Caridina enkii, Klotz & von Rintelen & Christodoulou, 2019

Klotz, Werner, von Rintelen, Thomas & Christodoulou, Magdalini, 2019, Middle East Caridina (Decapoda: Atyidae): Redescription of C. fossarum Heller, 1862, description of three new species, and remarks on the status of C. syriaca Bouvier, 1904 and C. babaulti basrensis Al-Adhub & Hamzah, 1987, Zoologischer Anzeiger 283, pp. 161-185 : 175-179

Caridina enkii sp. nov.

( Figs. 11 – 13)

Material examined

Holotype. ♂ cl 2.4 mm, Iraq, Shatt Al-Arab , Basrah, Khur Trad creek , leg. S.D. Salman 19.12.2011, OUMNH-ZC-2012-01-0078 . Paratypes. 2 ♂♂ cl 3.0 and 1.7 mm, 2 ♀♀, cl 3.7 and 2.3 mm, same data as holotype, OUMNH-ZC-2012-01-0079 .

Description

Cephalothorax and cephalic appendages. Medium-sized shrimp with carapace length 1.7 – 3.7 mm in apparently adult specimens (n = 5). Carapace ( Fig. 11 A ) smooth, antennal spine slightly below inferior orbital angle, pterygostomial angle rounded. Rostrum ( Fig. 11 A ) pointed, slightly sigmoid, armed with 20 – 22 teeth throughout dorsal margin, with 5 – 8 teeth on ventral margin, slightly overreaching antennular peduncle, 0.84 – 0.98 (n = 2) times as long as carapace. Rostrum formula 2 – 5 (3) + 17 – 18/5 – 8 (7). Eyes ( Fig. 11 A ) well developed with pigmented globular cornea. Antennula and antenna well developed. Antennular peduncle ( Fig. 11 B ) 0.76 – 0.88 (n = 2) times as long as carapace, first segment 1.81 – 2.27 (n = 2) times as long as second segment, distolateral angle with an acute projection 0.38 – 0.47 (n = 2) times as long as second segment; second segment 1.50 – 2.0 (n = 2) times length of third segment. Stylocerite pointed, reaching to 0.76 – 0.85 (n = 2) times length of basal segment of antennular peduncle. Scaphocerite ( Fig. 11 C ) with well-developed distolateral tooth, 3.71 – 4.13 (n = 2) times as long as wide.

Abdominal somites, telson and uropods. Sixth abdominal somite 0.47 – 0.63 (n = 2) times length of carapace, 2.05 – 2.11 (n = 2) times as long as fifth somite, 0.83 – 0.95 (median n = 2) times as long as telson. Telson ( Fig. 11 D, I ) slightly tapering distally, 3.33 (n = 1) times as long as proximally wide, distal margin convex, without a median projection, lateral angles not overreaching distal margin, with 5 or 6 (n = 2) pairs of dorsal short spiniform setae and one pair of short spiniform setae dorsolateral; distal margin with 5 or 8 (n = 2) strong spiniform setae, lateral pair longer than intermediate ones. Preanal carina ( Fig. 11 E ) rounded without a tooth or spine. Uropodal diaeresis ( Fig.11 F ) with 9 or 10 (n = 2) movable spiniform setae, outermost one shorter than lateral angle.

Mouthparts and branchia. Mandible ( Fig. 12 A ) without palp, incisor process ending in irregular teeth, molar process truncated. Lower lacinia of maxillula ( Fig. 12 B ) broadly rounded with long pappose setae and few rows of serrate setae near margin and scattered cuspidate setae proximal, upper lacinia elongate, with numerous distinct cuspidate setae flanked by a row of serrate setae on inner margin and few pappose setae subterminal, palp slender with few pappose setae and one cuspidate seta near tip. Upper endites of maxilla ( Fig. 12 C ) subdivided, furnished with numerous pappose, simple and papposerrate setae arranged in rows, palp slender, scaphognathite tapering posteriorly, fringed with long, curved serrulate setae at truncated posterior margin and plumose setae inferior. Palp of first maxilliped ( Fig. 12 D ) ending in a short finger-like extension, caridean lobe and flagellum with plumose setae, basis with numerous pappose, papposerrate and serrate setae arranged in rows and tufts. Podobranch on second maxilliped ( Fig. 12 E ) moderately developed; with few finger-like extensions distal, exopod slender, overreaching propodal segment, with long plumose setae distally; basis and merus with rows of pappose setae, distolateral margin of penultimate segment with several pappose and serrate setae; dactylus with numerous serrate setae flanked by a row of pappose setae. Third maxilliped ( Fig. 12 F ) slender, with one well developed and one strongly reduced arthrobranch; exopod slender, slightly overreaching the distal margin of antepenultimate segment, with few long plumose setae distally; antepenultimate segment of endopod slender, with several simple setae and some pappose setae basally and few plumose setae distally; penultimate segment slender, with straight lateral margins, with few plumose setae on dorsal and ventral margin, inner margin with rows of short serrate setae; ultimate segment shorter than or of same length as penultimate segment, tapering distally, ending in a claw-like curved spiniform setae (nail), proximal to the nail 7 – 12 cuspidate setae are arranged in two rows; inner margin dense beset with rows of serrated setae; epipod well developed, with distal hook. One moderately developed podobranch on second maxilliped, two arthrobranchs (one of them strongly reduced) on third maxilliped, first pereiopod without an arthrobranch. Pleurobranchs present on all pereiopods. Well-developed epipods (with hooks on distal end) present on third maxilliped and first four pereiopods. Setobranchs on all pereiopods.

