Ensigeropus cachinalito, Pérez-Schultheiss, 2017

Pérez-Schultheiss, Jorge, 2017, Ensigeropus, a new genus of the family Platyischnopidae (Amphipoda: Amphilochidea) from Northern Chile, Zootaxa 4311 (3), pp. 399-408 : 401-405

Ensigeropus cachinalito n. sp.

( Figs 1–4 )

Type material. Female holotype, 3.30 mm ( MNHNCL AMP-15243 ), Cachinalito (25°8’26.8’’S, 70°27’42.1’’W), North of Taltal, Antofagasta Region, Chile; 26-V-2016; Col. J. Pérez-Schultheiss, sand beach, between rocks . Paratype a: female, 2.90 mm ( MNHNCL AMP-15244 ), same data as holotype . Paratype b: female, 3.16 mm ( MNHNCL AMP-15245 ), same data as holotype . Paratype c: female, 3.50 mm ( MNHNCL AMP-15246 ), same data as holotype . Paratype d: female, 3.12 mm ( MNHNCL AMP-15247 ), same data as holotype . Paratype e: female, 3.14 mm ( MNHNCL AMP-15248 ), same data as holotype . Paratype f: female, 4.24 mm ( MNHNCL AMP-15249 ), Caleta Hornos (29°36’2.1’’S, 71°17’35.7’’W), Coquimbo Region, Chile; 28-V-2016; Col. J. Pérez- Schultheiss; Low sandy intertidal.

Type locality. Cachinalito (25°8’26.8’’S 70°27’42.1’’W), north of Taltal , Antofagasta Region, Chile.

Distribution. Known only from the type locality and from Caleta Hornos (29°36’2.1’’S 71°17’35.7’’W), Coquimbo Region.

Etymology. The specific epithet derived from the type locality, Cachinalito beach, in the Antofagasta region.

Diagnosis. As for the genus.

Description. Based on holotype, female, 3.30 mm. Head coniform, 0.2 × of body length, bearing a ventrodistal process between antenna 1, tip of rostrum cylindrical, with sensorial organ, ventral margin oblique, not excavated; eyes present. Antenna 1 reaching the end of article 5 of antenna 2; article 1 wider than long (1.5 ×); peduncular article 2 longer than article 3, with six distal simple setae; primary flagellum longer than peduncle (1.3 ×), with five articles; accessory flagellum with three articles. Antenna 2 peduncular article 4 anterior margin three groups of slender setae; peduncular article 5 about 0.7 × of article 4, anterior margin with two groups of four slender setae; flagellum 0.7 × of peduncle length, with six articles. Upper lip with a subrectangular lobe in upper portion. Mandible incisor large, poorly dentate, left lacinia mobilis 5-dentate, setal row with six setae, right lacinia mobilis slender and distally bifid, setal row with three robust setae, molar absent; palp article 2 smaller than article 3 (0.8 ×), with one single seta on anterior margin; article 3 with four distal setae. Maxilla 1 inner plate with one subdistal seta; outer plate with eight robust setae; palp slightly longer than outer plate, with five distal long setae. Maxilla 2 inner plate with eight distal setae; outer plate wider than inner plate, with eleven distal setae. Maxilliped inner plate not reaching end of article 1 of palp, with two distal setae; outer plate extending to about 1/2 of article 2, with four marginal setae; palp article 1 with one setae; article 2 with nine marginal setae; article 3 about 0.7 × article 2, anterior margin with four long setae, posterior margin with five long setae; dactylus slightly shorter than article 3 (0.8 ×), with subdistal spine undiscernible.

