Shrimps of the crangonid genus Paracrangon Dana ( Crustacea : Decapoda : Caridea ) from the northwestern Pacific : taxonomic review and description of a new species from Japan *

The northwestern Pacific species of the crangonid genus Paracrangon Dana, 1852 are reviewed. Five species, including one new species, are recognised from the region: P. echinata Dana, 1852 (type species of the genus), P. abei Kubo, 1937, P. furcata Kubo, 1937, P. okutanii Ohé and Takeda, 1986, and P. ostlingos sp. nov. The geographical range of P. okutanii is extended to the northern South China Sea off southwestern Taiwan, representing the first discovery of species of the genus from tropical waters in the western Pacific. These species are diagnosed and illustrated. They are classified into two informal species groups, the P. echinata species group (including P. echinata, P. abei and P. okutanii, and two species from other regions, P. areolata Faxon, 1893 and P. australis Hanamura, Wadley and Taylor, 1999) and the P. furcata species group (P. furcata and P. ostlingos sp. nov.). New findings on the morphology of the genus are presented. The monophyly of Paracrangon is highly corroborated by a number of autapomorphic characters, but its relationship to other crangonid genera remains obscure. A revised key to aid in the identification of the species of Paracrangon is presented.

General description: Body robust, weakly compressed laterally; integument firm, covered with short pubescence or curved setae, but devoid of scale-like structures, surface strongly sculptured.
Rostrum long and slender for crangonids, obliquely erect, compressed laterally, terminating acutely; ventral margin with strong, recurved tooth subproximally; rostral lateral carina blunt, occasionally obsolete, extending to orbital margin.Carapace principally with 4 teeth on middorsal carina, second tooth much smaller than others, occasionally reduced, fourth tooth on cardiac region also occasionally reduced; lateral surface with several carinae termed as follows: postorbital carina, hepatic carina, branchial carina, subbranchial carina, submarginal carina, cervical carina and branchiocardiac carina (Fig. 1).Postorbital carina connected with cervical carina, delineating shallowly depressed gastric region; hepatic carina supporting hepatic tooth, confluent with 2-branched branchial carina; subbranchial carina connected with branchiostegal tooth, extending posteriorly along ventral margin of carapace, occasionally connected with branchial carina posteriorly; branchiocardiac carina lying from base of fourth median tooth across cardiac region, confluent with postorbital carina; submarginal carina bordering ventral margin of carapace, accompanied by shallow groove.Orbital margin evenly concave, occasionally with small notch dorsad of base of antennal tooth.Branchiostegal tooth strong, weakly to strongly divergent; pterygostomial tooth small to strong, reaching or overreaching anterior margin of antennal basicerite, overlapped by branchiostegal tooth in lateral view.Postorbital suture extending from just superior to base of antennal tooth to about midlength of carapace.Thoracic sternum narrow, with 4 forwardly directed teeth decreasing in size posteriorly in males and nonspawning females (teeth corresponding to fifth to eighth thoracic somites); somites separated by distinct transverse sutures; in spawning females, posterior part of thoracic sternum deeply concave, posterior 2 sternal teeth completely reduced.
Abdomen with middorsal carinae at least on third to fifth somites, highest middorsal carina on third somite, sixth somite with 2 narrowly separated submedian carinae.First to fifth somites each with conspicuous lateral projection.Anterodorsal margin of first somite deeply concave; posterodorsal margin of second, fourth and fifth somites widely notched, that of third somite weakly produced posteriorly.Dorsolateral parts of terga of first to fifth somites each with broad transverse sulcus extending onto posterior part of pleuron.Pleura of first to fifth somites strongly produced ventrally, each usually terminating in acute tooth (except for P. ostlingos sp.nov.), decreasing in width toward posterior from second somite; lateral faces each with broad vertical sulcus on anterior part.Sixth somite with conspicuous posterolateral process; posteroventral tooth strong, flared laterally.First to fifth somites each with very strong sternal tooth (sternal teeth on first to third somites somewhat shortened in spawning females); sixth somite with pair of submedian teeth, being shorter than preceding sternal teeth.Telson tapering to acute tip; dorsal surface shallowly sulcate medially, with 3 pairs of small dorsolateral spines in posterior half.
