The genus Boreomysis G. O. Sars, 1869 (Peracarida, Mysida, Mysidae) in western Mexico Author Hernández-Payán, J. C. 0000-0003-1483-1289 Laboratorio de Invertebrados Bentónicos, Unidad Académica Mazatlán Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, P. O. Box 811, Mazatlán Sinaloa, 82000, Mexico. jose_carlos_11@hotmail.com Author Hendrickx, M. E. 0000-0001-9187-6080 Laboratorio de Invertebrados Bentónicos, Unidad Académica Mazatlán Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, P. O. Box 811, Mazatlán Sinaloa, 82000, Mexico. michel@ola.icmyl.unam.mx text Zootaxa 2024 2024-03-04 5418 5 501 527 http://dx.doi.org/10.11646/zootaxa.5418.5.4 journal article 10.11646/zootaxa.5418.5.4 1175-5326 10779931 668564FD-5AB7-458F-9449-EB6071E2DB7D Boreomysis arctica ( Krøyer, 1861 ) ( Figures 1‒8 ) Mysis arctica Krøyer, 1861: 34 , pl. 1, fig. 5a‒f. Boreomysis arctica .—G.O. Sars 1869: 330 (passim); 1872: 264; 1879: 10, pl. 11‒13; 1883: 9.— Zimmer 1909: 53 , figs. 71‒ 74.—W.M. Tattersall & O.S. Tattersall 1951: 132 , fig. 22.— Gordan 1957: 341 (list, complete synonymy).— Birstein & Tchindonova 1958: 284 , fig. 10.— Ii 1964 : 41.— Mauchline & Murano 1977: 49 (list).— Lagardère & Nouvel 1980: 385 .— Austin 1985: 560 (list).— Kathman et al . 1986: 104 .— Laubitz 1986: 15 .— Müller 1993: 22 .— Price 2004: 56 (list).— Petryashov 2005: 2 (list); 2009: 77, pl. 3, figs. 4, 6.— Hernández-Payán & Hendrickx 2020: 52 (table 1). Arctomysis arctica Czerniavsky, 1887: 7 . Boreomysis tregouboffi Băcescu, 1941a: 12 ; 1941b: 168 . Material examined. 13 males ; 12 females . Ovigerous females were not collected. TALUD IV. St. 20 ( 24°27’24” N , 108°35’16” W ), August 25, 2000 , 1 male ( CL 9.09 mm ) and 2 females ( CL 7.39, 10.67 mm ), BS operated at 1500‒ 1540 m ( ICML-EMU-12573 ) . TALUD VII. St. 4 ( 22°03’18” N , 106°34’42” W ), June 5, 2001 , 1 male (damaged), BS operated at 1200‒1230 m ( ICML-EMU-12574- A ); St. 12 ( 23°18’18” N , 107°26’48” W ), June 6, 2001 , 1 male ( CL 8.52 mm ), BS operated at 1040‒1120 m ( ICML-EMU-12574- B ); St. 13 ( 23°30’18” N , 107°44’00” W ), June 6, 2001 , 2 males ( CL 12.23 mm ; one damaged) and 2 females (damaged), BS operated at 1400‒1450 m ( ICML-EMU-12575- A ); St. 19 ( 24°16’12” N , 108°23’42” W ), June 7, 2001 , 1 female ( CL 9.97 mm ), BS operated at 1160‒1180 m ( ICML-EMU-12575- B ); St. 26 ( 24°25’24” N , 109°05’21” W ), June 8, 2001 , 1 female ( CL 6.73 mm ), BS operated at 1180‒1220 m ( ICMLEMU-12576- A ); St. 33-B ( 26°06’30” N , 110°06’42” W ), June 9, 2001 , 2 males ( CL 9.03, 10.37 mm ) and 1 female ( CL 6.55 mm ), BS operated at 1260‒1300 m ( ICML-EMU-12576- B ) . TALUD VIII. St. 3 ( 24°32’36” N , 109°30’30” W ), April 16, 2005 , 1 female ( CL 13.12 mm ), BS operated at 1600 m ( ICML-EMU-12577- A ); St. 10 ( 24°58’12” N , 110°16’06” W ), April 17, 2005 , 3 males ( CL 10.50‒10.89 mm ) and 1 female ( CL 8.08 mm ), BS operated at 1500 m ( ICML-EMU-12577- B ) . TALUD X. St. 18 ( 27°09’06” N , 111°46’54” W ), February 12, 2007 , 1 male ( CL 10.66 mm ) and 1 female ( CL 7.07 mm ), BS operated at 1526 m ( ICML-EMU-12578 ) . TALUD XII. St. 15 ( 17°25’33” N , 102°07’20” W ), March 30, 2008 , 1 male ( CL 12.12 mm ), BS operated at 2080‒2125 m ( ICML-EMU-12579 ) . TALUD XVI-B. St. 8 (29°23.8” N , 115°45.2” W ), May 24, 2014 , 2 females ( CL 11.19-11.83 mm ), BS operated at 1448 m ( ICML-EMU-12580- A ); St. 9 (29°20.89” N , 115°51” W ), May 31, 2014 , 1 male ( CL 12.50 mm ), BS operated at 1854 m ( ICML-EMU-12580- B ) . Description . Carapace ( Fig. 1A, B ) elongated, produced anteriorly to form subtriangular rostrum ending in an acute point, reaching about half the length of antennula article 1; anterolateral margins sharply produced; cervical sulcus well marked dorsally; posterodorsal margin reaching to posterior margin of ultimate thoracic segment. Eyes ( Fig. 1A, B ) large, circular; cornea