Mesopontonia brevicarpus, 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 : 652-654

Mesopontonia brevicarpus sp. nov.

( Figures 7 , 8 )

Material examined

La Réunion: MD 32 , stn DS173, 20 ° 51.59S, 55 ° 36.879E, 270 m, 8 September 1982, 1 ovig. ♀ (cl 2.56 mm), holotype; 1 „ (cl 2.53 mm), 1 ovig. ♀ (cl 2.77 mm), paratypes; 3 juveniles (MNHN-Na 14824) .

Description

A small-sized pontoniine shrimp of slender, subcylindrical body shape, closely resembling other species of the genus, such as M. gracilicarpus Bruce, 1990 and M. verrucimanus Bruce, 1996 .

Rostrum well developed, horizontal, compressed, extending anteriorly near to the end (ovig. ♀) or to the proximal third („) of distal segment of antennular peduncle, about 0.9 of carapace length, dorsal carina well developed, posteriorly elevated, dorsal margin convex, with eight evenly distributed acute teeth, first tooth with (ovig. ♀) or without („) basal suture, situated behind posterior orbital margin, distal tooth minute, lateral carinae obsolete, ventral carina feebly developed, margin slightly convex. Carapace smooth, glabrous, with epigastric spine at anterior 0.3 of carapace length, basal suture distinct, supraorbital and antennal spines absent, inferior orbital angle produced, hepatic spine well developed, slender, acute, reaching or extending to anterior margin of carapace, at about 0.12 of carapace length, well below level of inferior orbital angle, anterolateral angle of branchiostegite bluntly rounded. Abdomen and caudal fan without special features (the ovig. ♀ holotype lacks the caudal fan), as in M. gracilicarpus .

Antennae as in M. gracilicarpus .

Eye with well-developed large, globular, pigmented cornea, diameter about 0.23 of carapace length.

Mouthparts mainly undissected. Third maxilliped without exopod, ischiomerus and basis feebly separated, with a rudimentary arthrobranch.

First pereiopod with finger about 0.7 of palm length, tips hooked, cutting edge entire except convex subapically with fine pectinated serrates; carpus about 1.1 times chela length, 0.9 of merus length, coxa with small ventromedial process.

Second pereiopods well developed, markedly unequal, dissimilar. Major pereiopod with chela about 1.0–1.1 of carapace length, palm subcylindrical, 3.9 times longer than deep, covered with uniformly distributed small blunt tubercles, many with short simple setae distally, fingers about 0.5 of palm length, dactyl slender, about 4.0 times longer than proximal depth, tapering distally, with acute hooked tip, cutting edge with distal half sharp, with one low acute tooth at proximal 0.3 and a notch at proximal 0.38 of the cutting length, without dorsolateral flange; fixed finger with two acute teeth at proximal 0.25 and 0.38 on the cutting edge; carpus short, stout, unarmed, about 0.34 of palm length, sparsely tuberculate, about 2.0 times longer than distal width, merus about 0.85 of palm length, 7.0 times longer than wide, uniform, smooth, unarmed; ischium about 0.9 times merus length, 0.73 of palm length, 7.0 times longer than distal width, smooth, unarmed; basis and coxa without special features. Minor pereiopod with chela about 0.7 of carapace length, 0.95 of major chela palm length, palm subcylindrical, smooth, about 4.0 times longer than distal width, slightly tapering proximally, fingers subequal to palm, slender, with small hooked tips, cutting edges distally sharp, entire; carpus slender, about 0.75 of chela length, 8.0 times longer than distal width, smooth, unarmed; merus about 1.1 times carpus length, 11.0 times longer than distal width, subuniform, unarmed; basis and coxa without special features.

Ambulatory pereiopods slender. Third pereiopod with propod about 0.7 of carapace length, 17 times longer than wide, uniform, with a pair of long and slender distoventral spines, ventral border with similar spinules, size decreasing proximally, with long setae distodorsally; dactyl about 0.17 of propod length, slender, biunguiculate, with clearly demarcated unguis, about 3.3 times longer than proximal width, 0.70 of corpus length, corpus 2.3 times longer than proximal depth, compressed.

Measurements (mm)

Carapace length, 2.53–2.77; carapace and rostrum, 4.75–4.81; second pereiopod, major chela, 2.75; minor chela, 1.74./p>

Systematic position

The present species is closely related to M. gracilicarpus Bruce, 1990 ; it can be distinguished from the latter by the tuberculate major second pereiopod chela, relatively shorter carpus of minor second pereiopod (0.75 of chela length), and the hepatic spine on carapace reaching the anterior margin of carapace. In M. gracilicarpus , the major second pereiopod chela smooth, the carpus of minor second pereiopod 1.5 times chela length, and the hepatic spine not reaching to the anterior margin of carapace. Mesopontonia brevicarpus shares the tuberculate major chela of second pereiopod with M. verrucimanus Bruce, 1996 . It can be immediately distinguished from that species by the biunguiculate dactyls of ambulatory pereiopods.

Etymology

From brevis (Latin), short; carpus (Latin), wrist, with reference to the short carpus of major second pereiopod.

Remarks

With the addition of the new species, there are now seven species in the genus Mesopontonia , including the unnamed taxon, Mesopontonia sp. Bruce, 1996 . The key to Mesopontonia species provided by Bruce (1996) can be modified as following:

3. Second pereiopods markedly unequal............. 39 – Second pereiopods at most moderately unequal; carpus of minor second pereiopod shorter than chela................... 4

39. Palm of major second pereiopod tuberculate; carpus of minor second pereiopod shorter than chela; R. 1+8/2......... M. brevicarpus sp. nov.

– Palm of major second pereiopod smooth; carpus of minor second pereiopod about

1.5 times length of chela; R. 1+8/2...... M. gracilicarpus Bruce, 1990

Figures

Figure 7. Mesopontonia brevicarpus, new species. (a, d–g) Holotype ovigerous female; (b) paratype male; (c) juvenile (MNHN-Na 14824). (a) Carapace and anterior appendages; (b, c) carapace; (d) antennule; (e) first pereiopod; (f) same, chela; (g) same, apexes of fingers.

Figure 8. Mesopontonia brevicarpus, new species, holotype ovigerous female (MNHN-Na 14824). (a) Major second pereiopod; (b) same, chela; (c) same, fingers; (d) minor second pereiopod; (e) same, chela; (f) third pereiopod; (g) same, propod and dactyl; (h) same, distal propod and dactyl.