Eye-stalk short, slightly constricted at middle, without tubercles on dorsal surface; cornea well developed, darkly pigmented.
Antennular peduncles long, slender, overreaching midlength of scaphocerite; first segment longer than distal 2 segments combined, with short, rounded stylocerite bearing fringe of long setae.Flagella sexually dimorphic as in other crangonids; lateral flagellum longer in males than in females; mesial flagellum very short, slightly longer in males than in females.
Distribution: Northwestern Pacific southward to Taiwan; northeastern and southeastern Pacific southward to Peru; southwestern Pacific off southeastern Australia; sublittoral to 1400 m.

Remarks:
The genus Paracrangon is quite distinctive within the Crangonidae, and there is little doubt that the genus is monophyletic, as Christoffersen (1988) hypothesised.Autapomorphic characters of the genus include: greatly or completely reduced second pereopod; dorsally flexible abdomen which enables the shrimp to have a cataleptic position; strongly produced ventral margins of the first to sixth abdominal somites; the sixth abdominal somite armed with a pair of submedian teeth on the sternum proximally; densely setose cutting edge of the first chela; and exopod of the uropod bearing a distolateral lobe, instead of normal distolateral tooth (Christoffersen, 1988;present study).Possibly homoplastic characters are as follows: strongly erect rostrum with at least one strong ventral tooth (a similar character state is found in Rhynocrangon sharpi (Ortmann, 1895) and Sclerocrangon unidentata Komai and Takeda, 1989); unarmed posterior part of the telson (a similar character is found in species of Aegaeon and Pontocaris); basicerite unarmed at the ventrolateral distal angle (a similar character is found in Prionocrangon); strongly elongate carpocerite distinctly overreaching the antennal scale (a similar character is seen in Prionocrangon); the basally articulated distomesial spine ("pollex") of the subchela (a similar character is seen in several species of Philocheras and two species of Syncrangon; De Man, 1920;Kim and Hayashi, 2003); the presence of a dorsodistal projection on the carpi of the fourth and fifth pereopods (a similar character is found in species of Rhynocrangon; unpublished data); and the presence of a row of slender spines on the ventral margins of the propodi of the fourth and fifth pereopods (a similar character is found in Rhynocrangon; unpublished data).
It had been considered that the second pereopod was absent in the genus until Hanamura et al. (1999) demonstrated the presence of a rudimentary bud of the second pereopod in P. australis.This study demonstrates that the degree of the reduction of the second pereopods varies within the genus.In P. furcata and P. ostlingos sp.nov., the second pereopod is completely absent, while in the other species examined in this study, the second pereopod is represented by a rudimentary bud like in P. australis.It is worth mentioning that the reduction of the second pereopods is not accompanied by a reduction of the fifth thoracic sternite.The fifth thoracic sternite of Paracrangon species is well developed, bearing a strong median tooth, like other crangonid species.
In spite of the well-established monophyly of the genus, it is not easy to establish its sister group.Christoffersen (1988) hypothesised that the sister group of Paracrangon is a clade containing Prionocrangon and Vercoia.However, this hypothesis was based only on homoplastic characters.Our preliminary attempt to identify sister taxon of Paracrangon using the above mentioned apomorphic characters was not successful.It may be impossible to establish a sister group to Paracrangon without comprehensive molecular or genetic study.
In order to facilitate comparison between species, the homology of the median teeth on the carapace should be discussed.Judging from the different sizes of the teeth, we assume that there are four median teeth principally in species of Paracrangon.The second tooth is much smaller than the others, which are occasionally reduced according to species.For example, the second tooth is frequently absent in P. abei, while in P. furcata and P. ostlingos sp.nov., the fourth tooth on the cardiac region is reduced.The presence of five teeth in P. australis seems to be due to the further division of the third tooth into two teeth.