wider than long, strongly convex, without ocular process on upper surface. Antennular peduncle ( Fig. 1B‒D ) robust; article 1 rectangular, concave in lateral view, 6 short setae in middle of outer margin, inner margin with 3 thick setae on distal edge and 5 short setae on distal outer margin; article 2 smaller than the other two, 3 short setae on outer margin; article 3 longer than wide, distal margin with small protuberance with 3 short setae in middle of flagella. Antennal peduncle ( Fig. 1E ) about 0.5 times length of scale, articles 1‒3 subequal in length; article 1 with a prominent thorn on outer margin; article 2 with 4 distal setae on external margin; article 3 with 6 long distal setae on inner margin and 1 on outer margin. Antennal scale ( Fig. 1B, E ) long, slender, extending beyond distal edge of antennular peduncle by about 0.5 its length, about 4.5 times as long as wide, outer margin straight, without setae, inner margin setose; apical tooth well-marked, overreaching truncate apex by its entire length; a minute distal suture at inner corner. Labrum ( Fig. 2A ) subcircular, semi-symmetrical, posterior margin bilobed, with short, simple setae (left) and finely pitted (right). Mandibles ( Figs. 2B , 3A‒F ) palp long, broad proximally; article 1 short, without setae; article 2 longer than article 3, about 3 times broader proximally than distally, outer margins setose; article 3 slightly shorter than article 2, about 5‒6 times as long as broad, comb-shaped setae on distal 2/3 of inner margin, proximal 1/3 with a series of setae almost 2 times as long as distal setae, 4 long, plumose sub-marginal setae and sub-distal, long, simple seta; outer margin with 6 simple setae in proximal 1/3. Right mandible ( Figs. 2B , 3A‒C ) well developed, incisor process robust, composed of chitinous ridge with 4 strong teeth, second bifid; lacinia mobilis well developed between incisor process and par centralis, represented by 2 rows of small spinal setae, first row smaller than second, with smaller number of spines; pars centralis formed by a series of 8 strong apical setae united at their base; molar process subrectangular, longer than wide, with a series of parallel lamellae on crushing surface formed by small, sharp spines attached at their base, a series of small pores on edge of molar process. Left mandible ( Figs. 2B , 3D‒F ) incisor process composed of 1 chitinous ridge with 4 teeth; lacinia mobilis very well developed, consisting of 5 teeth, 4 in row, 2 outermost stronger and more prominent, 1 strong central tooth; pars centralis represented by series of 7 long lamellae with broad base, spiny on their margins; molar process similar to right mandible. FIGURE 1. Boreomysis arctica ( Krøyer, 1861 ) . Male (CL 11.02 mm; TL 27.42 mm) (ICML-EMU-12577-B). A, lateral view; B, cephalothorax with appendages, dorsal view; C, antennula, lateral view; D, same, dorsal view; E, antennal peduncle with scale, dorsal view, and magnification of scale tip (arrow). FIGURE 2. Boreomysis arctica ( Krøyer, 1861 ) . Male (CL 11.02 mm; TL27.42 mm) (ICML-EMU-12577-B). A, labrum, with magnification of posterior margin (arrow); B, left and right mandibles with mandibular palp; C, maxillula, with magnification of tip of external lobe (arrow); D, maxilla. FIGURE 3. Boreomysis arctica ( Krøyer, 1861 ) . Male (CL 11.07 mm; TL 27.42 mm) (ICML-EMU-12577-B). A‒C, right mandible; D‒F, left mandible. Maxillula ( Fig. 2C ) external lobe armed with 13 robust apical setae, 9 long, plumose setae on ventral surface; inner lobe with 4 long, plumose apical setae, 5 short plumose setae on inner margin, 1 simple, short setae on outer margin, and 4 short simple setae on ventral surface. Maxilla ( Fig. 2D ) with narrow, tapering exopodite, armed with 34 simple marginal setae; proximal endopodite article with 4 simple setae, distal article circle-shaped, densely