Speleonectes fuchscockburni, Neiber, Marco T., Hansen, Finja C., Iliffe, Thomas M., Gonzalez, Brett C. & Koenemann, Stefan, 2012

Neiber, Marco T., Hansen, Finja C., Iliffe, Thomas M., Gonzalez, Brett C. & Koenemann, Stefan, 2012, Molecular taxonomy of Speleonectes fuchscockburni, a new pseudocryptic species of Remipedia (Crustacea) from an anchialine cave system on the Yucatán Peninsula, Quintana Roo, Mexico, Zootaxa 3190, pp. 31-46 : 35-41

Speleonectes fuchscockburni n. sp.

( Figs. 2–6 )

S. tulumensis —Stemme et al. 2010: 8, fig. 1B. S. n. sp. X — Neiber et al. 2011: e19627.4, fig. 2; e19627.10, tab. 1.

Type locality. Cenote Crustacea (20° 46’ N, 86° 56’ W), near Puerto Morelos, Quintana Roo, Mexico.

Material examined. Holotype (Zoological Museum Hamburg ( ZMH) K- 43034) ca. 12 mm, 35 trunk segments; collected by T. M. Iliffe, 15 August 2009. Paratype 1 (study collection of S. Koenemann (SK) 09-003.1) ca. 12 mm, 30 trunk segments; collected by T. M. Iliffe, 17 August 2009. Paratype 2 (SK 09-005); identified as Speleonectes tulumensis in Stemme et al. 2010; ca. 16 mm, 35 trunk segments; collected by T. M. Iliffe, 17 August 2009. Paratype 3 (SK 09-004.1) approx. 8 mm, 29 trunk segments; collected by T. M. Iliffe, 15 August 2009. Paratype 4 ( ZMH K- 43035) ca. 4.5 mm, 17 trunk segments; collected by T. M. Iliffe, 11 August 2009. Paratype 5 (study collection of M. T. Neiber (MN) 2011-001) ca. 9.3 mm, 28 trunk segments; collected by B. C. Gonzalez, 2011. Paratypes 1 and 2 were dissected for the morphological descriptions; the anal somite of paratype 2 was used for DNA extraction. Paratype 3 was used for SEM.

Etymology. The new species name is inspired by the family of Olivier Fuchs of Cockburn, whose financial support through a BIOPAT sponsorship program contributes to a continuation of our research on Remipedia.

Diagnosis. Speleonectes fuchscockburni is a slender and comparatively small species ( Fig. 2 ), up to 16 mm in length; largest specimens with 35 trunk segments. All appendages sparsely setose. Terminal horseshoe-like claw complex of maxillae composed of 10–12 deeply incised denticles ( Figs. 5 B, C, F; 6B).

Description. The description of S. fuchscockburni is based on the holotype, paratype 1, and paratype 2.

Head shield ( Figs. 2 ; 3A; 6A) sub-rectangular, with rounded margins, tapering apically. First trunk segment partially covered by head shield, considerably smaller than subsequent trunk segments. Pleural tergites about four times wider than long, with rounded margins in anterior trunk region, becoming sub-trapezoidal in mid and posterior trunk. Sternites small, rounded; sternal bars isomorphic, sub-linear.

Female gonopores developed as semicircular, papilliform structures on the inner (posterior) protopodal surfaces of the seventh trunk limbs. Lobate male gonopores on trunk limbs 14 comparatively small and inconspicuous.

Frontal filaments each with slender medial process ( Figs. 4 C; 6A), reaching approximately one third of the length of main filament.

Antennule ( Fig. 4 A): Peduncular pad with a cluster of relatively few, soft, ribbon-like aesthetascs. Dorsal flagellum with 11–12 articles, about twice as long as head shield; ventral flagellum with 5–6 articles, reaching less than half the length of dorsal flagellum. Articles of both dorsal and ventral flagellum equipped with short, fine setae, and bi- to multiramous compound aesthetascs on distomedial margins.

Antenna ( Fig. 4 B): Proximal segment of protopod with 2 setae, distal segment with 5 setae. Exopod oval, twice as long as distal segment of protopod, with 17 long marginal setae. First segment of endopod with 3 setae; second segment with 5 setae; third segment with 9–12 setae, arranged in a double row along distal margin. All setae plumose.