The genus can be subdivided into two informal species groups by a number of characters, the first group (P.echinata species group) including P. echinata, P. areolata, P. abei, P. okutanii, and P. australis, and the second group (P.furcata species group) including P. furcata and P. ostlingos sp.nov.The characters distinguishing the two groups include: the development of the fourth median tooth on the carapace (well developed, acute in the P. echinata group versus greatly reduced in the P. furcata group); armature on the lateral face of the carapace (some additional teeth other than hepatic tooth present in the P. echinata group, versus only hepatic tooth present in the P. furcata group); structure of the subbranchial carina on the carapace (faintly branched to distinctly areolate in the P. echinata group versus simple in the P. furcata group); armature of the sixth abdominal somite (one or two lateral teeth present in the P. echinata group versus unarmed in the P. furcata group); shape of the telson (gradually tapering posteriorly in the P. echinata group versus rather abruptly tapering at the anterior 0.30 in the P. furcata group); armature of the dorsal surface of the telson (armed with a pair of submedian teeth or tubercles near the base in the P. echinata group versus unarmed in the P. furcata group); setation of the eye (lacking setae on the eye-stalk covering the corneal surface in the P. echinata group versus having numerous curved setae on the eye-stalk covering the corneal surface in the P. furcata group); development of the second pereopod (strap-like rudimentary bud in the P. echinata group versus completely reduced in the P. furcata group); structure of the propodus of the third pereopod (slender, naked in the P. echinata group versus relatively stout, setose in the P. furcata group); shape of the distolateral lobe of the uropodal exopod (narrow, variously dentate or lobate in the P. echinata group versus broad, obliquely truncate posteriorly in the P. furcata group).Fujikura et al. (1995Fujikura et al. ( , 1996) ) reported the occurrence of two non-identified species of Paracrangon from Sagami Bay and from a hydrothermally influenced area of the Minami Ensei Knoll, Okinawa Trough, respectively.The specific status of these two species remains unclear, as voucher specimens were not available for study.
Description: Rostrum (Fig. 2A) straight, 0.60-0.90times as long as carapace (0.60-0.70 times in spawning females); dorsal margin with 1 small tooth arising at about midlength; ventral margin subproximally with slightly recurved tooth reaching distal margin of basal segment of antennular peduncle and subdistally with 1 much smaller additional tooth.
Carapace (Fig. 2A, B) armed with 4 median teeth; first tooth acute, distinctly smaller than third tooth; second tooth conspicuous; third tooth PARACRANGON FROM THE NORTHWESTERN PACIFIC 517 fifth somites conspicuous, often spiniform.Pleura of first to fifth somites acutely produced ventrally, strongly flared laterally or posterolaterally, decreasing in width toward posterior, occasionally each with additional small tooth on anterior margin (Fig. 3I); median pleural carinae broad, not sharply ridged; posterolateral margins of fourth and fifth somites each with blunt to acute tooth near articular knob.Sixth somite with 2 median carinae separated by distinct median groove; posterodorsal margin produced as subquadrate lobe; lateral surface with 2 greatly unequal teeth (dorsal tooth small, arising from level of midlength of somite; ventral tooth strong, directed laterally, arising somewhat anterior to dorsal tooth); posteroventral tooth very strong, directed laterally.Telson (Fig. 2E) gradually tapering posteriorly, with 1 pair of submedian teeth on dorsal surface near base.Eye-stalk (Fig. 2A, B) without setae covering corneal surface; cornea moderately large, not dilated.
Antennular peduncle (Fig. 2A, B) moderately slender, not reaching to slightly overreaching distal margin of antennal scale in females, overreaching it by length of third segment in males.Lateral flagellum composed of 15-24 articles in females, 26-41 articles in males; mesial flagellum composed of 9-10 articles in females, 10-14 articles in males.
Antennal scale (Fig. 2B) about 2.40 times as long as wide, with strongly produced blade far overreaching distolateral tooth.
