The Genus Pseudoxomysis (Crustacea : Mysidacea : Mysidae : Leptomysini), With Description Of A New Species From The Timor Sea

10 Pages·2001·3.5 MB·

by  M Murano

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I14(4):887-896. 2001.
The genus Pseudoxomysis (Crustacea: Mysidacea: Mysidae:
Leptomysini), with description of a new species from the Timor Sea
Masaaki Murano
Institute of Environmental Ecology, METOCEAN Environment Inc., Riemon 1334-5,
Ooigawa-cho, Shida-gun, Shizuoka 421-0212, Japan
—
Abstract. Two species of Pseudoxomysis are discussed. The present occur-
rence ofP. caudaensis in coastal waters of Indonesia is only the second record
for the species since Nouvel established it based on specimens from Vietnam.
A new species, Pseudoxomysis incisa, is described from the Sahul Shelf, Timor
Sea. The new species is distinguished from the other species of the genus, P.
caudaensis, by the smooth body, the third segment of the mandibular palp
furnished with two series of setae on the outer margin, the endopod of the
fourth male pleopod extending to the distal end of the fourth exopod segment,
and the endopod of the uropod armed with 50 spines on the inner margin.
The genus Pseudoxomysis was estab- orly into triangular rostral plate with round-
lished by Nouvel (1973) to accommodate ed apex. Antennal scale lanceolate with
P. caudaensis collected from near Nha rounded apex, setose all around. Labrum
Trang, Vietnam. At that time he moved provided with strong frontal process. Distal
Doxomysis longiura Pillai, 1963, to this ge- segment of endopod of maxilla expanded
nus. Since then, no further reports of this distally, shorter than broad, distal margin
genus have been presented. The Pseudox- nearly straight, with about 10 similar-sized
omysis specimens in my possession are strong spines, outer margin naked, clearly
composed of two species, P. caudaensis longer than inner. Endopods of third to
Nouvel, 1973, and an undescribed species. eighth thoracic limbs with carpopropodus
Those identified as P. caudaensis were col- divided into 3 subsegments by transverse
lected in Tegal, locatedin the northerncoast articulation, terminal claw setiform. Exo-
of Java Island, Indonesia, by Mulyadi and pod offourth pleopod ofmale 7-segmented;
were presented in my study. The specimens ultimate segment small, with 2 simple setae
of the supposed new species were collected on terminal end, penultimate and antepen-
offthe Sahul Shelfin the Timor Sea during ultimate segments armed with strong mod-
a cruise (KH-72-1) ofHakuho Maru ofthe ified seta. Endopod of fourth pleopod of
Ocean Research Institute, University ofTo- male 6-segmented, considerably shorter
kyo. This latter species is described herein. than exopod, without modified setae. Fe-
All the specimens examined are deposited male pleopods rudimentary. Female with 3
in the National Science Museum, Tokyo pairs of oostegites. Endopod of uropod
(NSMT). armed with spines along inner margin. Tel-
son with deep apical incision furnishedwith
Systematics spinules on either side and pair ofplumose
setae arising from anteriorend. Lateral mar-
Genus Pseudoxomysis Nouvel, 1973
gin of telson wit—h spines throughout.
Pseudoxomysis Nouvel, 1973: 131-132. Type species. Pseudoxomysis caudaen-
— sis Nouvel,—1973.
Diagnosis. Carapace produced anteri- Remarks. Nouvel (1973) mentioned
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three major characters that distinguish (4.5 mm), 1 immature female with half-
Pseudoxomysis from the closely allied ge- grown marsupium (4.4 mm) and 1 juvenile
nus, Doxomysis, and its related genera, as (2.7 mm); Tegal, northern coast of central
follows; the labrum with a strong frontal Java, Indonesia, 3 June 1994, plankton net,
process, the distal endopod segment of the collected by Mu—lyadi.
maxilla with the outer margin longer than Description. Carapace produced ante-
the inner, and the endopods of the third to riorly into triangular rostral plate with
eighth thoracic limbs with the carpopropo- rounded apex extending to proximal third
dus divided into 3 subsegments by the of first segment of antennular peduncle
transverse articulation. (Fig. lA, B), posteriorly shortened, last 2
When Nouvel (1973) established Pseu- thoracic somites visible dorsally. Anterolat-
doxomysis, he suggested that Doxomysis eral corner of carapace rounded.
