, dorsal; L: right second pleopod, lateral. C–G, K, L, setae omitted.

T. Saito and J. Okuno

88

of 3 articles, distal article oval, furnished with
dense setae, intermediate article longest, distallywith tuft of setae; molar and incisor processes
clearly separated; molar surface oval, without
distinct tooth, distal margin of incisor process
truncated, armed with short, stout teeth. Maxillule (Fig. 3C) robust, with simple, slender endopod tapering distally; coxal endite suboval, withsubmarginal row of stiff setae on outer surface;basial endite moderately broad, truncated distally,
with several slender spines and sparse, longspiniform setae. Maxilla (Fig. 3D) with curved,
slender endopod; coxal and basial endites bothbilobed; scaphognathite well developed, anterior
lobe subquadrate distally, posterior lobe short,widened posteromesially. First maxilliped (Fig.
4E) with broad endopod, tapering distally; coxal
endite bilobed; basial endite large, subtriangular,
with concave mesial margin; exopod withwell-developed flagellum; epipod large, feebly
bilobed. Second maxilliped (Fig. 3F) with endopod; dactylus tapering distally; propodus anteromesially truncated, subequal in length todactylus; carpus cup-shaped; merus about twice
as long as carpus, oblong, mesial margin pecti-

Table 2.

nate; ischium about half of meral length; basis
and coxa incompletely fused with one another,
trace of articulation still discernible; epipod oval,
with well-developed, lamellate podobranch; exopod with well-developed flagellum. Third maxilliped (Fig. 3G) overreaching tip of antennal scaleby lengths of dactylus and propodus; dactylus tapering distally, lateral margins of dactylus andpropodus furnished with long setae, distomesial
surface with shallow depression filled with dense
grooming setae; carpus armed with tiny lateralspine; merus armed with dorsolateral row of 3
strong spines and lateral row of 3 spines, decreasing in size posteriorly; ischium compressed,
armed with ventromesial row of 7 small spinesand dorsolateral row of 6 strong spines, decreasing in size posteriorly; exopod with well developed, unsegmented flagellum, distally with dense
setae.
Gill formula shown in Table 2.
First pereopod (Fig. 3H) small, slender, unarmed, overreaching tip of antennal scale bylength of chela, with well-developed grooming
apparatus; dactylus 0.5 of chela length; palm
subcylindrical; carpus slender, 1.5 of chela

Gill formulae of Microprosthema fujitai sp. nov. and M. lubricum sp. nov.

M. fuijitai
Maxillipeds

Pleurobranchs
Arthrobranchs
Podobranch
Epipods
Exopods

Pereopods

1

2

3

1

2

3

4

5

—
1
—
1
1

—
1
1
1
1

1
2
—
1
1

1
2
—
1
—

1
2
—
1
—

1
2
—
1
—

1
2
—
1
—

1
—
—
—
—

M. lubricum
Maxillipeds

Pleurobranchs
Arthrobranchs
Podobranch
Epipods
Exopods

Pereopods

1

2

3

1

2

3

4

5

—
1
—
1
1

—
1
1
1
1

1
2
—
1
1

1
2
—
1
—

1
2
—
1
—

1
2
—
1
—

1
2
—
—
—

1
—
—
—
—

Two New Shrimps of Microprosthema

length; merus 0.8 of carpal length; ischium 0.7 ofmeral length. Second pereopod (Fig. 3I) longer
than first pereopod, unarmed, overreaching tip of89

antennal scale by lengths of chela and carpus;
dactylus 0.4 of chela length; palm subcylindrical;
carpus 1.7 times as long as chela; merus 0.9 ofFig. 4. Microprosthema fujitai sp. nov. Holotype, female (cl 3.0 mm), NSMT-Cr 21265, Okinawa Island, theRyukyu Islands. A: right third pereopod, chela, carpus and merus, mesial; B: same, chela and carpus, dorsal;
C: same, carpus, merus and ischium, lateral.

