Introduction

The genus Ampelisca Krøyer, 1842 is the most speciose of the family Ampeliscidae with more than 150 benthic species distributed worldwide inhabiting sediments as tubicolous infauna from intertidal to 4,000 m depth (^{Souza-Filho et al., 2009}). The first records of the American Tropical Pacific species of the genus Ampelisca were documented by ^{Holmes (1908)}. Later, ^{Chapman (2007)} and ^{Cadien et al. (2018)} contributed to the knowledge of Ampelisca fauna of the Northeastern Pacific Ocean; however, the most important contribution to the taxonomy of this genus in the Eastern Pacific Ocean was published by ^{Barnard (1954)}. So far, 14 species of Ampelisca have been recorded from the Gulf of California (^{Brusca & Hendrickx, 2005}), and 25 species from the Eastern Tropical Pacific Ocean as benthic components (^{García-Madrigal, 2007}).

The organisms analysed in the present paper were obtained in a research project focused on marine invertebrates inhabiting the sandy bottom from northern Santa Margarita Island, off the west coast of the Baja California Peninsula, Mexico. Within these organisms, specimens of the genus Ampelisca were examined and turned out to belong to an undescribed new species. The present work contributes with the description of a new species of Ampelisca and presents an identification key for the 3 most similar Ampelisca species. In addition, a checklist for Ampelisca species documented from the Eastern Tropical Pacific, including their geographic distribution and habitat depth, is provided herein (Table 1).

Material and methods

The material was obtained with a van Veen grab of 0.3 m² from sandy bottom samples at the northern coast of Santa Margarita Island, Mexico. Samples were filtered with 0.5 and 1 mm sieves and fixed with 75% ethanol. The amphipods were separated and identified at the Crustacean Laboratory, of the Facultad de Estudios Superiores Iztacala (FES-I) of UNAM. Specimens of Ampelisca were examined, dissected and illustrated using a dissecting stereoscopic microscope MOTIC SMZ-168 equipped with a camera lucida. Mouthparts and small appendages were illustrated using a MOTIC BA-210 compound microscope also equipped with a camera lucida. Illustrations were completed in Corel Draw V.12. The terminology and taxonomic classification were taken from ^{Barnard (1954)} and ^{Souza-Filho et al. (2009)}. Specimens are deposited in the National Crustacean Collection (CNCR), of the Instituto de Biología, UNAM, in Mexico City, and in the Collection of the Crustacean Laboratory (CLI), at FES-I, UNAM.

Description

Order Amphipoda Latreille, 1816

Suborder Amphilochidea Boeck, 1871

Family Ampeliscidae Krøyer, 1842

Genus Ampelisca Krøyer, 1842

Ampelisca capetilloi sp. nov. Ortiz, Winfield & González-Salazar

(Figs. 1-4)(f2, f3)

http://zoobank.org/urn:lsid:zoobank.org:act:8D9EEE6D-47F6-46E9-A736-55DEC59C25E8

Diagnosis. Head longer than pereonites 1-2 combined, ventral margin oblique. Antenna 1 reaching end of antenna 2 peduncle. Antenna 2 peduncle article 4, 1.3 × length article 5. Mandible with 8 accessory setae; palp article 3, 0.8 × as article 2 length. Coxae 2-3 with small concavity on anterior margin. Gnathopod 1 propodus palm margin with 7 distal setae. Gnathopod 2 merus with 4 long posterodistal setae; carpus posterior margin with 28 long simple setae. Pereopod 4 merus anterior margin with 22 setae; posterior margin with 24 long setae. Pereopod 7 basis reaching mid portion of merus; posterior margin almost straight; ventral margin with 26 short setae; merus posterodistal lobe very large, extending to end of carpus; with 10 plumose setae. Pleonite 3 dorsal margin smooth. Epimeron 3 posteroventral angle produced into large spine. Urosomite 1 slightly sinuous dorsally. Telson cleft 0.7 × length; each lobe with 3 dorsal setae.