longiura Pillai, 1963, should be transferred Eye slightly compressed dorso-ventrally,
to this genus, because D. longiura, de- 1.5 times as long as broad; cornea devel-
scribed and illustrated by Pillai (1963, oped, as broad as eyestalk; eyestalk 1.5
1964), was in agreement with this genus in times longer than cornea, without papilli-
the characteristics of the maxilla and tho- formprocess on dorsal surface (Fig. lA, B).
racic endopods, and with respect to the la- Antennular peduncle of female more
brum he received a private letter from Pillai slender than that of male; first segment
that the lip is anteriorly prolonged into a twice as long as broad, armed with several
spine though short and apically broad and setae at outer distal corner and 1 seta at
rounded (Nouvel 1973). In 1973, however, inner distal corner; second segment short,
Pillai described and illustrated this species wider than long, armed with 1 long seta
in detail, but omitted to describe the la- near distal end of inner margin and 1 short
brum. Liu & Wang (1986) also examined seta on middle of outer margin; third seg-
D. longiura specimens from northern areas ment connected with second obliquely, as
of the South China Sea and stated that the long as first, twice as long as broad, armed
anterior margin of the labrum was not with 1 long seta on middle of inner margin
armed with a spine. and 1 short and 2 long setae at inner distal
At least, the labrum in D. longiura lacks corner (Fig. lA). In male, first peduncular
such a strong frontal process as seen in P. segment 1.5 times as long as broad, armed
caudaensis. Furthermore, D. longiura is with several setae at outer distal corner and
different from Pseudoxomysis in having a 1 seta at innerdistal corner; second segment
notable papilla on the eyestalk and fine spi- short, armed with 1 short seta on middle of
nules between proximal two lateral spines outer margin, no setae on inner margin;
of the telson. Considering these circum- third segment longer than first, 1.5 times as
stances, it is judged that the transfer of D. long as broad, armed with 1 long and 1 mi-
longiura to Pseudoxomysis should be can- nute setae at inner distal corner (Fig. IB).
celed. As a result, the genus Pseudoxomysis Antennal scale extending slightly beyond
comprises only two species which are de- distal margin of antennular peduncle in fe-
scribed in this paper. male and to distal end in male, lanceolate
with rounded apex, more than 6 times as
Pseudoxomysis caudaensis Nouvel, 1973 long as widestpart at proximal fourth; outer
Figs. 1, 2 margin nearly straight, apical suture at
about distal tenth (Fig. IC). Antennal pe-
Pseudoxomysis caudaensis Nouvel, 1973:
duncle barely reaching middle of scale, 3-
132-141, figs. 1-25.
segmented, second segment longest (Fig.
Material—{NSMT-Cr 13404) 1 adult fe- IC). Antennal sympod with 1 stout spine at
male with embryos (5.4 mm), 1 adult male anterolateral corner (Fig. IC).
VOLUME 114, NUMBER 4 889
Mandible with masticatory edge devel- less than twice as long as endopod, 7-seg-
oped; palp narrow, third segment half as mented, ultimate segment small, with pair
long as second, with 7 feathered setae on of simple setae on terminal end; penulti-
distal third of outer margin (Fig. ID). Max- mate segment 3 times as long as ultimate
illule with outer lobe armed with 12 stout segment, with 1 strong seta overreaching tip
spines on distal margin and 3 setae on ven- of terminal setae for half of its length; an-
tral surface; inner lobe armed with 3 strong tepenultimate segment shorter than suc-
and 1 slender setae on distal margin, 4 setae ceeding one, with 1 strong seta extending
on outer margin, 2 setae on inner margin slightly beyond apex ofterminal setae; each
and 4 setae on ventral surface (Fig. IE). of proximal 4 segments with pair of ordi-
Maxilla with second segment of endopod nary plumose setae (Fig. 2B). Endopod of
greatly expanded distally, shorter than fourth pleopod 6-segmented, only extend-
broad; outer margin naked, 1.5 times longer ing to distal margin of third segment ofex-
than inner, so that distal margin clearly in- opod, without modified setae (Fig. 2B). En-
clined towards mouth; distal margin very dopod of fifth pleopod 6-segmented, first
slightly concave, nearly 3 times as broad as segment with triangular lobe tipped with
at base, armed with 9 strong spines and 2 seta on outer margin in addition to usual
setae; inner distal corner with 6 barbed se- side lobe; exopod 7-segmented, longer than
tae (Fig. IF). Labrum with strong frontal endopod (Fig. 2C).
