Palaemonella komaii, Li & Bruce, 2006

Li, Xinzheng & Bruce, Alexander J., 2006, Further Indo-West Pacific palaemonoid shrimps (Crustacea: Decapoda: Palaemonoidea), principally from the New Caledonian region, Journal of Natural History 40 (11 - 12), pp. 611-738 : 657-663

Palaemonella komaii sp. nov.

( Figures 9–11 )

Material examined

Tonga: BORDAU 2, Vava’u group, stn DW 1583, 327– 360 m, 18 ° 379S, 174 ° 039W, 13 June 2000, 1 „ holotype (MNHN-Na 15482). Fiji: stn CP 1445, 17 ° 109S, 178 ° 429W, 350– 365 m, coll. Bouchet, Waren and Richer de Forges , 3 March 1999, 1 „ paratype (MNHN- Na 15600) .

Description

Holotype. A small pontoniine shrimp of subcylindrical body form. Most of pereiopods lost, only detached right first and both fifth pereiopods present.

Carapace smooth, glabrous. Rostrum well developed, shallow, compressed, straight and horizontal, extending beyond anterodorsal margin of second segment of antennular peduncle, about 0.8 of carapace length; dorsal margin with seven (excluding epigastric spine) acute teeth distributed along whole length, interdental spaces smaller anteriorly, first tooth situated slightly posterior to posterior orbital margin; lateral carinae indistinct; ventral margin with two small acute teeth on distal third, smaller than dorsal teeth; interdental spaces and proximal ventral carina feebly setose. Supraorbital spine absent; epigastric spine similar to dorsal rostral teeth, situated at anterior 0.3 of the carapace length; orbit feebly developed, inferior orbital angle feebly produced, bluntly round in lateral view, postorbital carina distinct; antennal spine large slender marginal, distinct below the inferior orbital angle, far exceeding inferior orbital angle, reaching to distal margin of antennal basicerite; hepatic spine distinctly smaller than antennal spine, slender, situated far below level of antennal spine and near to anterolateral angle of carapace, below first dorsal rostral tooth in lateral view; anterolateral angle of carapace not produced, bluntly rounded.

Abdominal segments smooth, glabrous; sixth segment about 1.85 times length of fifth, subcylindrical, about 1.80 times longer than deep, subuniform, posterolateral angle acute, posteroventral angle with small acute tooth; pleura of first three segments broadly rounded, fourth and fifth posteriorly produced, fourth with posteroventral angle rounded, fifth with posteroventral angle with acute tooth. Telson about 1.19 times sixth abdominal segment length, about 3.4 times longer than anterior width, lateral margins curved ventrally, convergent, posterior margin about 0.4 of anterior margin width, rounded; dorsal surface with two pairs of developed acute dorsolateral spines at 0.33 and 0.67 of telson length, the spines 0.085 of telson length; three pairs of posterior spines, lateral spines short, similar to dorsal spines, about 0.05 of telson length, intermediate spines long, robust, about 0.22 of telson length, submedian spines slender, about 0.5 of intermediate spine length.

Eye well developed, cornea and stalk distinct compressed, width of cornea 0.28 of postorbital carapace length, accessory pigment spot distinct, fused with cornea; stalk thinner than cornea, length 0.9 of corneal width, 1.16 of its width.

Antennular peduncle slender, exceeding rostrum; proximal segment about 2.24 times longer than width, with slender acute stylocerite laterally, reaching to about 0.42 of segment length, anterolateral margin feebly produced, with well-developed slender acute lateral tooth; statocyst small; medial margin setose, with ventromedial tooth at about 0.5 of length; intermediate segment obliquely articulated with distal segment dorsal length about 0.3 of proximal segment length, 2.1 of width; distal segment subequal to intermediate segment, slender, about 2.6 times longer than distal width; upper flagellum biramous, with 18 proximal segments of rami fused, shorter free ramus with three segments, with about seven groups of aesthetascs; longer ramus, slender, filiform; lower flagellum slender, filiform.

Antennal basicerite robust, with acute distolateral tooth; carpocerite about 0.29 of scaphocerite length, about 3.2 times longer than width, subcylindrical; flagellum lost; scaphocerite well developed, distinctly exceeding antennular peduncle, slender, about 4.0 times longer than wide, greatest width at about 0.4 of length, distal margin bluntly rounded, lateral margin feebly concave, with strong acute distolateral tooth, overreaching distal lamella.

Epistome with median carina. Fourth thoracic sternite with slender finger-like median process, fifth with well-developed posterior transverse ridge separated by deep median notch, with pair of large acute spines on ridge adjacent to notch; sixth and seventh sternites narrow and unarmed; eighth armed with short stout anteriorly directed median process.

