Plesionika longidactylus, Li & Komai, 2003

Li, Xinzheng & Komai, Tomoyuki, 2003, Pandaloid Shrimps From The Northern South China Sea, With Description Of A New Species Of Plesionika (Crustacea: Decapoda: Caridea), Raffles Bulletin of Zoology 51 (2), pp. 257-275 : 262-265

Plesionika longidactylus , new species

( Figs. 2-5 )

Material examined. – Holotype – male (cl 4.6 mm) ( IOCAS), CN R38 B-26, 17 30’N, 109 30’E, 106 m, sand, AT, coll. F Xu, 14 Jul.1959

Paratypes – 2 ovig. females (cl 3.8, 4.2 mm)( IOCAS), 1 ovig. female (cl 4.4 mm) ( CBM), CN 2-11 , Beibu Bay , 18 45’N, 108 45’E, 54.5 m, mud, BT, coll. Z. Fan, 25 Jan.1959 ; 1 ovig. female (cl 4.8 mm) ( IOCAS), CN L56 B-84, 20 30’N, 112 00’E, 72 m, muddy sand, AT, coll. X. Ma, 20 Apr.1959 ; 1 ovig. female (cl 3.5 mm) ( IOCAS), CN N96 B-103, 19 30’N, 111 15’E, 89 m, sand, AT, coll. Z. Tang, 29 Oct.1959; 1 male (cl 4.3 mm)( CBM) , 1 ovig. female (cl 4.6 mm) ( IOCAS), CN N206 B-71, 17 30’N, 109 30’E, 115 m, sandy mud, AT, coll. S. Shen, 14 May.1960 .

Diagnosis. – Rostrum far overreaching antennal scale, 1.10- 1.26 times as long as carapace, armed dorsally with 5 moderately large teeth in posterior 0.50-0.60, including 1 arising from anterior 0.10-0.18 of carapace length, each with obscurely barbed tip, and with 2 tiny subapical teeth, ventral margin with 10-13 teeth; third abdominal somite not compressed dorsally, unarmed on posterodorsal margin; fourth and fifth abdominal somites each with posteroventral tooth on pleuron; telson slightly shorter than sixth abdominal somite, bearing 4 pairs of dorsolateral spines, including 1 pair adjacent to lateral pair of posterior spine; third maxilliped with ultimate segment about 1.4 times as long as penultimate segment; anterior 3 pairs of pereopods with well developed, strap-like epipods each bearing terminal hook; second pereopods greatly unequal, left with 25-30 carpal articles, right with 8 carpal articles; third pereopod with dactylus 0.48-0.60 times as long as propodus.

Description of holotype (male). – Rostrum slender, curving somewhat dorsally, far overreaching antennal scale, 1.26 times as long as carapace; dorsal margin armed with 5 moderately large, widely spaced teeth in posterior 0.55, including 1 arising from level of 0.10 of carapace length, last 3 barbed and with distinct basal suture, and 2 tiny teeth near apex of rostrum, leaving subdistal 0.45 unarmed; ventral margin armed over most length with 13 small but distinct, discretely spaced teeth. Carapace with orbit regularly concave in dorsal portion and very faintly convex in ventral portion above antennal spine; antennal spine larger than pterygostomian spine; median postrostral ridge faintly concave, somewhat compressed, but not sharp, very short, not extending posteriorly to midlength of carapace.

Abdomen with third somite unarmed on posterodorsal margin, posterior part of tergum not compressed into median subcarinate ridge. Pleura of anterior three somites broadly rounded, those of fourth and fifth somites terminating posteroventrally in small, sharp tooth, ventral margins slightly sinuous. Sixth somite about twice as long as fifth somite and 2.40 times as long as maximum height; posterolateral process terminating sharply; posteroventral angle with small spine. Telson slightly shorter than sixth somite, with 4 pairs of dorsolateral spines, including 1 pair adjacent to lateral pair of posterior spine, anteriormost pair arising somewhat anterior to level of midlength; posterior margin with 2 pairs of spines, lateral pair longer than mesial pair.

Eye somewhat compressed in lateral view, pyriform in dorsal view, maximum diameter 0.27 times of carapace length; ocellus large, lingulate, circular, in broad contact with remainder of cornea.

Antennular peduncle with small but distinct tooth on ventromesial margin of basal segment; stylocerite rounded distally, reaching about level of midlength of basal peduncular segment; ultimate segment somewhat longer than penultimate segment; outer flagellum with aesthetasc-bearing portion slightly shorter than carapace.

Antennal scale 0.82 times as long as carapace, 4.57 times as long as broad, lateral margin nearly straight, distolateral tooth distinctly overreaching truncate distal margin of blade. Basicerite with small ventrolateral distal tooth. Carpocerite not reaching to midlength of antennal scale.

Mouthparts typical of genus. Mandible with 3 small distal teeth on incisor process; palp 3-segmented. Maxillule with palp bilobed terminally. Maxilla with proximal endite bilobed, distal lobe very small; distal endite deeply bilobed; palp consisting of single lobe, rather abruptly tapering distally, reaching anterior margin of distal endite; scaphognathite with rounded posterior lobe fringed posteriorly with short setae. First maxilliped with 2- segmented endopod distinctly overreaching anterior margin of distal endite; caridean lobe moderately broad; epipod large, distinctly bilobed. Second maxilliped with 6- segmented endopod; dactylus narrow; exopod long, slender. Third maxilliped slender, reaching beyond distal margin of antennal scale; ultimate segment 1.40 times as long as penultimate segment; exopod overreaching midlength of ultimate segment; epipod with terminal hook.