process (Fig. IG). Endopod of uropod overreaching distal
Endopod of first thoracic limb robust; end of telson for V4 of its length, armed
lobe from basis rather small, armed with along inner margin with about 37 spines of
many stout plumose setae; preischium and variable length (Fig. 2D, E). Exopod ofuro-
ischium expanded medially, wider than pod overreaching apex of telson for more
long; merus relatively slender, twice as long than V3 of its length (Fig. 2E).
as broad; dactylus wider than long, fur- Telson (Fig. 2E, F) as long as last ab-
nished with stout setae (Fig. IH). Endopod dominal somite, 1.7 times as long as broad
of second thoracic limb rather slender; mer- at base, abruptly narrowing towards proxi-
us as long as carpopropodus and dactylus mal third, parallel-sided in middle third and
combined; dactylus as long as broad, armed then gradually narrowing distally. Lateral
with setae arranged radially (Fig. II). En- margin armed with about 21 spines
dopods ofthird to eighth thoracic limbs lost throughout, spines longer in female than in
in all specimens. Exopods of first to eighth male; each apex with single stout spine.
thoracic limbs with flagelliform portion 8- Apical cleft Vs as long as telson and U-
or 9-segmented; basal plate small, with out- shaped in female, Va as long and V-shaped
er distal corner pointed (Fig. IH, I). in male, furnished on either side with 2 dis-
First to fifth abdominal somites subequal, tal spines and 16-18 spinules; pair of plu-
sixth somite 1.5 times longer than fifth. mose setae arising from anterior end of
Second to sixth abdominal somites hispid. cleft. —
Each of second to fifth abdominal somites Remarks. The present specimens agree
with small process along ventral median in main characteristics with the description
line. of Pseudoxomysis caudaensis Nouvel,
Pleopods of male biramous, natatory. 1973, but some minor differences are ap-
First pleopod with endopod reduced into parent. The endopod ofthe fourth male ple-
short, unsegmented lobe, exopod 7-seg- opod is slightly less than half as long as
mented (Fig. 2A). Second and third pleo- exopod and extends to the distal end ofthe
pods with 7-segmented exopod and 6-seg- third segment of the exopod in the present
mented endopod, exopod longer than en- specimen, while in the type specimens it is
dopod. Exopod of fourth pleopod slightly slightly more than half as long as exopod
890 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
iDFH
Fig. L Pseiidoxomysis caudaensis Nouvel, A, C-I, adult female; B, adult male. A, anterior end of adult
female; B, anterior end of adult male; C, antenna; D, mandible and mandibular palp; E, maxillule; F, maxilla;
G, labrum; H, first thoracic limb; I, endopod ofsecond thoracic limb.
VOLUME 114, NUMBER 4 891
Fig. 2. Pseudoxomysis caudaensisNouvel, A—C, F, adult male; D, E, adultfemale. A, firstpleopod ofmale;
B, fourth pleopod of male; C, fifth pleopod of male; D, endopod of uropod; E, uropod and telson, female; F,
telson, male.
892 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
and extends to the middle of the third seg- than that of female. In male first segment
ment. In the type specimens the telson is with several setae on anterolateral corner
narrower and several proximal lateral and 1 seta on anteromedial corner, second
spines arise from the dorsal surface rather segment shortest, third segment about as
than from the lateral margin, while in the long as first, 1.3 times longer than broad,
present specimens the spines arise from the with 3 setae on anteromedial corner (Fig.
lateral margin. — 3A). In female first segment more than
Distribution. The type specimens were twice as long as broad, second segment
collected from Cauda Bay near Nha Trang, with 1 seta on anteromedial corner, third
Vietnam, and the present specimens from segment slightly shorter than first, slightly
Tegal, northern coast ofthe central Java, In- less than twice as long as broad, with 1 seta
donesia. This species seems to be a coastal on middle of medial margin and 6 setae on
form in Southeast Asia. anteromedial margin (Fig. 3B).