Mouthparts typical of the genus. Mandible with corpus moderately robust, with developed palp with three distal setae and one lateral seta; molar process normal, with four strong blunt teeth, lower inner tooth bilobed; incisor process robust, distally with three (right) or four (left) stout acute teeth, central tooth smaller than outer teeth. Maxillula with feebly bilobed palp, upper lobe tapering tip acute, recurved; upper lacinia robust, distal margin feebly rounded with two rows of acute spines; lower lacinia robust, distally rounded, with simple setae. Maxilla with short simple non-setose palp, tip acute; basal endite deeply bilobed, upper lobe stouter than lower, with simple setae distally; coxal endite obsolete; scaphognathite well developed, about 3.3 times longer than central width. First maxilliped with simple seta on palp subapically; caridean lobe well developed, with simple setae laterally, exopod with well-developed flagellum, with three long distal plumose setae; basal endite with medial margin with dense simple short setae, coxal endite with medial margin with numerous spines; epipod large, triangular, feebly bilobed. Second maxilliped with normal endopod, dactylar segment about 3.96 times longer than broad, with numerous serrulate spines medially; propodal segment broad, subtriangular, with distal margin with numerous long slender setae; carpus and ischiomerus without special features; basis with distomedial angle acute, with several short setae; coxa feebly produced medially, with four to five simple setae; exopod with slender flagellum with three simple setae distally; epipod oval, with rectangular bilobed podobrach. Third maxilliped with robust endopod, extending distally to end of the carpocerite, ischiomerus and basis fused incompletely, combined segment length about 8.3 times central width, setose medially; intermediate segment about 0.77 of combined proximal segment length, 6.8 times longer than distal width, with eight groups of slender setae medially; terminal segment about 0.44 of combined proximal segment length, distally tapering, about 5.1 times longer than proximal width, with eight dense groups of setae medially and laterally and distal setae; exopod with robust flagellum reaching to 0.83 of combined segment, with four simple plumose setae distally; coxa feebly produced medially, with lobed lateral plate; arthrobranch distinct.

First pereiopods slender, exceeding tip of rostrum by length of chela and distal 0.8 carpus; chela slender, with palm feebly compressed, about 2.7 times longer than maximal depth, at about proximal 0.27 of length with five transverse rows of short cleaning setae proximoventrally; fingers 1.1 times palm length, slender, tapering, cutting edges sharp, entire, tips hooked, with several groups of setae laterally; carpus slender, distally feebly swollen, about 1.13 of chela length, 7.8 times longer than distal width, with row of ventral serrulate cleaning setae subdistally; merus subuniform, about 1.2 times chela length, 11.8 times longer than central width, ventral surface plain, with distinct distoventral groove; ischium 0.63 times length of chela, 6.1 times longer than distal, subuniform, with several long setae proximoventrally; basis with ventral margin sinuous, with two short blunt processes, proximal process setose; coxa with well-developed ventromedial process, setose and lobed.

Ambulatory pereiopods long, slender. Fifth pereiopod exceeds carpocerite by dactyl, propod and carpus, exceeds scaphocerite by dactyl and propod; dactyl long and slender, simple, feebly curved, about 0.17 of propod length, 10.6 times proximal depth, external margin with six long simple setae from 0.4 to 0.7 of dactyl length, outer side with lateral sensory seta at 0.74 of dactyl length; propod uniform, about 1.22 of carapace length, 41.4 times longer than distal width, subdivided into six segments, with pair of short slender simple distoventral spines, three single spines distributed respectively at distoventral margin of third to fifth subsegments, two long setae on distodorsal margin of propod; carpus slender, uniform, about 0.6 of propod length, 21.15 times longer than distal width, unarmed; merus 0.8 of propod length, 27.9 times longer than wide, uniform, unarmed; ischium 0.4 of propod length, 11.9 times longer than distal width, uniform; basis and coxa without special features.

Uropod distinctly exceeding telson; protopodite with posterolateral angle acute; exopod 3.0 times longer than central width, lateral border near straight, with small acute distal tooth and long and acute mobile spine medially, diaeresis distinct; endopod about 0.88 of exopod length, 3.3 times longer than wide.

Paratype. Right second and left fifth pereiopods detached.

