Mysidium (Mysidium) winfieldi, Hendrickx & Hernández-Payán & Gómez-Gutierrez, 2023

Hendrickx, Michel E., Hernández-Payán, José Carlos & Gómez-Gutierrez, Jaime, 2023, On a small collection of mysids (Crustacea, Peracarida, Mysida) from the southern Gulf of California, western Mexico, with the description of new species of Mysidium and Cubanomysis, Zootaxa 5360 (2), pp. 194-218 : 195-203

publication ID	https://doi.org/ 10.11646/zootaxa.5360.2.2
publication LSID	lsid:zoobank.org:pub:48554152-4466-4ED7-A50F-4464A1722FE7
DOI	https://doi.org/10.5281/zenodo.10167428
persistent identifier	https://treatment.plazi.org/id/03CF8793-FF9B-FFAE-FF2C-B942FC52A93F
treatment provided by	Plazi
scientific name	Mysidium (Mysidium) winfieldi
status	sp. nov.

Treatment

Mysidium (Mysidium) winfieldi sp. nov. Hendrickx & Hernández-Payán

( Fig. 1‒6 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 )

Material examined. Holotype, 1 male (CL 1.16 mm, TL 2.70 mm), November 16, 2010, west of Cleofas Island (21°16’N, 106°14’W), Mexico, about 5 m depth (ICML-EMU-13270) GoogleMaps . Allotype, 1 female (CL 1.15 mm, TL 2.72 mm), November 19, 2010, east of Maria Madre Island (21°40’N, 106°32’W), Mexico, about 5 m depth ( ICMLEMU- 13271 ) GoogleMaps . Paratype, 1 female (CL 1.12 mm, TL 2.90 mm), November 17, 2010, northeast of Cleofas Island (21°20’N, 106°14’W), Mexico, about 5 m depth (ICML-EMU-13477) GoogleMaps . Paratype, 1 male (CL 1.18 mm, TL 3.19 mm), north of San Juanico Island (21°46’N, 106°40’W), Mexico, November 19, 2010, subsurface (ICML-EMU-13272) GoogleMaps .

Diagnosis. Carapace antero-lateral edges rounded; rostrum triangular. Cornea semi-circular in dorsal view, its diameter about 1.6‒1.7 the length of terminal article of antennular peduncle. Appendix masculina about 2.5 times longer than wide, proximal 2/3 expanded ventrally, with a comb-like row of setae, distal 1/3 with a tuft of setae. Distodorsal margin of the antennular peduncle article 3 with a single lobe ending in a sharp spinule between the base of the flagella, article trapezoidal; article 1 with short distolateral process with 3 long setae. Antenna peduncle reaching to about 0.5 the length of the scale proximal article; antennal scale about 4.8 times longer than wide, reaching well beyond antennular peduncle. Median article of mandibular palp expanded at mid-length. Carpopropodus of thoracopod 1‒2 with single article, of 3‒6 with 3 articles, of 7‒8 with 2 articles; merus of carpopropodus 3 with simple, non-serrated setae. Exopod of male 4 th pleopod 4-articulated, articles 2‒4 decreasing in size distally; two proximal articles naked, articles 3 and 4 each with one unbranched, modified seta. Uropodal endopod maximum width 0.32 times total length; portion of endopod measured from the distal edge of the statocyst to the tip of the endopod about 2/3 total endopod length. Telson linguiform, about 1.75 as long as wide, lateral margins slightly convex, converging to a rounded tip, without distal indentation; 35 robust, articulated setae on the distal half of the lateral margins, setae regularly increasing in size towards tip.

Description (based on male holotype) (ICML-EMU-13270). Carapace elongated, slightly produced anteriorly in a triangular process.

Eyes ( Fig. 1A View FIGURE 1 ) large, cornea wider than peduncle, width 1.6‒1.7 length of terminal antennular article.

Antennula ( Fig. 1A, D View FIGURE 1 ) with article 1 rectangular, inner distolateral process with 3 long setae; article 2 the shortest; article 3 as long as article 1, distally wider, naked, a small lobe ending in a sharp spinule on the distodorsal margin between the base of the flagella. Appendix masculina ( Fig. 1B View FIGURE 1 ) lanceolate, about 2.5 times as long as wide, proximal 2/3 expanded ventrally, with a comb-like row of setae, apex with a tuft of setae.

