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1 May 2003 Syncrangon, a New Crangonid Genus, with Redescriptions of S. angusticauda (De Haan) and S. dentata (Balss) (Crustacea, Decapoda, Caridea) from East Asian Waters
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Abstract

A new genus of the crangonid shrimps, Syncrangon, is proposed for Crangon angusticauda De Haan, 1849 and (C. Sclerocrangon) angusticauda var. dentata Balss, 1914, both from East Asian waters. The new genus is readily distinguished from all known genera of the Crangonidae by the flattened middorsal carina and the deep groove on each lateral side of the middorsal carina on the third to sixth abdominal somites. Syncrangon angusticauda new combination has previously been assigned to the genus Metacrangon, while S. dentata new combination has not been reported since the original description. These two species are easily distinguished from each other by many characters, especially the rostral and abdominal features. They are redescribed and illustrated in detail.

INTRODUCTION

The family Crangonidae, which is characterized by the subchlate first pereopod and the filiform third pereopod, is now recognized to contain about 160 species belonging to 20 genera (Holthuis, 1993). Ten years ago, the Crangonidae was one of the most poorly taxonomically progressed groups in the infraorder Caridea (Holthuis, 1993; Komai, 1994). Although several taxa were recently improved (Chan, 1996; Wicksten, 1996; Komai, 1996, 1997a, b; Hayashi and Kim, 1999; Kim and Komai, 2002), the taxonomic status of many taxa in the Crangonidae is incompletely known yet. One of the problematical species is Metacrangon angusticauda (De Haan, 1849). This species was originally described as Crangon angusticauda in “Fauna Japonica.” Since then, it was often reported as Sclerocrangon angusticauda from the coastal waters of Japanese temperate region, especially seagrass beds and rocky or sandy shore (e.g., Ortmann, 1890; De Man, 1907; Parisi, 1919; Yokoya, 1933; Miyake, 1961; Miyake et al., 1962; Kikuchi, 1962, 1966, 1968; Harada, 1968; Fujino, 1978; Matsumiya et al., 1978; Sekiguchi, 1982; Imanaka et al., 1984). Zarenkov (1965), who divided the genera Crangon Fabricius, 1798 s.l. and Sclerocrangon G. O. Sars, 1883 s.l. into five genera, Crangon s.s., Mesocrangon Zarenkov, 1965, Metacrangon Zarenkov, 1965, Rhynocrangon, Zarenkov, 1965, Sclerocrangon s.s., placed this species in the genus Metacrangon. Recent authors have followed his classification (e.g., Miyake, 1982, 1991, 1998; Ito and Watanabe, 1992; Komai et al., 1992; Komai, 1994, 1999; Minemizu, 2000). In spite of many publications about the faunal study, the generic position of M. angusticauda is unsettlsed (Komai, 1994), and no detailed description of this species has been published. Another taxon, Crangon (Sclerocrangon) angusticauda var. dentata Balss, 1914 was described by Balss (1914) from off Zushi [original spelled as “Dzushi”] and Negishi, Yokohama, Pacific coast of central Japan, at depths of 45–130 m. It, however, has not been reported since the original description. The taxonomic status of this taxon remained unclear. Material from the Pacific coast of central Japan and the southern part of the Sea of Japan has enabled us to diagnose it as a distinct species.

Close examination of many specimens of these two species collected from various East Asian localities reveals that there is no precise genus, to which they can be referred. The present study, therefore, proposes a new genus Syncrangon for these two species. Syncrangon is more closely related to Sclerocrangon than to Metacrangon and also has characteristic features, which warrants its separation at the generic level. Syncrangon angusticauda and S. dentata, are readily distinguishable from each other in a number of differences such as the rostral features, the armament of the carapace and abdomen, the relative length of the telson, the scaphocerite and the dactylus of fifth pereopod, and the vertical distribution.

Specimens examined in the present study are deposited in the Kitakyushu Museum and Institute of Natural History (KMNH) with a code of IvR, National Fisheries University, Shimonoseki (NFU), Showa Memorial Institute, National Science Museum, Tokyo (NSMT) with a code of Cr R, and the Laboratory of Invertebrate Zoology, Department of Marine Biology, Pukyong National University, Pusan (PUIZ). Specimens formerly belonging to the Zoological Laboratory of Kyushu University, Fukuoka (ZLKU) are now deposited in KMNH. The postorbital carapace length (CL), which was measured from posterior margin of the orbit to the posterior middorsal margin of the carapace, is used as an indication of the size of the specimens.

SYSTEMATICS

Family Crangonidae Haworth, 1825

Syncrangon new genus

Diagnosis. – Body small, rather robust; integument moderately firm and sculptured. Rostrum short, reaching to or slightly beyond distal margin of cornea, directed forward, depressed, with acute or subacute apex; ventral plane moderately deep; lateral margin unarmed. Carapace with gastric region not depressed below general level of carapace; middorsal carina with 2 prominent spines; submedian gastric region without spine or longitudinal carina; cardiac region with 2 transverse grooves; postorbital carina distinct but unarmed; hepatic spine strong, supported by short or long carina; branchiostegal spine strong, nearly straight; pterygostomian spine much smaller than antennal spine; orbital cleft moderately deep; longitudinal suture extending posteri-orly from just superior to antennal spine; hepatic groove distinct. Third to sixth abdominal somites with flattened middorsal carina accompanied by deep groove on either lateral side, that of sixth somite notched posteriorly; pleura of first to fifth somites rounded or bluntly produced ventrally, without any spine or tooth marginally; sixth somite with poster-oventral angles nearly parallel, not flared laterally in dorsal view. Telson tapering to acute tip, with submedian carinae and median groove, bearing 3 pairs of small dorsolateral spines. First to fifth abdominal sternites with median spines, at least in males and non-spawning females. Eye with cornea well developed, eyestalk with rounded dorsal tubercle. Proximal antennular segment with acute spine on longitudinal carina on ventral surface. Stylocerite broad, rather square. Scaphocerite broad, 1.69–2.68 times as long as width, with well developed blade; lateral margin straight or slightly convex. Palm of first pereopod with distomesial spine (‘thumb’) articulated at base; merus with dorsodistal tooth but without distolateral tooth, mesial margin with obtuse tooth. Second pereopod chelate, reaching about anterior 1/3 of palm of first pereopod. Fourth and fifth pereopods with dactylus subspatulate, propodus with or without small spines. Pleurobranchs of fourth to eighth thoracic somites inclined anteriorly. Endopod of second to fourth pleopods divided into 2 segments, but that of fifth pereopod small and not segmented in females; all endopods small, not segmented in males, without appendix interna in both sexes; in males second pleopod with appendix masculina well developed, endopod vestigial.

