Cteniobathynella boutini Camacho and Lagnika, 2024

Camacho, A. I., Mas-Peinado, P., Lagnika, M., Martin, P., Dorda, B. A. & Rey, I., 2024, First record of Bathynellacea (Crustacea: Malacostraca) in Benin (West Africa): two new species and their phylogenetic position within the Parabathynellidae family, Journal of Natural History 58 (17 - 20), pp. 570-602 : 585-589

Cteniobathynella boutini Camacho and Lagnika sp. n.

( Figures 5 and 6 )

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Material examined

Type locality. Modern well ( BEN128 ) (9.72573°N, 1.84716°E, 387 m. alt.; WGS84), Moné , Djougou, Donga, Benin (West Africa), 16/08/2018 (one male and one female); collected by M . Lagnika, J . Hotepko and P. Martin.

Type material. Holotype male ( MNCN 20.04 /20,701), allotype female ( MNCN 20.04 / 20,702), type series comprised of the two specimens, each on individual slides, and two DNA samples as the DNA types ( MNCN / ADN 54871 male and MNCN / ADN 54872 female).

Description

Body. Total length of holotype 0.84 mm, and of allotype 0.90 mm. Body elongated, segments widening towards the posterior end. Head one-third longer than wide. All drawings are of the (male) holotype except one figure of the antenna of the allotype (female).

Antennule. ( Figure 5 (a)). Six-segmented; length of first three articles as long as the other three articles combined; sixth article as long as the first and second articles but only a third as wide; inner flagellum rectangular, large, half the height of the fourth article; setation as in Figure 5a ; article three with only one smooth seta; article five with two terminal aesthetascs of different length; sixth article with three aesthetascs, one shorter than the other two. AI longer than the AII.

Antenna. ( Figure 5 (b)). Five-segmented; almost as long as the first five articles of AI; first two articles are similar and very short; the last three are long and of equal length; last article with three setae: two smooth and one plumose; setal formula: 0/0 + 1/1 + 0/1 + 0/3(1).

Antenna of the allotype. ( Figure 5 (c)). Similar to the holotype’s but without a seta on the second article and with four setae on the last article, the outermost one very small and thick, resembling a small spine; setal formula: 0/0/1 + 0/1 + 0/4(1).

Labrum. ( Figure 5 (d)). Distal edge slightly concave, with 12 teeth, the lateral ones slightly larger than the central ones.

Mandible. ( Figure 5 (e)). Pars incisiva with four teeth on the distal part, and a well-developed tooth on the ventral edge; pars molaris with three claws, the two most proximal claws joined and with many fine hairs; mandibular palp one-segmented, inserted very high, at the level of the tooth of ventral edge, with a distal seta that reaches the end of the pars incisiva.

Maxillule. ( Figure 5 (f)). Proximal endite with two long serrulate claws and two smaller claws also with setules; distal endite with five very thin claws with denticles, located on the distal third of MxI, and with three small, unequal sub-terminal smooth setae on the outer distal margin.

Maxilla. ( Figure 5 (g)). Three-segmented; basal article very short, armed with one smooth seta; second article three times as long as wide, with nine setae (4 + 1 on medial region) and a very small third article with one strong terminal claw and two setae. Setal formula: 1/9/2 + 1.

Thoracopods I to VII. ( Figure 6 (a–g)). Well developed, length gradually increasing from I to IV, last three thoracopods similar in length; epipod absent on Th I–III ( Figure 6 (a–c)) but present on Th IV–VII ( Figure 6 (d–f)), small, one-third the length of the basipod; basipod with one smooth seta on the distal inner corner in Th I–VII. Exopod two-segmented, from ThIII to ThVI is about as long as endopod, slightly shorter in TVII; basal article about as long as the first two articles of the endopod, except in ThI and II, where it is slightly shorter; exopod with two barbed setae on the first article, one very long barbed and one plumose seta on the second article, and a group of strong ctenidia at the base of the inner setae; article one 2.5 times as long as article two in all Ths. Endopod four-segmented; first article short, similar in length in all Ths, half as long as articles two and three, which are similar in length and in appearance in all Ths and both with clusters of strong spinules along the inner margin; the fourth article small, with two claws and one smooth seta on Th I and one claw and one seta on the rest of Ths; outer distal seta on second article always plumose; outer small seta on third article of Th I-VII smooth, as a small spine. Setal formula of endopod: Th I, 1 + 0/0 + 1/0 + 1/3(1); Th II–VII, 0 + 0/0 + 1/ 0 + 1/2(1).

