Palaemon khori, Grave & Al-Maslamani, 2006

Grave, S. De & Al-Maslamani, I., 2006, A new species of Palaemon (Crustacea, Decapoda, Palaemonidae) from Qatar, Zootaxa 1187 (1), pp. 37-46 : 38-45

Palaemon khori sp. nov. ( Figs. 1–4)

Material examined. Holotype: ovigerous female post orbital carapace length (pocl) 6.4 mm; collected by hand net amongst pneumatophores of Avicennia marina at low tide from

a creek on the northern side of Al­Khor Bay , east coast of Qatar, 51º33'30" E 25º 41'30"N; 11 April 2003, leg. I. Al­Maslamani ( RMNH D51663) .

Paratypes: 3 ovigerous female (pocl 6.0– 6.2 mm), 1 female (pocl 5.8 mm), 16 males (pocl 3.7–4.5 mm); same data as holotype ( RMNH D51664 ); 1 ovigerous female (pocl 6.5 mm), 9 males (pocl 3.5–4.3 mm), same data as holotype ( NHM 2006.91 – 100 ); 3 ovigerous females (pocl 5.5–6.0 mm), 4 males (pocl 3.7–4.2 mm), same data as holotype ( OUMNH ZC.2006­05­001); 1 male (pocl 4.4 mm), fully dissected, same data as holotype ( OUMNH ZC.2006­05­002); 1 ovigerous female (pocl 6.8 mm), fully dissected, same data as holotype ( OUMNH ZC.2006­05­003)

Non­type material: 61 males, same data as holotype ( OUMNH ZC.2006­05­004) .

Description. A small sized Palaemon . Rostrum well developed, nearly straight in basal part, gently upturned in distal part ( Fig. 1A); approximately 1.25–1.50 x post­orbital carapace length, over­reaching antennal scale by about one third of its length ( Fig. 1A). Abdomen of usual shape in Palaemon species ; fifth pleuron near­quadrate ( Fig. 1B); sixth somite with small tooth at posteroventral angle; sixth somite 1.8–2.0 x length of fifth somite, near equal in length to telson ( Fig. 1B).

Upper margin of rostrum with 7 teeth, posteriormost of which is situated posterior to orbital margin; two posteriormost teeth articulated; one subapical tooth present, separated from next dorsal tooth by naked interval; small setae present between each tooth in proximal half of each interval; 3–5 ventral teeth present (median value 4) in distal half of rostrum; proximal half of rostrum naked, furnished with double row of plumose setae ( Fig. 1D).

Carapace glabrous ( Fig. 1A); branchiostegal spine same size as antennal spine ( Fig. 1D), placed on margin of carapace below branchiostegal suture; branchiostegal suture short, ventrally curved in posterior half.

Telson ( Fig. 1G) with length­width ratio 0.29–0.36; two pairs of dorsal spines present, non marginal, placed at approximately 0.5 and 0.8 of telson length; margin distal to proximal pair of spines compartmentalised, furnished with series of small setae ( Figs. 1G–H); posterior margin drawn out into to sharp point, reaching to about a quarter to a third of the length of the mesial pair of spines; posterior margin furnished with two pairs of spines, mesial pair more than twice as longs as marginal pair; a pair of plumose setae mesially ( Fig. 1H).

Eye stout ( Fig. 1C), cornea as broad as stalk, furnished with small ocellus on mesial side.

First thoracic sternite of males with distally placed median spine, with an additional proximally placed ridge, furnished with a broad median notch.; second thoracic sternite of males with proximal ridge, medially deeply bifurcating; fifth thoracic sternite with median, blunt spine; median spine present on abdominal somite between first pleopods. Thoracic ornamentation of females similar, but with low plumose carina across fifth sternite. Pre­anal carina low ( Fig. 1I), two small bosses present, each furnished with small setae.

Uropods slightly over­reaching telson, normal in shape ( Fig. 1E); mobile lateral spine over­reaching fixed one ( Fig. 1F).

Antennular peduncle with stylocerite reaching to 0.4 x length of basal segment ( Fig. 2A); distolateral spine of basal segment slightly over­reaching convex distal margin of lateral extension; basal segment longer than second and third segment combined; second and third segment near equal in length; dorsolateral antennular flagellum comprised of two rami, approximately 2.5–3 times as long as carapace, fused portion ( Fig. 2B) near equal to free rami; ventromesial flagellum about twice as long as carapace length.

Antennal peduncle as usual ( Fig. 1A, D; Fig. 2C), basicerite armed with large lateral tooth ( Fig. 1D); flagellum 4.5–5.0 times as long as carapace; scaphocerite about 3.5 times as long as wide, lateral margin nearly straight, distal tooth well developed, not reaching end of blade ( Fig. 2C).

Mouthparts as usual for Palaemon species. Mandible with palp ( Fig. 2D), incisor process armed with two strong lateral and two mesial teeth; mandibular palp two segmented, furnished with single distal seta ( Fig. 2E); third maxilliped well developed, basal segment with small disto­lateral tooth, placed below distal margin ( Fig. 2F).

