Acanthoniscus Gosse 1851
Creators: name: Rodríguez-Cabrera, Tomás M.
name: de Armas, Luis F.
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Isopoda
Delatorreiidae
Acanthoniscus

description: Genus Acanthoniscus Gosse, 1851
(Figs. 1–8)
Acanthoniscus White, 1847: 99 (Nomen nudum). — Schomburgk, 1848: 658 (Nomen nudum).
Acanthoniscus Gosse, 1851: 65.
Acanthoniscus Kinahan,1859:197–198,plate200–201. — Budde-Lund, 1879: 5. — Budde-Lund, 1885: 241.— Richardson, 1901:562, 569.— Richardson, 1905: 636–637 (repeated the description of Kinahan, 1859). — Richardson, 1909: 432. — Budde-Lund, 1910: 11. — Arcangeli, 1927: 135. — Van Name, 1936: 401–402. — Clark and Presswell, 2001:154. — Schmalfuss, 2003: 4. — Schmidt and Leistikow, 2004: 4. — Boyko et al., 2008.
Type species. Acanthoniscus spiniger Gosse, 1851, by monotypy.
Other species included. Acanthoniscus richardsonae sp. nov.
Diagnosis (emended). Body of fragile general appearance, with endoantennal conglobation ability involving all body segments (Figs. 2–4); coxal plates enlarged and fused with tergites, with more or less complex inner tooth-like processes forming cleft or schisma (except coxal plate 4, which lacks tooth-like processes) (Figs. 2C, 4F–G). Cephalothorax with upper margin of frontal shield irregular, forming lateral and median lobes (not antennal lobes); profrons with wide shallow depressions on each side divided by very low median ridge holding second antennae; dorsal surface with small spiniform tubercles and/or medium-sized, club-like spines (Figs. 2, 4). Eyes composed of 16 ommatidia (Figs. 2, 4). Pereon tergites covered with long, slightly sinuous dorsolateral spines and smaller posteromedian and lateral spines, sometimes with paramedian spiniform tubercles; with lateral spiniform tubercle near anterior margin of pereonites 2–7 and directed forward, as part of outer structures involved during conglobation;epimera1enlarged,with posterior angle and outer margin broadly rounded, anterior angle more acutely produced; epimera 2–7 enlarged and with acutely produced outer angle; male sternite 7 simple, without bilobed caudal process (Figs. 2–4, 8). Pleon tergites 3–4 with pair of small posteromedian spines or spiniform tubercles; epimera of pleonites 3–5 enlarged and acutely produced (Figs. 2–4). Pleotelson “hourglass-shaped,” with basal part wider than distal part, distal margin broadly convex and ending in 2 triangular projections separated by notch, basal half with 2 dorsal spines 1.3–1.5 times as long as pleotelson, widely surpassing its distal margin and uropod exopodite tip (Figs. 2, 4, 8). Uropod sympodite asymmetric and dorsoventrally f lattened, filling gap between pleotelson and fifth pleon epimera, broader at base, medial margin deeply concave and irregular, with inner lobe above and basal with respect to insertion point of exopodite which, together with wide transversal dorsal furrow, engaging with pleotelson, outer margin from slightly to widely convex, and medial-posterior angle acutely produced (more or less sharp-pointed); uropod endopodite laterally compressed (outer surface concave to engage with medial margin of uropod sympodite), inserted near base of sympodite and not surpassing distal margin of pleotelson, but it may surpass posterior margin of uropod sympodite (e.g., A. spiniger); uropod exopodite extremely long (longer than sympodite), narrow, and slightly curved (stick-shaped), inserted on medial margin of sympodite (visible dorsally and ventrally) and widely surpassing posterior margin of sympodite (by 60–80% of its length) and posterior margin of pleotelson (Figs. 2, 4, 8). Pereiopod dactylus with simple, straight to curved dactylar seta, inner claw, sickle-shaped ungual seta (shorter than inner claw and not surpassing basal half of outer claw length), and other smaller setae similar to aesthetascs of antennae (Fig. 5I, J). First antenna 3-jointed (Fig. 5E–F). Second antenna long and slender, sum of its articles being 2.5 times width of cephalothorax, flagellum 2-jointed and with 2 groups of aesthetascs on distal article (Fig. 5A–D). Pleopods with single spiracle lungs (Fig. 7).
Distribution. Jamaica (Fig. 1).
Comparisons. The genus Acanthoniscus very much resembles other specialized(spiny) forms of Old World Armadillidae, such as the genera Calmanesia Collinge, 1922, Echinodillo Jackson, 1933, Laureola Barnard, 1960, Pseudolaureola Kwon, Ferrara and Taiti, 1992, and Tridentodillo Jackson, 1933 (e.g., Collinge, 1922; Jackson, 1933; Barnard, 1958; 1960a; 1960b; Green, 1963; Vandel, 1977; Kwon et al., 1992; Dalens, 1998). However, Acanthoniscus can be readily distinguished from all those other genera by the combination of its unique pleotelson-uropod pattern and its spine arrangement (see Diagnosis above).
Remarks. Schmalfuss (2003) tentatively listed Acanthoniscus and its type species, A.spiniger, under the family Delatorreidae (it is still listed as such by Boyko et al., 2008, an on-line database), probably because several species in this family (genera Pseudarmadillo de Saussure, 1857 and Cuzcodinella Armas and Juarrero de Verona, 1999) have the body covered with long and sharp-pointed spines similar to Acanthoniscus (see Vandel, 1973a; Armas and Juarrero de Varona, 1999; Juarrero de Varona and Armas, 2003a; 2003b; Armas and Rodríguez-Cabrera, 2016). However, Delatorreidae strongly differ from Armadillidae in the cephalothorax (presence of antennal lobes and furrows in Delatorreidae), number of eye ommatidia (six in Delatorreidae), and the uropod pattern (exopodite very short and inserted on the inner corner of the posterior margin of the sympodite in Delatorreidae) (Armas and Juarrero de Varona, 1999; Schmidt, 2003).
The general pattern of the uropod in Acanthoniscus led Schmidt and Leistikow (2004: 4) to suggest that it might belong to the heterogeneous family Scleropactidae (Schmidt, 2002; 2003; 2007; 2008). The flagellum of the second antenna may be either 2-jointed or 3-jointed in Scleropactidae (Schmidt, 2003; 2007; 2008). In Scleropactidae and Acanthoniscus the uropod exopodite is inserted on the medial margin of the sympodite and widely surpasses its posterior margin(see Discussion for other divergent forms in Armadillidae; Fig. 8), but the pleotelson in Scleropactidae is subtriangular and much shorter than the uropod sympodite, with the uropod endopodite widely surpassing the distal margins of both the uropod sympodite and the pleotelson.
In a key to the genera of the Oniscidae, Richardson (1901: 562) included Acanthoniscus as having “the flagellum of the external antennae quadri-articulate.” However, this information must be erroneous, since the f lagellum of the second antenna in this genus was unknown until the present contribution, as stated also by Kinahan (1859: 198) and Richardson (1909: 432).
description: Published as part of Rodríguez-Cabrera, Tomás M. & de Armas, Luis F., 2023, Taxonomy of the enigmatic genus Acanthoniscus Gosse, 1851 (Isopoda: Oniscidea: Armadillidae), from Jamaica, with the description of a new species, pp. 1-25 in Nauplius (e 2023006) (e 2023006) 31 on pages 3-6, DOI: 10.1590/2358-2936e2023006, http://zenodo.org/record/10716764