Antennal scale lanceolate with rounded
Pseudoxomysis incisa, new species apex, extending beyond distal end ofanten-
Figs. 3, 4 nular peduncle for 1/7 of its length in male
— and for 1/6 in female, about 5.5 times as
Type series. Holotype (NSMT-Cr long as maximum breadth at about proxi-
13401), adult male (6.4 mm); allotype mal third, with suture at distal tenth, setose
(NSMT-Cr 13402), adult female with em- all around; inner margin convex; outer mar-
bryos (5.4 mm); paratypes (NSMT-Cr gin straight (Fig. 3A-C). Antennal peduncle
13403), 6 adult males (5.2-5.8 mm), 6 adult short, reaching middle of antennal scale,
females (4.7-5.9 mm), 3 ofwhich (4.7, 5.6, second segment longest. Antennal sympod
5.9 mm) bear embryos; Sahul Shelf, with spine at anterolateral corner.
12°17.3'S, 129°40.9'E to 12°17.2'S, Mandible with masticatory edge devel-
129°41.8'E; 49-52 m; 24 June 1972; col- oped. Mandibular palp narrow, third seg-
lected with plankton net installed in mouth ment half as long as second, outer margin
of 3-m beam trawl during Hakuho Maru armed with 2 series of setae, 10 proximal
Cruise (KH-72-1).— setae becoming longerdistally, featheredon
Othermaterial. 17 adult males (5.2-6.4 proximal half, 5 distal setae ofequal length
mm), 13 adult females (4.7-5.9 mm), 4 im- feathered along whole length (Fig. 3D).
mature males, 9 immature females; collec- Maxillule, outer lobe armed with 11 stout
tion data same —as type series. spines on distal margin and 3 setae on ven-
Description. Body smooth. Carapace tral surface; inner lobe armed with 3 strong
produced frontally into triangular rostral and 1 slender setae on distal margin, 4 setae
plate with narrowly rounded apex extend- on outer margin, 3 setae on inner margin
ing to proximal third to middle of first seg- and 7 setae on ventral surface (Fig. 3E).
ment of antennular peduncle, lateral margin Maxilla with second segment of endopod
ofrostrum slightly concave or straight (Fig. greatly expanded distally, outer margin lon-
3A, B). Anterolateral corner of carapace ger than inner, naked, distal margin trun-
rounded. Posterior margin slightly emargin- cate, 3 times broader than basal margin,
ate, leaving last 2 thoracic somites exposed armed with 9 stout, naked spines, outer 2
dorsally. spines, especially outermost one, consider-
Eye relatively large; cornea occupying ably longer than others (Fig. 3F). Labrum
about halfofwhole eye, slightly wider than armed on frontal margin with pointed, long,
eyestalk; eyestalk hispid on proximal cor- robust process (Fig. 3G).
ners, without papilliform process on dorsal Endopod of first thoracic limb robust;
surface (Fig. 3A, B). lobe from basis armed with many stout plu-
Antennularpeduncle ofmale morerobust mose setae, preischium and ischium ex-
VOLUME 114, NUMBER 4 893
Fig. 3. Pseudoxomysis incisa, new species, A, C-I: holotype; B: allotype. A, anteriorend ofadult male; B,
anterior end of adult female; C, antennal scale; D, mandible and mandibular palp; E, maxillule; F, maxilla; G,
labrum; H, first thoracic limb; I, endopod ofsecond thoracic limb.
894 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
Fig.4. Pseudoxomysisincisa, newspecies.A,allotype;B,oneofmaleparatypes; C-G,holotype.A,endopod
of third thoracic hmb without dactylus; B, endopod of seventh thoracic limb; C, fourth pleopod of male; D,
distal part of exopod of fourth male pleopod; E, fifth pleopod of male; F, endopod of uropod; G, uropod and
telson.
VOLUME 114, NUMBER 4 895
Table 1. -Morphological differences between Pseudoxomysis caudaensis Nouvel, 1973 and P. incisa, new
species.
