Dulichiella celestun, a new species of amphipod (Crustacea: Amphipoda: Melitidae) from the Gulf of Mexico, with a key and zoogeographic remarks for the genus in the western Atlantic Author Paz-Ríos, Carlos E. Author Ardisson, Pedro-Luis text Zootaxa 2014 3774 5 430 440 journal article 46263 10.11646/zootaxa.3774.5.2 250c07dd-1331-4443-9728-b98dcbd2bbf1 1175-5326 224702 73AE79BD-909F-4D92-B2DA-0182C94AEBCB Dulichiella celestun sp. nov. Figures 1–6 Holotype . Male (dissected and drawn), 4.7 mm, Celestun coastal lagoon, Yucatan, Mexico , 20°46’18’’N , 90°24’26’’W , 5 April 1995 , muddy bottom, 1 m , Birge-Ekman box core, coll. P.-L. Ardisson, CYMX-1-DC. Paratypes . Male (dissected and drawn), 7.4 mm (without head), data as for holotype , CYMX-2-DC. Male (dissected and drawn), 6.4 mm, data as for holotype , CYMX-3-DC. Female (dissected and drawn), 6.5 mm, data as for holotype , CYMX-4-DC. Seven females, data as for holotype , ECOSUR0163. Additional material. Thirty-five females, data as for holotype , CYMX-5-DC. Type locality. Celestun coastal lagoon, Yucatan, Mexico . Etymology. The species name is derived from the type locality of the species. Celestun in the Mayan language means ‘horror stone’. Diagnosis. Truncated lateral cephalic lobe. Mandibular palp article 1 with inner margin produced distally. Gnathopod 2 propodus distolateral crown with four spines. Pereopods 3–7 dactylar unguis anterior margin with two accessory spines. Urosomite 3 with four dorsal spines. Description. Based on male holotype (CYMX-1-DC) and two male paratypes (CYMX-2-DC and CYMX-3- DC). Body small. Head, eyes well-developed, ovate; lateral cephalic lobe broad, truncated, anteroventral corner with one slender seta (broken in the male holotype , see the female paratype ). Antennae 1–2, peduncle and flagellum weakly setose. Antenna 1 peduncular article 1 shorter than article 2, with three robust setae along posterior margin; accessory flagellum four-articulate. Antenna 2 peduncular article 2 cone gland not reaching to the end of peduncular article 3; article 4 slightly longer than article 5. Mandible left and right incisor six- and fivedentate, respectively; left and right lacinia mobilis four- and five-dentate, respectively; left and right accessory robust setae with row of ten slender blades; molar triturative, with plumose seta; palp three-articulate, article 1 longer than broad, inner margin article 1 produced distally, article 2 slightly longer than article 3. Maxilla 1, inner plate with two apical plumose setae, outer plate with nine serrate robust setae; palp two-articulate, article 1 with two slender setae on outer distal corner, apical part of palp article 2 with five robust and five slender setae. Maxilliped inner plate with three robust setae, five plumose setae and two slender setae on apical part; outer plate with two apical plumose setae. Gnathopod 1 coxa anteroventral corner not produced, anterior margin slightly concave, posteroventral corner notch present; merus and carpus facially setulose, carpus longer than propodus; propodus small, linear, palm convex, posterodistal corner defined by one robust setae; dactylus with one seta on anterior margin. Gnathopod 2 coxa posteroventral corner with small notch; right and left side dissimilar, asymmetrical in size, left side (larger) chelate, right side (smaller) subchelate; (larger) propodus distolateral crown with four spines (first spine rounded; second and third spine subacute; fourth spine weak), palm sinusoidal, posterodistal corner produced, upturned, dactylus fitting into posterodistal corner; dactylus apically blunt; (smaller) merus with sharp posteroventral spine; palm convex, posteroventral corner with two robust setae; dactylus with one seta on anterior margin. Pereopods 3– 7 dactylar unguis anterior margin with two accessory spines. Pereopods 3–4 similar. Pereopods 5–7 basis posterior margin straight. Pereopods 6–7 carpus and propodus with bunches of long slender setae. Pleonite/urosomite segments with relatively strong posterodorsal spines, dorsal spine formula (11– 10–9–6–4 –4). Pleonites 1–3 and urosomite 1–2 with sparse dorsal setae. Epimeron 1 posteroventral corner with small acute spine and ventral margin without setae. Epimeron 2 posteroventral corner acute and ventral margin with two robust setae. Epimeron 3 posteroventral corner produced with posterior margin smooth and ventral margin with three robust setae. Urosomite 1 with spine at midline, no conspicuous medial gape. Urosomite 2 with two groups of one large