Branchial formula as follows (r: rudimentary): i0289-0003-20-5-669-e1.gif

Type species. – Crangon angusticauda De Haan, 1849 by the present designation.

Species included. – Syncrangon angusticauda (De Haan, 1849) new combination and Syncrangon dentata (Balss, 1914) new combination.

Distribution. – Sea of Japan from Tsugaru Strait to Yuya Bay, northeastern coast of East China Sea (Jeju Island and Amakusa Islands), Pacific coast of Japan from Inubozaki to Kii Peninsula, and Seto Inland Sea; intertidal to 130 m.

Etymology. – The genus name is derived from the Greek prefix syn-(together) plus the generic name Crangon, referring to the taxonomic relation to the genus Crangon and related genera. Gender is feminine.

Remarks. – Syncrangon is unique in the Crangonidae in the third to sixth abdominal somites with a flattened middorsal carina accompanied by a deep groove on either lateral side.

Although the species of the new genus previously assigned to Sclerocrangon or Metacrangon, Syncrangon is more closely related to Sclerocrangon than to Metacrangon in having the non-depressed gastric region on the carapace, in the lack of the submedian spines of the carapace, and in the vestigial endopod of the second pleopod being much shorter than the appendix masculina in males. However, in addition to the abdominal grooves, the new genus is further distinguished from the latter two genera by having the following features: the possession of two transverse grooves on the cardiac region of the carapace, the lack of the lateral carina of the sixth abdominal somite, the non-flared poster-oventral angle of the sixth abdominal somite, the movable distomesial spine (‘thumb’) of the palm of first pereopod, and the mesial spine on the merus of first pereopod. The movable distomesial spine (‘thumb’) of the palm of first pereopod is an unique character in the genus Crangon and related genera (Argis Krøyer, 1842, Sclerocrangon, Notocrangon Coutière, 1900, Neocrangon Zarenkov, 1965, Mesocrangon, Metacrangon, Rhynocrangon). This character is shown in Paracrangon Dana, 1852 and some species of Philocheras Stebbing, 1900.

Comparison of the fecundity also supports that Syncrangon differs from both Sclerocrangon and Metacrangon. The egg size and number of the genus Crangon and related genera, including Sclerocrangon and Metacrangon, are summarized by Zarenkov (1965). In Syncrangon the eggs are 0.46–0.56[.infinity]0.34–0.38 mm in diameter and about 600 in number. These are smaller and much more than those of Metacrangon (1.75–2.50[.infinity]1.50–2.20 mm in diameter; less than 50 in number) and are much smaller than those of Sclerocrangon (2.15–5.00[.infinity]2.00–4.85 mm in diameter; about 52–1735 in number). The egg size and number in Syncrangon are similar to those of Crangon (see Zarenkov, 1965; Komai, 1994).

A recent key to the genera of the family Crangonidae has been provided by Holthuis (1993). To include Syncrangon his key may be readily augmented as follows:

  • 14. Endopod of second male pleopod with the appendix masculina shorter than the blade .......... Rhynocrangon

  • – Blade of endopod of second male pleopod strongly reduced, much shorter than appendix masculina... 14a

  • 14a. Carapace without transverse groove on cardiac region. Sixth abdominal somite with sharp or obtuse submedian carinae and its lateral sides not grooved...................... Sclerocrangon

  • – Carapace with two transverse grooves on cardiac region. Sixth abdominal somite with flattened middorsal carina and its lateral sides grooved...................... Syncrangon

Syncrangon angusticauda (De Haan, 1849) new combination (Figs. 13)

Crangon angusticauda De Haan, 1849: 189, pl. 45, fig. 15 [type locality: Japan]; Stimpson, 1860: 25; Herklots, 1861: 147 (list); Nakazawa, 1927: 1028, fig. 1978.

Cheraphilus angusticaudaKinahan, 1862: 57 (list).

Sclerocrangon angusticaudaOrtmann, 1890: 533; De Man, 1907: 408; 1920: 251 (list); Parisi, 1919: 90, pl. 6, Fig. 6; Yokoya, 1933: 40; Miyake, 1961: 9; Miyake et al., 1962: 124; Kubo, 1965: 624, fig. 1809; Kikuchi, 1962: 140; 1966: table 7; 1968: 180; Harada, 1968: 82; Fujino, 1978: 25; Matsumiya et al., 1978: 28; Sekiguchi, 1982: 25; Imanaka et al., 1984: 52.

Crangon (Sclerocrangon) angusticaudaOrtmann, 1895: 179; Balss, 1914: 65.

Metacrangon angusticaudaZarenkov, 1965: 1765 (list); Miyake, 1982: 71, 189 (list); 1991: 189 (list); 1998: 188 (list); Ito and Watanabe, 1992: 107; Komai et al., 1992: 195 (list); Komai, 1994: 97; 1999: 59; Minemizu, 2000: 114, 2 unnumbered figs.

Mesocrangon sp. – Kojima and Hanabuchi, 1981: 45.