Antennal sympod ( Fig. 1F View FIGURE 1 ) with a long, acute spine at outer distal angle; peduncle short, distal article reaching about 0.4 length of the antennal scale, at most reaching distal margin of article 1 of antennular peduncle; scale slender, total length about 4.8 times its width, subdistal suture separating distal and proximal portions, distal portion about 0.2 times scale total length.

Mandibular palp ( Fig. 2A View FIGURE 2 ) with proximal article short, naked; median article with a strong, widely triangular projection at mid-length, long, simple setae on both margins; terminal article about 0.5 length of median article, with 5 long, simple setae and 7 bent, barbed setae near apex. Mandibles as illustrated ( Fig. 2B, C View FIGURE 2 ); right with incisor 2-cuspate, lacinia produced into 2 cusps, spine row absent, molar field oval, finely setose, a posterior tuft of long setae; left with incisor 6-cuspate, lacinia 2-cuspate, spine row with 8 denticulated spines, molar field finely striated, a posterior tuft of hair.

Labrum ( Fig. 2D View FIGURE 2 ) symmetrical, posterior margin wider than anterior, convex, armed with row of about 36 small setae.

Maxillula ( Fig. 2E View FIGURE 2 ) outer lobe with one robust, long, surface seta, 10 robust apical setae; inner lobe with 3 long, robust apical setae, these setae with some spines on inner margin, and about 5 shorter setae.

Maxilla ( Fig. 2F View FIGURE 2 ) exopod well developed, distally slender, with 14 long, simple setae on outer margin, 2-articulated palp, 3 setose endites, the middle endite with a robust serrate seta.

Thoracopods ( Figs. 3A‒D View FIGURE 3 , 4A‒D View FIGURE 4 ) increasing in size from 1 to 5, decreasing in size from 6 to 8; flagellum of exopod 1‒8 with 8 articles. Carpopropodus of thoracopod 3‒6 with 3 articles, of thoracopod 7‒8 with 2 articles. Thoracopod 1 ( Fig. 3A View FIGURE 3 ) basis with projecting, densely setose endite; ischium, merus, and carpopropodus about same length; preischium shorter, with 5 short setae; ischium with 7 lateral plus 1 subterminal setae; merus with 7 lateral plus 1 subterminal setae; carpopropodus with 7 laterodistal setae, 3 and 4 on each margin; dactylus about 0.3 times length of propodus, with 9 plumose and simple setae, nail straight, slightly longer than dactylus. Thoracopod 2 ( Fig. 3B View FIGURE 3 ) carpus and propodus about the same length, merus about 0.5 their length; merus with 7 setae, carpus with 7 setae, propodus with 12 setae, dactylus about 0.3 times length of propodus, with 12 plumose and simple setae, nail straight, about 1.5 times length of dactylus. Thoracopod 3 ( Fig. 3C View FIGURE 3 ) basis with 4 short, plumose distal setae on inner margin; preischium naked; ischium, merus, and carpopropodus with long, simple setae on inner margin; distal article of carpopropodus with 5 long setae, the longest serrated, dactylus naked, nail curved. Thoracopods 4‒8 ( Figs. 3D View FIGURE 3 , 4A‒D View FIGURE 4 ) similar to 3 rd, merus longer than carpopropodus 3 (4‒6) or 2 (7 and 8) articles combined.

Pleopods ( Fig. 5A‒E View FIGURE 5 ) 1‒3 and 5 vestigial; pleopod 1 bilobed, with 6 and 5 setae respectively; pleopods 2, 3 and 5 rod-like, with a weak widening at about mid-length, number of setae is 11, 10, and 11 respectively (as illustrated). Pleopod 4 endopod with 3 long, 2 medium, and one short setae. Exopod with 4 articles, articles decreasing in size from the 2nd to the 4 th (proportions: 55:16:11:6); article 2 with a distal, plumose seta; terminal seta on article 3 slightly longer than articles 1‒3 combined, with minute setulae on distal portion; article 4 terminal seta plumose in its distal half.