90

T. Saito and J. Okuno

carpal length; ischium 0.6 of meral length. Third
pereopod (Fig. 4A–C) strongest, overreaching tipof antennal scale by lengths of chela and carpus;
chela 1.6 times as long as carapace; dactylus 0.4
of chela length, terminating in hooked unguis,armed with 4 small spines on dorsal margin, cutting edge armed proximally with stout, triangular
tooth, remaining parts entire; fixed finger generally similar to dactylus, cutting edge armed proximally with large blunt teeth opposed into depression on dactylus; palm subcylindrical, 2.4

times longer than wide, dorsomesial surface
armed with 2 rows of several spines, ventromesial margin armed with irregular rows of several
small spines, dorsolateral surface armed withrow of several smaller spines; carpus slightly
widened distally, about 4.2 times longer thanwide, 1.3 of chela length, dorsal surface armed
with 2 rows of 5 or 6 large spines, distalmost
strongest, dorsomesial margin grooved longitudinally, ventromesial margin armed with irregularrow of several small spines; merus 0.8 carpal

Fig. 5. Microprosthema fujitai sp. nov. Allotype, male (cl 2.0 mm), NSMT-Cr 21266, Okinawa Island, theRyukyu Islands. Whole animal in lateral view.

Two New Shrimps of Microprosthema

length, dorsal margin armed with row of 6 strong
spines, ventral margin armed with row of 8
spines, decreasing in size posteriorly, mesial surface armed with 1 spine; ischium 0.6 meral
length, dorsal margin armed with 1 strong spineand 2 or 3 additional small spines, ventral margin
serrated.
Fourth and fifth pereopods (Fig. 3J) similar,
long, slender; dactyli compressed laterally, 5.7
times longer than wide, biunguiculate; propodi
3.5 of dactylar length, subdivided into 4 articles,
ventral surfaces armed with about 20 movablespines; carpi 2.4 of propodal length, subdivided
into 5 articles; meri entire, 0.8 of carpal length;
ischia entire, 0.6 meral length.
First pleopod (Fig. 3K) uniramous, shortest.
Second to fifth pleopods biramous. Second pleopod (Fig. 3L) with basipodite shorter than exopodite, but longer than endopodite, mesial mar-91

gin unarmed. Third to fifth pleopods generally
similar, decreasing in size posteriorly.
Uropod (Fig. 2D) with protopodite stout, lateral margin terminating in acute process, with 1acute tooth posteroventrally; exopod broad, overreaching to posterior margin of telson, lateral
margin nearly straight, terminating in acutetooth, with row of 8 or 9 acute teeth, dorsal surface with 2 smooth longitudinal carinae, unarmed; endopod tapering distally, overreaching
posterior margin of exopod, lateral margin armed
with 3 or 4 acute teeth, distal part unarmed, dorsal surface with a longitudinal carina, unarmedor armed with spine proximally.
Male characteristics. Rostrum (Fig. 5) 0.69
of carapace length; dorsal margin armed with 5
teeth, ventral margin with 2 subdistal teeth. Sixth
thoracic sternite (Fig. 6A) with pair of narrow,triangular lobes, each distolateral angle armed

Fig. 6. Microprosthema fujitai sp. nov. Allotype, male (cl 2.0 mm), NSMT-Cr 21266, Okinawa Island, theRyukyu Islands. A: sixth to eighth thoracic sternites. B: right third pereopod, chela and carpus, mesial; C:
same, chela and carpus, dorsal; D: same, merus and ischium, lateral.

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T. Saito and J. Okuno

Fig. 7. Microprosthema fujitai sp. nov. Photographs showing living animals in an aquarium, Maeda-misaki, Okinawa Island, the Ryukyu Islands; A: NSMT-Cr 21265, holotype female (cl 3.0 mm), B: NSMT-Cr 21266, allotype male (cl 2.0 mm).