Pereiopods. First and second pereiopods chelate. Chela of first pereiopod ( Fig. 11 G ) caridinoid in shape, with well-developed palm, 2.21 – 2.27 (n = 2) times as long as wide, 1.13 times as long as carpus; tips of fingers rounded, without hooks; dactylus 3.0 – 3.38 (n = 2) times as long as wide, 1.40 – 1.42 (n = 2) times as long as palm, with tufts of setae distally; carpus slender, slightly excavated distally, 2.31 times as long as wide, 1.07 times as long as merus. Merus not inflated, 3.50 times as long as wide. Chela of second pereiopod ( Fig. 11 H ) caridinoid in shape, with well-developed palm, 2.57 – 2.71 (n = 2) times as long as wide, 0.76 – 0.78 (n = 2) times as long as carpus; tips of fingers rounded, without hooks, dactylus 1.69 – 3.41 (n = 2) times as long as wide, 1.57 – 2.25 (n = 2) times as long as palm, with tufts setae distally; carpus slender, 5.13 – 6.13 (n = 2) times as long as wide, 1.07 – 1.09 (n = 2) times as long as merus. Merus not inflated, 5.0 – 6.0 (n = 2) times as long as wide. Third pereiopod ( Fig. 13 A ) sexually dimorphic; dactylus ( Fig. 13 B ) 5.17 times as long as wide (terminal claw and spiniform setae on flexor margin included), terminating in 1 large claw, with 19 accessory spiniform setae on flexor margin in males, 3.33 times as long as wide terminating in one large claw with 10 accessory spiniform setae on flexor margin in females; propodus strongly dilated distally and with numerous small spiniform setae on subdistal inner margin in adult males, less dilated in females and subadult males, propodus 5.39 times as long as wide, 2.0 times as long as dactylus in the adult male specimen measured, 10.31 times as long as wide, 3.35 times as long as dactylus in the female; carpus 4.0 – 4.50 (n = 2) times as long as wide, 0.66 – 0.73 (n = 2) times as long as propodus, 0.52 – 0.55 (n = 2) times as long as merus, with one large spiniform setae near distal margin; merus 8.20 – 8.50 (n = 2) times as long as wide, 1.82 – 1.93 (n = 2) times as long as carpus, bearing three strong movable spiniform setae on externo-inferior margin; ischium with one spiniform seta. Fourth pereipopod, similar to third but slightly smaller. Fifth pereiopod ( Fig. 13 C ) slender; dactylus ( Fig. 13 D ) 4.55 – 4.64 (n = 2) times as long as wide (terminal claw and spiniform setae on flexor margin included), terminating in one large claw, with 29 – 31 spiniform setae on flexor margin; propodus with small spiniform setae on ventral margin, slightly more densely in distal part, distal pair of spiniform setae not enlarged, propodus 10.46 – 11.67 (n = 2) times as long as wide, 2.67 – 2.80 (n = 2) times as long as dactylus; carpus 5.33 – 5.57 (n = 2) times as long as wide, 0.57 (n = 2) times as long as propodus, 0.70 – 0.71 (n = 2) times as long as merus, with 1 strong spiniform seta near distal margin; merus 6.33 – 6.88 (n = 2) times as long as wide, 1.41 – 1.43 (n = 2) times as long as carpus, bearing 2 strong appressed movable spiniform setae on externo-inferior margin. Ischium without a spiniform seta.