Colour in life: Body generally light brown, overlaid with small brown or black spots; distinct larger spots of same hue along dorsal and ventral margins of carapace and abdomen; gastric region of carapace translucent, thus gut visible throughout integument.
Distribution: Northwest coast of North America from Alaska to La Jolla, California; Sea of Okhotsk, Sea of Japan southward to Korea Strait, Pacific coast of northern Japan southward to Iwate Prefecture; at depths of 18-250 m (Butler, 1980;present study).
Remarks: Paracrangon echinata is most closely related to P. abei.Differences between the two species are discussed under the account of the latter species.
Paracrangon echinata has been reported from both western and eastern sides of the North Pacific Ocean, although there have been no records from the intervening Bering Sea.Our comparison between the East Asian specimens with a single specimen from Alaska revealed no significant morphological differences between them.Therefore, the lack of records of P. echinata from the Bering Sea may simply reflect insufficient collecting efforts.Reexamination of the specimens (two males) from Sagami Bay, central Japan, referred to P. echinata by Balss (1914), has revealed that they actually represent P. okutanii.The available information strongly suggests that P. echinata is a cold water species, restricted to northern Japan (Hokkaido and Tohoku District) in the Pacific coast of Japanese mainland.The bathymetric range of the species is also restricted to sublittoral to 250 m.Kubo, 1937 (Figs. 5, 6) Paracrangon abei Kubo, 1937: 3, Figs.2, 3 (type locality: Kumanonada off Nagashima, Mie Prefecture, Japan); 1965: 623, Fig. 1007; Miyake et al., 1962: 124;Ouchi, 1960: 180;Miyake, 1982: 67, unnumbered Fig. , 189 (list); Ohé and Takeda, 1986: 80 (key); Doi, 1989: 54, 59, 60;Miyake, 1991: 67, unnumbered Fig. , 188 (list); Komai, 1994: 83 (list), 99; Miyake, 1998: 67, unnumbered Fig. , 189 (list); Hanamura et al., 1999: 316 (key).Abdomen (Fig. 5C, D) with first and second somites rounded dorsally, third to fifth somites each with distinct median carina, highest carina on third somite; posterodorsal margin of third somite weakly produced; transverse carinae on second to fifth somites conspicuous.Lateral tubercles on first to fourth somites blunt, that of fifth spiniform.Pleura of first to fifth somites acutely produced ventrally, somewhat to strongly flared laterally or posterolaterally, decreasing in width toward posterior from second somite, without additional small tooth on anterior margin, accompanying median pleural carinae broad, not sharply ridged; posterolateral margins of fourth and fifth somites each with acute tooth near articular knob.Sixth somite with 2 median carinae separated by distinct median groove; posterodorsal margin produced as subquadrate lobe; lateral surface with 2 greatly unequal teeth (dorsal tooth weak, arising from level of midlength of somite; ventral tooth strong, directed posterolaterally, arising slightly anterior to dorsal tooth); posteroventral tooth very strong, directed laterally.Telson (Fig. 5E) tapering posteriorly, with 1 pair of submedian teeth on dorsal surface near base.
Antennular peduncle (Fig. 5A, B) moderately slender, not reaching distal margin of antennal scale in females, overreaching it by half length of third segment in males.Lateral flagellum composed of 15 articles in females, 22-31 articles in males; mesial flagellum composed of 6 articles in females, 8-10 articles in males.
Color in life: Unknown.
Distribution: Known only from Kumano-nada off Mie Prefecture and southern part of the Sea of Japan; at depths of 50-311 m.
Remarks: Kubo (1937) described P. abei based on five specimens, including two males and three ovigerous females.A holotype was not designated, and thus the specimens are syntypes.One lot containing one male and one ovigerous female labeled as "Paracrangon abei sp.nov." was located in the collection studied by I. Kubo, which is housed in the Tokyo University of Marine Science and Technology.Although no further information is given in the attached label, we assume that these specimens are part of the syntypes, as they agree well with the original description of P. abei.