Material Examined. – Pacific coast of central Japan.Off Amatsukominato, Boso Peninsula, 13 Apr. 1941, coll. Ocean Research Institute, University of Tokyo, 1 ♂ (3.4 mm), 1 (4.2 mm), 9 ovig. ♀ (5.6–6.4 mm), NFU 530-2-2286. – Tokyo Bay, 35°20.0′N, 139°40.5′E, 25 m, beam trawl, 19 July 1993, coll. J. Ueda, 1 ovig. ♀(6.2 mm), NFU 530-2-2287. –Hayama, Sagami Bay, 8 Feb. 1962, 1 ovig. ♀ (5.9 mm), NSMT-Cr R: 1992. –Kurosaki, Sagami Bay, rocky shore, 18 Mar. 1964, 1 ♂ (4.0 mm), NSMT-Cr R: 2225. – Nachikatsuura, Kii Peninsula, Zostera bed, 23 Dec. 1982, coll. K. Nomura, 1 ♀ (4.9 mm), NFU 530-2-2288.

Seto Inland Sea. Bisan Strait and Harimanada Sea, 20–40 m, small trawl, Jan. 1989, coll. K. Yokoyama, 1 ♀(6.8mm), 1 ovig. ♀(6.1 mm), NFU 530-2-2289. –Mashima Island, off Hirao, Suounada Sea, tide pool, hand net, 31 July 1997, coll. T. Hamano, 1 ♂ (2.4 mm), NFU 530-2-2290. –Off Ohzai, Beppu Bay, shrimp trawl, 24–25 May 1978, 1 ♂ (3.8 mm), NFU 530-2-2291. –Beppu Bay, date unknown, coll. K. Ogawa, 1 ovig. ♀(6.0 mm), NFU 530-2-2292.

Northeastern coast of East China Sea. Hamduck, Northeast of Jeju Island, 10 m, Zostera bed, beam trawl, 10 June 1994, coll. J. N. Kim, 1 ♀(4.5 mm), PUIZ 77. –Tomioka Bay, Amakusa Islands, Zostera bed, 24 Apr. 1959, coll. T. Kikuchi, 6 ♂ (2.2–4.0 mm), 1 ♀ (6.7 mm), 4 ovig. ♀ (6.8–7.0 mm), ZLKU 2108–2118. –Tomioka Bay, Amakusa Islands, 19 July 1959, 1 ♂(3.3 mm), 1 ♀(5.0 mm), KMNH IvR 000,018. –Amakusa Islands, 27 May 1967, 1 ♂ (3.9 mm), 4 ♀(4.0–6.2 mm), 10 ovig. ♀(5.0–6.4 mm), KMNH IvR 000,019.

Sea of Japan. Toyama Bay, Gelidium amansii bed, 22 July 1977, coll. N. Horii, 1 ♂ (2.0 mm), NFU 530-2-2293. – Yuya Bay, 10–30 m, beam trawl, coll. K. Kojima, referred to Mesocrangon sp. by Kojima and Hanabuchi (1981); 13 Dec. 1976, 1 ♀(5.9 mm); 3 Feb. 1977, 1 ♀ (6.8 mm); 15 Mar. 1977, 1 ovig. ♀ (7.6 mm); 20 Aug. 1977, 1 ♀ (2.6 mm); 27 Feb. 1989, 1♀ (6.2 mm), 1 ovig. ♀ (6.9 mm); date unknown, 1 juv. (1.7 mm), NFU 530-2-2294.

Type material. – No longer extant (Yamaguchi, 1993).

Diagnosis. – Rostrum 0.20–0.33 times as long as cara-pace, triangular, rounded or subacute distally. Carapace slightly longer than wide; middorsal carina moderately high; carina continued from hepatic spine short and oblique. First and second abdominal somites without middorsal carina; third to fifth somites with low flattened middorsal carina, that of fifth somite smooth, not produced posteriorly; pleura of first to fifth somites rounded ventrally. Telson 0.72–0.84 times as long as carapace in females. Scaphocerite 0.45– 0.56 times as long as carapace in females, 0.63–0.71 times in males. Fifth pereopod with carpus as long as or longer than dactylus.

Description of females. – Body (Fig. 1) stout, depressed dorsoventrally. Integument moderately firm, sculptured, covered with pubescence and sparse long plumose setae.

Fig. 1

Syncrangon angusticauda (De Haan, 1849). Female (CL 5.9 mm; NFU 530-2-2294) from Yuya Bay. Entire animal in lateral view (top) and dorsal view (bottom). Scale 1 mm.

i0289-0003-20-5-669-f01.gif

Rostrum (Figs. 1 and 2a) short, reaching or falling slightly short of distal end of cornea, 0.20–0.33 times as long as carapace, triangular, rounded distally in large specimens, subacute in small specimens, directed forward; dorsal surface concave, with somewhat raised lateral margins; ventral carina obtuse, moderately deep, distal margin oblique in lateral view. Carapace (Figs. 1 and 2a) slightly longer than wide; gastric region not depressed below general level of carapace; middorsal carina moderately high, extending from just posterior of rostral base to nearly posterior margin of carapace, armed with 2 prominent anteriorly curved spines and median small tubercle, anterior spine somewhat smaller than posterior spine, arising from just behind level of posterior orbital margin, posterior spine arising from about 1/2 of carapace, median tubercle situated in front of posterior spine, with several long plumose setae anteriorly; antennal spine moderately strong, slightly ascending, reaching level of anterior 1/3 of rostrum, accompanied by shallow furrow inferiorly; branchiostegal spine strong, directed forward, reaching tip of rostrum, supported by sharp carina extending to anterior 1/5 of carapace; pterygostomian spine weak; hepatic spine strong, reaching level of base of anterior middorsal spine, supported by oblique short carina, followed by hepatic groove along inferior part of its base; orbital notch deep; 2 transverse grooves between middorsal carina and postorbital carina on cardiac region, bearing setae on posterior margin, anterior groove (cervical groove) curved anteriorly, extending from base of posterior middorsal spine to nearly 1/2 of postorbital carina, posterior groove slightly curved posteriorly, extending from posterior 1/4 of middorsal carina to posterior 1/4 of postorbital carina; postorbital carina continued from rostral lateral margin and slightly curved downward just behind antennal spine, and extending nearly to posterior end of middorsal carina; longitudinal suture originating from anterior margin of carapace just superior to antennal spine, extending backwards along postorbital carina to almost 1/2 of carapace.