Labrum ( Fig. 4 D) with rounded corners, bearing a few fine setae, and an apical field with densely packed fine setae that surround a funnel-shaped cavity equipped with a simple row of small denticles on each side.

Mandible ( Fig. 4 E–G): Molar process oval, equipped with numerous fine setae of unequal length (longest along outer margins). Left incisor process with 4 stout denticles; left lacina mobilis with 3 acuminate denticles ( Fig. 4 G). Right incisor process with 3 stout denticles; right lacina mobilis with 3 denticles (one of which broad, tricuspid) ( Fig. 4 F).

Maxillule ( Figs. 5 A, D–E; 6A): Endite of first (basal) segment long and slender, with a single stout apical seta and 5–6 slender sub-apical setae, one of which serrated ( Fig. 5 D). Endite of second segment rather long and broad, with 9 mostly short and stout setae on distal margin that are partially arranged in a double row, and 2 pairs of subapical setae (the proximal pair very short, the distal pair long and slender). Third segment with a robust, conical endite, bearing 2 robust and bluntly serrated setae ( Fig. 5 E), and a pair of slender, simple setae on distal margin. Lacertus (fourth segment) very robust, triangular in shape, much longer than segments 1–3, medial margin expanded, with tapering, cone-shaped endite, bearing 2 robust serrate setae, accompanied by 5 simple slender setae. Fifth segment slightly shorter and less broad than lacertus, with a cluster of few setae of unequal length on distomedial margin. Sixth segment very short, with several clusters of setae. Terminal claw long, with a medioproximal cluster of setae.

Maxilla ( Figs. 5 B, F; 6B): Much more slender than maxillule. First endite of first segment with 3 lobate endites, each equipped with different arrangements of 1 short stout seta, 1 long stout arcuate seta (absent on first endite), and several simple setae of unequal length. Endite of second segment broad and rounded, with 1 short stout and 3 long simple setae. Lacertus (third segment) long, medial margin slightly expanded, with 5 simple setae. Fourth segment shorter than lacertus, mediodistal margin distinctly expanded, with 2 setae. Fifth segment shorter than fourth segment, sub-quadratic, distomedial margin with 1 short and 2 long simple setae. Sixth segment slightly longer than fifth segment, with a few setae on distomedial and distoposterior margins. Terminal claw forming semicircular arch (horseshoe-type) composed of 10–12 deeply incised denticles flanked by a single stout denticle posteriorly; thumb-like pad opposing the claw complex well developed, bearing approximately 9 filamentous, flexible setae ( Figs. 5 F; 6B).

Maxilliped ( Fig. 5 C): Longer than maxilla. Proximal segments 1–3 with convoluted joint complex, bearing a few medial setae each. Lacertus (fourth segment) long, medial margin even, slightly expanded, bearing four setae on proximal corner. Fifth segment slightly shorter than lacertus, distomedial margin expanded, with several setae of unequal length. Sixth segment slightly shorter than previous segment, with 4 long setae on mediodistal margin. Seventh segment shorter than sixth segment, with 2 long and 2 short setae on distomedial margin, and several short setae on posterior margin. Eighth segment somewhat longer than seventh segment, bearing several setae on distomedial and distoposterior margins. Terminal claw similar to that of maxilla. Segments 1–8 exclusively with simple setae.

Trunk limbs: Protopod without setae, carrying two paddle-shaped branches, the four-segmented endopod and the three-segmented exopod. Endopod slightly shorter and narrower than exopod (except on first trunk limb pair). Trunk limbs largest in mid trunk region, becoming gradually smaller towards the posterior portion of the trunk. Trunk limbs of first postcephalic segment reduced ( Fig. 3 B), i.e., distinctly smaller than following trunk limbs. Arrangement and number of setae on first trunk limbs similar to those of larger trunk limbs.

