Pacificabathynella yupik Camacho & Newell & Crete & Dorda & Casado & Rey 2015, sp. nov.

Pacificabathynella yupik sp. nov.

(Figures 1–5)

Material examined

Type locality. Kwethluk River, tributary of Kuskokwim River western Alaska (USA); coordinates N60.34520, W161.089146 and Z 1268 (WGS84); 24 June 2012 (32 females, five males and five subadult specimens); collected by Zach Crete. All specimens collected belong to the type series, 37 morphotypes, together with DNA extractions from five subadult specimens used for molecular analysis, five DNA types.

Details of the description are based on all adult specimens. The holotype is a male (MNCN 20.04 /10092), the allotype is a female (MNCN 20.04 /10093) and the morphological type series contains four males (MNCN 20.04 /10125 to 10128) and 31 females (MNCN 20.04 /10094 to 10124). The molecular type series contains five DNAtypes (MNCN /ADN 29963 to MNCN / ADN 29967).

Abbreviations used: Th, thoracopod; A.I, antennule; A.II, antenna; Md, mandible, Mx.I, maxillule and Mx.II maxilla.

Description

Body. Total length of holotype 1.11 mm and allotype 1.11 mm. Total length of males 1.11 – 0.90 mm, of females 1.18 – 0.74 mm. For variability see Table 3. Body not very elongated; almost cylindrical, approximately nine times as long as wide; segments slightly widening towards posterior end. Head as long as wide. Pleotelson with one plumose dorsal seta on either side, similar to furcal rami. All drawings are of the holotype (male) except for Th VIII and one figure of Md, paragnath and Th VI that belong to the allotype (female).

Antennula (Figure 2A). Seven-segmented; length of first three segments similar to other four segments combined; segments four and five smaller than others and with similar length; sixth segment shorter than seventh that is the longest; inner flagellum almost trapezoidal; setation as in Figure 2A; two aesthetascs on sixth and three on seventh segments. A.I slightly longer than antenna.

Antenna (Figure 2B). Eight-segmented; slightly shorter than A.I; first four segments almost as long as fifth and sixth; eighth terminal segments slightly longer than seventh and is the longest; setal formula: 0/0/2+exp/2+0/2+0/0/2+2/5; exopod, as long as second segment, with two terminal setae, one of these a bifurcated sensory seta; ventromedial seta absent.

Labrum (Figure 2C). With a small central protuberance at the distal smooth free edge, flanked by slight protrusions, most evident on ventral side and with a visible small denticle in one of these protrusions.

Paragnath (Figure 2D, E). Short, almost square, with rounded distal part and very thick setulation on all surfaces on distal half.

Mandible (Figure 2F and G). Palp with three segments, terminal segment (Figure 2G) with two long and strong barbed claws, more or less cylindrical without expansions. Masticatory part (Figure 2F, H): incisor process (pars incisiva) with two teeth; processus incisivus accessorius with one tooth and one long seta-like tooth; pars molaris with two dentate structures, like two crowns, parallel to main axis of teeth, the first (the nearest to processus incisivus accessorius) with consistantly three strong denticles and the other with small denticles, except the most distal which is a strong tooth.

Maxillule (Figure 2I). Proximal endite with four setae; distal endite with six teeth, four with denticles and two more, setae-like, and with three plumose setae and tufts of long setules on outer margin.

Maxilla (Figure 2J). Four segments; setal formula 7, 3, 7, 5.

Thoracopods I–VII (Figures 3A–E, 4A–B). Sexual dimorphism present on Th VI. Th I (Figure 3A) smaller than others; Th II (Figure 3B) to V (Figure 3E) similar in size and Th VII (Figure 4B) a few longer than others. Th I without epipod; coxa with a long and strong plumose seta; basipod with two smoth setae and a tuft of long fine setules near base. Epipod present on Th II – VII, small in Th II – V, half the length of basipod; as long as the basipod on Th VI and VII. Exopod with one segment on all thoracopods, shorter than endopod in all cases, almost like the first two segments in Th I – III and Th VII and slightly longer than the first two segments in Th IV and V; with five barbed setae, two terminal, one dorsal and two ventral. Endopod with four segments in all thoracopods, setal formulae (number of setae on basipod in brackets):

Th I: (2) 5+0/5+1/4+0/4

Th II: (3) 3+0/3+1/3+0/4

Th III: (2) 2+0/2+1/2+0/4

Th IV: (1) 2+0/2+1/2+0/4

Th V: (1) 1+0/2+1/2+0/3

Th VI: (0) 1+0/0+1/2(1)

Th VII: (0) 1+0/0+1/0+0/2(1)

Thoracopod VI (Figure 5A,B) with aberrant structure, with only three segments in endopod: first segment broader than usual, second segment broad and dilated bearing on outer margin strong medially curved seta, third segment small with two setae, one long and another shorter.

