Montanabathynella pecosensis, Camacho & Mas-Peinado & Hutchins & Schwartz & Dorda & Casado & Rey, 2021

Camacho, A. I., Mas-Peinado, P., Hutchins, B. T., Schwartz, B. F., Dorda, B. A., Casado, A. & Rey, I., 2021, New stygofauna from Texas, USA: three new species of Parabathynellidae (Crustacea: Bathynellacea), Journal of Natural History 55 (15 - 16), pp. 979-1007 : 987-990

Montanabathynella pecosensis sp. nov. Camacho and Hutchins, 2021

( Figures 2–3 )

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Material examined ( Table 1)

Type locality. Live Oak Creek , Crockett County, Texas, USA ( WGS 84 30.74220ºN, − 101.6739ºW, 655 m amsl): holotype female ( MNCN 20.04 /20164 slide and MNCN / ADN 54864 DNA extract), coll . 13 July 2015 by B. Hutchins and D . Belleny (sample 150713- H2) . Furthermore , one juvenile specimen from same location, same collectors and date (sample 150713-H3) .

The female holotype preserved on one slide together with its DNA extract ( MNCN / ADN 54864) ( Table 2) constitutes the type series .

Description. Body. Total length of holotype 1.2 mm. Body elongated, segments widening towards posterior end. Head longer than broad.

Antennule ( Figure 2 (a)). Almost 50% longer than AII. 7-segmented; first three segments longer than last four segments combined; first segment longest, second and third segments similar to last two, fifth segment shortest; fifth segment with five smooth setae; inner flagellum almost square; setation as in Figure 2 (a); fifth segment with two aesthetascs, segments 6 and 7 each with three terminal aesthetascs.

Antenna ( Figure 2 (b)). 6-segmented; first three segments combined as long as fourth and fifth combined; second segment without setae but with small teeth; sixth segment longest, with one subterminal plumose seta and three smooth terminal setae; setal formula: 0 + 0/0 + 0/1 + 1/0 + 1/0 + 0/4.

Labrum ( Figure 2 (c)). Almost flat, with eight main teeth, and four (2- or 3-cuspidate) teeth at each angle; ventral surface with several rows of fine spinules.

Mandible ( Figure 2 (d)). Pars incisiva with four well-developed teeth and triangular small proximal tooth as in Figure 2 (d); pars molaris with six claws, four of which strong and denticulate, two more proximal setulose, smaller and joined basally; mandibular palp not exceeding pars incisiva.

Maxillule ( Figure 2 (e)). Proximal endite with four unequal claws; distal endite with eight claws, two apical smooth whereas the rest denticulate; three simple setae subdistally on outer margin of endite, as figured.

Maxilla ( Figure 2 (f)). 4-segmented, setal formula: 2, 5, 15, 4.

Thoracopods I–VII ( Figure 3 (a–g)). Well developed; length gradually increasing from ThI to ThIV ( Figure 3 (a–d)); ThV ( Figure 3 (e)) and VI ( Figure 3 (f)) similar in length; last thoracopods ( Figure 3 (g)) as short as first; ThI without epipod; well developed epipod on ThII to VII, each about half length of corresponding basipod. Basipod of all Ths with one short distolateral, smooth seta. Exopods 2-segmented (ThI; Figure 3 (a)), 3-segmented (ThII and ThVII; Figure 3 (b,g)), 4-segmented (ThIII; Figure 3 (c)) or 5-segmented (ThIV-VI; Figures 3 (d–f)); exopod of ThI, II and VII shorter than corresponding endopod, rami similar in length in ThIII, and exopod longer than endopod in ThV–VI; all exopodal segments provided with two barbed setae (with groups of ctenidia at base), except terminal one, with one smooth and one plumose seta, and proximal segment of ThI and II with three barbed setae. Endopod 4-segmented, first segment short, second and third long and similar in length, both with a cluster of strong spinules along outer margin; fourth segment reduced with two smooth strong claws and one simple seta, all inner setae on segments smooth; outer seta on first and second segments of ThI–VII plumose. Setal formula of endopod as follows:

ThI 1 + 2/2 + 1/2 + 1/3(1)

ThII–IV 0 + 1/2 + 1/1 + 1/3(1)

ThV 0 + 1/1 + 1/0 + 1/3(1)

ThVI 0 + 0/1 + 1/0 + 1/3(1)

ThVII 0 + 0/0 + 1/0 + 1/3(1)

Female t horacopod VIII ( Figure 3 (h)). 2-segmented; trapezoidal basal segment almost 3 times as long as and much wider than second segment, with four teeth; second segment almost square, with three long terminal setae, of which two smooth and one plumose.

Pleotelson. Without ventral seta. Anal operculum not pronounced, almost flat.

First pleopods. Absent.

Uropod ( Figure 2 (g)). Sympod 3.5 times as long as wide and 1.5 times longer than corresponding rami, with 14 barbed spines about equal in length except distal-most, twice longer than rest. Endopod as long as exopod, with three spines along distal half of inner margin, of which two proximal small whereas distal-most strong and enlarged; distal margin of segment with strong opposable spine forming a sort of forceps with distal-most spine on inner margin; distolateral angle of segment with one plumose and two barbed setae; basal part of segment with isolated plumose seta not reaching distal end of segment. Exopod with seven barbed setae and one plumose basal seta.

Furca ( Figure 3 (i)). Each ramus almost triangular, with 11 barbed spines, of which terminal two longer than rest; two plumose setae of unequal length disposed dorsally, shorter one not reaching tip of terminal spines.

Etymology. The specific name, pecosensis , refers to the Pecos River, because Live Oak Creek, where the new species was found, is a tributary of that famous river.

Taxonomic remarks

Unfortunately, we have not been able to study the male ThVIII of Montanabathynella pecosensis sp. nov. since no males have been found in the samples. However, the morphology of the female is close to that of Montanabathynella salish , the type species of Montanabathynella , suggesting the new taxon belongs in this genus. The new species is smaller than M. salish , and the main features of the two are compared in Table 3. Common features of the two species are: 6-segmented antenna; 4-segmented MxII; multisegmented (three or more segments) exopod of thoracopods I to VII; outer plumose seta present on first and second segments of Th I–VII; female thoracopod VIII 2-segmented with three setae; pleopods absent; two strong spines opposable as forceps on distal end of endopod of uropods; ventral seta absent on pleotelson. Montanabathynella pecosensis sp. nov. differs from M. salish in the following features ( Table 3): AI with shorter segments two and five (the fifth segment especially is much shorter in the new species); AII first three segments short (especially the third one, which is much longe in M. salish ) second segment without setae, and sixth with a plumose seta; labrum with fewer teeth; MxI with only eight teeth on distal endite (vs nine on M. salish ) and three lateral setae similar in (Continued) length; MxII with five setae on second segment and only 19 on distal segments (vs 21 in salish); epipod present on ThII and III (vs absent in M. salish ); basipod of thoracopods almost square (vs rectangular and very large in M. salish ); thoracopods with fewer segments on exopod and fewer setae on segments of endopod; exopod of all thoracopods with plumose setae on distal segment (vs setae barbed in M. salish ); female ThVIII with two segments of very different length and width and with only one of the three setae present on the distal segment plumose; uropod with fewer setae on both exopod and endopod, both rami similar in length with only two small subterminal spines on endopod; furcal rami with fewer spines and anal operculum unpronounced.

Figures

Figure 2. Montanabathynella pecosensis sp. nov. Female holotype. (a) Antennule (dorsal view); (b) antenna (dorsal view); (c) labrum; (d) mandible; (e) maxillule; (f) maxilla; (g) uropod.

Figure 3. Montanabathynella pecosensis sp. nov. Female holotype. (a) Thoracopod I; (b) thoracopod II; (c) thoracopod II; (d) thoracopod IV; (e) thoracopod V; (f) thoracopod VI; (g): thoracopod VII; (h) thoracopod VIII (latero-caudal view); (i) furca (dorsal view).