Paracrangon abei is most closely related to P. echinata.The two species share the following features: the faintly branched or reticulate subbranchial carina on the carapace; and the possession of two lateral teeth on the sixth abdominal somite.However, P. abei differs from P. echinata in the following particulars.The first median tooth on the carapace of P. abei extends dorsally as far as the third tooth and distally two-or three-toothed.In P. echinata, the first tooth on the carapace is shorter than the third tooth, and is simply acute.The second median tooth on the carapace of P. abei is absent or greatly reduced in minute tubercle, while it is conspicuous, acute in P. echinata.The distolateral lobe of the uropodal exopod is distally three-toothed in P. abei, while the lobe of P. echinata is divided into two projections, of which lateral one is an acute tooth, and the mesial one is rounded lobule.The dactylus of the fifth pereopod may be shorter in P. abei than in P. echinata (0.38-0.43 times as long as the propodus versus 0.50-0.55times as long).Further, the spination of the third median tooth on the carapace is useful in distinguishing the two species, although this is not reliable because of variation in P. abei.The third tooth of P. abei is occasionally three-to five-toothed distally, rather than always simply acute in P. echinata.In addition, it is suggested that the body size of P. abei is smaller than that of P. echinata.Ovigerous females of P. abei are 10.2-10.3mm in cl, while those of P. echinata are 13.6-20.8mm in cl.The two specimens from the Sea of Japan identified by Miyake et al. (1961) as P. abei have been examined, and their identification is confirmed.Therefore, the two previous records of P. abei from the Sea of Japan (Ouchi, 1960;Doi, 1986) are considered correct, although the specimens used by them were not available for study.Ohé and Takeda, 1986 (Figs. 7, 8) Paracrangon echinata -Balss, 1914: 72.Not Paracrangon echinata Dana, 1852.Paracrangon sp.-Okutani, 1969, pl. 1, Fig. 4. Paracrangon okutanii Ohé and Takeda, 1986: 76, Figs. 2, 3 (type locality: Sagami Bay, Japan); Komai, 1994: 99 (list); Miyake, 1998: 189 (list); Hanamura et al., 1999: 316 (key).
Carapace (Fig. 7A, B) armed with 4 median teeth over entire length; first tooth narrower, but slightly longer than third tooth, acute; second tooth much smaller than others, usually with small accessory projection on anterior margin; third tooth acute; fourth tooth slightly shorter than third tooth, acute, rarely reduced to small tubercle; antennal tooth short to moderately long, somewhat diverging, not reaching distal margin of eye; branchiostegal tooth long and slender, strongly diverging, but not reaching level of distal margin of basal segment of antennular peduncle; pterygostomian tooth much longer than antennal tooth, reaching to proximal 0.20-0.25 of antennal scale; hepatic tooth strong, confluent with branchial carina.Orbital notch absent.Postorbital carina armed with 1 small tooth at cross point with cervical carina; branchiocardiac carina unarmed or armed with 1 small tubercle or tooth; upper branch of branchial carina unarmed; lower branch armed with 2 strong teeth, extending to posterolateral angle of carapace; subbranchial carina forming distinct reticulate structure, connected with branchial carina; posterolateral submarginal carina distinct.Intercarinal spaces deeply depressed below.Posterolateral angle somewhat flared laterally.
Antennular peduncle (Fig. 7A, B) slender, overreaching distal margin of antennal scale by length of third segment and 0.25-0.30 of second segment in females and males.Lateral flagellum composed of 18-21 articles in females, 34-35 articles in males; mesial flagellum composed of 6-9 articles in females, 11-14 articles in males.
Color in life: Body generally light brown, with darker tint on rostrum and pleural teeth; pereopods brown.
Distribution: Pacific coast of central Japan from Sagami-nada to Kii Peninsula and northeastern Taiwan; at depths of 350-1400 m.

Remarks:
The present specimens agree well with the original description of P. okutanii by Ohé and Takeda (1986), so there was no necessity to reexamine the type specimens.The specimens from southwestern Taiwan greatly extend the geographical range of this species to the northern part of the South China Sea.This species is the first representative of the genus occurring in tropical waters in the western Pacific.