First pereiopods equal in size and shape, falling short of end of scaphocerite; fingers as long as palm ( Fig. 3A); ischium shorter than merus, furnished with marginal carina; propodus 1.3–1.5 times as long as carpus.

Second pereiopods slightly over­reaching scaphocerite; fingers approximately half as long as palm ( Fig. 3B); opposable margins weakly ornamented, with small low boss proximately on each finger ( Fig. 3c); tip furnished with single blunt spine; carpus 1.2 times length of merus, propodus 1.3 times as long as carpus, chelae about 0.7–0.8 times as long as propodus.

Third pereiopod gracile ( Fig. 3D), ischium about half length of merus, unarmed; carpus about half length of propodus, armed with three single spines along inferior margin, and a pair of spines at the infero­distal angle; dactylus short, about 0.4 x length of propodus, relatively stout.

Fourth pereiopod ( Fig. 3E) similar to third pereiopod, propodus relatively longer, armed with three single spines along inferior margin, and a pair of spines at the infero­distal angle; dactylus short, about 0.3 x length of propodus, relatively stout.

Fifth pereiopod ( Fig. 3F) similar to fourth pereiopod, propodus armed with armed with two single spines along inferior margin, infero­distal setal brush well developed, extending proximally to about 0.3 of propodus length; dactylus short, about 0.25 x length of propodus, relatively stout.

Endopod of male first pleopod ( Fig. 2G) reaching slightly beyond mid­length of exopod; mesial margin sinuous, without notch.

Appendix masculina of male second pleopod ( Fig 2I) reaching to 0.75 of endopod, appendix interna reaching to approximately 0.90 of appendix masculina ( Fig. 2J); appendix masculina furnished with 12 long spines in single row near lateral margin and three in a terminal cluster ( Fig. 2J).

Eggs numerous, size approximately 1.0 x 0.6 mm (eyed embryo).

Variation. As is the norm in Palaemon species , a certain amount of rostral variation was observed in P. khori . sp. nov. ( Fig. 4). The majority of specimens harbour 7 teeth on the dorsal side of the rostrum, of which as a rule only the two most basal ones are articulated. The number of ventral rostral teeth varies from 3 to 5, 4 being the median ( Fig. 4). In very few examples, the rostrum is relatively gracile ( Fig. 4E) but does not approach the form exhibited by P. debilis sensu Chace (1972) The majority of specimens are more deep bladed ( Fig. 4A–D, F–G). The length ratio of the fixed versus free portion of the dorsolateral antennular flagellum varies from 1.00:0.50 through to 1.00:1.11, with a mean value of 1.00:0.80. There is little variation in relative lengths of the appendix masculina and interna, with the appendix interna reaching to 0.89–0.91 x length of the appendix masculina. Equally, there is little variation in the tip of the telson reaching from 0.26–0.34 x the length of the medial spines; whilst the length/width ratio of the telson varies from 0.29– 0.36. No significant sexual variation in these parameters could be observed.

Derivation of name. From the Arabic word khor, meaning lagoon, in reference to the species living amongst lagoonal mangrove roots.

Habitat. During the twelve month study period of the ecological project, P. khori sp. nov. was exclusively encountered between the pneumatophores of Avicennia marina . All life stages, from postlarvae through to ovigerous females were encountered, suggesting the population is resident in this habitat. Despite exhaustive searches throughout the bay, no specimens were encountered in intertidal and subtidal seagrass beds and mudflats, nor any other habitat available within the bay. Associated fauna included non­identified isopods and amphipods which occur amongst the epiphytic red algae ( Polysiphonia sp ) associated with the mangrove roots, and which also are the main component of the diet of P.khori sp. nov., based on examination of gut contents.

Discussion. Palaemon khori sp. nov. is closely related to P.debilis Dana , as defined by Chace (1972). The new species shares with P. debilis a number of taxonomically important features, such as the fused portion of the upper antennular flagella near equal to the free part, the size and marginal placement of the branchiostegal spine, and the poorly developed armature of the chelae of the second pereiopod. Nevertheless, the new species differs from P. debilis sensu Chace (1972) in the following characteristics: rostrum near horizontal, not gracile (versus strongly upturned and gracile); fifth pleuron near quadrate (versus acuminate); telson wider, less elongate; tip of the telson reaching to about 0.3 x length of medial spines (versus 0.6); medial spines longer, more gracile; endopod of first male pleopod without mesial notch; appendix interna reaching to about 0.9 x length of appendix masculina (versus 0.70); and the length/width ratio of the scaphocerite.

The marginal setation of the distal half of the telson was very noticeable in P.khori sp. nov., as was the presence of a disto­lateral tooth on the basal segment of the third maxilliped, but as these have not been noted yet in any other Palaemon species , it remains to be seen if this will further distinguish the two species. Similarly, the sternal armature has been poorly documented in Palaemon species (see Van Xuan, 1992), and is unknown in P.debilis sensu stricto populations, and indeed for the majority of Palaemon species.

As many morphological details here described for P. khori sp. nov. are not described and/or illustrated in the numerous Indo­Pacific wide records of P. debilis sensu lato, a full comparison must await a more detailed study of this species complex across its reported geographical range, which is beyond the scope of the present study.