dorsolateral robust seta. Urosomite 3 with small dorsal setae, with four dorsal spines. Uropod 1 with basofacial seta on the peduncle. Uropod 3 outer ramus very long (about two x peduncle), with a few long setae arising from spine groups on dorsal margin. Telson deeply cleft with four dorsal robust setae and two ventral setae on each lobe. Female (sexually dimorphic characters). Based on female paratype , CYMX-4-DC. Pleonite/urosomite dorsal spine formula (11–11– 12 –6–6–4). Gnathopod 1, palm convex; posteroventral corner with one robust seta; dactylus anterior margin with two setae; posterior margin crenulate. Gnathopod 2 subequal in size, similar to smaller gnathopod 2 of male; palm convex; posteroventral corner with three robust setae; dactylus anterior margin with two setae; posterior margin crenulate. Pereopod 7 basis posterior margin slightly subsigmoid, tapering distally. Variation. Gnathopod 2 propodus distolateral crown with second spine rounded on the male paratype CYMX- 3-DC. Male paratypes deviated from the dorsal spine formula described from the male holotype formula (10/9–9– 9–5–6/5–4/3). Pereopods 6–7 in the largest male specimen ( paratype CYMX-2-DC) showed bunches of long slender setae on basis, merus, carpus and propodus. FIGURE 1. Dulichiella celestun sp. nov. , holotype male, 4.7 mm, CYMX-1-DC, Celestun coastal lagoon, Yucatan, Mexico. Scale represents 1 mm. FIGURE 2. Dulichiella celestun sp. nov. , holotype male, 4.7 mm, CYMX-1-DC, Celestun coastal lagoon, Yucatan, Mexico. Scale represents 0.1 mm. Remarks. Dulichiella celestun sp. nov. differs from all species in the genus by having the urosomite 3 of males and the female paratype with four dorsal spines; three specimens out of the four examined in this paper showed this particular characteristic. A morphological comparison of the Dulichiella species in the western Atlantic is presented in Table 1 . Dulichiella celestun sp. nov. presents similarly to D. appendiculata and D. lecroyae four spines on the distolateral crown of male gnathopod 2; on the other hand, it differentiates first from D. appendiculata by presenting an article 1 of mandibular palp produced distally, a carpus longer than the propodus of gnathopod 1, a dorsal formula more spinose, a pereopods 6–7 carpus and propodus with bunches of long slender setae, and an urosomite 3 with four dorsal spines. Secondly, it differentiates from D. lecroyae by a truncated lateral cephalic lobe, a peduncular article 1 of antenna 1 with three robust setae on posterior margin, a pereopods 3–7 dactylar unguis anterior margin with two accessory spines, a dorsal formula more spinose, and an urosomite 3 with four dorsal spines. Habitat. Marine epibenthic, in shallow water on muddy bottoms at depth of 1 m . Distribution. So far only known from the type locality, the Celestun coastal lagoon, Yucatan, Mexico . FIGURE 3. Dulichiella celestun sp. nov. , holotype male, 4.7 mm, CYMX-1-DC, paratype female, 6.5 mm, CYMX-4-DC, Celestun coastal lagoon, Yucatan, Mexico. Scales represent 0.2 mm. FIGURE 4. Dulichiella celestun sp. nov. , holotype male, 4.7 mm, CYMX-1-DC, Celestun coastal lagoon, Yucatan, Mexico. Scales represent 0.2 mm. FIGURE 5. Dulichiella celestun sp. nov. , holotype male, 4.7 mm, CYMX-1-DC, paratype male (U3”), 7.4 mm, CYMX-2-DC, Celestun coastal lagoon, Yucatan, Mexico. Scales represent 0.2 mm. Key to species of Dulichiella in the western Atlantic (modified from Lowry & Springthorpe 2007 ) 1. Gnathopod 2 propodus distolateral crown with three spines................................................... 2 – Gnathopod 2 propodus distolateral crown with four spines.................................................... 3 2. Gnathopod 2 propodus distolateral crown with acute spines. Epimeron 3 posterior margin smooth distally...... D. terminos – Gnathopod 2 propodus distolateral crown with rounded spines. Epimeron 3 posterior margin serrate distally... D. anisochir 3. Head with rounded lateral cephalic lobe. Pereopods 3–7 dactylar ungues with one accessory spine on anterior margin................................................................................................... D. lecroyae – Head with truncated lateral cephalic lobe. Pereopods 3–7 dactylar ungues with two accessory spines on anterior margin... 4 4. Mandibular palp article 1 with inner margin produced distally. Urosomite 3 with four dorsal spines..... D. celestun sp. nov. – Mandibular palp article 1 with inner margin not produced distally. Urosomite 3 with two dorsal spines.... D. appendiculata