Gnathopods 1 and 2 strongly chelate, the first slightly smaller. Gnathopod 1 coxa subrectangular, posterior margin convex with three setae, ventral margin with two seta; basis medially inflated with two setae on anterior margin; ischium and merus subequal in length; carpus posterodistal angle slightly excavated, with three slender setae, about 0.7 × of propodus length; propodus proximally broad, anterodistal margin with five setae, posterior margin with three groups of two setae, palm strongly obtuse, chelate projection 0.32 × of posterior margin, with a distal flake; dactylus fitting palm. Gnathopod 2 coxa slightly widened distally, longer than wide (1.3 ×), posteroventral angle with two seta; basis slender, 4.23 × as long as wide, anterior margin with two short setae; ischium and merus subequal in length; carpus about 0.8 × of propodus, posterodistal angle slightly excavated with three setae; propodus slightly widened proximally, anterodistal angle with five long setae, posterior margin with ten setae, palm strongly obtuse, chelate projection 0.32 × of posterior margin; dactylus fitting palm. Pereopod 3 coxa longer than wide (1.5 ×), posteroventral angle with two setae, posterior margin straight; basis anterior margin with two short setae, posterior margin with one long seta, posterodistal angle with three long setae; ischium posterior margin with two setae; merus moderately inflated, about 2.3 × as long as wide, anterodistal angle with three long setae; posterior margin with thirteen long setae; carpus about 0.47 × of merus, posterior margin with eight long setae, posterodistal corner with two long robust setae, distal margin with three long setae; propodus longer than carpus (1.1 ×), anterodistal angle with one short setae, subdistal margin with five strong setae; dactylus about 0.6 × of propodus, curved, with one seta on anterior margin. Pereopod 4 coxa wider than long (1.24 ×), posterior margin of lobe slightly convex; basis posterior margin with three long setae and posterodistal angle with one long seta; ischium posterior margin with two setae; merus moderately inflated, about 2.5 × as long as wide, anterodistal angle with four long setae, posterior margin with sixteen long setae; carpus about 0.47 × of merus, posterior margin with nine long setae, posterodistal corner with one long robust seta; propodus as long as carpus (0.9 ×), subdistal margin with seven robust setae; dactylus about 0.6 × of propodus and curved. Pereopod 5 coxa wider than long (1.4 ×), with strong posteroventral rounded lobe, posteroventral margin of lobe with four short and one long setae; basis broad, 1.8 × as long as wide, anterior margin with one long seta, anterodistal angle with two long setae; ischium anterodistal angle with two long setae; merus posterior margin produced, anterior margin with two combs of setae (4–7), posterior margin with three combs of setae (2–3–6), with one short spine in the position of the last two combs; carpus nearly as long as merus, anterior margin with two combs of setae (6–6), posterior margin with two combs of setae (3–4), with one short spine in the position of the combs; propodus slender, 2.9 × as long as wide, both anterior and posterior margin with two combs of setae (2–2 and 5–3); dactylus styliform, about 0.7 × of propodus length. Pereopod 6 coxa wider than long (1.3 ×), with strong posteroventral rounded lobe, posterior margin with one short setae, ventral margin of the lobe with three slender setae; basis ovate, 1.2 × as long as wide, anterior margin with five long setae, anterodistal angle with three long setae and one short seta, posterodistal angle produced; ischium anterodistal angle with two long setae and one short seta; merus expanded posteriorly, anterior margin with three combs of setae (6–6–7), posterior margin with six combs of long setae (1–1–2–4–5–6), with one short spine in the position of the combs four to six, posterodistal lobe extending about 1/3 of carpus length, with a facial-subdistal comb of six robust setae; carpus slightly longer than merus (1.1 ×), anterior margin with four combs of setae (3–3–6–5), posterior margin with three combs of setae (3–4–5), with one spine in the position of the two last combs; propodus slender, 4.0 × as long as wide, anterior margin with three combs of setae (3–3–3), posterior margin with three combs of setae (1–5–3); dactylus styliform, about 0.7 × of propodus length. Pereopod 7 coxa wider than long (3.3 ×), posterior margin acute; basis 1.1 × as long as wide, anterior margin with three short robust setae, anterodistal angle with one long and one short seta, posterior margin with a elongate tooth, as long as 0.41 × the basis wide; ischium anterodistal angle with one short robust setae; merus slightly expanded posteriorly, anterior margin with six combs of setae (1–2–3–3–3–3), posterior margin with four combs of setae (2–3–3–3), with one spine in the position of the three last combs, with a facial-subdistal robust seta; carpus shorter than merus (0.8 ×), anterior margin with four combs of setae (1–2–3–2), posterior margin with three combs of setae (4–3–4); propodus slender, 6 × as long as wide, anterior margin with three combs of setae (2–2–2), posterior margin with three combs of setae (1–3–3); dactylus styliform¸ as long as 0.8 × the propodus length.

Epimeron 1 rounded, with three plumose setae on ventral margin. Epimeron 2 posteroventral angle produced into a long spine, ventral margin with two setae. Epimeron 3 posteroventral angle produced into a long spine, ventral margin with three setae. Uropod 1 peduncle dorsomedial margin with three setae, the distal stronger, and lateral with two basofacial setae, with one robust distolateral setae; inner ramus slightly shorter than outer ramus, with one proximal short and curved setae, one short and two marginal long setae and five distal robust setae; outer ramus with three marginal short setae and four distal robust setae. Uropod 2 shorter than uropod 1, peduncle with three marginal robust setae, distolateral corner produced into a large spine; inner ramus about 0.8 × of outer ramus, with one marginal robust seta and four distal setae; outer ramus with two marginal robust seta and five distal setae. Uropod 3 about 0.28 × of body length, peduncle outer margin with one robust setae, inner and outer distal angles with one and two robust setae, respectively; inner ramus scale-like, distally with one robust and one slender seta; outer ramus 2-articulate, very elongate, 3.2 × of peduncle length, article 1 about 1.1 × of article 2, inner margin with three combs of setae (1–1–2), outer margin with three combs (1–2–4), article 2 inner margin with three combs of setae (1–1–2), outer margin with two combs of setae (2–2), distally ended in two spines, separated by one slender short seta. Telson slightly wider than long (1.1 ×), emarginate (25%), lobes apically bicuspidate, armed with one short slender and two robust setae, lateral margins with one middle brush of two long slender setae and two pappose setae.