Uropod exopod ( Fig. 6A View FIGURE 6 ) about 5.7 times as long as wide, 1.6 times as long as telson; uropodal endopod maximum width about 0.32 times its total length, 1.2 times as long as telson; portion of the endopod measured from the distal edge of the statocyst to the tip of the endopod about twice the distance from the endopod proximal margin to the distal edge of the statocyst.

Telson ( Fig. 6B View FIGURE 6 ) about 2.3 times as long as wide, wider proximally, linguiform, lateral margins slightly convex proximally, almost straight in their middle-portion, posterior part of margins converging to a rounded tip; 35 lateral and terminal robust setae in distal 0.4, regularly increasing in size towards the telson tip (no clear difference between marginal and terminal setae).

Female. Similar to male. Antennula ( Fig. 1C, E View FIGURE 1 ) peduncle with article 1 the longest, rectangular, proportionally longer and more slender than in male, inner distolateral process with 3 long setae; article 2 the shortest; article 3 shorter than article 1, distally wider, naked, a small lobe ending in a sharp spinule on the distodorsal margin between the base of the flagella. Pleopods 1‒5 ( Fig. 5F‒J View FIGURE 5 ) vestigial, rod-like, of similar length; pleopod 1 naked; pleopod 2 with 3 long, subterminal, setae; pleopod 3‒5 with 3 long, subterminal setae and 1 terminal seta.

Type locality. West of Cleofas Island GoogleMaps (21°16’N, 106°14’W), southern Baja California, Mexico. Only known locality to date.

Etymology. The new species is named after our colleague and friend Dr. Ignacio Winfield Aguilar, Facultad de Estudios Superiores Iztacala, UNAM, in recognition of his remarkable contribution to the knowledge of Peracarida of Mexico and the Americas.

Remarks. According to Wittmann & Wirtz (2019), who proposed the establishment of a division of the genus Mysidium in four subgenera, M. winfieldi sp. nov. closely matches the diagnosis of the subgenus Mysidium Dana, 1852 , due to the following characters (male): carpopropodus of third thoracic appendage 3-articulated, its merus with simple, non-serrated setae; third pleopod widening at about 50% distance from basis; sympod of 4 th male pleopod without setae on rostral surface, exopod 4-articulated, the two proximal articles naked, the 3rd and 4 th articles each with one unbranched modified seta; telson entire, without distal indentation.

Including Mysidium winfieldi sp. nov., the genus Mysidium currently contains eleven species, all distributed in the Americas ( Ortiz et al. 2017a, Wittmann & Writz 2019). Of these, three are distributed in the eastern Pacific: M. ricketsii Harrison & Bowman, 1987 , M. pumae Ortiz, Hendrickx & Winfield, 2016 , and M. winfieldi sp. nov. The other six species have been described for shallow water in the tropical and subtropical western Atlantic ( Ortiz et al. 2017a, Wittmann & Writz 2019). Mysidium winfieldi sp. nov. is therefore the third species of the genus recorded in the eastern Pacific. Mysidium rickettsi has been recorded from off Punta Marcial (type locality), in Bahía de Ohuira, and off Islas Tres Marías, Gulf of California, Mexico ( Harrison & Bowman 1987, Wittmann & Wirtz 2019). It has also been recorded from stomach contents of fishes captured in four localities in the southern Gulf of California ( Harrison & Bowman 1987). Mysidium pumae is known only from Mazatlán, in the SE Gulf of California ( Ortiz et al. 2017b). Mysidium winfieldi sp. nov. is currently known only from around the Tres Marías Islands, on the eastern side of the Gulf of California entrance.