Pleopods. Endopod of male's first pleopod ( Fig. 13 E ) slender leaf-like, distally with a long tapered appendix interna furnished with numerous small cincunnuli near tip, 4.0 – 4.29 (n = 2) times as long as proximal width, 0.57 – 0.58 (n = 2) times as long as exopod, with long simple setae on outer margin, with somewhat shorter simple setae on inner margin. Appendix masculina on male second pleopod ( Fig. 13 F – G) rod-like, 12.0 – 14.33 (n = 2) times as long as wide, 0.81 – 0.83 (n = 2) times as long as endopod, armed with strong spiniform setae on inner margin and distal margin; appendix interna arising from about 0.4 times length of appendix masculina, reaching to 0.57 – 0.65 of appendix masculina.

Sexual dimorphism. Males similar to females except size, third and fourth pereiopods and sexual appendages. The main morphological differences from females lead in the shape and spinulation of distal segments of third and fourth pereiopods ( Fig. 13 A – B) and structure of the endopod of first pleopod ( Fig. 13 E ) as well as the presence of an appendix masculina in second pleopod ( Fig. 13 F – G).

Reproductive biology. Unknown as no ovigerous females could be included in the present study.

Size. Postorbital carapace length of apparently adult specimens 1.7 – 3.7 mm.

Colouration. Unknown.

Etymology. C. enkii sp. nov. is named after Enki, the god of Abzu, the primeval freshwater sea located within earth in the Sumerian mythology.

Distribution. C. enkii sp. nov. is known only from a tributary (Khur Trad creek) of the river Shatt Al-Arab in southern Iraq ( Fig. 1 B ).

Remarks. C. enkii sp. nov. is similar to C. fossarum in general morphology and showing a distinct sexual dimorphism of the third pereiopod. The proposed new species can be differed from C. fossarum by the more developed sexual appendages of male specimens. The endopod of the first pleopod of males is more slender, 4.0 – 4.29 times as long as wide vs. 3.33 – 3.85 times as long as wide in C. fossarum , both the outer and inner margin are beset with long simple setae (vs. with long setae on outer and distal margin, with few short pappose setae on basal part of inner margin in C. fossarum ), appendix masculina 12.0 – 14.33 times as long as wide, 0.81 – 0.83 times as long as endopod vs. 7.69 times as long as wide, 0.57 times as long as endopod in C. fossarum . The appendix interna is reaching to 0.57 – 0.65 length of appendix masculina vs. reaching almost to tip of appendix masculina in C. fossarum . In addition, the pereiopods of C. enkii sp. nov. are more slender compared to C. fossarum , e.g., propodus of fifth pereiopod 10.46 – 11.67 times as long as wide vs. 7.71 – 9.20 times in C. fossarum , carpus of this appendage 5.33 – 5.57 times as long as wide vs. 4.0 – 4.21 times in C. fossarum .

C. enkii sp. nov. was found by checking a sample with C. babaulti basrensis from the Khur Trad creek near Basrah, Iraq. Compared to the well-preserved specimens of C. babaulti basrensis in this sample, the five specimens of C. enkii sp. nov. are in a rather poor condition rising some doubts as to whether these specimens were really collected and preserved together with the specimens of C. babaulti basrensis . As no other hints could be found indicating that the samples were mixed either during collection or later in the museum, Khur Trad creek near Basrah, Iraq was considered as the type locality of the proposed new species.

Figures

Fig. 11. Caridina enkii sp. nov., male, OUMNH 2012-01-079: A, cephalothorax and cephalic appendages; B, antennula; C, antenna; D, telson; E, preanal carina; F, uropodal diaeresis; G, first pereiopod; H, second pereiopod; I, terminal part of telson. Scale bars indicate 0.5 mm.

Fig. 12. Caridina enkii sp. nov., male, OUMNH 2012-01-0079: A, mandible B, maxillula; C, maxilla; D, first maxilliped; E, second maxilliped; F, third maxilliped. Scale bars indicate 0.5 mm.

Fig.13. Caridina enkii sp. nov., male, OUMNH 2012-01-0079: A, third pereiopod; B, dactylus of third pereiopod; C, fifth pereiopod; D, dactylus of fifth pereiopod; E, first pleopod; F, second pleopod; G, appendix masculina and appendix interna. Scale bars indicate 0.5 mm.

Fig. 1. A, Origin of sequenced specimens (for details see Table 1); B, Map showing the geographic distribution of Caridina species in the Middle East.