Fig. 2

Syncrangon angusticauda (De Haan, 1849). Female (CL 5.9 mm; NFU 530-2-2294) from Yuya Bay. Appendages dissected from left side. a, anterior part of carapace, lateral; b, eye, ventral; c, antennule, lateral; d, antenna, ventral; e, mandible, external and internal; f, maxillule, external; g, maxilla, external; h, first maxilliped, external; i, second maxilliped, external; j, third maxilliped, flexor; k, first pleopod, ventral, exopodal setae omitted; l, second pleopod, ventral, exopodal setae omitted; m, telson and uropod, dorsal.

i0289-0003-20-5-669-f02.gif

Four posterior thoracic sternites each with high median ridge, especially that on fifth somite with acute process ante-riorly, diminishing in size posteriorly in non-spawning specimens; these ridges except for that on fifth somite vanished in spawning specimens.

Abdomen (Fig. 1) having first and second somites without middorsal carina; third to sixth somites furnished each with flattened middorsal carina, those of third to fifth somites low, that of third somite convex laterally, those of fourth and sixth somites narrowed posteriorly, that of sixth somite high, faintly grooved at anterior 2/3 medially and notched posteri-orly; each carina with marginal setae. Tergum of first somite with transverse groove medially, parallel with posterior margin; that of second somite with X-shaped transverse groove in dorsal view, junction of transverse grooves (X-shaped groove) produced anteriorly into blunt protuberance in lateral view; those of third to fifth somites with T-shaped deep grooves on each lateral side of middorsal carina. Lateral margin of first somite with longitudinal carina throughout its length; that of second somite with longitudinal broad groove continued from anterior transverse groove on tergum; those of third and fourth somites concave anteriorly, that of fourth somite with short transverse groove posteriorly continued from T-shaped groove on tergum; that of fifth with 2 oblique grooves, inferior groove continued from T-shaped groove on tergum. Pleura of first to fifth somites rounded ventrally. Sixth somite 0.49–0.58 times as long as carapace, 1.56– 1.88 times as long as proximal depth, provided with anterior transverse short groove followed by longitudinal deep groove under middorsal carina; posterolateral process strong, sharply pointed; posteroventral corner sharply pointed. Telson (Fig. 2m) 0.72–0.84 times as long as cara-pace, tapering into acute tip, with paired submedian carinae and deep median groove; 2 pairs of dorsolateral spines on submedian carinae, anterior pair situated at about anterior 2/5, posterior pair at about 1/2 between anterior pair and posterior end of telson; posterolateral corner with small spine on each side of acute tip.

Anterior five abdominal sternites in non-spawning specimens each with sharp median process, those processes directed anteriorly on first and second sternites, directed ventrally on third and fourth sternites, directed posteriorly on fifth sternite; those processes except that of fifth sternite reduced to tubercles in spawning specimens; acute preanal spine present.

Eye (Fig. 2b) with cornea well developed, as long as eyestalk; eyestalk somewhat inflated basally, provided with rounded dorsal tubercle and minute ventral spine.

Antennule (Fig. 2c) with peduncle falling slightly short of 1/2 of scaphocerite; distal segment with rather acute process dorsally, proximal 2 segments with blunt protuberance at distolateral angle; proximal segment almost twice as long as distal 2 segments combined, with acute spine on ventral margin. Stylocerite broad, rather square, reaching anterior 1/3 of proximal segment; lateral margin nearly straight, terminating in blunt projection anteriorly. Outer flagellum reaching beyond scaphocerite by at least distal 1/3, composed of 7–15 articles, increasing with growth, bearing aesthetascs ventrally. Inner flagellum with setae on each article, almost as long as and more slender than outer one.

Antenna (Fig. 2d) with scaphocerite moderately stout, 0.45–0.56 times as long as carapace, 1.69–2.27 times as long as width, lateral margin slightly convex; distolateral spine straight, slightly exceeding distal margin of rounded blade. Basicerite with blunt ventrolateral process; carpocerite reaching level of distal 1/4 of scaphocerite.

Mouthparts similar to other crangonids. Mandible (Fig. 2e) armed with 4 teeth distally, ventral tooth stronger than other 3 teeth. Maxillule (Fig. 2f) with proximal endite slightly tapered; distal endite strongly curved inward, distal margin rather rounded, with 7 strong spines; palp moderately curved upward, with stout seta apically, distoventral margin concave. Maxilla (Fig. 2g) with endite reduced; endopod slender, curved inward; scaphognathite broad, anterior lobe slightly curved inward, posterior lobe somewhat elongated, posterior margin fringed with long setae. First maxilliped (Fig. 2h) with endopod elongate, overreaching anterior margin of epipod; exopod with peduncle longer than endopod, caridean lobe narrow, with well developed lash; epipod moderately large, triangularly elongated, posterior lobe falcate. Second maxilliped (Fig. 2i) with endopod pediform, dactylus with 3 spines on mesial margin and assemblage of short setae distally, propodus with several spines and scattered setae on mesial margin; exopod with well developed lash; epipod well developed, wing-like shape. Third maxilliped (Fig. 2j) rather depressed dorsoventrally, exceeding distal end of scaphocerite by 1/2 of ultimate segment; distal 2 segments with serial stout setae on mesial margin; ultimate segment longer than penultimate segment, about 4.5 times as long as width; penultimate segment about 2.5 times as long as width; antepenultimate segment shorter than distal 2 segments combined, armed with 2 small subdistal spines on ventral surface; exopod with well developed lash; coxal lateral process (epipod) small, rounded laterally.