Description. Based on holotype female (CNCR 35569); female body 7.2 mm length. Lateral view (Fig. 1). Head longer than pereonites 1 and 2 combined; anterior front margin slightly incised; lower front margin oblique, straight; upper pair of eyes behind upper margin of antenna 1; lower pair at lateral angle on head. Antenna 1 reaching end of peduncle of antenna 2; peduncle article 1 not dilated distally, devoid of setae; peduncle article 2, 1.3 × article 1 length; peduncle article 3, 0.8 article 1 length; flagellum 7-articulate. Antenna 2 reaching pereonite 6; peduncle article 4, 1.3 article 5 length, devoid of setae ventrally; flagellum 1.3 length peduncle; flagellum 14-articulate.

Mouthparts (Fig. 2A-G). Maxilliped (Fig. 2A-C), inner plate not reaching end of palp article 1; apex with 1 molariform tooth and 5 long and 1 short setae; outer plate not reaching end of palp article 2; 7 molariform setae at inner margin; 5 robust setae on distal margin; inner margin of palp article 2 with 26 long setae; outer margin with 3 distal setae, 2.8 × article 3 length; article 3 quadrangular with 16 distal robust setae; article 4 as long as 3, with 4 distal setae. Maxilla 1 (Fig. 2D), inner plate small, expanded, with apical and subapical setae; outer plate with 9 robust setae; palp article 2 expanded distally; 4 × length article 1, with 3 distal cusps, 4 robust setae, and 10 simple facial setae. Lower lip (Fig. 2E), inner plate not fully developed; outer plate rounded, with tiny setae on inner side of each plate; mandible lobe present. Maxilla 2 (Fig. 2F), outer plate 1.4 × wider than inner plate; inner plate with 20 long distal simple setae, 6 oblique facial simple setae, 14 long curved tip setae, and 7 simple short setae. Mandible with 5 incisive teeth (Fig. 2G); lacinia mobilis with 5 teeth; accessory setal row with 8 rakers; molar well developed, triturative; palp article 2 not expanded, 10 setae on inner margin; 4 on outer margin; article 3, 0.8 × as length article 2; 5 setae on inner margin; one midway on outer margin; palp article 3 with 2 long simple distal setae; 5 long simple setae on inner margin; one seta on outer margin.

Gnathopod 1 (Fig. 3A). Coxa 2.6 × longer than wide; general surface covered with sparse short setae; ventral margin rounded, lined with short setae; basis posterior margin proximal half with 6 marginal and 2 submarginal setae; distal posterior margin with 2 separated setae; anterior margin with 5 setae; ischium posterior margin with 1 short and 3 long pectinate setae; merus distal half with long lateral and posterior setae; anterior margin with 9 equidistant setae; carpus as thick as merus; 1.2 × propodus length; anterior margin with 7 distal setae; posterior margin distal half with 5 long, 2 robust and 4 short setae; dactylus 0.5 × length propodus; with 5 distal setae.

Gnathopod 2 (Fig. 3B). Coxa 1.4 × longer than wide; anterodistal margin rounded; with a subdistal set of setae. Both oostegite and gill 0.9 × coxa 2 length; basis as long as merus and carpus combined; with 16 long setae; ischium with 2 postero distal long setae; merus with 4 long posterodistal setae; carpus posterior margin with 28 long simple setae; anterodistal corner with one distal seta; propodus anterior margin with 8 long simple setae; distal half of posterior margin with 15 long simple setae; dactylus as long as propodus; posterior margin with 4 setae.

Pereopod 3 (Fig. 3C). Coxa twice as long as wide; distal margin rounded with subdistal set of setae; oostegite and gill, 1.2 times coxa 3 length; basis 1.1 length of merus and carpus combined; basis posterior margin with 11 setae; anterior margin with short setae; ischium posterior margin with short setae; merus anterior margin with 7 setae, posterior margin with 8 long and 2 short setae; carpus 0.5 length of propodus; posterior margin with 6 long setae; anterior margin naked; propodus anterior margin with 7 setae; posterior margin naked; dactylus as long as carpus and propodus combined, slender.

Pereopod 4 (Fig. 3D). Coxa as long as wide; quadrangular; with well-developed posterior lobe; ventral margin covered with tiny setae; oostegite and gill 1.2 times coxa 4 length; basis as long as merus, carpus and propodus combined; posterior margin distal half covered with tuft of 17 long setae; anterior margin with 8 short setae; ischium naked; merus anterior margin with 22 setae; posterior margins covered with 24 long setae; carpus short; with 7 long setae; dactylus 1.2 times carpus and propodus length combined, naked.