As Hanamura et al. (1999) mentioned, P. okutanii appears close to two geographically greatly separated species, P. areolata from the eastern Pacific and P. australis from southeastern Australia.These three species share a similar pattern of armature and sculpture on the carapace, the sharp median carinae on the second to fifth abdominal pleura, the presence of a single lateral tooth on the sixth abdominal somite, and the elongate carpi of the fourth and fifth pereopods being subequal in length to the propodi.Further, the three species usually occur in deep-water.Paracrangon okutanii can be distinguished from P. areolata by the conspicuous fourth median tooth on the carapace and the shorter dactylus of the fifth pereopod (0.20-0.25 times as long as the propodus versus 0.30 or more times as long).The fourth median tooth of P. areolata is greatly reduced.From P. australis, P. okutanii seems to differ in the simple third median tooth on the carapace and the shape of the distolateral lobe of the uropodal exopod.In P. australis, the third median tooth on the carapace is further subdivided into two acute teeth, raising the total number of the median teeth to five.The distolateral lobe of the uropodal exopod of P. okutanii bears a minute basally articulated spine flanked by two rounded lobules on the distal margin, while it is simply rounded in P. australis.
Paracrangon okutanii is immediately separated from other northwestern Pacific species of the genus by the distinctly reticulate subbranchial carina on the carapace and the possession of a single lateral tooth on the sixth abdominal somite.
As mentioned before, the specimens from Sagami Bay identified as P. echinata by Balss (1914) actually represent P. okutanii.
Carapace (Fig. 9A, B) armed with 2 or 3 acute median teeth in anterior half; first and third teeth relatively small compared to those of species of P. separated by faint median groove; posterodorsal margin slightly produced; lateral surface unarmed; posteroventral tooth strong, directed posterolaterally.Telson (Fig. 9E) rather abruptly tapering in posterior 0.70, lacking submedian pair of teeth on dorsal surface near base.Eye-stalk (Fig. 9F) with numerous long curved setae covering corneal surface; cornea moderately large, not dilated.
Distribution: Known only from Kumano-nada and Tosa Bay, Pacific coast of southwest Japan; at depths of 200-400 m.
Remarks: This species was described on the basis of a syntypic series of ten specimens, including one male and nine ovigerous females (Kubo, 1937).One lot containing a single ovigerous female specimen, labelled as "Paracrangon furcata sp.nov.", was located in the crustacean collection studied by I. Kubo, housed in Tokyo University of Marine Science and Technology.The specimen is dried, and extremely in poor condition; and no further data is given on the attached label.Nevertheless, the presence of two prominent median teeth on the carapace and the acute pleura of the first to fifth somites are still evident in the specimen.We assume this specimen as one of the syntypes of P. furcata.Fortunately, several supplemental specimens, including four topotypic specimens from Kumano-nada, have been available during the present study.
Although the supplemental specimens agree generally with the original description by Kubo (1937), inconsistencies are found in the shape of the subproximal ventral tooth of the rostrum and the armature of the propodi of the fourth and fifth pereopods.Kubo (1937) noted that the subproximal tooth of the rostrum is "forked".However, none of the present specimens has a "forked" subproximal tooth, although the ventral margin of the tooth is somewhat produced, protuberant.The female syntype illustrated by Kubo (1937) was not located, and it is difficult to determine whether or not this discrepancy is due to misinterpretation by Kubo (1937).Kubo (1937) mentioned that there were no spines on the ventral margins of the propodi of the fourth and fifth pereopods.In the present specimens, however, the propodi are armed with row of slender spines like other congeneric species, though these spines are easily broken off.Although either or both of the two characters were used as key characters by previous authors (Kubo, 1937;Ohé and Takeda, 1986;Hanamura et al., 1999), it has been revealed that they are not reliable.