First pereopod (Fig. 3a, b) stout, reaching beyond distal end of scaphocerite by 1/2 of palm; chela (Fig. 3b) with palm 2.28–2.85 times as long as width, cutting edge strongly oblique and feebly convex; distomesial spine (‘thumb’) strong, articulated at base; carpus short, armed with strong lateral spine distoventrally and distolateral blunt process; merus with rather weak spine on dorsodistal margin and moderately strong spine on middle of mesial margin. Second pereopod (Fig. 3c, d) chelate, slender, reaching distal end of scaphocerite; chela (Fig. 3d) with dactylus about 0.35 times as long as palm, fingers with numerous minute spinules on anterior 1/2 of both cutting edges; carpus 1.71– 2.09 times as long as chela; coxa with wing-like process laterally. Third pereopod (Fig. 3e, f) slender, overreaching distal end of scaphocerite by dactylus; dactylus (Fig. 3f) short, 0.40–0.64 times as long as propodus, tapering distally, bearing fine setae distally; carpus 1.22–2.13 times as long as distal 2 segments combined. Fourth pereopod (Fig. 3g, h) stouter than third pereopod, reaching distal end of scaphocerite, strongly setose; dactylus (Fig. 3h) slightly compressed laterally, subspatulate, apex terminating in corneous spine inserted on dorsal lobule; propodus 1.53–1.90 times as long as dactylus, ventral margin with 4–8 serial stout setae; carpus 0.81–1.00 times as long as dactylus. Fifth pereopod (Fig. 3i, j) similar but less setose than fourth pereopod, falling slightly short of distal end of scaphocerite; propodus 1.56–2.00 times as long as dactylus, ventral margin with 3–7 serial stout setae; carpus 1.00–1.23 times as long as dactylus.

Fig. 3

Syncrangon angusticauda (De Haan, 1849). a–j, female (CL 5.9 mm; NFU 530-2-2294) from Yuya Bay; k–n, male (CL 3.8 mm; NFU 530-2-2291) from Beppu Bay. Appendages dissected from left side. a, first pereopod, lateral; b, same, chela, flexor; c, second pereopod, lateral; d, same, chela, lateral; e, third pereopod, lateral; f, same, dactylus, lateral; g, fourth pereopod, lateral; h, same, distal part of dactylus, lateral; i, fifth pereopod, lateral; j, same, distal part of dactylus, lateral; k, anterior part of carapace and cephalic appendages, dorsal; l, first pleopod, ventral, exopodal setae omitted; m, second pleopod, ventral, exopodal setae omitted; n, same, endopod and appendix masculina, dorsal.

i0289-0003-20-5-669-f03.gif

Five pleurobranchs present on fourth to eighth thoracic somites, inclined anteriorly.

First pleopod (Fig. 2k) with endopod not segmented, reaching about 1/2 of exopod; mesial margin with fine setae. Second pleopod (Fig. 2l) with endopod reaching about 1/2 of exopod, 2-segmented, distal segment with marginal setae, proximal segment with rather long setae on mesial margin. Endopods of third and fourth pleopods similar to that of second, diminishing in size posteriorly; that of fifth pleopod vestigial, not segmented.

Uropod (Fig. 2m) with endopod reaching tip of telson; exopod falling slightly short of tip of telson, with small spine just mesial to acute posterolateral spine, transverse suture distinct.

Eggs small, globular, 0.46–0.56[.infinity]0.34–0.38 mm in diameter and about 600 in number in specimen of CL 5.1 mm.

Description of males. – Body smaller and more slender than in females.

Sixth somite 0.68–0.79 times as long as carapace, 1.80–2.14 times as long as proximal depth. Telson 0.88– 1.06 times as long as carapace.

Outer antennular flagellum (Fig. 3k) overreaching scaphocerite by more than distal 1/2, composed of 10–18 articles.

Scaphocerite (Fig. 3k) 0.63–0.71 times as long as car-apace, 2.13–2.68 times as long as width, lateral margin nearly straight; distolateral spine entirely exceeding distal margin of truncate blade.

First pleopod (Fig. 3l) with endopod very short, narrowed distally, with short setae on mesial and distal margins. Second pleopod (Fig. 3m) with endopod strongly reduced, rounded laterally, fringed with plumose setae; appendix masculina (Fig. 3n) longer than endopod, reaching proximal 1/4 of exopod, mesial margin somewhat ridged, bearing many stout setae dorsally. Endopods of third to fifth pleopods small, diminishing in size posteriorly.

Coloration. – The coloration of the body is variable. Specimens from off Amatsukominato, Pacific coast of central Japan: carapace and abdomen dark brown mottled yellowish white except for sixth abdominal somite always dark brown. Specimen from Kurosaki, Sagami Bay: dorsal part of carapace grayish brown; dorsal part of first to fifth abdominal somites yellowish white, sixth abdominal somite brown; ventral part of carapace, pleura of first to fifth abdominal somites and telson brownish black. Minemizu (2000: 114) published two similar color photographs of this species from Osezaki, Suruga Bay. He described them as follows: body black except for cephalic appendages, first to third and fifth abdominal somites white; posterodorsal margin of carapace with 2 blue spots.

Size. – Males CL 2.0–4.0 mm, females CL 2.6–6.8 mm, ovigerous females CL 5.0–7.6 mm, juvenile CL 1.7 mm.

Distribution. – Pacific coast of central Japan (Inubozaki, Boso Peninsula, Tokyo Bay, Sagami Bay, Izu Peninsula, Suruga Bay, Ise Bay, and Kii Peninsula), Seto Inland Sea (Harimanada Sea, Bisan Strait, Suounada Sea, and Beppu Bay), northeastern coast of East China Sea (Jeju Island, Shishiki Bay, Nagasaki Pref., and Amakusa Islands), Sea of Japan (Toyama Bay, off Tottori Pref., Sakai Channel, Shi-mane Pref., and Yuya Bay) and Tsugaru Strait (Hakodate); intertidal to 40 m.

Ecological note. – This species commonly occurs in algal and seagrass beds (Stimpson, 1860; Miyake, 1961; Kikuchi, 1962, 1966, 1968; Fujino, 1978; present study). In Tomioka Bay, Amakusa Islands, Japan, the species appears principally in the Zostera belt from January to June, and this period coincides with the ovigerous season of the species (Kikuchi, 1966). They feed on large amphipods and megalopa of crabs but do not contain other organisms or sand particles in their stomach (Kikuchi, 1966).