Pereopod 5 (Fig. 3E). Basis nearly rounded, anterior margin with 19 setae; posterior margin rounded, with 4 tiny setae; ischium short, naked; merus 0.8 × propodus length, naked; carpus anterior margin with 9 tiny and 3 distal setae; posterior margin with 3 submarginal, 4 distal setae; propodus anterior margin with 6 tiny setae; posterior margin with 2 submarginal setae; dactylus short, with 3 accessory spines and 2 setae.

Pereopod 6 (Fig. 3F). Basis subquadrate; anterior margin with 16 setae; merus 0.7 × length carpus; anterior margin with 2 long and 2 short setae; carpus 1.3 × propodus length; posterodistal corner drawn out, bearing 3 long and 3 short setae; posterior margin with 3 robust submarginal setae: anterior margins with 10 setae; propodus anterior margin with 13 setae; dactylus short with 4 short and 1 long accessory spines and 2 setae.

Pereopod 7 (Fig. 3G). Basis reaching mid portion of merus; posterior margin almost straight, ventral margin with 26 short setae; ischium shorter than merus; anterodistal corner with 2 setae; merus posterodistal lobe very large; longer than carpus; lobe margin with 10 plumose setae; anterodistal corner with 2 setae; carpus anterodistal corner with 2 setae; propodus 2.3 × carpus length, expanded, twice as long as wide; posteroventral corner with 1 seta; dactylus 0.5 × propodus length, curved anterodistally.

Uropod 1 not reaching end of uropod 2 (Fig. 4B, E); peduncle 1.1 × rami length; a distal robust seta; rami subequal in length; outer ramus naked, inner ramus with 3 robust setae on inner margin. Uropod 2 peduncle 1.2 × rami length (Fig. 4C, E); 2 robust setae on outer margin; outer ramus with 10 lateral short robust setae, and 1 long subdistal; inner ramus with 5 lateral robust setae and 1 distal one. Uropod 3 peduncle 0.6 × rami length (Fig. 4D, E); rami poorly foliaceous; outer ramus with 5 subdistal setae; inner ramus with tuft of setae medially, 1 long and 1 short subdistally. Telson cleft 0.7 × length; each lobe with 3 dorsal setae placed in line; notched tip with simple setae (Fig. 4A).

Pleonite 3 dorsal margin smooth (Fig. 4E); urosomite 1 slightly sinuous dorsally, with 2 tiny posterodorsal setae. Epimera (Figs. 1, 4E). Epimera 1-2 posteroventral corners rounded; epimeron 3 posteroventral corner with strong tooth, with no previous large, rounded process.

Taxonomic summary

Type material. Holotype ovigerous female (5 eggs); 7.2 mm length; van Veen grab; 15 m depth; sandy bottom; March 13, 2017; collector Jan González Salazar; N Santa Margarita Island, off the west coast of the Baja California Peninsula, Mexico; CNCR35569. Paratypes: 2 juvenile females; 4.9 and 4.1 mm; somewhat damaged; collected with holotype; CLI-141.

Type locality. North coast of Santa Margarita Island, off the west coast of the Baja California Peninsula, Baja California Sur, Mexico, 24°30'10.34" N, 111°59'53.23" W.

Etymology. Species dedicated to Norberto Capetillo Piñar, Federación de Sociedades Cooperativas Pesqueras Zona Centro, Baja California Sur, México.

Distribution. This species is known only from the type locality, north coast of Santa Margarita Island, off the west coast of the Baja California Peninsula, Mexico.

Figure 1 Ampelisca capetilloi sp. nov. Lateral view of body. CNCR35569. 

Figure 2 Ampelisca capetilloi sp. nov. A-C, Maxilliped; A, outer lobe; B, inner lobe; C, palp; D, maxilla 1; E, lower lip; F. maxilla 2; G, mandible and palp. CNCR35569. 

Figure 3 Ampelisca capetilloi sp. nov. A, Gnathopod 1; B, gnathopod 2; C, pereopod 3; D, pereopod 4; E, pereopod 5; F, pereopod 6; G, peropod 7. CNCR35569. 

Figure 4 Ampelisca capetilloi sp. nov. A, Telson; B, uropod 1; C, uropod 2; D, uropod 3; E, lateral view of pleonal segment 3, urosoma, pleopods and telson. CNCR35569. 