Larger trunk limbs (represented by trunk limb 14, Fig. 3 D) with first exopodal segment bearing 1–4 long plumose setae on distolateral margin (in relation to limb axis), and up to 4 serrate stout setae ( Fig. 3 C) on distolateral corner. Second exopodal segment equipped with 3–6 and 3–5 long plumose setae on distolateral and distomedial margins, respectively; distolateral corner with 3–6 stout serrate setae, distomedial corner bearing 1 stout serrate seta. Third segment oval, longer than second segment, with several long plumose marginal setae. First endopodal segment with 1 short plumose seta on distolateral margin. Second endopodal segment with 1–3 long plumose setae and 1–2 stout serrate setae on distolateral margin and corner; distomedial corner with 2–3 stout serrate setae. Outer margin of third endopod segment with 3–6 long plumose setae and 1–3 stout serrate setae on distolateral corner; inner margin with up to three long plumose setae and 2–5 stout serrate setae on distomedial corner. Fourth segment slightly longer than second segment, with several long plumose setae along margin.

Anal segment ( Fig. 3 E) distinctly longer than wide, caudal rami long and slender, three times the length of anal segment, with few fine lateral and apical setae.

Morphological affinities and biogeographic distribution. With respect to morphological characters, the closest relatives of S. fuchscockburni are S. tulumensis and S. cf. tulumensis , both from Mexico. Speleonectes cf. tulumensis and S. fuchscockburni occur in different sections of the Cenote Crustacea cave system at the northeastern coast of the Yucatán Peninsula, while S. tulumensis has been reported from a number of caves (e.g., Cenote Carwash ( Yager 1987b), Cenote Najaron ( Yager 1987b), and Cenote Mayan Blue ( Pohlman et al. 1997)) further south on the same coast (see Fig. 1A ). The northern-most caves from which S. tulumensis has been reported, Cenote Ponderosa (= Cenote Eden; 20° 29' N, 87° 15' W) and Cenote Chac Mool (20° 30' N, 87° 14' W) (see e.g., Neiber et al. 2011), are separated from Cenote Crustacea by a gap of approximately 45 km.

Speleonectes cf. tulumensis is the only remipede that has been found in high abundances. It inhabits cave passages on the eastern side of Cenote Crustacea. The new species S. fuchscockburni has been collected from newly discovered cave passages on the opposite or western side of Cenote Crustacea.

At a first glance, all three speleonectids from the Yucatán Peninsula are morphologically quite similar. Speleonectes cf. tulumensis appears generally longer and sturdier than S. tulumensis , while S. fuchscockburni n. sp. is smaller than the former two, sharing the same diagnostic features that distinguish the speleonectids from the Yucatán Peninsula. These include the large cone-shaped endite on maxillular segment four, the slender and sparsely setose maxillae and maxillipeds, and the distinct caudal rami, reaching more than 2.5 times the length of the anal somite.

Speleonectes fuchscockburni can be distinguished from S. tulumensis and S. cf. tulumensis by the dentition of the terminal claw of the maxilla. Speleonectes fuchscockburni n. sp. possesses 10–12 deeply incised denticles ( Figs. 5 F; 6B). In contrast to this, S. tulumensis and S. cf. tulumensis are equipped with more than 25 only slightly incised denticles.

In general, adult specimens of S. tulumensis (27.5–30.2 mm, 36–38 trunk segments; Yager 1987b; Yager 1994a, b; Felgenhauer et al. 1992; Yager & Carpenter 1999; Koenemann et al. 2006) and S. cf. tulumensis (20.6– 40.8 mm, 35–42 trunk segments; Koenemann et al. 2006) are larger than adult specimens of S. fuchscockburni (12– 16 mm, 30–35 trunk segments).

In S. tulumensis , the ventral flagellum of the antennule has 9–10 segments, while in S. fuchscockburni , it consists of only 5–6 segments ( Fig. 4 A). The dorsal flagellum is composed of 11–12 segments in both species. The ventral flagellum of the antennule of S. tulumensis reaches about one half to two thirds of the length of the dorsal flagellum ( Yager 1987b; Felgenhauer et al. 1992). In contrast, the ventral flagellum of the antennule of S. fuchscockbumi reaches only about 40% of the length of the dorsal flagellum.