Ecology. Ensigeropus cachinalito n. gen., n. sp. is an intertidal burrower in sand beaches. The specimens were collected in association with the phoxocephalid Pseudfoxiphalus setosus Andres, 1991 and Bathyporeiapus ruffoi Escofet, 1971 .

Remarks. Two characters of Ensigeropus n. gen. are not present in any other platyischnopid. A rectangular lobe is protruding dorsally in the upper lip, showing a dorsal margin straight medially when mounted on a slide, but apparently concave in non-dissected specimens. Barnard & Drummond (1979: 2) considered the upper lip as a problematic structure for generic delimitation, because “reflect observations that may be subject to various interpretations”, but their comments are founded specially in attributes of the ventral margin, unlike Ensigeropus n.

gen., whose rectangular lobe in the upper lip is located in a frontal-upper position, up to now not reported in the family.

The second singular character is the absence of a defined molar in the mandibles. In platyischnopids, this structure shows a variable degree of development, but in all the cases, the grinding surface is at least well defined and delimited. In Ensigeropus n. gen. the molar is completely absent, with neither indication of his presence, except by some circular cuticular structures.

The new taxon is closely related to the western hemisphere genera Eudevenopus Thomas & Barnard, 1983 and Tiburonella Thomas & Barnard, 1983 , especially in the well-developed rostrum, the rectangular coxa 1 and the prehensile pereopods 3–4, with dactyli recurved (see table 1). Among them, Ensigeropus n. gen. is most similar to Eudevenopus in the inner plate of maxilla 1 with only one seta, and the telson distally emarginated, with lateral brush of long slender setae; but the right lacinia mobilis is distally bifid, and differentiated from the rakers, as in Tiburonella .

Ensigeropus n. gen. differs from Eudevenopus and Tiburonella in the posteriorly sharp coxa and basis of pereopod 7 with an elongate posterior tooth, characters present only in some eastern hemisphere genera, especially Tomituka Barnard & Drummond, 1979 . However, the similarity with this genus is only superficial, as there are several other characters that differ, such as the configuration of the mandibular palp and incisor, structure of the coxa 1, length of carpus of both gnathopods, and telson degree of clefting/emargination and number of lateral setae. Additionally, Ensigeropus n. gen. differs from Eudevenopus in the distally widened basis of pereopod 5 (at least half the length), most similar to Tiburonella , but in this genus the basis is widened in all his length.

Ensigeropus cachinalito n. gen., n. sp. is the second platyischnopid described from Chile, after Eudevenopus gracilipes ( Schellenberg, 1931) , a species known only from the type specimen collected in Valparaíso, but widely distributed in north-central Chile (unpublished observation). The new species can be easily differentiated, even in the field, by the conspicuous tooth in basis of pereopod 7. Additionally, although both species could be found in a same locality, they appear to inhabit in different habitat, as Eudevenopus gracilipes is eminently subtidal, while Ensigeropus cachinalito n. gen., n. sp. is intertidal.

Figures

FIGURE 1. Ensigeropus cachinalito n. gen., n. sp., holotype female (3.30 mm; MNHNCL AMP- 15243) antennae, uropods and telson. Scale: 0.1 mm. Paratype “ a ” female (2.99 mm; MNHNCL AMP- 15244), habitus. Scale: 0.5 mm.

FIGURE 2. Ensigeropus cachinalito n. gen., n. sp., holotype female (3.30 mm; MNHNCL AMP- 15243) upper lip, lower lip, maxillae and maxilliped. Paratype female “ a ” (2.9 mm; MNHNCL AMP- 15244), mandibles. Scale: 0.05 mm.

FIGURE 3. Ensigeropus cachinalito n. gen., n. sp., holotype female (3.30 mm; MNHNCL AMP- 15243) Gnathopods and pereopods. Scale: 0.1 mm.

FIGURE 4. Ensigeropus cachinalito n. gen., n. sp., holotype female (3.30 mm; MNHNCL AMP- 15243) Pereopods. Scale: 0.1 mm.