Micratya cooki, Karge, Andreas, Page, Timothy J. & Klotz, Werner, 2013

Karge, Andreas, Page, Timothy J. & Klotz, Werner, 2013, A new species of freshwater shrimp of the genus Micratya (Decapoda: Atyidae: Caridea) from Puerto Rico, Zootaxa 3608 (5), pp. 357-368 : 362-365

Micratya cooki sp. nov.

( Figs. 5 A–O, 6P–W, 7A)

Material examined. Holotype ov. female, cl 4.9 mm, tl 16.6 mm (MNHN-IU-2011-6057), Río Guayanés, Puerto Rico; Paratypes 1 female, cl 3.5 mm (MNHN-IU-2011-6058), Río Guayanés, Puerto Rico; 1 female, cl 4.9 mm (MNHN-IU-2011-6059), Río Grande de Manatí, Puerto Rico; 1 ov. female, cl 5.0 mm (OUMNH.ZC-2012.05.001), Río Guayanés, Puerto Rico; Others 2 males, cl 3.1–3.7 mm, 6 females, cl 3.1–4.9 mm (MNHN-IU-2011-6060) Río Coamo, Puerto Rico; 1 male, cl 4.0 mm, 4 females, cl 3.9–5.3 mm (MNHN-IU-2011-6061) Río Guanajibo, Puerto Rico; 6 females, cl 3.9–4.9 mm, 6 ov. females 4.2–4.8 mm (OUMNH.ZC-2012.05.002), Río Guayanés, Puerto Rico; 2 males, cl 3.1–3.3 mm, 1 ov. female, cl 6.6 mm, 6 females, cl. 4.1–5.2 mm (OUMNH.ZC-2012.05.003), Río Coamo, Puerto Rico; 1 male, cl 4.0 mm (OUMNH.ZC-2012.05.004), Río Coamo, Puerto Rico; leg. B.D. Cook, J. Hughes and P. Hernandez-Garcia, February 2006.

Diagnosis. Rostrum ( Fig. 5 A–B) short, reaching near to end of basal segment of antennular peduncle, 0.21–0.31 times as long as carapace, armed dorsally with 3 to 9 (most 5–7) teeth without teeth on carapace posterior to orbital margin, 0 to 2 ventral teeth (most 1–2). Chela of first pereiopod ( Fig. 6 P) 2.55–2.84 as long as wide, dactylus 5.10–6.00 times as long as wide; carpus 0.89–0.97 times as long as wide. Chela of second pereiopod ( Fig. 6 Q) 2.20–2.63 times as long as wide, dactylus 5.36–6.00 times as long wide; carpus 0.94–1.10 times as long as wide. Propodus of fifth pereiopod ( Fig. 6 T–U) 6.45–9.33 times long as wide; dactylus 0.25–0.40 long as propodus, dactylus with 1 large claw and 17–30 spines on flexor margin (most 17–22). Endopod of male first pleopod ( Fig. 6 V) 2 times as long as proximal width, appendix interna strong. Preanal carina ( Fig. 5 D) rounded, with a distinct tooth. Uropodal diaeresis ( Fig. 5 E) with 16–18 movable spinules.

Description. Rostrum ( Fig. 5 A–B) short, reaching near to end of basal segment of antennular peduncle, 0.21–0.31 times as long as carapace, armed dorsally with 3 to 9 (mostly 5–7) teeth without teeth on carapace posterior to orbital margin, 0 to 2 ventral teeth (mostly 1–2); rostral formula: 0 + 3–9 / 0–2.

Inferior orbital angle fused with antennal spine. Pterygostomial angle broadly rounded. Antennular peduncle 0.39–0.46 times as long as carapace, second segment 0.30–0.35 times length of basal segment, third segment 0.67–0.92 times as length of second segment. Stylocerite 0.75–0.90 times as long as basal segment of antennular peduncle. Scaphocerite ( Fig. 5 C) 2.41 times as long as wide.

Sixth abdominal somite 0.38–0.46 times length of carapace, 1.12–1.34 times as long as fifth somite, 0.80–0.91 shorter than telson. Telson ( Figs. 5 F–G) 1.92–2.35 times as long as proximally wide, distal margin broadly rounded, with median projection, with 5 or 6 pairs of dorsal and 1 pair of dorsolateral spinules, distal end with 10–12 spines, intermediate spines with fine bristles and longer than lateral pair. Preanal carina ( Fig. 5 D) rounded, with a distinct tooth. Uropodal diaeresis ( Fig. 5 E) with 16–18 movable spinules.

Incisor process of mandible ( Fig. 5 O) ending in irregular teeth, molar process truncated. Lower lacinia of maxillula ( Fig. 5 N) broadly subrectangular, upper lacinia elongate, with numerous distinct teeth on inner margin, palp slender with few simple setae at tip. Upper endites of maxilla ( Fig. 5 L) subdivided, palp slender, scaphognathite tapering posteriorly, fringed with long, curved setae at posterior margin. Palp of first maxilliped ( Fig. 5 J–K) ending in an elongated triangular projection. Podobranch on second maxilliped ( Fig. 5 I) well developed. Third maxilliped ( Fig. 5 H) with 1 well developed and 1 rudimentary arthrobranch, ending in a rounded tip in most specimens (a short distal spine is visible in one specimen), ultimate segment as long as penultimate segment. Pleurobranchs present on first to fourth pereiopod. First pereiopod without arthrobranch. Well developed epipods present on third maxilliped and first 3 pereiopods.