Remarks. – Since the original description by De Haan (1849), the present species has been described in fragmentary form by subsequent authors (e.g., Ortmann, 1890; De Man, 1907; Parisi, 1919; Nakazawa, 1927; Kubo, 1965). Our observations show that the following several important characteristics have not been mentioned by them: a small tubercle is present in front of the posterior median spine on the carapace; the distomesial spine (‘thumb’) is articulated on the propodus of first pereopod at base; the merus of first pereopod is provided with a spine on the middle of mesial margin; and the appendix masculina on the second pleopod in males is longer than the endopod. Most of these features are useful for generic recognition in the Crangonidae.

Kojima and Hanabuchi (1981) reported an unidentified species of Mesocrangon in their ecological study in Yuya Bay, southern Sea of Japan. Reexamination of the specimens used by Kojima and Hanabuchi (1981) has shown that they actually represent S. angusticauda.

Syncrangon dentata (Balss, 1914) new combination (Figs. 46)

Crangon (Sclerocrangon) angusticauda var. dentata Balss, 1914: 65, fig. 40 [type locality: Negishi, Yokohama, Tokyo Bay and off Zushi, Sagami Bay, Pacific coast of central Japan].

Sclerocrangon angusticauda var. dentataDe Man, 1920: 251 (list).

Material Examined. – Pacific coast of central Japan.Tokyo Bay, 35°20.0′N, 139°40.5′E, 25 m, beam trawl, 22 Mar. 1995, coll. J. Ueda, 3 ♂(3.0–3.4 mm), NFU 530-2-2295. – Amadai-ba, Sagami Bay, 62–65 m, 19 July 1962, 1 ♂ (2.4 mm), NSMT-Cr R: 2048. –Off Northwest of Jogashima Island, Sagami Bay, 61–62 m, 6 Feb. 1964, 1 ♀(4.3 mm), NSMT-Cr R: 2205. –Off Northwest of Jogajima Island, Sagami Bay, 65–75 m, 13 Feb. 1965, 1 ♂ (2.8 mm), 2 ♀ (3.5, J.-N. Kim and K.-I. Hayashi 3.7 mm), NSMT-Cr R: 2332.

Sea of Japan. Off Tsushima Island, 34°16.0′N, 129°31.5′E, 105 m, sand and shells, 5 Aug. 1968, coll. RV Genkai-Maru of the Fukuoka Fisheries Research Laboratory, 1 ♀(2.2 mm), KMNH IvR 000,020.

Type material. – Syntypes: 1 ♀, Negishi, Yokohama, Tokyo Bay, 45 m, coll. F. Doflein; 2 juvs., Zushi, Sagami Bay, 130 m, 9 Nov. 1904, coll. F. Doflein, deposited in Zoologisches Sammlung des Bayerischen Staates, München. However, the type material could not be located (Dr. T. Komai of the Natural History Museum and Institute, Chiba, pers. comm.).

Diagnosis. – Rostrum 0.32–0.41 times as long as cara-pace, terminating in conical projection, lateral margins nearly parallel. Carapace slightly shorter than wide; middorsal carina considerably high, carina (branchial carina) continued from hepatic spine long and directed backward. First to second abdominal somites with short middorsal carina, each produced anteriorly as blunt process; third to fifth somites with relatively high but dorsally flattened middorsal carina, that of fifth somite weakly produced posteriorly; pleura of first to fifth somites bluntly produced ventrally. Telson 0.91–0.95 times as long as carapace in females. Scaphocerite 0.60–0.68 times as long as carapace in females, 0.69–0.78 times in males. Fifth pereopod with carpus shorter than dactylus.

Description of females. – Body (Fig. 4) small, moderately stout, subcylinderical. Integument moderately thick, sculptured, covered with fine setae, particularly each carina with sparse long plumose setae.

Fig. 4

Syncrangon dentata (Balss, 1914). Female (CL 4.3 mm; NSMT-Cr R: 2205) from off Northwest of Jogashima Island, Sagami Bay. Entire animal in lateral view (top) and dorsal view (bottom). Scale 1 mm.

i0289-0003-20-5-669-f04.gif

Rostrum (Figs. 4 and 5a) broad and short, 0.32–0.41 times as long as carapace, directed forward, terminating in conical projection in dorsal view; dorsal surface concave, lateral margins nearly parallel; ventral carina obtuse, deep, distal margin with lobe-like projection in lateral view. Cara-pace (Figs. 4 and 5a) slightly shorter than wide; gastric region not depressed below general level of carapace; middorsal carina very high, extending from just posterior of rostral base to posterior margin of carapace, armed with 2 strong spines anteriorly curved and median small tubercle, anterior spine directed forward, arising from level of posterior orbital margin, posterior spine larger than anterior one, arising from about posterior 1/3 of carapace, median tuber-cle situated just in front of posterior spine, bearing several long plumose setae anteriorly; antennal spine moderately strong, rather ascending, falling short of end of rostrum, with shallow furrow inferiorly; branchiostegal spine strong, slightly convergent, directed forward, reaching or reaching slightly beyond end of rostrum, supported by sharp carina extending anterior 1/6 of carapace; pterygostomian spine minute; hepatic spine moderately strong, supported by long longitudinal carina (branchial carina) extending to level of posterior end of middorsal carina, followed by hepatic groove along inferior part of its base; orbital notch moderately deep; 2 transverse cardiac grooves with marginal setae posteriorly, anterior groove (cervical groove) extending from base of median tubercle to anterior 1/3 of postorbital carina, posterior groove extending from posterior 1/5 of middorsal carina to posterior 1/3 of postorbital carina; postorbital carina continued from lateral margin of rostrum, extending from level of posterior end of middorsal carina; longitudinal suture situated on antennal spine, extending backwards along postorbital carina to level of 1/2 of cara-pace.