Male thoracopod VIII. ( Figure 5 (h–i)). Rectangular; with outer lobe located at the middle of the thoracopod, short and fused with the basipod and with a small rounded distal extension; penial lobes with an extension that reaches the distal end of the basipod with which it is fused; rounded exopod that protrudes beyond the distal end of basipod; the basipod is well developed on the latero-external face, without setae, and with distal end bilobed; endopod similar to exopod, with a smooth long seta.

Pleopods. Absent.

Uropods. ( Figure 6 (h)). Sympod nearly 5 times as long as wide, 2 times as long as the endopod and exopod, which are similar in length; five barbed spines of similar length located in the distal third of the sympod, half the size of the apical spine of the endopod; endopod 3 times as long as wide, with a long apical spine (20% shorter than the endopod) with setules and five setae, two terminal barbed and three latero-external plumose setae, with four groups of strong ctenidia on the dorsal side; exopod with two terminal barbed setae of different lengths.

Pleotelson. A ventro-lateral seta on each side. Anal operculum not protruded.

Furcal rami. ( Figure 6 (i)). Almost square, with three thick barbed spines, the largest of which is the distal one, followed by the middle and then the most proximal one; a membrane with setules at the base of the spines along the distal edge; unequal plumose setae on dorsal side of furcal rami.

Etymology

The species name ‘ boutini ’ is dedicated to our colleague Claude Boutin, who was a pioneer in the study of the underground aquatic environment in Africa, particularly in Benin, where stygofauna were completely unknown before collaborations were initiated under his impetus.

Remarks

The new species Cteniobathynella boutini is, together with C. caparti , one of the smallest species of the genus, measuring less than 1 mm. However, C. boutini sp. n. differs from the other species of the genus in the traits detailed in Table 3 . The new species may or may not have a seta on the second article of AII, which is always present in the rest of the African species, and it has three or four setae on the last article, whereas the other species always have three setae. The new species has a single claw on the last article of MxII, in contrast to the two on the other species. In addition, it has a single seta on the first article, whereas the others have two or none. All species lack an epipod on ThI, but C. boutini sp. n. also does not have one on ThII and ThIII. Regarding the proportions of the articles of thoracopod exopod, the first article is always twice as long as the second in all species. Exopod to endopod article proportions reveal two types of ThI: (1) the first article of the exopod is shorter than the first two articles of the endopod, and the exopod reaches the middle of the third article of the endopod ( C. teocchii , C. calmani , C. capparti and the new species); and (2) the first article of the exopod is the same length as the first two articles of the endopod, and the exopod reaches the middle of the third endopod article (type 2a, C. leleupi ) or is the same length as the first three endopod articles (type 2b, C. bakeri ) (ThI of C. essaumeri has not been described to date). The second type with the two alternative configurations is the one that is repeated in all the other thoracopods: ThII to ThVII of C. teocchii and C. calmani present type 2a, and the rest of the species, including the new one, present the most frequent type, 2b. Males of the new species have a small endopod on ThVIII; in C. leleupi and C. teocchii (the only other species for which ThVIII has been described), the endopod is reduced to two setae. Cteniobathynella boutini sp. n. lacks pleopods like all species of the genus. In the new species, the sympod of the uropod is homonomous with few spines; this is similar to almost all the other species except C. caparti , which has a longer distal spine, and C. essaumeri , which has more than double the number of spines (10–12), all equal in size. The new species has five setae on the endopod of the uropod, whereas the rest of the species only have three or four. The exopod and endopod of the uropod are almost the same length in the new species, as in C. calmani , C. caparti and C. teocchii ; in the other species, the endopod is longer than the exopod. With respect to habitat, most of the African species were found in the interstitial environment of rivers. Only the new species and C. calmani were found in manufactured water well supply.

Figures

Figure 5. Cteniobathynella boutini sp. n. (a,b, d–i) Male holotype. (a) Antennule (dorsal view); (b) antenna (dorsal view); (c) antenna, female allotype (dorsal view); (d) labrum; (e) mandible; (f) maxillule; (g) maxilla (dorsal view); (h) thoracopod VIII (latero-internal view); (i) thoracopod VIII (latero-external view). Scale bars in mm.

Figure 6. Cteniobathynellaboutini boutini sp. n. Male holotype. (a) Thoracopod I; (b) thoracopod II; (c) thoracopod III; (d) thoracopod IV; (e) thoracopod V; (f) thoracopod VI; (g) thoracopod VII; (h) uropod (latero-external view); (i) furcal rami (dorsal view). Scale bars in mm.