Discussion

Of all the American Tropical Pacific species of the genus Ampelisca (Table 1), only A. brevisimulata ^{Barnard, 1954}, A. eoa Gurjanova, 1951, A. hancocki ^{Barnard, 1954}, A. mexicana, ^{Barnard, 1954}, A. macrocephala Liljeborg, 1862, A. pacifica ^{Holmes, 1908}, and A. capetilloi sp. nov., have posteroventral corner of epimeron 3 with strong tooth. Of them, A. mexicana, A. pugetica, and A. capetilloi sp. nov., also have merus of pereopod 7 highly dilated backward.

On the other hand, ^{Barnard (1954)} did not present graphical information on the mouthparts of the species of Ampeliscidae collected by the Velero III and Velero IV, which makes its identification difficult, especially when it comes to closely related species. This is the case of A. mexicana and A. capetilloi sp. nov., both are very similar if the mouthparts and certain complementary details of the morphology of the former are not given (see the taxonomic key included below). The figures of A. mexicana presented by Barnard are generally considered sufficient for its identification (^{Jiménez et al., 2018}). So, it is very likely that specimens of A. capetilloi sp. nov. have been previously misidentified as A. mexicana, especially when the current distribution of A. mexicana is so wide (from Punta Canoas, Baja California to Peru) (^{Barnard, 1954}; ^{García-Madrigal, 2007}; ^{Jiménez et al., 2018}) (Table 1). The analysis of additional material to be collected in the region could confirm this assumption.

Moreover, A. capetilloi sp. nov. differs from A. araucana, Guerrero, 1963, with a South Pacific Eastern American distribution, by having the antenna 1 as long as the tip of peduncle article 5 of antenna 2 (shorter in A. araucana), lower border of head straight (convex in A. araucana), coxae 2 and 3 anterior margin with concavity (none in A. araucana), uropod 1 not surpassing tip of uropod 2 (surpassing in A. araucana), pereopod 4 basis posterior margin with a tuft of 18 long setae (10 in A. araucana), basis posteroventral margin pereopod 7 with 26 setae (20 in A. araucana), and dactylus half-length of propodus (0.8 × length of propodus in A. araucana).

Further, A. capetilloi sp. nov. differs from A. moreirai^{Valerio-Berardo and Wakabara, 2006}, a species from Brazilian waters by having the antenna 1 reaching the tip of antenna 2 peduncle (shorter in A. moreirai); mandibular palp article 3 with 1 distal and 6 marginal setae (3 distal and 1 subdistal setae in A. moreirai), 8 mandible rakers (9 in A. moreirai); maxilla 2 inner plate with 13 distal curved setae (all straight in A. mareirai), lower lip well developed (not so in A. moreirai), coxae 2 and 3 with anterior margin concavity (without concavities in A. moreirai), pereopod 4 basis with long setae on posterior margin (long setae on both margins in A. moreirai), pereopod 6 basis wider than long (longer than wide in A. moreirai), telson dorsally with 3 setae located longitudinally and in line (devoid of setae in A. moreirai).

Finally, A. capetilloi sp. nov. differs from A. longipropoda^{Valerio-Berardo, 2007}, another Brazilian species (^{Valerio-Berardo, 2007}), by having the antenna 1 reaching the peduncle of antenna 2 (shorter in A. longipropoda), mandible with 8 rakers and 8 setae on article 2 of palp (with 6 rakers and one seta on article 2 of palp in A. longipropoda), maxilla inner plate with 14 curved tip setae (10 straight setae in A. longipropoda), coxa 1 with entire anterior margin (with notch on posteroventral margin in A. longipropoda), gnatopod 1 propodus shorter than carpus (subequals in A, longipropoda), gnatopod 2 posterior margin of basis and carpus densely setose (with less setae in A, longiporpoda), coxa 2 with submarginal ventral setae (marginals in A. longipropoda), pereopod 6 dactylus with 4 short and 1 large accessory spines and 2 setae (2 short and 1 long accessory spines in A, longipropoda); basis of pereopod 7 with 26 setae (9 in A. longipropoda).

Acknowledgments

Special thanks to Martin Thiel from Universidad Católica del Norte, Coquimbo, and Jorge A. Pérez Schultheiss, from Museo Nacional de Historia Natural de Santiago, both from Chile, for searching the original description of Ampelisca araucana. We also thank two anonymous reviewers for their helpful comments.