Yprezethinus, PARKER, 2022
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publication ID |
https://doi.org/ 10.11646/palaeoentomology.5.5.6 |
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publication LSID |
lsid:zoobank.org:pub:1665808E-F970-48D3-B35D-2FB684E79FA3 |
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DOI |
https://doi.org/10.5281/zenodo.7383838 |
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persistent identifier |
https://treatment.plazi.org/id/2DEC8AE3-3EBA-4791-A08E-AFDAD243E43A |
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taxon LSID |
lsid:zoobank.org:act:2DEC8AE3-3EBA-4791-A08E-AFDAD243E43A |
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treatment provided by |
Plazi |
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scientific name |
Yprezethinus |
| status |
gen. nov. |
Yprezethinus gen. nov.
urn:lsid:zoobank.org:act:2DEC8AE3-3EBA-4791-A08E-AFDAD243E43A
Type species. Yprezethinus grimaldii sp. nov. here designated.
Etymology. The generic name is a combination of “Ypresian” and Zethinus Raffray , a Recent bythinoplectine genus to which the new taxon is phylogenetically close.
Diagnosis. The new genus, Yprezethinus , and its single species, Y. grimaldii , can be distinguished from all other Pselaphinae by the following combination of characters: (1) Head laterally excavate, with fossae extending from clypeus to anterior margin of eye; capable of holding retracted maxillary palpi; (2) antenna 11-segmented with enlarged ovular club formed from tightly appressed antennomeres 10 and 11; (3) maxillary palpomere 3 approximately twice as long as wide, ~2/3 palpomere 2 length, bearing narrow, elongate, apically globose tubercle; (4) maxillary palpomere 4 shorter than 3, rounded-conical,bearing narrow, apically globose tubercle (similar to that of palpomere 3), as well as prominent apical pseudosegment; (5) procoxae and metacoxae contiguous; (6) tarsi seemingly 2-segmented, with short first visible segment (probable composite of tarsomeres 1 and 2) and long second visible segment (probable tarsomere 3); and (7) all tarsi with single claws.
Description. Body length: ~ 0.8 mm. Body form relatively flattened and elongate (“euplectite body form” sensu Parker, 2016a) ( Fig. 1A View FIGURE 1 ).
Head
Head transverse, with prominent frontal rostrum extending from clypeus to anterior margins of eyes (rostrum challenging to visualize in the holotype Tad-130 but discernable with specimen in dorsal view). Lateral margins of head deeply excavate, with large dorsal fossae that extend either side of frontal rostrum to anterior margins of eyes ( Fig. 1B View FIGURE 1 ). Antennae mounted on underside of frontal rostrum. Antennae composed of 11 antennomeres; antennal clubs formed from tightly appressed antennomeres 10 and 11, separation of these segments observable as a narrow groove encircling the club ( Fig. 1C View FIGURE 1 ; “ sillon annulaire ” sensu Coulon, 1989). Maxillary palpi 4-segmented with conspicuous additional 5th apical pseudosegment ( Fig. 1B View FIGURE 1 , APs). Maxillary palpomere 3 enlarged, longer than palpomere 4. Both palpomeres 3 and 4 bearing narrow, elongate, apically globose tubercles on dorsal faces ( Fig. 1B, D View FIGURE 1 ). Maxillary palpi capable of retracting into lateral excavations of head. Head venter with median gular sulcus.
Thorax
Prothorax approximately as wide as long; subequal in width to head. Prothoracic morphology largely occluded. Pterothorax ~1.7× longer and ~1.3× wider than prothorax. Dorsal and ventral fovea are mostly indiscernible in Tad-130, but mesoventrite bearing possible lateral mesocoxal fovea (LMCF) following the foveal system of Pselaphinae from Chandler (2001). Apparent carina extending from mesocoxal cavity to lateral margin of mesoventrite.
Abdomen
Abdomen approximately equal in width to pterothorax and ~1.3× pterothorax length. Dorsal view of abdomen occluded, but five tergites (IV–VIII) visible. Tergites IV–VI subequal in length and width; VII ~ 1.2× longer than VI, narrowing posteriad; VIII ~ 0.5× shorter than VII, narrowing to abdominal apex. Distinct paratergites present on at least tergites V–VII (those on IV likely present but occluded). Six sternites clearly visible (III– VIII) ( Fig. 1A View FIGURE 1 ); entire apical margin of sternite III visible between and laterally to metacoxae.