Description: Rostrum (Figs. 11, 12A; broken in holotype) 0.60 times as long as carapace, slightly curved; dorsal margin unarmed; ventral margin subproximally with stout, slightly recurved tooth not reaching level of distal margin of basal segment of antennular peduncle (ventral margin of tooth convex, but not protuberant) and subdistally with 1 smaller additional tooth.
Carapace (Figs. 11, 12A, B) armed with 3 median teeth on anterior half, fourth tooth on cardiac region completely reduced or represented by tiny tubercle; first and third teeth relatively small compared with those of P. echinata species group, first tooth acute, third tooth weaker than first tooth, acute or subacute; second tooth tiny, occasionally reduced to tubercle; antennal tooth short, slightly diverging, not reaching distal margin of eye; branchiostegal tooth relatively weak, slightly diverging, not reaching level of distal margin of basal segment of antennular peduncle; pterygostomian tooth weaker than antennal tooth, not reaching anterior margin of antennal basicerite; lateral surface of carapace unarmed other than relatively weak hepatic tooth; hepatic tooth continuous with branchial carina.Orbital notch absent.somite with 2 median carinae separated by faint median groove; posterodorsal margin slightly produced; lateral surface unarmed; posteroventral tooth relatively weak, directed laterally.Telson (Fig. 12E) rather abruptly tapering at anterior 0.30, with median pair of low tubercles on dorsal surface near base.
Antennular peduncle (Fig. 12A, B) slender, overreaching distal margin of antennal scale by length of third segment and 0.40 of second segment in males.Outer flagellum composed of 16-18 articles in males; inner flagellum composed of 4-6 articles in males.
Color in life: Body and appendages generally light brown.
Distribution: Known only from Boso Peninsula and Sagami-nada, Pacific coast of central Japan; at depths of 257-323 m.
Etymology: From the Greek ostlingos, meaning curled hair, denoting the curling setae on the eyestalk partially obscuring the corneal surface.
Remarks: As mentioned before, this new species is closely related to P. furcata.The new species is readily separated from P. furcata by the rather blunt pleura of the first to fifth abdominal somites and the shorter dactyli of the fourth and fifth pereopods (0.20-0.27 times as long as the propodus versus 0.50-0.54times as long).Further, the size of the antennal tooth and the relative length of the propodus of the third pereopod serve to distinguish the two species.The antennal and pterygostomian teeth are much shorter in the new species than in P. furcata.The propodus of the third pereopod is proportionally longer in P. ostlingos than in P. furcata (0.50 times as long as the carpus versus 0.35-0.40times as long).Although this comparison is made between different sexes, these differences are not the subject of sexual dimorphism in other species of Paracrangon, and therefore the specific separation is warranted.Furthermore, habitats of the two species appear different.The specimens of P. ostlingos sp.nov.have been collected from hard bottom with rich sponge and gorgonarian growth (personal observation), while the specimens of P. furcata came from fishery grounds of commercial trawlers (Kubo, 1937;Hayashi, 1986;Sakaji, 2001;present study).DISCUSSION Hanamura et al. (1999) briefly discussed the biogeography of Paracrangon.The currently available data suggests that Paracrangon is exclusively distributed in the Pacific Ocean.The highest species richness is found in temperate East Asian waters, where five of the seven known species occur, while there is no species endemic to the tropical region.Four of the five species (P.abei, P. furcata, P. okutanii and P. ostlingos sp.nov.) are endemic to East Asian waters, while P. echinata appears to be widely distributed in the northern North Pacific, extending to the northwest coast of United States.As mentioned above, P. okutanii extends the geographical range to the northern part of the South China Sea, representing a sole representative of the genus occurring in tropical waters in the western Pacific.The relatively recent discovery of P. australis from southern Australian waters by Hanamura et al. (1999) is highly remarkable, as all other known species are distributed in the North Pacific except for P. areolata that occurs also in the southeastern Pacific.Morphological similarities discussed would seem to suggest that the speciation events in Paracrangon were caused by complex processes of global tectonic movements in the Pacific Ocean and local isolation of populations in the northwest Pacific region.Future studies on phylogeny of Paracrangon will be of great interest in the biogeographical aspects.