p. caudaensis P. incisa,
Nouvel, 1973 newspecies
Abdomen Hispid Smooth
Mandibularpalp Third segment with a single series of Third segment with 2 series ofsetae on
setae on outer distal margin outer margin
Fourth pleopod ofmale Exopod slightly less than twice as long Exopod 1.5 times as long as endopod;
as endopod; endopod extending to endopod extending to distal end of
middle to distal end ofthird exopod fourth exopod segment
segment
Uropod Endopod armed with 37 spines along Endopod armed with about 50 spines
inner margin; exopod overreaching along inner margin; exopod over-
distal end oftelson for more than Vz reaching distal end oftelson for near-
ofits length ly halfofits length
panded medially, wider than long, merus ment small, nearly Vi of preceding one in
relatively slender, twice as long as broad, length, armed with 2 naked, equal-sized se-
dactylus wider than long, hirsute (Fig. 3H). tae on distal end (Fig. 4C, D). Endopod of
Endopod of second thoracic limb rather fourth pleopod extending to distal margin
slender, merus as long as carpopropodus of fourth segment of exopod, 6-segmented,
and dactylus together, dactylus longer than without modified setae, first 4 segments
broad, with terminal claw strong (Fig. 31). with naked accessory seta (Fig. 4C). Fifth
Endopods of third to eighth thoracic limbs pleopod with 7-segmented exopod and 6-
slender, with carpopropodus divided into 3 segmented endopod; first segment of en-
subsegments by transverse articulations dopod with slender lobe tipped with seta in
(Fig. 4A, B). addition to usual side lobe; third and fourth
First 5 abdominal somites subequal, sixth segments of endopod with naked accessory
somite 1.3 times longer than preceding one. seta (Fig. 4E). Side lobe on second to fifth
Male pleopods developed, biramous. endopods broad (Fig. 4C, E).
First pleopod with unsegmented endopod Uropod slender, setose all around; endo-
and 7-segmented exopod. Second and third pod extending beyond distal end of telson
pleopods with 7-segmented exopod and 6- for Va of its length, furnished with about 50
segmented endopod, endopod shorter than spines on inner margin from statocyst re-
exopod. Exopod of fourth pleopod 1.5 gion to apex; exopod overreaching telson
times longer than endopod, 7-segmented; for nearly half of its length (Fig. 4F, G).
antepenultimate segment shorter than pre- Telson slightly shorter than last abdomi-
ceding one, armed with 2 setae, one short, nal somite, 1.7 times as long as maximum
arising from outer distal corner, the other basal width, abruptly narrowing near base,
markedly robust, arising from near distal then gradually towards apex. Lateral mar-
end and reaching tip of terminal setae, gin oftelson armed with 16-19 acute spines
curved inwardly; penultimate segment 1.5 arranged sparsely in proximal half and
times longer but narrower than preceding densely in distal half, proximalmost spine
one, armed with 2 unequal setae on distal stout, arising at widest part, proximal sec-
margin, shorter one as long as ultimate seg- ond and third spines arising from dorsal
ment, longer one 1.5 times longer than seg- surface near margin. Each apical lobe
ment supporting it, straight, with short armed with 1, occasionally 2, strong spines
spine-like setae on distal half; ultimate seg- on apex and 2 spines near distal end ofcleft
896 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
margin. Cleft extending to about V3 oftelson tute of Science, for allowing me to examine
length, armed with 16 or 17 spinules on ei- the Pseudoxomysis caudaensis specimens.
ther side, anterior end with pair ofplumose
setae between which small sinus is present Literature Cited
(Fig. 4G). — Liu R., & S. Wang. 1986. Studies on Mysinae (Crus-
Etymology. The specific name incisa is tacea—Mysidacea) of the nortliern South China
from the Latin incisus = cut into, derived Sea. Studia Marina Sinica 26:159-202. (In
from caedo = to cut, in reference to the Chinese with English abstract.)
Nouvel, H. 1973. Pseudoxomysis caudaensis n. gen.,
apiRceamlacrlkesft.—ofTthhee tperlessoenn.t new species dis- nM.ersp.d,ecCrhuistnaecememriydsiiodnaaclee.—(LeBputlolemtyisnindie)ldaeSol-a
tinctly belongs to the genus Pseudoxomysis ciete d'Histoire naturelle de Toulouse 109:131-
in the characters ofthe maxilla, labrum and 141.
third to eighth thoracic endopods. From the Pillai, N. K. 1963. On a new mys—id from the inshore
waters ofthe Keralacoast. JournaloftheMa-
other species of the genus, P. caudaensis,
rine Biological AssociationofIndia5:248-262.
the new species is distinguished as shown . 1964. Report on the Mysidacea in the collec-
in Table 1. tions of the Central Marine Fisheries Res—earch
In—stitute, Mamdapam Camp, South India Part
Acknowledgments I. ^Journal of the Marine Biological Associa-
tion ofIndia 6:1-41.
I would like to thank Dr. Mulyadi, Di- b.o1o9k73t.oMtyhseiIdnatceernaatoifontahle IZnodoipalnanOkcteoann.CoHlalnedc--
vision of Zoology, Research and Develop- tions, vol. 4, Papers on the Zooplankton Col-
ment Center for Biology, Indonesian Insti- lections ofthe IIOE, 125 pp.