Males of M. winfieldi sp. nov. differs from the two eastern Pacific species by the following main characters:

Antennula. In M. rickettsi there is a pair of small lobes ending in a sharp spinule on the distodorsal margin of the peduncle third article, one at the base of each flagellum ( Harrison & Bowman 1987: fig. 1C) vs. only one such lobe in M. winfieldi sp. nov., located between the base of the two flagella. In M. pumae , there is a single, unconspicuous lobe with a minute spine between the base of the flagella. The third antennular article is squarish to rectangular in M. rickettsi and M. pumae vs. trapezoidal and proportionally longer in M. winfieldi sp. nov. In the three species, there is a short distolateral process in article 1, but this process is naked in M. rickettsi vs. bearing 2 long setae in M. pumae and 3 long setae in M. winfieldi sp. nov.

Antenna. In M. winfieldi sp. nov. and M. rickettsi , the peduncle reaches to about 0.5 the length of the scale proximal article, while in M. pumae it is proportionally much shorter, reaching to 0.3 of this length.

Pleopod 4 of male. Brattegard (1969) and Harrison & Bowman (1987) consider the relative length of articles of the exopod of the male 4 th pleopod as a useful distinguishing character in Mysidium . In M. pumae , proportions of the 4 articles of the exopod are variable, with the proximal very long and the distal 3 very short, almost equal in length, less than 1/3 the length of the proximal article (38:12:10:11); in M. rickettsi proportion is 58:14:14:14, the distal 3 of similar length; in M. winfieldi sp. nov. proportion is 55:16:11:6, the distal 3 progressively diminishing in length, the 4 th article being about half the length of the 3rd. Another major difference between Mysidium pumae and the other two eastern Pacific species, M. rickettsi and M. winfieldi sp. nov., is in the seta from article 3 of exopod which is bifid in M. pumae and entire in the other two species; in both M. rickettsi and M. winfieldi sp. nov. the distal portion of this seta bears minute setulae. Endopod of 4 th male pleopod bears 3 long and 2 short setae in M. pumae , 6 medium and one long setae in M. rickettsi , and 3 long, 2 medium, and one short setae in M. winfieldi sp. nov.

Telson of M. winfieldi sp. nov. is about 1.75 as long as wide vs. a little over twice as long as wide in M. rickettsi and 2.3 times in M. pumae ; in M. winfieldi sp. nov. it is linguiform, much wider proximally and with a rounded apex, vs. subrectangular with an almost straight terminal margin in M. pumae . In Mysidium winfieldi sp. nov. the telson bears a total of 35 robust setae in the distal 40% of its length vs. 60‒74 setae in M. rickettsi and 63‒69 setae in M. pumae . Setae in M. winfieldi sp. nov. are also comparatively more robust than in the other two species, and regularly increase in size towards the rounded tip, while in M. rickettsi and in M. pumae the distal setae are more closely set and smaller than the setae in the lateral margins of the telson. In M. winfieldi sp. nov. it is difficult to distinguish marginal setae from terminal (tip) setae because of the regularly convex margins of the telson that converge to a rounded tip.

Uropodal endopod is proportionally much wider in its proximal part (level of the statocyst) in M. winfieldi sp. nov. (0.32 times total length) than in M. rickettsi (0.19 times total length) and M. pumae (0.24); the portion of the endopod measured from the distal edge of the statocyst to the tip of the endopod is about twice the length from the endopod proximal margin to the distal edge of the statocyst in M. winfieldi sp. nov. vs. slightly over 3 times in M. rickettsi and about 3.6 times in M. pumae .

Mysidium winfieldi sp. nov. features a tongue-shaped telson, with lateral margins slightly convex proximally, almost straight in their middle-portion, with posterior part of margins converging to a rounded tip. When compared with the remaining eight species of Mysidium occurring in the West Atlantic, telson is shallowly emarginated in M. gracile ( Dana, 1852) and distinctly excavated in M. colombiae (Zimmer, 1915) , M. antillarum Wittmann, 2019 , and M. iliffei Băcescu, 1991 ; it ends in a triangular projection in M. triangulare Wittmann, 2019 . The distal (terminal) margin of the telson is straight to shallowly convex in M. integrum W.M. Tattersall, 1951 , M. cubanense Băcescu & Ortiz, 1984 and M. rubroculatum Băcescu & Ortiz, 1984 , and these species feature a rectangular-shaped telson ( Harrison & Bowman 1987, Ortiz et al. 2017, Wittmann & Wirtz 2019).