In comparison, the prehensile limbs of S. tulumensis appear to be longer and more slender than those of S. fuchscockburni , which are rather compact in appearance. This impression is also confirmed by the relatively closer arrangement of the maxillular and maxillary endites in the new species. The endite of the first segment of the maxillule is equipped with six setae (a very stout apical seta and five fine sub-apical setae) in S. fuchscockburni , whereas the first endite of the maxillule of S. tulumensis bears a stout apical and six fine sub-apical setae. The endite of the fourth maxillular segment is triangular in outline with a distinctly expanded medial margin in S. fuchscockburni . The same segment in S. tulumensis is relatively longer and narrower. The second endite of the first maxillar segment is equipped with two setae in S. fuchscockburni , but bears only a single long seta in S. tulumensis . The fourth maxillar segment of the new species is distinctly expanded in its mediodistal portion. Such an expansion is not observed in S. tulumensis , so that this segment is comparatively narrower than in S. fuchscockburni . It is also notable that the antennule, the prehensile appendages and also the trunk limbs of S. fuchscockburni are somewhat less setose than the corresponding appendages of S. tulumensis ( Yager 1987b; Felgenhauer et al. 1992).

Interestingly, the first trunk limb pair of paratype 2 (16 mm) is approximately twice as large as that of paratype 1 (12 mm), although the difference in length of the two specimens only amounts to 4 mm.

Figures

FIGURE 2. Speleonectes fuchscockburni n. sp. Living animal. A, habitus. B, head region. Photographs by Brett C. Gonzalez.

FIGURE 3. Speleonectes fuchscockburni n. sp. A, holotype, B – E, paratype 1 (12 mm). A, dorsal view of head shield and trunk segments 1 – 4. B, natatory limb of trunk segment 1. C, short serrate corner seta of trunk limbs (freehand drawing). D, natatory limb of trunk segment 14. E, anal somite with caudal rami. Scale bars: A = 0.3 mm; B – D, E = 0.1 mm. Continuous lines were used to outline articulated structures such as segments and setae, dotted lines to indicate covered structures, and dashed lines for the reconstruction of structures that were damaged during dissection.

FIGURE 4. Speleonectes fuchscockburni n. sp. A – B, D, paratype 1 (12 mm). C, E – G, paratype 2 (16 mm). A, antennule. B, antenna. C, frontal filament. D, labrum. E, right mandible. F, processus incisivus (left) and lacina mobilis (right) of right mandible. G, processus incisivus (left) and lacina mobilis (right) of left mandible. Scale bars: A – E = 0.1 mm. See Fig. 3 for details regarding different line types.

FIGURE 5. Speleonectes fuchscockburni n. sp. A – F, paratype 1 (12 mm). A, maxillule. B, maxilla. C, maxilliped. D, slender serrate seta of endite of maxillular segment 1. E, stout, rasp-like seta of endite of maxillular segment 3. F, terminal claw complex of maxilla. Scale bars: A – C = 0.1 mm. See Fig. 3 for details regarding different line types.

FIGURE 6. Speleonectes fuchscockburni n. sp. A – B, paratype 3, SEM micrographs. A, ventrolateral view of head. B, terminal claw complex of maxilla. Adr = antennule, dorsal ramus; Avr = antennule, ventral ramus; d = denticles of terminal claw; ff = frontal filaments; hs = head shield; htc = horseshoe-type terminal claw; mx = maxilla; mxl = maxillule; mxp = maxilliped; sp = sternal plate; tp = thumb-like pad with setae.

FIGURE 1. A, map of the northeastern region of the Yucatán Peninsula (shown on insert), with locations of cenotes from which Mexican speleonectids have been reported: 1 = Cenote Crustacea; 2 = Cenote Chac Mool; 3 = Cenote Ponderosa; 4 = Cenote Tajama Ha; 5 = Cenote Carwash; 6 = Cenote Vaca Ha; 7 = Cenote Temple of Doom; 8 = Cenote Najaron; 9 = Cenote Mayan Blue. B, map of the Sistema Crustacea cave showing the main cenote entrance pool, underwater cave passages, and the approximate regions within the cave inhabited by: 1 = S peleonectes tulumensis Yager, 1987 b; 2 = S. fuchscockburni n. sp.