setose on both margins, setae long, plumose; 3 subrectangular endites, distal margins with simple and plumose setae; protopod with dense covering of long, simple setae, interspersed with 7 long, plumose setae. Thoracopod 1 ( Fig. 4A ) short, thin; gnathobase of endopod with well-developed elongated lobe, 1 series of long plumose setae on outer margin; pre-ischium with 6 plumose setae; ischium with 7 long plumose setae on inner margin, 2 short simple setae on ventral face, outer margin without setae; merus short, broad, with 16 long, plumose setae on inner margin, several single setae on outer margin and on ventral surface; carpo-propodus short, with 4 simple setae on inner margin, several single setae on outer margin, and few setae on ventral surface; dactylus short, triangular with several setae on margins and ventral face; nail curved, shorter than dactylus, distal half with setulae; exopod more than 2 times as long as endopod, 22-articulated, each article with long plumose setae. Thoracopod 2 ( Fig. 4B ) endopod longer than first, shorter than 3 and 4; endopod elongated, not distally subchelated; short, naked pre-ischium; ischium armed with long, simple setae on inner margin; merus and carpo-propodus armed with a series of long, simple setae on inner margin; dactylus with simple setae, 1 series of 6 short, serrated setae on inner margin; exopod slightly shorter than endopod, 23-articulated, each article with long, plumose setae. Thoracopods 3‒8 ( Figs. 4C, D , 5A‒D ) similar; elongated endopod; pre-ischium naked; ischium and merus with long, simple setae on inner margin; carpus with 1 series of long and short setae on inner margin; propodus divided into 2 subsegments, proximal shorter than distal; dactylus and nail forming long claw; exopod shorter than endopod, 24-articulated, each article with long, plumose setae. Penis ( Fig. 5E ) elongated, about 3 times as long as wide, slightly wider distally, distally covered with moderately long setae. Abdominal somites 1‒6 without spines ( Fig. 1A ). Male pleopods ( Fig. 6A‒E ) biramous, well developed; exopods multi-articulated (23‒29 articles), longer than corresponding endopods, 2‒5 with long, plumose setae in both margins, first with plumose setae on outer margin only; first pleopod endopod uniarticulated, a well developed elongated lobe, about 1/3 the length of the corresponding exopod, tapering distally, 16 short, comb-like simple setae on proximal half of inner margin, 2 rows of long plumose setae (8 + 5) on ventral surface. Pleopods 2‒5 endopods multi-articulated (21‒23 articles), pseudobranchial lobes short, about 1/2 length of first endopod, falciform, outer margin with small bump at about mid-length, bump armed with 4 long, simple setae. Uropods ( Fig. 7A ) long, thin; exopod about 1.2 times telson length, about 5.3 as long as wide, about 1.2 times as long as endopod, outer margin armed with 2 similar robust setae; endopod about 6.6 as long as wide, inner margin armed in proximal third with 2‒3 robust setae. Telson ( Fig. 7B ) linguiform, about 3.3 times as long as wide, maximum width about 2.6 times minimum width; margins proximal 1/3 naked, remaining 2/3 with 32‒41 setae, including long setae and intermediate clusters of 2‒5 shorter setae; distal cleft ( Fig. 8A‒C ) V-shaped, deep, about 1/7 of total telson length; base of cleft wide, rounded, without slit; inner margins of cleft armed with 23‒26 robust setae each, setae increasing in size towards distal part of the cleft, spine-like, closely set, articulated at base; 3 long, robust setae on each lobe of apex, middle seta longest. Females . Marsupium of female comprised of 7 pairs of oostegites. Female pleopods ( Fig. 6F‒J ) uniramous, well developed, increasing in size posteriorly, long and plumose setae on inner margin, 1 series of short, simple setae at their base. Size (Material examined). Males, CL 