Two New Shrimps of Microprosthemawith 1 acute spine; seventh sternite with pair ofbroad, triangular lobes, each distolateral angle
produced with acute spine, lateral and anteromesial margins armed with a few acute spines;
eighth sternite with pair of trapezoid lobes, eachdistolateral angle rounded or produced anteriorly
terminating in acute spine, each lateral marginunarmed. First pleonal somite (Fig. 5) with posterior section of pleura bearing a few small teeth
ventrally. Chela of third pereopod (Fig. 6B–D)
1.9 times as long as carapace.
Coloration in life. Body and appendages(Fig. 7A, B) generally transparent. Rostrum
transparent with sparse small red dots extending
to epigastric region. Carapace transparent withsparse red dots on anterior and posterior margins.
First to fifth pleura red. Telson and uropods
transparent. Antennal scale with sparse red dots
and flagellum transparent. Eye stalk transparent.
Third maxillipeds generally transparent, withsparse red dots on dorsomesial margin of ischia.
Third pereopods generally orange in female, colorless in male; fingers white in distal halves; carpus and merus orange in female, light orange in
male; ischia transparent.
Distribution. Presently known only from
Okinawa Island, the Ryukyu Islands, Japan; at
depths of 3–8 m.
Remarks. The new species Microprosthema
fujitai is most similar to M. plumicorne in thegeneral armature of the pleonal somites, theshape of the third pereopod, and the subdivisionof the carpi and propodi of the fourth and fifth
pereopods. Comparison with the original description of M. plumicorne (Richters, 1880) revealed
that the new species is distinguished from the latter by the following characters: (1) the rostrum isshort, not reaching to the tip of the antennal
scale, and the rate of the rostral length againstthat of the postorbital carapace is 0.63–0.69 in
M. fujitai, whereas it extends beyond the tip of
the antennal scale and it is about 1.0 in M. plumicorne; (2) spines on the carapace are much fewerin M. fujitai than in M. plumicorne (cf. Richters,
1880: 167, pl. 18, fig. 16); and (3) the posterior
part of the third pleonal somite is smooth in M.

93

fujitai, whereas it possesses a median carina in
M. plumicorne.
Etymology. Named after Dr. Yoshihisa Fujita
of University Education Center, University of the
Ryukyus and Marine Learning Center, for his
contributions to the survey on the crustacean diversity in the Ryukyu Islands.
Microprosthema lubricum sp. nov.
[New Japanese Name: Subesube-sango-hime-ebi](Figs. 8–11)

Material examined. Holotype: CMNH-ZC
01067, ovigerous female (cl 3.3 mm), Agenashiku Islet, the Kerama Islands, the Ryukyu Islands, 3 m, 25 July 1999, coll. A. Ono.
Non-type: FLMNH UF Arthropoda 16363,
ovigerous female (cl 2.4 mm), French Polynesia,
Society Islands, Moorea, mid-way between Sheraton and Gump station, backreef lagoon, sandflat with coral rubble, under massive corals andcoral rubble, 2–4 m, hand and dip net, 11 November 2008, coll. A. Anker.
Diagnosis. Small-sized spongicolid shrimp
with somewhat depressed body form. Rostrum
armed with 1 dorsal and 1 ventral subdistal tooth.
Carapace glabrous, with cervical and branchiostegal grooves. Pleura of second to fifth
somites each lacking sulci; pleuron of sixth
somite unarmed. Cornea darkly pigmented. Antennal scale armed with 4 lateral teeth. Ischiumof third maxilliped possessing dorsolateral spine.
Palm of third pereopod glabrous. Dactyli offourth and fifth pereopods biunguiculate; propodi
and carpi indistinctly subdivided. Fourth pereopod lacking epipod.
Description of holotype female. Rostrum(Figs. 8, 9A, B) slender, directed slightly downward, feebly ventrad overreaching antennal basicerite, 0.24 of carapace length, narrowly triangular in dorsal view; dorsal margin armed with 1
small subapical tooth; ventral margin with 1
small subapical tooth, situated posterior to levelof dorsal tooth; lateral margin unarmed.
Carapace (Figs. 8, 9A, B) with postrostral median ridge extending to epigastric region; postor-