Legs
Procoxae and mesocoxae projecting ventrally, contiguous at midline. Metacoxae relatively flat and broadly conical, contiguous at midline, projecting posteriorly ( Fig. 1E View FIGURE 1 ). Trochanters of all legs short such that apex of coxa sits adjacent to base of femur. Tarsi with two visible tarsomeres; first visible tarsomeres very short ( Fig. 1F View FIGURE 1 ).
Elytra and flight wings
Taxonomic characters of the elytra are mostly occluded in Tad-130, but putative humeral carina present. Flight wings present.
Remarks. Yprezethinus belongs to the tribe Bythinoplectini based on its possession of the following combination of characters: (1) head with prominent frontal rostrum; (2) margins of head anterior to eyes deeply excavate, capable of accommodating the retracted maxillary palpi ( Fig. 1B View FIGURE 1 ); (3) complex maxillary palpi, with palpomere 3 subequal to or longer than 4 (3 longer than 4 in Yprezethinus ) ( Fig. 1B View FIGURE 1 ); (4) contiguous metacoxae ( Fig. 1E View FIGURE 1 ), a plesiomorphic state in Pselaphinae , seen in the supertribes Faronitae and Euplectitae (the latter including Bythinoplectini ); (5) tarsi composed of 2 visible segments ( Fig. 1F View FIGURE 1 ; Coulon 1989) argued that the first visible tarsomere is actually composed of the dorsum of morphological tarsomere 1 and the venter of morphological tarsomere 2); (6) tarsi with single claws ( Fig. 1F View FIGURE 1 ). Within Bythinoplectini , Yprezethinus is placed within the subtribe Bythinoplectina on account of the lateral margins of the head being completely excavate, from clypeus (below the antennal insertions of the frontal rostrum), extending posteriorly to the eyes ( Coulon, 1989; Chandler, 2001).
To my knowledge, Yprezethinus is the first described fossil representative of Bythinoplectini . According to Coulon’s (1989) generic revision of Bythinoplectini , Yprezethinus belongs within informal “Section V” of this tribe, a group of eight genera distributed in the Neotropical and Afrotropical ecozones that all possess maxillary palpomeres 3 and 4 with narrow, elongate, apically globose tubercles—a putative synapomorphy ( Fig. 1B, D View FIGURE 1 ). Within Section V, Yprezethinus appears to be extremely close to a putatively monophyletic group of similar genera centered on Zethinus Raffray (herein the “ Zethinus -group”). For comparison to extant Zethinus - group character states, confocal images of the cephalic morphology of two species of Zethinus are shown in Figure 2 View FIGURE 2 . Zethinus illustrates clearly the laterally excavate head of the subtribe Bythinoplectina , in which the antennae are mounted on a frontal rostrum, below which the maxillary palpi can be fully retracted into large fossae ( Fig. 2A–C View FIGURE 2 ). Zethinus also exemplifies the characteristic Section V maxillary palp morphology, with palpomeres 3 and 4 bearing elongate tubercles ( Fig. 2D View FIGURE 2 ). Genera within the Zethinus -group are distinguished from the remaining Section V Bythinoplectini genera by the morphology of the antennal club, which is spherical or ovoid and composed of the apical-most two antennomeres that are tightly appressed hemispheres ( Fig. 2A View FIGURE 2 ; note that in Zethinus species, the apical two antennomeres are 7 and 8). Yprezethinus possesses similar antennal club morphology ( Fig. 1C View FIGURE 1 ). Yprezethinus is therefore placed into crowngroup Bythinoplectini , and the Zethinus -group of Section V specifically.
Importantly, Zethinus -group genera possess a maximum of nine antennomeres ( Dichozethinus Jeannel has eight antennomeres; Zethinus Raffray and Pseudozethinus Coulon both have nine). Yprezethinus is therefore distinguished from these other genera by its possession of 11 antennomeres—the plesiomorphic condition in Pselaphinae ( Chandler, 2001; Parker, 2016a). Hence, I hypothesize that although Yprezethinus sits within the bythinoplectine crown, it is a stem-lineage of the Zethinus -group, which has not undergone any of the antennomere fusions or losses characteristic of crowngroup members of this putative clade. If Section V bythinoplectines as a whole form a monophyletic group, then the genus Hendecameros Comellini may represent an early-branching lineage: this taxon possesses the plesiomorphic character states of 11-segmented antennae and distinct (non-appressed) antennomeres 10 and 11 ( Coulon, 1989). I speculate that Yprezethinus may capture a transitional form between a Hendecameros- like ancestor and Recent Zethinus -group genera, in which antennomeres 10 and 11 show the derived state of appression, but no reduction in antennomere number has yet occurred.
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.