Pacificabathynella stanfordi, Camacho & Newell & Reid, 2009

Camacho, A. I., Newell, R. L. & Reid, B., 2009, New records of Bathynellacea (Syncarida, Bathynellidae) in North America: three new species of the genus Pacificabathynella from Montana, USA, Journal of Natural History 43 (29 - 30), pp. 1805-1834 : 1820-1825

Pacificabathynella stanfordi sp. nov.

( Figures 4 , 5 )

Material examined

Type locality. Flathead County, Graham Channel upstream-well, 14 April 1989 (four males and four females were collected), Montana, USA. Other localities from Montana: Flathead County, St-SR-well, 3 May 1989 (two males and one female) ; Flathead County, well station SR, 2 April 1989 (two males and three females were collected) ; Flathead County, Nyack Channel of Flathead river-down-well, 1 May 1989 (six males and six females) ; Flathead County, Walters well, 31 March 1989 (10 males, six females and two young) ; Flathead County, Graham Field west well, 16 July 1989 (six females) ; Flathead County, Sargent North well, 6 November 2003 (six females) ; Flathead County, Great Bear well, 9 November 2003 (two males and five females) ; Mt Flathead County, Middle Fork , Flathead R. Nyack aquifer, Tadpole B well, 30 April 2004 (three females and one male) . The details of the new description are based on all specimens. The holotype is a male and the allotype is a female and the type series contains 63 additional specimens (26 males and 38 females) . (Holotype MNCN20.04 /8093, allotype MNCN20.04 /8094 and type series MNCN20.04 /8095.)

Description

Body. Total length of holotype (male) 0.77 mm and allotype (female) 0.60 mm. Largest male total length 0.82 mm, smallest 0.53 mm; largest female total length 0.81 mm, smallest 0.60 mm. For variability see Table 4. Body form not very elongated, almost cylindrical; approximately 13 times long as wide. Pleotelson with one barbed dorsal seta on either side, shorter than furcal rami.

Antennule ( Figure 4A ). Seven segments; length of first three segments slightly longer than other four segments; segment five smaller than others, half length of segment four; setulation as in Figure 4 (A); three aesthetascs of different length on segments six and seven. A.I slightly shorter than A.II.

Antenna ( Figure 4B ). Seven segments; length of first three segments half length of last four; setal formula: 0/2+exp/2+0/2+0/0+0/2+2/5; ventromedial seta of exopod absent, with two terminal setae, one a bifurcated sensory seta.

Paragnath ( Figure 4C ). Rounded with one distinctive tooth on distal part, very thick setulation at the distal end.

Mandible ( Figure 4D,D ¢). Palp with three segments, terminal segment with two claws, not very long, with sparse setulation; second segment more or less cylindrical without expansions. Incisor process (pars incisiva) with two teeth; processus incisivus accessorius with one tooth, one long seta-like tooth; pars molaris with two structures dentate, the more distal with four teeth, other with small similar denticles located at edges, two most distal slightly larger.

Maxillule ( Figure 4E ). Proximal endite with four setae; distal endite with six teeth, four strong teeth with denticles, other two thin, setae-like; outer margin with three plumose setae.

Maxilla ( Figure 4F ). Four segments; setal formula 7, 4, 7, 5.

Thoracopods I to VII ( Figure 5A–G ). Sexual dimorphism present in Th. VI. Th. I ( Figure 5A ) a little smaller; Th. II-VII ( Figure 5B–H ) very similar in size. Th. I and II without epipod; coxa of Th. I with long, strong plumose seta, basipod with three setae. Exopod with one segment on all thoracopods, shorter than endopod in all cases; with five barbed setae, two terminal, one dorsal, two ventral. Endopod with four segments in all thoracopods, setal formulae (number of setae of basipod in brackets):

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

Th. II ( Figure 5B ): (2) 3+0/3+1/2+0/4

Th. III ( Figure 5C ): (2) 2+0/2+1/2+0/4

Th. IV ( Figure 5D ): (1) 2+0/2+1/2+0/3

Th. V ( Figure 5E ): (1) 1+0/1+1/2+0/3

Th. VI ( Figure 5F ): (0) 0+0/0+1/2(1)

Th. VII ( Figure 5G ): (0) 1+0/0+1/0+0/2(1)

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

Male thoracopod VIII ( Figure 4G–I ). Longitudinal axis of coxa and basipod form angle of 25°. Penial region with frontal lobe, inner lobe, outer lobe. Frontal lobe has two lobules, completely covers outer and inner lobes. Inner lobe has distal region divided into two areas with almost square projection on internal side. Outer lobe smallest, with conical aspect with fine setae. Basipod with distal, well-developed, crest-like protuberance with two rows of setules distally on inner side, one distal-lateral barbed seta. Endopod one-segmented, half length of exopod, one smooth distal seta. Exopod well developed with five setae.