94

T. Saito and J. Okuno

Fig. 8. Microprosthema lubricum sp. nov. Holotype, ovigerous female (cl 3.3 mm), CMNH-ZC 01067, Agenashiku Islet, the Kerama Islands, the Ryukyu Islands. Whole animal in lateral view.

bital region unarmed; orbital margin concave, inferior orbital angle low, rounded; pterygostomial
margin rounded, with a few minute spines; gastric region unarmed; cervical and branchiostegalgrooves distinct, posterior margins unarmed;
branchial region unarmed.
Sixth thoracic sternite (Fig. 9C) with medially
jointed triangular lobe, each distolateral angle
ending in large acute spine, ventral surface concave. Seventh sternite with paired, circular lobes,
each distolateral angle rounded, ventral surface
concave, unarmed. Eighth sternite with paired
triangular plates, each distolateral angle rounded,
ventral surface concave, unarmed.
Pleonal somites (Fig. 8) not sculptured. First
pleonal somite short, divided in two sections by
distinct transverse carina; anterior section withpleuron unarmed laterally, posteroventrally ending in process supported by short transverse carina, posterior section with pleuron unarmed laterally, posteroventral margin unarmed. Second to
fifth pleura without sulci, ventral margins rounded, unramed. Second pleonal somite anteriorly
with two transverse carinae, anterior one feeble,
posterior one distinct, ending at middle of pleuron (Fig. 8). Third somite longest, posterodorsal
margin not produced posteriorly. Telson (Fig.
9D) oblong, slightly constricted near base, slight-

ly narrowing distally, length 1.9 times maximum
width; dorsal surface with shallow mediangroove flanked by dorsolateral carinae each bearing row of 3 and 1 strong, symmetrically situatedspines, and a pair of small spines proximally; lateral margins each armed 1 strong spine at midlength; posterior margin rounded, armed with 3
small spine.
Eye (Fig. 9A, B) well developed, cornea hemispherical, darkly pigmented; eyestalk unarmed.
Antennular peduncle (Fig. 9A, B) reaching midlength of antennal scale; first segment subequal
to distal two segments combined, stylocerite
acute, slightly curved inward; second segmentwith strong distomesial and strong distolateralspine; third segment with rounded distal margin;
flagella slender, long, 3.5 times longer than carapace. Antenna (Fig. 9A, B) with stout basicerite
bearing moderately small spine at distolateralangle, ventrolateral margin unarmed; antennal
scale twice as broad, lateral margin nearlystraight, armed with 4 teeth, dorsal surface with
2 longitudinal carinae; carpocerite short, reaching distal end of antennular peduncle, unarmedor armed with small distolateral spine; flagellum
slender, long, 5.2 times longer than carapace.
Mouthparts similar to those of M. fujitai sp.
nov. Mandible (Fig. 10A) robust; palp consistingTwo New Shrimps of Microprosthema

95

Fig. 9. Microprosthema lubricum sp. nov. Holotype, ovigerous female (cl 3.3 mm), CMNH-ZC 01067, Agenashiku Islet, the Kerama Islands, the Ryukyu Islands. A: carapace and cephalic appendages, lateral; B:
same, dorsal; C: sixth to eighth thoracic sternites; D: sixth pleonal somite, telson and right uropods, dorsal.
Setae omitted.