Fig. 5

Syncrangon dentata (Balss, 1914). Female (CL 4.3 mm; NSMT-Cr R: 2205) from off Northwest of Jogashima Island, Sagami Bay. Appendages dissected from left side. a, anterior part of carapace, lateral; b, antennule, ventral; c, antenna, ventral; d, mandible, external and internal; e, maxillule, external; f, maxilla, external; g, first maxilliped, external; h, second maxilliped, external; i, third maxilliped, flexor; j, first pleopod, ventral, exopodal setae omitted; k, second pleopod, ventral, exopodal setae omitted; l, uropod and telson, dorsal.

i0289-0003-20-5-669-f05.gif

Four posterior thoracic sternites furnished each with median ridge, diminishing in size posteriorly in non-spawning specimens.

Abdomen (Fig. 4) provided with relatively high, but dor-sally flattened middorsal carina on first to sixth somites, those of first and second somites short, with strong blunt process anteriorly, that of third somite broadened posteri-orly, those of fourth to sixth somites narrowed posteriorly, that of fifth somite somewhat produced posteriorly, that of sixth somite weakly grooved at anterior 2/3 medially and notched posteriorly; each carina with marginal setae. Terga of first and second somites with transverse groove posteri-orly, continued from posterolateral margin of middorsal carina, parallel with posterior margin, that of second somite with anterior transverse groove continued from posterior groove; those of third to fifth somites with T-shaped deep groove. Lateral margin of first somite with longitudinal carina throughout its length; that of second somite with oblique broad groove continued from anterior transverse groove on tergum; third to fifth somites strongly sculptured. Pleura of first to fifth somites strongly sculptured, bluntly produced ventrally, that of first somite with short sinuous carina ante-riorly, those of fourth and fifth somites bluntly produced posteriorly. Sixth somite 0.56–0.73 times as long as carapace, 1.44–1.68 times as long as proximal depth, provided with longitudinal deep groove on lateral margin under middorsal carina; posterolateral spine strong; posteroventral corner pointed. Telson (Fig. 5l) moderately long, 0.91–0.95 times as long as carapace, provided with paired submedian carinae and moderately deep middorsal groove; submedian carinae armed with 2 pairs of dorsolateral spines, anterior pair situated at 1/2 of telson, posterior pair at distal 1/4 of telson; posterior margin sharply pointed, with paired lateral spines.

Anterior five abdominal sternites provided each with sharp median process, these processes directed ventrally on anterior 4 sternites, directed posteriorly on fifth sternite in non-spawning specimens; preanal spine acute.

Eye (Fig. 4) large, with cornea moderately large; eye-stalk provided with rounded dorsal tubercle, without ventral spine.

Antennule (Fig. 5b) with peduncle reaching 1/2 of scaphocerite; proximal 2 segments of peduncle with blunt distolateral process; proximal segment distinctly longer than distal 2 segments combined, with acute spine on ventromesial ridge. Stylocerite broad, subsquare, slightly reaching beyond 1/2 of proximal segment; lateral margin slightly concave, terminating in obtuse process anteriorly. Outer flagellum overreaching distal end of scaphocerite by at least distal 1/5, composed of 7–9 articles, increasing with growth, bearing aesthetascs on ventral margin. Inner flagellum setose, subequal in length to and more slender than outer one.

Antenna (Fig. 5c) with scaphocerite broad, 0.60–0.68 times as long as carapace, 2.00–2.14 times as long as width, lateral margin slightly sinuous; distolateral spine exceeding distal margin of rounded blade. Basicerite with ventrolateral process rounded, divergent laterally; carpocerite reaching level of distal 1/5 of scaphocerite; flagellum shorter than body length.

Mouthparts similar to those of S. angusticauda (Fig. 5d–i). Third maxilliped (Fig. 5i) overreaching distal end of scaphocerite by 1/2 of ultimate segment, strongly setose particularly on mesial margin; distal 2 segments with serial spines mesially; ultimate segment about 5 times as long as width; penultimate segment about 3 times as long as width; antepenultimate segment shorter than distal 2 segments combined, bearing 2 small subdistal spines ventrally; exopod with lash well developed; epipod with lateral margin rounded.

First pereopod (Fig. 6a, b) moderately stout, overreaching distal end of scaphocerite by 1/2 of palm; chela (Fig. 6b) with palm 2.13–2.60 times as long as width, cutting edge strongly oblique and convex; distomesial spine (‘thumb’) strong, movable; carpus armed with strong lateral spine on distoventral corner and distolateral strong protuberance; merus with rather strong spine on dorsodistal margin and moderate subacute spine on midmesial margin. Second pereopod (Fig. 6c, d) slender, slightly reaching beyond distal end of scaphocerite; chela (Fig. 6d) with dactylus 0.35 times as long as palm, fingers with numerous minute spinules on both cutting edges distally; carpus 1.78–2.00 times as long as chela; merus subequal with carpus in length; coxa with lateral process. Third pereopod (Fig. 6e) slender, overreaching distal end of scaphocerite by distal 2 segments; dactylus 0.63–0.67 times as long as propodus; carpus 1.30–1.70 times as long as distal 2 segments combined; merus shorter than carpus. Fourth pereopod (Fig. 6f) moderately stout, slightly reaching beyond distal end of scaphocerite; dactylus subspatulate, acute distally; propodus 1.29–1.67 times as long as dactylus; carpus 0.50–0.78 times as long as dactylus; merus slightly shorter than propodus. Fifth pereopod (Fig. 6g) similar to fourth pereopod, reaching distal end of scaphocerite; propodus 1.30–1.76 times as long as dactylus; carpus 0.67–0.86 times as long as dactylus.

Fig. 6

Syncrangon dentata (Balss, 1914). a–g, female (CL 4.3 mm; NSMT-Cr R: 2205) from off Northwest of Jogashima Island, Sagami Bay; h–k, male (CL 3.4 mm; NFU 530-2-2295) from Tokyo Bay. Appendages dissected from left side. a, first pereopod, lateral; b, same, chela, flexor; c, second pereopod, lateral; d, same, chela, lateral; e, third pereopod, lateral; f, fourth pereopod, lateral; g, fifth pereopod, lateral; h, anterior part of carapace and cephalic appendages, dorsal; i, first pleopod, ventral, exopodal setae omitted; j, second pleopod, ventral, exopodal setae omitted; k, same, endopod and appendix masculina, dorsal.

i0289-0003-20-5-669-f06.gif

Pleurobranchs present on fourth to eighth thoracic somites.