Chela of first pereiopod ( Fig. 5 P) 2.55–2.84 as long as wide, 1.54–1.76 times length of carpus; dactylus 5.10–6.00 times as long as wide, no visible palm; carpus 0.89–0.97 times as long as wide, distally excavated, 0.64–0.74 times length of merus. Merus 0.84–0.91 times as long as chela. Chela of second pereiopod 2.20–2.63 times as long as wide, 1.62–2.10 times length of carpus; dactylus 5.36–6.00 times as long as wide, no visible palm; carpus 0.94–1.10 times as long as wide, distally excavated, 0.48–0.60 times length of merus; merus 0.98–1.04 times as long as chela. Third pereiopod ( Figs. 6 R–S) slender, propodus 4.15–5.63 times as long as wide, 2.16–2.64 times as long as dactylus; dactylus 2.21–3.17 times as long as wide (terminal spine included), terminating in one large claw with 4 or 5 accessory spines on flexor margin, second spine very small; carpus 2.86–3.17 times as long as wide, 0.84–0.93 times as long as propodus, 0.43–0.46 times as long as merus; merus 4.32–4.79 times as long as wide, 2.16–2.30 times length of carpus. Fifth pereiopod slender ( Figs. 6 T–U), propodus 6.45–9.33 times as long as wide, dactylus 0.25–0.40 long as propodus and 2.71–3.00 times as long as wide (terminal spine included), terminating in 1 large claw and 17–30 spines on flexor margin (most 17–22); carpus 2.81–3.78 times as long as wide, 0.60–0.64 times as long as propodus, 0.66–0.78 times as long as merus; merus 3.63–4.29 times as long as wide, 1.27–1.51 times length of carpus.

Endopod of male first pleopod ( Fig. 6 V) elongated, 2 times as long as proximal width, 0.43 times as long as exopod, with a strong appendix interna, variable in shape. Appendix masculina on male second pleopod ( Fig. 6 W, 7A) slender, 0.86 times long as endopod, spines extending to midlength of appendix masculina. Appendix interna reaching half of appendix masculina and well into the spinulated part of the appendix masculina.

Egg size of overigerous females 0.26–0.29 x 0.48–0.50 mm.

Etymology. Micratya cooki is dedicated to Ben Cook, the collector of the new species.

Distribution. Micratya cooki is known from some streams in Puerto Rico. The small egg size, suggesting prolonged larval development similar to M. poeyi , and lack of phylogeographic structure across the large island of Puerto Rico (Cook et al. 2009), both indicate that it probably has a wider distributional range in the Caribbean.

Remarks. Micratya cooki is very similar to Micratya poeyi (F.E. Guèrin-Méneville, 1855) . It can be distinguished from M. poeyi in the armature of the dactyli on the fifth pereiopod (with 17–30 spinules on flexor margin vs. 24–43 in M. poeyi ), the armature of the uropodal diaeresis (16–18 movable spinules vs. 20–23 in M. poeyi ) and a different armature of the distal margin of the telson (10–12 distal spines vs. 14–16 distal spines in M. poeyi ). The armature of the rostrum is more variable in M. cooki which lacks teeth on carapace posterior to orbital margin ( M. poeyi with 0–2) and armed dorsally with 3–9 teeth ( M. poeyi with 7–9), ventral teeth with 0–4 vs. 1–4 in M. poeyi . Male specimens can distinghuished by the spinulation of the appendix masculina ( Fig. 7 ). In M. poeyi the spines are located near distal end of appendix masculina, the tip of appendix interna does not reach to the spinulated part of the appendix masculina. In M. cooki the spines extend more proximally, the tip of appendix interna reaches into the spinulated part of the appendix masculina. In living specimens, M. poeyi has 3 distinct white vertical color bands on a dark body (see Karge & Klotz 2008, p120), while the living color patterns of M. cooki are not yet clear but may resemble one of the two other color patterns recognized by Chace & Hobbs (1969). Although both species are very similar in morphological characteristics, they can be clearly distinguished by molecular data.

Figures

FIGURE 5. Micratya cooki sp. nov., female (cl 4.9 mm) (OUMNH. ZC- 2012.05.002): A. cephalothorax, B. rostrum, C. scaphocerite, D. preanal carina, E. uropodal diaeresis, F. telson, G. posterior portion of telson, H. third maxilliped, I. second maxilliped, J. first maxilliped, K. palp of first maxilliped, L. maxilla, M. palp of maxilla, N. maxillula, O. mandible. Scale bars indicate 2.0 mm (A), 1.0 mm (B, F, H) 0.5 mm (C, D, E, G, I, J, L, M, N, O), without scale (K).

FIGURE 6. Micratya cooki sp. nov., female (cl 4.9 mm) (OUMNH. ZC- 2012.05.002): P. first pereiopod, Q. second pereiopod, R. third pereiopod, S. dactylus of third pereiopod, T. fifth pereiopod, U. dactylus of fifth pereiopod, V. male (cl 3.73) (MNHN- IU- 2011 - 6060) first pleopod, W. male second pleopod. Scale bars indicate 1.0 mm (P, Q, R, T), 0.5 mm (S, U, V, W).

FIGURE 7. SEM of appendix masculina. (A) Micratya cooki sp. nov. (MNHN-IU- 2011 - 6060), (B) M. poeyi (MNHN-IU- 2011 - 6063). Scale bars indicate 100 µm in both images.