of 3 articles, distal article oval, intermediate article longest; molar and incisor processes clearly
separated; molar surface oval, without distinct
tooth, distal margin of incisor process truncated,
armed with short, stout teeth. Maxillule (Fig.
10B) robust, with simple, slender endopod tapering distally; coxal endite suboval; basial endite
moderately broad, truncated distally. Maxilla(Fig. 10C) with slender endopod; coxal andbasial endites both bilobed; scaphognathite welldeveloped, anterior lobe subquadrate distally,
posterior lobe short, widened posteromesially.
First maxilliped (Fig. 10D) with broad endopod,

tapering distally; coxal endite bilobed; basial endite large, subtriangular; exopod with well-developed flagellum; epipod large, feebly bilobed.
Second maxilliped (Fig. 10E) with endopod;
dactylus tapering distally; propodus anteromesially truncated, subequal in length to dactylus;
carpus cup-shaped; merus about twice as long as
carpus, oblong; ischium about half of meral
length; basis and coxa incompletely fused with
one another, trace of articulation still discernible;
epipod oval, with well-developed, lamellate
podobranch; exopod with well-developed flagellum. Third maxilliped (Fig. 10F) reaching tip of

96

T. Saito and J. Okuno

Fig. 10. Microprosthema lubricum sp. nov. Holotype, ovigerous female (cl 3.3 mm), CMNH-ZC 01067, Agenashiku Islet, the Kerama Islands, the Ryukyu Islands. A: left mandible, ventral; B: left maxillule, ventral; C:
left maxilla, ventral; D: left first maxilliped, ventral; E: left second maxilliped, ventral; F: left third maxilliped, ventral; G: left first pereopod, lateral; H: left second pereopod, lateral; I: left third pereopod, lateral; J:
left fourth pereopod, lateral; K: left first pleopod, dorsal; L: left second pleopod, lateral. C–F, K, L, setae
omitted.

Two New Shrimps of Microprosthemaantennal scale by length of dactylus; dactylus tapering distally, lateral margins of dactylus andpropodus furnished with long setae, distomesial
surface with shallow depression filled with dense
grooming setae; carpus unarmed, ventrodistal
margin produced into blunt process; merus with
1 small distolateral spine and dorsolateral row of
2 larger spines; ischium compressed, armed with
1 larger distolateral spine; exopod with well-developed, unsegmented flagellum, distally with
dense setae.
Gill formula shown in Table 2.
First pereopod (Fig. 10G) small, slender, unarmed, reaching tip of antennal scale by lengthsof chela and half of carpus, with well-developed
grooming apparatus; dactylus half of chela
length; palm subcylindrical; carpus slender, 1.4
of chela length; merus 0.8 of carpal length; ischium 0.7 of meral length. Second pereopod (Fig.
10H) longer than first pereopod, unarmed, overreaching tip of antennal scale by lengths of chela
and carpus; dactylus 0.4 of chela length; palm
subcylindrical; carpus 1.6 times as long as chela;
merus 0.8 of carpal length; ischium 0.6 of meral
length. Third pereopod (Fig. 10I) strongest,
reaching tip of antennal scale by lengths of chela
and carpus; dactylus 0.4 of chela length, terminating in strongly hooked unguis, unarmed on
dorsal and lateral margins, cutting edge armed
proximally with stout, triangular tooth, remaining
parts entire; fixed finger generally similar todactylus, cutting edge armed proximally withlarge blunt teeth opposed into depression on
dactylus; palm subcylindrical, 3.0 times longer
than wide, dorsolateral and ventromesial margins
unarmed, lateral surface unarmed; carpus slightly
widened distally, about 5.7 times longer thanwide, 0.7 of chela length, dorsal margin armed
with sparse row of 2 strong spines, ventral margin armed with 1 tiny spine on midlength; merus
subequal to slightly shorter than carpal length,
ventral margin armed with row of 2 strong
spines; ischium 0.6 of meral length, unarmed.
Fourth and fifth pereopods (Fig. 10J) similar,
long, slender; dactyli compressed laterally, 3.8
times longer than wide, biunguiculate; propodi