First pleopods ( Figure 4J ). Two segments, first segment with one seta; second segment with six setae.

Female thoracopod VIII allotype ( Figure 4K ). Coxa with one small, barbed, lateral seta; large epipod, almost twice length of basipod; endopod one-segmented, with two apical setae of similar length; exopod a little longer than endopod, with two apical smooth setae of different lengths.

Female thoracopod VI allotype. 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 on basipod of thoracopods similar to male.

Uropods ( Figure 5I ). Sympod slightly longer than endopod, twice as long as wide, with six equal spines on distal end; endopod one-third longer than exopod, with five strong claws, two distal-most longest (five times length of most basal), with two very long terminal setae and with two shorter ones located dorsolaterally, all barbed; exopod with seven setae, two terminal, one subterminal, three medial and one basal. Endopod with spinous projection at distal outer corner ( Figure 5I ).

Furcal rami ( Figure 5J,H ). Almost square, bearing five spines; long dorsal spine almost half length of second spine, second spine 30% longer than third medial spine, third spine slightly longer than fourth, fourth almost twice length of fifth.

Variability

The variability that we have found is very small, in spite of the fact that we have studied many specimens from many different samples. The observed variability only affects the observed number of setae on the different segments of the endopods of thoracopods I to V on males and females (see Table 5):

The setal formula variation from the holotype is:

Th. I: 4–5+0/3–4+1/3–4+0/4

Th. II: 2–3+0/2–3+1/2–3+0/4

Th. III: 2+0/2+1/2+0/4

Th. IV: 2+0/2+1/1–2+0/3

Th. V: 1+0/1+1/1–2+0/3

Etymology

The species name is derived from Dr Jack Stanford, Director of the University of Montana’s Flathead Lake Biological Station, and long-time pioneer in the study of hyporheic communities and floodplain aquifer ecosystems.

Remarks

Pacificabathynella stanfordi sp. nov. is the smallest known species of the genus (see Tables 3 and 4); the largest specimens are similar to small P. kalispellensis sp. nov. This species has the smallest number of setae on thoracopods and uropods within the genus (see Table 3). This is a unique species of the genus in that it has five setae on the exopod of thoracopods I to VII. Only six setae are present on the second segment of the first pleopod, while in the other known species the pleopod has seven setae. Pacificabathynella stanfordi sp. nov. has only five spines on the endopod and seven setae on the exopod of the uropods ( Figure 2I ). The setal formula of the endopod of the thoracopods is unique (see Table 5).

Perhaps the species that has more characters in common is P. ruthae sp. nov. (see Table 3), although the latter is a much larger species. On the uropod both species have six spines on the sympod; however, the endopod and exopod differ between the species, the new species having only five and seven spines respectively. The furca is similar in both species, and very different from the furca of P. sequoiae . One spine one is longer than the other, and is similar to the dorsal spines; all furcal spines are very similar. The male thoracopod VIII is very different in both species. The coxa of the female thoracopod VIII only has one seta as in P. ruthae sp. nov., and the epipod is bigger in P. stanfordi sp. nov.

Figures

Figure 2. Pacificabathynella kalispellensis sp. nov., male holotype. (A) Thoracopod I; (B) thoracopod II; (C) thoracopod III; (D) thoracopod IV; (E) thoracopod V and (F) thoracopod VII. Scale bar in mm.

Figure 4. Pacificabathynella stanfordi sp. nov. (A–J) male holotype. (A) Antennule (dorsal view); (B) antenna (dorsal view); (C) paragnath; (D) mandible, (D′) mandible masticatory part; (E) maxillule (dorsal view); (F) maxilla (dorsal view); (G) thoracopod VIII (latero-external view); (H) thoracopod VIII (latero-internal view); (I) thoracopod VIII (frontal view); (J) first pleopod and (K) thoracopod VIII female (frontal view). Scale bar in mm. Abbreviations: F. lb, frontal lobe; I. lb, inner lobe; O. lb, outer lobe; Prj, projection of inner lobe; Bsp, basipod; Crt. bsp, crest-like protruberance of basipod; Endp, endopod; Exp, exopod.

Figure 5. Pacificabathynella stanfordi sp. nov., male holotype. (A) Thoracopod I; (B) thoracopod II; (C) thoracopod III; (D) thoracopod IV; (E) thoracopod V; (F) thoracopod VI; (G) thoracopod VII; (H) telson and furcal ramis; (I) uropod (latero-external view) and (J) furcal rami (dorsal view). Scale bar in mm.