Liropus alarconi n. sp. (Figs 2–5) Material. Holotype male, 1.66 mm, ICML-EMU-12988, Parque Nacional Marino Los Arcos, Puerto Vallarta, Jalisco, M e xico, 20°32’46.83” N; 105°17’32.82” W, 24 m, 10 October 2018, found on T. helium, coll. Adolfo Tortolero. Paratype: female, 2.40 mm, ICML-EMU-12989, same data as holotype; male, 1.75 mm, ICML-EMU-12990, same locality, 30 m, 04 October 2019, found on T. helium, coll. A. Tortolero; female 2.17 mm, ICML-EMU-12991 same data as ICML-EMU-12990. Diagnosis. Head without projections, eyes present. Antenna 1 flagellum two-articulate. Palp of third article of maxilliped without distal projection. Basis of gnathopod 2 slightly longer than pereonite 2. Pereonites 2–5 with dorsodistal projection. Pereonite 3 with mediolateral projection in male. Pereopods 3 and 4 one-articulate. Pereopod 5 two-articulate. Abdomen without appendages. Etymology: The specific name alarconi, is named in honor of the father of the first author Oscar Alarcón. Distribution: Know only from the type locality. Description. Holotype, male (1.66 mm) Head rounded, without projections; eyes present; pereonite 1 fused with head, suture present; pereonite 3 with mediolateral projection; pereonites 2–5 with one dorsodistal projection, that in pereonite 2 backward projected, that in pereonites 3–5 downward projected; pereonite 5 the longest, pereonite 7 the shortest (Fig. 2). Gills (Fig. 2A) at middle of pereonites 3–4, small, semicircular, slightly longer than wide. Mouthparts. Upper lip (Fig. 3A) symmetrically bilobate, without setulae. Mandibles (Fig. 3E–F) with developed triturative molar, marginally dentate; palp of left mandible (Fig. 3E) three-articulate, second article the longest, with medial seta, setal formula of distal article: 1-x-1, being x=4, incisor and lacinia mobilis 5-dentate, followed by three pectinate setae; right mandible (Fig. 3F) incisor 5-dentate, lacinia mobilis distally serrated, followed by two pectinated setae. Molar flake not seen. Lower lip (Fig. 3B) inner and outer lobes well defined, without setae. Maxilla 1(Fig. 3C) outer lobe with six distal spines; palp two-articulate, distal article with tree apical spines and one subapical seta. Maxilla 2 (Fig. 3D) inner and outer lobes similar, with apical setae. Maxilliped (Fig. 3G) inner lobes small, about 1/3 of outer lobes length, with two apical setae; outer plates oval, with four apical and three mesial setae; palps four-articulate, scarcely setose, second article the longest, articles 1–2 with one submedial setae, article 3 not distally projected; article 4 triangular, slightly curved, distally setulated. Antennae (Fig. 4A–B). Antenna 1 (Fig. 4A) about 1.5 times Antenna 2 length, peduncular article 1 with lateral bulge at distal end with distal setae, peduncular article 2 the largest with one distal setae, peduncular article 3 the shortest, medially swollen; flagellum two-articulate, basal article with medial and distal setae, distal article, with apical setae. Antenna 2 (Fig. 4B) shorter than Antenna 1, basal article with distally projected acute gland cone, fourth article swollen, flagellum two-segmented with long apical setae. Gnathopods (Fig. 4C–E). Gnathopod 1(Fig. 4D), basis slightly larger than ischium and merus combined, propodus triangular, with two proximal grasping spines, dactylus distally bifid. Gnathopod 2 (Fig. 4C) inserted on anterior half of pereonite 2, basis twice as long as the ischium and merus combined, ischium rectangular, merus rounded, carpus short and triangular, propodus oval, proximal projection provided with one large grasping spine, palm ventrally setose, dactylus smooth and elongate. Pereopods (Fig. 5A–E). Pereopods 3–4 (Fig. 5A, B) one-articulate, with two distal setae. Pereopod 5 (Fig. 5C) two-articulate, inserted on middle of pereonite 5, second article with five setae. Pereopods 6 and 7 (Fig. 5D, E) sixarticulate, propodus with row of ventral setae and proximal grasping spine, dactylus elongated, curved. Penes (Fig. 5F) medially located, sub rectangular, distally rounded. Abdomen (Fig. 5F). Lacking appendages, a pair of lobes and single dorsal lobe Paratype female ICML-EMU-12989 (Fig. 2B, 3E, 5G) Body length 2.40 mm. Similar to the male, except for the following characteristics: presence of oostegites on pereonite 3 and 4, setose on pereonite 3 (Fig. 2B); pereonite 3 lacking a mediolateral projection. Abdomen with a pair of lateral lobes with setae at middle and with single dorsal lobe (Fig. 5G). Habitat: The specimens were collected on two samples of the marine sponge T. helium, at 24 and 30 m depth in association to the caprellids Aciconula acanthosoma and L. isabelensis. Remarks. Considering the 15 reported species (including the present material) from the Liropus recorded worldwide, L. alarconi n. sp. is close to L. japonicus Mori, 1995 from the North-west Pacific and L. gurui GuerraGarcía et al. 2015 from the Caribbean Sea. All three species have a two-articulated flagellum on antenna 1, peduncular article 1 of antenna 1 with lateral bulge on distal end and peduncular articles 2–3 swollen distally; head without projections; pereonites 2–4 without anterolateral projections; pereopods 3 and 4 one-articulate and pereopod 5 two-articulate. Gnathopod 2 of L. japonicus, presents an irregular process at the base, its propodus has a medial deep triangular cleft with roughly serrate margins distally (Mori, 1995), while in L. alarconi n. sp., it is smooth and lacks the cleft in contrast to L. gurui. However, L. alarconi n. sp. can be distinguished easily from L. japonicus and L. gurui in pereonites 2–5 each with one dorsodistal projection (pereonite 2, backward projected; pereonites 3–5 downward projected). Liropus gurui has been recorded at depths from 45 to 70 m collected from the mesophotic coral ecosystems in Puerto Rico, Caribbean Sea (Guerra-García et al. 2018); while L. japonicus has been collected from the dead coral masses covered with algae and sessile animals (Mori, 1995). Liropus alarconi n. sp. has been recorded at 25 to 30 m depth associated to the tropical marine sponge T. helium near to coralline patches similar to L. isabelensis which has been recorded in a coralline environment in Mexican Pacific coast (Alarcón-Ortega et al. 2017b).

Published as part of Alarcón-Ortega, Lucy C. & Carballo, José L., 2022, Description of a new species of Liropus (Crustacea, Amphipoda) from Puerto Vallarta, Pacific coast of Mexico, pp. 528-536 in Zootaxa 5154 (5) on pages 530-535, DOI: 10.11646/zootaxa.5154.5.2, http://zenodo.org/record/6655447