97

5.0 times longer than dactylar length, indistinctly
subdivided into 2 articles, ventral surfaces armed
with about 20 movable spines; carpi 2.3 times
longer than propodal length, indistinctly subdivided into 3 or 4 articles, with small spine onventrodistal angle; meri entire, 0.7 of carpal
length; ischia entire, half meral length.
First pleopod (Fig. 10K) uniramous, shortest.
Second to fifth pleopods biramous. Second pleopod (Fig. 10L) with basipodite shorter than exopodite, but longer than endopodite, mesial margin unarmed. Third to fifth pleopods generally
similar, decreasing in size posteriorly.
Uropod (Fig. 9D) with protopodite stout, lateral margin terminating in acute process; exopod
broad, falling slightly short of posterior marginof telson, lateral margin nearly straight, terminating in acute tooth, with row of 10 acute teeth,
dorsal surface with 2 smooth longitudinal carinae, unarmed; endopod rounded distally, overreaching posterior margin of exopod, proximal
half of lateral margin armed with acute tooth,distal part armed with acute tooth, dorsal surface
with 1 longitudinal carina, armed with 1 strong
spine subproximally.
Coloration in life. Body and appendages
generally transparent (Fig. 11). Third pereopods
whitish transparent.
Distribution. Known from Agenashiku Islet,
Kerama Islands, the Ryukyu Islands, Japan, andSociety Islands, French Polynesia; at depths of
2–4 m.
Remarks. The specimen from Moorea, Society Islands, French Polynesia (FLMNH UF
Arthropoda 16363) is slightly variable in the following characters: 1) the lateral margin of antennal scale is armed with 3 teeth; 2) the carpi offourth and fifth pereopods are subdivided into
4–5 articles; 3) the lateral margins of the uropodal exopods are armed with 8–9 teeth; and 4) thelateral margin of the right uropodal endopod isarmed with 3 acute teeth.
In the reduced armature on the body and thoracic appendages, this new species superficiallyresembles species of some other spongicolid genera, such as Spongicoloides or Spongiocaris, but

98T. Saito and J. Okuno

Fig. 11. Microprosthema lubricum sp. nov. Ovigerous female (cl 2.4 mm), FLMNH UF Arthropoda 16363, Society Islands, French Polynesia. Photographs showing living animal under a microscope. A: whole animal,
dorsal; B: same, lateral.

Two New Shrimps of Microprosthema

the following characters place the new species in
Microprosthema: (1) the telson is oblong, withthe posterior margin rounded with three spines;(2) the uropodal endopod provides a single longitudinal carina; (3) the third maxilliped has a longand slender exopod; (4) the first pereopod has agrooming apparatus; (5) the lateral margin of thetelson is armed with a single tooth; and (6) the
dactyli of the fourth and fifth pereopods are biunguiculate (Holthuis, 1993). However, Microprosthema lubricum sp. nov. appears unique within
the genus in the generally glabrous carapace andthird pereopodal chela, the rostrum having a single tiny subdistal tooth on the dorsal and ventral
margins, and the lack of epipod on the fourth
pereopod.
Etymology. The specific name is derived fromthe Latin, lubricus (smooth), in reference to thegenerally reduced armature on the body and thoracic appendages in this new species.
Acknowledgements
We are very grateful to Drs. A. Anker(FMNH), Y. Fujita (University Education Center,
University of Ryukyus and Marine Learning
Center), H. Komatsu (NSMT), A. Ono (Zamami,
Okinawa), M. Shimomura (KMNH), and J. C.
Walker (USNM) for providing us with specimens
and valuable information in this study. Cordial
thanks are extended to Dr. T. Komai (CBM) for
improvements of an early draft, loan of comparative specimens, technical advice and encouragement. The authors appreciate the helpful reviewsof the manuscript by Drs. J. W. Goy (Departmentof Biology, Harding University) and J. W. Martin(Natural History Museum of Los Angeles County). This study was partially supported by research grants from the Narishige Zoological Science Award to the first author. We also thank thestaff of the aquarium for technical advice and encouragement.
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