8.52‒12.50 mm ; females, CL 6.55‒13.12 mm . FIGURE 4. Boreomysis arctica ( Krøyer, 1861 ) . Male (CL 11.07mm; TL 27.42 mm) (ICML-EMU-12577-B). A, thoracopod 1 with magnification of distal articles (arrow); B, thoracopod 2 with magnification of distal articles (arrow); C, thoracopod 3; D, thoracopod 4. FIGURE 5. Boreomysis arctica ( Krøyer, 1861 ) . Male (CL 11.07 mm; TL 27.42 mm) (ICML-EMU-12577-B). A, thoracopod 5; B, thoracopod 6, with magnification of dactylus (arrow); C, thoracopod 7; D, thoracopod 8; E, penis. FIGURE 6. Boreomysis arctica ( Krøyer, 1861 ) . A‒E, male (CL 11.07 mm; TL 27.42 mm) (ICML-EMU-12577-B); F‒J, female (CL 11.02 mm; TL, 26.90 mm) (ICML-EMU-12577-B). A‒E, pleopods 1 to 5; F‒J, pleopods 1 to 5. New records in Mexico . Boreomysis arctica is now recorded in the Mexican Pacific, in 13 locations: ten in the central and southern Gulf of California, two off the west coast of the Baja California Peninsula, and one off the SW coast of Mexico ( Fig. 9 ), thus indicating it is a widespread and rather frequent species in western Mexico . Hernández-Payán & Hendrickx (2020) briefly included B. arctica in a list of species of mysids known to occur in western Mexico , referring to the same material reported in detail herein. FIGURE 7. Boreomysis arctica ( Krøyer, 1861 ) . Male (CL 11.07 mm; TL, 27.42 mm) (ICML-EMU-12577-B). A, uropodal endopod and exopod, dorsal view; B, telson, dorsal view, with magnification of distal cleft basal part (arrow). FIGURE 8. A‒C, Boreomysis arctica ( Krøyer, 1861 ) . Male (CL 11.07 mm; TL, 27.42 mm) (ICML-EMU-12577-B); D‒F, Boreomysis californica Ortmann, 1894 . Female (CL 10.21 mm; TL 18.73 mm) (ICML-EMU-12544-A). A, D, distal part of telson, dorsal view; B, E, same, enlarged cleft; C, F, same, enlarged basal part of cleft. Geographic distribution . Widely distributed in the boreal waters of the Arctic Ocean, extending southward on eastern slope from Norway to British Isles, Bay of Biscay and Mediterranean (W.M. Tattersall 1951 ); from western Greenland to New England shores in East Atlantic (W.M. Tattersall & O.S. Tattersall 1951 ). In North Pacific, B. arctica is found off coast of Japan , to Sea of Okhotsk, Bering Sea and extends its distribution to coast of California (“Albatross” station 4541). Widely distributed off western Mexico ( Fig. 9 ) (this study). FIGURE 9. Localities in western Mexico where Boreomysis arctica ( Krøyer, 1861 ) was collected during this study. Bathymetric distribution . Because stratified (discrete) samples were not available during our studies, the material examined herein were collected at unknown depths during sampling operations within the water column, from surface to 1040‒2125 m (all caught with a BS). According to Hargreaves (1997) , B. arctica occurs between 497 and 955 m depth, with maximum abundance between 555 and 925 m . Remarks. The materials examined herein fit well with the descriptions of B. arctica by various authors. This includes: the eye with a large, circular cornea, the relative length of the rostral spine, the length-width proportion of the antennal scale, its truncate tip and extension of its distal, marginal spine, the long uniarticulated endopod of the male first pleopod, about 1/3 the length of the corresponding exopod, the shape and proportions of the telson, and the presence of two or three setae on the uropodal endopod margin (G.O. Sars 1879 , W.M. Tattersall & O.S. Tattersall 1951 ). Boreomysis arctica differs from the other species recorded in the eastern Pacific by one or several of the following characters: antennal scale slender; eye cornea wide, crescent-shaped, peduncle without ocular tubercle; male pleopod 1 endopod long, oval-shaped, densely setose; three long setae on the inner margin of the uropodal endopod; base of the telson cleft rounded; margins of telson with mixed short and long setae.