First pleopod (Fig. 5j) with endopod not segmented, reaching distal 1/3 of exopod, with sparse short setae mesially. Second pleopod (Fig. 5k) with endopod reaching distal 1/3 of exopod, curved laterally, with 2 segments, distal segment with short setae marginally, proximal segment with short setae mesially. Endopods of third and fourth pleopods similar to that of second, diminishing in size posteriorly; that of fifth pleopod small, not segmented.

Uropod (Fig. 5l) with endopod extending beyond tip of telson; exopod failing to reach distal margin of endopod, with small spine just mesial to acute posterolateral spine, transverse suture distinct, oblique.

Description of males. – Body rather smaller and more slender than females.

Sixth somite 0.71–0.82 times as long as carapace, 1.54–1.85 times as long as proximal depth. Telson 0.96– 1.15 times as long as carapace.

Outer antennular flagellum (Fig. 6h) reaching beyond scaphocerite by more than distal 1/2, composed of 9–18 articles.

Scaphocerite (Fig. 6h) 0.69–0.78 times as long as car-apace, 2.06–2.52 times as long as width; distolateral spine totally exceeding distal margin of truncate blade.

First pleopod (Fig. 6i) with endopod very short, curved laterally, rounded distally, with marginal setae mesially. Second pleopod (Fig. 6j, k) with endopod rudimentary, rounded laterally, fringed with setae; appendix masculina (Fig. 6k) elongate, longer than endopod, reaching proximal 1/3 of exopod, bearing many stout setae on dorsal margin. Endo-pods of third to fifth pleopods vestigial, diminishing in size posteriorly.

Coloration. – Unavailable.

Size. – Males CL 2.4–3.4 mm, females CL 2.2–4.3 mm

Distribution. – Pacific coast of central Japan (Tokyo Bay and Sagami Bay) and southern Sea of Japan (Tsushima Island); 25–130 m.

Remarks. – This species was first described as Crangon (Sclerocrangon) angusticauda var. dentata by Balss (1914) based on one female and two juvenile specimens. Balss (1914) compared his specimens with those of the nominal typical form and pointed out the following morphological differences in the abdomen and telson between the two forms: (1) the first and second somites armed each with a middorsal process anteriorly (absent in the typical form); (2) the third and fourth somites provided each with a high broad middorsal carina (low in the typical form); (3) the middorsal carinae of fifth and sixth somites pointed poster-iroly (rounded in the typical form); and (4) the telson without any spine (two pairs of dorsal spines present in the typical form). Also, he additionally mentioned that the rostrum was anteriorly broader than that of typical form and that the middorsal carina of the carapace was higher than that of the typical form. Our comparison confirmed that all but the fourth character are reliable in distinguishing the two species. We have found that there are three pairs of dorsolateral spines on the telson in our specimens. It is reasonable to consider that the spines were missing in the syntypes or that Balss (1914) overlooked the presence of the spines.

Close comparison has revealed the following many additional differences which justify the separation of Balss' (1914) form as a distinct species: (1) the rostrum is longer in S. dentata than in S. angusticauda (0.32–0.41 times as long as carapace versus 0.20–0.33 times); (2) the ventral carina of the rostrum is deeper in S. dentata than in S. angusticauda; (3) the carina continued from the hepatic spine on the carapace is longer in S. dentata than in S. angusticauda; (4) the ventral margin of the pleura on the first to fifth abdominal somites is bluntly produced in S. dentata, while rounded in S. angusticauda; (5) in females, the telson is longer in S. dentata than in S. angusticauda (0.91–0.95 times as long as carapace versus 0.72–0.84 times); (6) the comparative length of the scaphocerite in relation to the car-apace in females is longer in S. dentata than in S. angusticauda (0.60–0.68 times as long as carapace versus 0.45– 0.56 times); and (7) the carpus of fifth pereopod is shorter than the dactylus in S. dentata, while longer than the dactylus in S. angusticauda (0.67–0.86 times as long as dactylus versus 1.00–1.23 times). Also, the known vertical distribution differs between the two species, S. dentata occurring in rather deeper water than S. angusticauda (25–130 m as against intertidal to 40 m).

The present species has been recorded only from Negishi, Yokohama, Tokyo Bay and off Zushi, Sagami Bay, Pacific coast of central Japan. The present material from Tsushima Island, southern Sea of Japan extends the known geographical range of the species.

Acknowledgments

We wish to express our sincere thanks to the following scientists and institutions for donations or loans of specimens in this study: Drs. Tatsuo Hamano, Naojirou Horii, Taiji Kikuchi, Kikkuo Kojima, Yoshitaka Yabumoto and Koji Yokogawa, and Mrs. Keiichi Nomura, Kazutoshi Ogawa and Junji Ueda, and NSMT, Fukuoka Fisheries Research Laboratory and Ocean Research Institute, University of Tokyo. We are grateful to Drs. Sammy De Grave, Martin Lindsey Christoffersen and Masatsune Takeda for kindly reviewing the manuscript. We also thank Dr. Tomoyuki Komai for information about the syntypes of Syncrangon dentata and for critical reading of the manuscript. This work was supported by Korean Research Foundation Grant (KRF-2001-050-D00038) for the senior author (JNK).

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Jung Nyun Kim and Ken-Ichi Hayashi "Syncrangon, a New Crangonid Genus, with Redescriptions of S. angusticauda (De Haan) and S. dentata (Balss) (Crustacea, Decapoda, Caridea) from East Asian Waters," Zoological Science 20(5), (1 May 2003). https://doi.org/10.2108/zsj.20.669
Received: 21 September 2002; Accepted: 1 February 2003; Published: 1 May 2003
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