Male thoracopod VIII (Figure 5A,B). Longitudinal axis of coxa and basipod form 25° angle. Penial region with frontal lobe, inner lobe, outer lobe. Frontal lobe with two lobules on distal end. Inner lobe more or less similarly developed as frontal lobe, distal region with projection claw (Prj) on internal side. Outer lobe with two well-developed lobules. Basipod very large, with rows of setules on inner side, with distal and very welldeveloped, crest-like protuberance and with one lateral-subdistal smooth seta and other distal. Endopod one-segmented, small, 1/4 length of exopod, with small denticles. Exopod well developed, longer than basipod, with five setae.

Pleopod I (Figure 5D). Two segments, first segment with one very long plumose seta; second segment with seven setae, the three distal of different length and plumose.

Female thoracopod VIII of the allotype (Figure 5C). Coxa with one small, barbed lateral seta; very large epipod, twice as long as basipod; endopod one-segmented, with two apical barbed setae of different length; exopod two times as long as endopod, with three setae, two apical, all smooth, but differing in length.

Female thoracopod VI of the allotype (Figure 4C). Exopod one-segmented and with five setae, as in other thoracopods; endopod four-segmented, setal formula 1+0/0+1/0 +0/2(1). Number of setae on segments of endopod and basipod of thoracopods differs between female and male. Setal formulae of allotype (number of setae of basipod in brackets):

Th I: (3) 5+0/4+1/4+0/4

Th II: (4) 2+0/4+1/3+0/4

Th III: (2) 3+0/3+1/3+0/4

Th IV: (2) 2+0/2+1/2+0/4

Th V: (1) 2+0/2+1/2+0/4

Th VI: (0) 1+0/0+1/0+0/2(1)

Th VII: (1) 1+0/0+1/0+0/2(1)

Uropods (Figure 5E). Sympod almost as long as endopod, rectangular, twice as long as wide, with five distal equal spines; endopod 15% longer than exopod, with five strong claws (distal two longest, the most distal almost twice as long as fourth and almost four times as long as most basal, and the latter slightly shorter than the second), with two very long distal barbed setae and two plumose setae located dorsolaterally; exopod with seven setae, two terminal, three medial and two basal. Endopod with spinous projection at the distal outer corner.

Pleotelson (Figure 5F). With one long, plumose dorsal seta on either side near base of furca.

Furcal rami (Figure 5F). Almost square, bearing five spines; dorsal spine similar to third, slightly longer than fourth and almost 70% length of second spine and first spine twice as long as second spine.

Variability

The observed variability affects the number of setae of the different segments of the endopods of the thoracopods I to III on females (see Table 4).

The setal formulae of females different from those of the allotype (number of setae of basipod in brackets):

Th I: (3)5+0/4 – 5+1/3 – 4+0/4

Th II: (4) 3+0/3 – 4+1/3+0/4

Th III: (2) 2 – 3+0/2 – 3+1/3+0/4

Etymology

The species name, as a tribute, is taken from the name Yup ’ ik Eskimo, the Alaska native people on the lower Kuskokwim where the new species was collected. Substantive in apposition.

Remarks

Paci fi cabathynella yupik sp. nov. is small within the genus, similar in size to P. stanfordi and is as small as P. kalispellensis (Table 3). This is the species with the highest number of unique characters within the genus (see Tables 5 and 4): A II eight-segmented and slightly shorter than A I; the pars molaris of the mandible has fewer teeth than in other species; on the second segment of the maxilla has only three setae (Figure 2J), whereas it has four setae in all other congeners; the setal formulae of the endopods of the thoracopods are unique (see Table 4) and are more like P. stanfordi, which has the scantiest setal armature, with exopod having only five setae in both species (six in other three spp.); the endopod of male Th VIII has no seta (Figure 5A, B); this species has low number of spines on the endopod of the uropod (five) as P. stanfordi and the endopod of the uropod is similar to the sympod in size.

Paci fi cabathynella yupik sp. nov., despite its several unique characters, closely resembles P. stanfordi except in body size (see Table 5 and figures). On the uropod, both species have five spines on the endopod and seven setae on the exopod, but differ in their sympodal armature. The furca of the new species is closest to P. kalispellensis, the first spine being much longer than the others, but the dorsal spine is shorter in the new species and small in P. Sequoiae. All furcal spines are very similar in the other species. Thoracopod VIII in both sexes of the new species is closest to the condition in P. kalispellensis.