Similar to holotype. Rostrum dorsal margin with five acute teeth (except epigastric spine). First pereiopods exceeding tip of rostrum by length of chela and distal two-thirds of carpus. Second pereiopods similar and equal, very slender and elongate, exceeding tip of rostrum by length of chela, carpus and distal two-thirds of merus; chela 1.7 times carapace length, palm subcylindrical, subuniform, smooth, distinctly curved at fingers articulate, 4.3 times longer than central depth, fingers smooth, 0.8 of palm length, with hooked tips, dactyl 7.2 times longer than proximal depth, cutting edge entire with two small teeth at proximal 0.25 and 0.35 length, distal tooth larger than proximal tooth, distal 0.6 cutting edge entire, fixed finger similar to dactyl, cutting edge with five to six small teeth on proximal 0.34 length, distal two teeth larger than proximal teeth, distal three-quarters cutting edge entire; carpus unarmed, distally swollen, 0.9 of palm length, 6.2 times longer than distal width; merus uniform, unarmed, 1.18 of palm length, subuniform, 10.7 times longer than width; ischium unarmed, slightly dorsoventrally compressed, slightly proximally tapered, about 0.71 of palm length, 9.1 times longer than distal width; basis and coxa normal. Third pereiopod exceeds scaphocerite tip by propod and dactyl; dactyl long and slender, simple, feebly curved, 0.21 of propod length, 8.0 times proximal depth, external margin with eight long simple setae from 0.4 to 0.75 of dactyl length; propod uniform, 0.97 of carapace length, 34.4 times longer than width, subdivided into four (left) or five (right) segments, with pair of short slender simple distoventral spines, three single spines distributed respectively at distoventral margin of third to fifth subsegments, two long setae on distodorsal margin of propod and two long setae on distodorsal margin of subsegments; carpus slender, uniform, 0.6 of propod length, 16.6 times longer than distal width, unarmed; merus, slender, uniform, subequal to propod, 23.4 times longer than wide, unarmed; ischium 0.44 of propod length, 10.1 times longer than distal width, uniform; basis and coxa without special features. Fourth and fifth pereiopods similar to third, fourth exceeds scaphocerite tip by dactyl and distal three-fifths of propod, propod divided into five (left) or four (right) subsegments; fifth pereiopod longer than fourth, exceeds scaphocerite tip by propod and dactyl, propod divided into five subsegments.

Measurements (mm)

Holotype. Carapace length, 3.39; carapace and rostrum, 6.06; total body length (proximally), 16.8; first pereiopod, chela, 1.95; third pereiopod, propod, 4.14.

Paratype. Carapace length, 3.62; carapace and rostrum, 6.22; first pereiopod, chela, 1.92; second pereiopod, chela, 6.04, third pereiopod, propod, 3.51.

Systematic position

Palaemonella komaii sp. nov. is very close to P. dolichodactylus Bruce, 1991 and P. hachijo Okuno, 1999 , sharing the features of very long and slender ambulatory pereiopods with the dactyl more than 8.0 times longer than basal depth and with several long setae on dorsal dactyl margin, propod more than 26 times longer than width. The new species can be easily distinguished from P. hachijo by the subsegmented and more slender and longer ambulatory propod, and the position of hepatic spine on the carapace which is lower and more anterior, close to the anteroventral angle of the carapace. It differs from P. dolichodactylus in the position of the hepatic spine on the carapace which is lower and more anterior, close to the anteroventral angle of the carapace, the longer antennal spine, which is longer than the hepatic spine and extends to the anterior margin of the basicerite, the ambulatory propod is more slender and longer (41.4 to 26 times longer than distal width).

Etymology

The specific name is given in honour of the Japanese carcinologist, Dr Tomoyuki Komai.

Remarks

The extremely long and slender ambulatory pereiopods with the dactyl more than eight times longer than its depth and with several long setae on dorsal dactyl margin, the propod more than 26 times longer than wide separate the new species and its allied species, P. dolichodactylus Bruce, 1991 and P. hachijo Okuno, 1999 , from the other species of the genus Palaemonella . They may form a ‘‘ P. dolichodactylus species complex’’. The new species looks like an intermediate form between P. dolichodactylus and P. hachijo , in the features of antennal spine and segmented ambulatory propod. But the ambulatory pereiopod varies with increasing habitat depth: shortest and most robust in P. hachijo (shallow waters, 0–45 m); moderately long and slender in P. dolichodactylus (shallow to deep waters, 16–250 m); longest and most slender in P. komaii (deep water, 327–360 m). The posteroventral angle of the fifth abdominal somite is not a stable character to distinguish P. dolichodactylus and P. hachijo , as used by Okuno (1999) and Bruce (2002b), because all specimens of P. dolichodactylus we have checked (including the two specimens of Bruce 1991a) have acute tooth on the posteroventral angle of fifth abdominal pleuron.

Figures

Figure 9. Palaemonella komaii, new species, holotype male (MNHN-Na 15482). (a) Carapace and anterior appendages; (b) anterior carapace; (c) telson; (d) eye, dorsal view; (e) antennule; (f) same, distal shorter free ramus of upper flagellum; (g) antenna.

Figure 10. Palaemonella komaii, new species, holotype male (MNHN-Na 15482). (a) Mandible; (b) maxillula; (c) maxilla; (d) first maxilliped; (e) second maxilliped; (f) third maxilliped.

Figure 11. Palaemonella komaii, new species. (a–c, g–i) Holotype male (MNHN-Na 15482); (d–f) paratype male (MNHN-Na 15600). (a) First pereipod; (b) same, chela; (c) same, coxa, basis and ishium; (d) second pereiopod, right; (e) same, chela; (f) third pereiopod, left; (g) fifth pereiopod, left; (h) same, distal propodal subsegment and dactyl; (i) uropod.