Pereopods with well developed, terminally hooked epipods on anterior 3 pairs. First pereopod minutely chelate, long, slender, overreaching distal margin of antennal scale by full length of propodus; propodus 0.57 times as long as carpus; carpus elongate, 0.85 times as long as merus; ischium with ventrodistal portion produced, terminating acutely; ventral surface with few spinules. Second pereopod represented only by left overreaching antennal scale by length of chela and 0.30 of carpus; chela slightly longer than distalmost article of carpus; carpus composed of 30 articles; merus almost as long as ischium. Third pereopod overreaching antennal scale by length of dactylus, propodus and half of carpus; dactylus elongate, 0.57 times as long as propodus, slightly curved, terminating in simple, acuminate unguis, no accessory spinules on flexor margin; propodus with few setae; carpus 0.72 times as long as propodus, unarmed; merus 1.18 times as long as carapace, with 8 spines along the flexor margin, the apical one near to the apex of merus and located on the outside of the flexor margin; ischium with 2 ventral spine. Fourth pereopod similar to third, overreaching antennal scale by length of dactylus and propodus. Fifth pereopod overreaching antennal scale by length of dactylus and half of propodus; dactylus 0.48 times as long as propodus; carpus 0.70 times as long as propodus, unarmed; merus as long as carapace, with 7 spines along the flexor margin, the apical one near to the apex of merus and located on the outside of the flexor margin; ischium without ventral spine.

Endopod of male first pleopod with mesial margin slightly sinuous, notch separating appendix interna and distal lobe of endopod distinct. Appendix masculina on second pleopod reaching distal end of appendix interna, armed with about 11 long spines. Exopod of third pleopod 0.32 times as long as carapace. Endopod of uropod overreaching posterior end of telson; exopod longer and bearing movable spine mesial to distolateral tooth.

Description of paratypes. – Paratypes generally similar to holotype. Ventral margin of rostrum with 10-12 teeth. Right (shorter) second pereopod with 8-9 carpal articles; left (longer) second pereopod with 25-29 carpal articles; the dactylus of third pereopod is 0.48-0.60 times as long as propodus; eggs small, diameter along longer axis 0.4 mm.

Distribution. – Known only from the northern part of the South China Sea, at depths of 55- 115 m. The type locality is in Beibu Bay at a depth of 106 m.

Etymology. – The species is named after its elongate dactyli of third to fifth pereopods. The name is used as a noun in apposition.

Remarks. – This new species appears close to P. exigua ( Rathbun, 1906) from Hawaii, P. mexicana Chace, 1937 , from the eastern Pacific and P. pumila Chace, 1985 , from the Philippines, all of which have the teeth on the postrostral crest bluntly barbed. Comparisons with the published descriptions of these three species ( Rathbun, 1906; Chace, 1937, 1985) have shown that the new species is immediately distinguished from these three taxa by the blunt, rather than acute, antennular stylocerite, elongate dactyli of the third to fifth pereopods (0.48-0.60 times as long as propodus versus less than 0.40 times as long) and the presence of epipods on the first to third pereopods. In P. exigua , the first and second pereopods bear epipods, while in P. mexicana and P. pumila , the anterior four pereopods have epipods. Further, the presence of only one postrostral tooth and the absence of prominent accessory spinules on pereopod dactyli distinguish the new species from P. exigua . From P. mexicana , the new species is separated by the fewer dorsal rostral teeth and distinctly shorter stylocerite, which falls short of the distal end of the basal antennular segment, rather than slightly overreaching that. Finally, the unarmed carpi of the third and fourth pereopods distinguish the new species from P. pumila .

Figures

Fig. 2. Plesionika longidactylus, new species. a, body, lateral view; b, eye; c, antennule; d, antenna; e, mandible, ventral view; f, same, dorsal view; g, maxillula; h, maxilla. Holotype male from northern South China Sea (R38B-26, IOCAS). Scales = 1 mm.

Fig. 3. Plesionika longidactylus, new species. a, b, anterior carapace, lateral view; c, right first maxilliped, ventral view; d, right second maxilliped, ventral view; e, right third maxilliped, dorsal view; f, right first pereopod, lateral view; g, same, ischium, mesial view; h, same, lateral view. a, c-h, holotype, male from northern South China Sea (R38B-26, IOCAS); b, paratype ovigerous female from northern South China Sea (L56B-84, IOCAS). Scales = 1 mm (a-f); 0.5 mm (g, h).

Fig. 4. Plesionika longidactylus, new species. a, right second pereopod, lateral view; b, left second pereopod, lateral view; c, right third pereopod, mesial view; d, same, ischium and merus, lateral ventral view; e, same, dactylus, lateral view; f, same, mesial view; g, right fifth pereopod, mesial view. a, paratype ovigerous female from Beibu Bay (CN 2-11, IOCAS); b-g, holotype, male from northern South China Sea (R38B-26, IOCAS). Scales = 2 mm (a-d, g); 0.5 mm (e, f).

Fig. 5. Plesionika longidactylus, new species. a, abdomen, lateral view; b, right first pleopod, ventral view; c, left second pleopod, ventral view; d, telson, dorsal view. a, paratype, ovigerous female from Beibu Bay (CN 2-11, CBM); b-d, holotype, male from northern South China Sea (R38B-26, IOCAS). Scales = 2 mm (a); 1 mm (b-d).