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. 2026 Jan 22:14:e20594.
doi: 10.7717/peerj.20594. eCollection 2026.

Insights on the enigmatic millipede order Siphoniulida (Myriapoda, Diplopoda): a new species bearing ozopores and its phylogenetic implications

Ernesto Recuero  1 , E Karen López-Estrada  2   3 , Curt W Harden  4   5
Affiliations

Insights on the enigmatic millipede order Siphoniulida (Myriapoda, Diplopoda): a new species bearing ozopores and its phylogenetic implications

Ernesto Recuero et al. PeerJ. .

Abstract

The millipede order Siphoniulida is one of the most enigmatic and rare groups within Diplopoda, with fewer than 10 complete specimens known from two extant species and two amber fossils. This study presents the discovery of a new species, Siphoniulus porosus sp. nov., from a tropical montane cloud forest in Veracruz, Mexico, representing the highest elevation record for the order in the New World. We obtained the first molecular data for the order, a DNA barcode sequence of the Cytochrome C Oxidase I (COI). Detailed morphological analysis using scanning electron microscopy (SEM) showed that, unlike previously described species, Siphoniulus porosus sp. nov. exhibits ozopores, challenging the current understanding that Siphoniulida lack these structures. Phylogenetic analyses using both Maximum Parsimony and Bayesian methods were conducted, including a reassessment of existing morphological data considering the presence of ozopores in Siphoniulida as the ancestral state for this character. The results suggest a phylogentic position within the subterclass Eugnatha, though relationships in this group are not resolved. This discovery indicates a potentially greater diversity of Siphoniulida in the Neotropical Region and highlights the need for further exploration of montane cloud forests to discover additional species.

Keywords: Cytochrome C Oxidase I; Dark taxa; Helminthomorpha; Montane cloud forest; Morphology; Phylogeny; Taxonomy.

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Conflict of interest statement

The authors declare there are no competing interests.

Figures

Figure 1
Figure 1. Map showing the known distribution of neotropical Siphoniulida, and associated forest ecosystems in Mexico; Siphoniulus porosus sp. nov (yellow star), S. neotropicus (black square), S. aff. neotropicus (red circles).
Map Source Credit: QGIS v.3.30 (http://qgis.org/) using a publicly available layer of potential vegetation of Mexico (Rzedowski, 1990), obtained from CONABIO’s Geoportal (dataset ID: vpr4mgw, available at: http://geoportal.conabio.gob.mx/metadatos/doc/html/vpr4mgw.html), CC BY-NC 2.5 MX.
Figure 2
Figure 2. Maximum parsimony tree showing obtained phylogenetic relationships among Diplopoda orders.
Maximum parsimony 50% majority-rule consensus tree of 1,000 bootstrap replicates, showing phylogenetic relationships among Diplopoda orders. Numbers above branches indicate unweighted MP bootstrap values/weighted MP bootstrap values/Bayesian posterior probabilities.
Figure 3
Figure 3. Siphoniulus porosus sp. nov., general habitus of female holotype (CNAC).
(A) Whole specimen, lateral view. (B) Anterior part of body, lateral view. (C) Anterior part of body, ventral view. (D) Posterior part of body, lateral view. (E) Posterior part of body, ventral view. (F) Midbody segments, ventral view. (G) Midbody rings, dorsal view. Scale bars = one mm.
Figure 4
Figure 4. Siphoniulus porosus sp. nov., SEM images of female holotype (CNAC).
(A) Head, antennae and anterior rings, anterior-ventral view. (B) Head, antenna and anterior rings, lateral view. (C) Right antenna, frontal view. (D) Antennomeres 5-7, frontal view. (E) Right antenna, lateral view. (F) Laminar sensilla on antennomere 6. (G) Clypeal region, showing button-like sensilla, and first leg pair. (H) Close-up of a button-like sensillum on clypeal region.
Figure 5
Figure 5. Siphoniulus porosus sp. nov., SEM images of female holotype (CNAC).
(A) anterior part of body, lateral view (black arrow indicates position of first ozopores); (B) close-up of ozopore on ring 8; (C) midbody rings, lateral view; (D) anterior part of ring 16 on lateral view, showing prozonite, metazonite and ozopores; (E) close-up of ozopore on ring 16; (F) Internal view of a midbody ring wit soft tissues digested (white arrows indicate the suture-like structure in the leg tarsi); (G) close-up of ozopore on midbody ring, internal view.
Figure 6
Figure 6. Siphoniulus porosus sp. nov., SEM images of female holotype (CNAC).
(A, B) ventral view of midbody rings showing walking legs and sternites (white arrows indicate the suture-like structure in the leg tarsi); (C) terminal rings, dorsal view; (D) terminal rings, ventrolateral view; (E, F) close-up of spinnerets; (G) second leg pair.
See this image and copyright information in PMC

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