Stenosoma Leach, 1814

Santos, Antonio Murias dos, Xavier, Raquel, Zenboudji, Saliha, Branco, Tristao & Branco, Madalena, 2011, Stenosoma stephenseni sp. n. (Isopoda, Idoteidae), from the southwestern Mediterranean, with a note on the nomenclatural status of Synisoma Collinge, 1917, ZooKeys 141, pp. 29-44 : 30-33

Genus Stenosoma Leach, 1814

Stenosoma Leach, 1814: 433.- Leach, 1815: 365.- Samouelle, 1819: 107.- Desmarest, 1823: 374.- Desmarest, 1825: 290.- Latreille, 1829: 139.- Moore, 1839: 294.- Lucas, 1840: 259.- Hope, 1851: 26.- Dollfus, 1894: 5.- Dollfus, 1896: 54.- Gerstaecker, 1901: 218.- Norman, 1904: 444.- Norman & Scott, 1906: 47.- Tattersal, 1911: 230.- Stephensen, 1915: 15.

Leptosoma Risso, 1826: 107 (no type species designated, see text).- Rathke, 1837: 384.- Lamarck, 1838: 270.- Hope, 1851: 26.

Synisoma Collinge, 1917: 750 (type species Stenosoma acuminatum Leach, 1814, by subsequent designation of Kussakin, 1982). Monod, 1923: 97.- Monod, 1925: 70.- Amar, 1957: 74.- Daguerre de Hureaux, 1968: 87.- Naylor, 1972: 46.- Nu nomura, 1974: 6.- Prunus & Pantoustier, 1976: 259.- Kussakin, 1982: 184. Brusca, 1984: 107.- Rezig, 1989: 30.- Ormsby, 1991: 758.- Hedo & Junoy, 1999: 88.- Poore, 2001: 221.- Castellanos & Junoy, 2005: 1461.

Type species.

Stenosoma acuminatum Leach, 1814, by subsequent designation of Kussakin, 1982 (under Article 67.8).

Remarks.

The genus Stenosoma was described by Leach (1814) simultaneously in two different parts of the Brewster’s Edinburgh Encyclopaedia: in the main section “Crustaceology” (p. 404), and in the Appendix which was published as an integral part of that section (pp. 429-434). Leach (1815) also re-described Stenosoma in his popular work "A tabular view of the external characters of four classes of animals, which Linné arranged under Insecta", a reference erroneously cited as the original description by many authors (e.g. Collinge 1917; Kussakin 1982; Junoy and Castelló 2003). In neither of those publications was a type species designated.

In page 404 of the section “Crustaceology”, Stenosoma was clearly described as a tentative subdivision of the genus Idotea . After the general description of Idotea (numbered as Genus LXIV), Leach (1814) split it into "Genus Stenosoma of Leach. ● body linear, external antennae very long" and "●● Body thickest in the middle. Idotea , Leach". In the first division, Leach placed only one nominal species, Idotea hectica Pallas, 1772, and in the second division he placed two nominal species, Oniscus entomon Linnaeus, 1758 and Oniscus oestrum Linnaeus, 1758. The fact that neither " Stenosoma of Leach" nor " Idotea , Leach" are numbered (as are all other genera in the section) and do not appear either in the list of genera and families at the beginning of the section (as does "Genus LXIV. Idotea ", on page 386) or in the marginal notes or the index, shows that at this stage Leach was not yet sure whether genus rank should be accorded to these divisions.

In the Appendix (p. 433), however, Stenosoma is re-described as a genus on its own, this time numbered “XI”, immediately after Idotea (which is Genus X). There, Leach reformulated the diagnosis of Stenosoma ("external antennae longer than the body, the third longer than the fourth joint; body linear"), and included two nominal species, Idotea hectica Pallas, 1772 and Stenosoma acuminatum Leach, 1814. So, under Articles 12.1 and 12.2.5, the name Stenosoma Leach, 1814 is available from page 404, where it is treated as a division of Idotea Fabricius, 1798, and from page 433 of the same publication where it is ranked as a genus. Under Article 24.1, precedence must be accorded to the name proposed at higher rank, i.e., Stenosoma as a genus, in page 433 of the Appendix. The important point here is that on page 433 Leach included in his genus the nominal species Idotea hectica Pallas, 1772 and Stenosoma acuminatum Leach, 1814. Therefore, Stenosoma acuminatum Leach, 1814 is eligible as type species of Stenosoma Leach, 1814 (Articles 67.2 and 67.2.1).

The genus Stenosoma was quickly adopted by some leading French zoologists (e.g., Desmarest 1825; Latreille 1829), but others saw no reason to separate the species included within it from the well established genus Idotea Fabricius, 1798 (e.g., Milne-Edwards 1840; Bate and Westwood 1868). Meanwhile, congeneric species were being described from the Mediterranean. Risso (1816) described Idotea lanciformis from Nice (France) and later ( Risso 1826) described two species from the same region in the new genus Leptosoma ( Leptosoma appendiculatum Risso, 1826, and Leptosoma lanceolatum Risso 1826), establishing, in part, the diagnosis for the genus that is still in use: the postabdomen (pleotelson) is unarticulated, resulting from the coalescence of the last four pleomeres, without (almost) any trace of segmentation. Rathke (1837) described Leptosoma capito from the Black Sea, and Lucas (1849) described Idotea carinata and Idotea angustata from Algeria. By the end of the 1880s there were at least 11 different species names (in the genera Stenosoma , Leptosoma and Idotea ) for idoteids with unarticulated post-abdomen occurring in the North East Atlantic and the Mediterranean.

In his comprehensive monograph of the Idoteidae , Miers (1881) followed the more conservative approach of Milne-Edwards (1840) and Bate and Westwood (1868) and placed in the genus Idotea all species described as Stenosoma and Leptosoma . Later, Dollfus (1896) opted to separate the genera Idotea Fabricius, 1798, and Stenosoma Leach, 1814, laying the basis for the current taxonomy of this group. He recognized problems with Leach’s oversimplified diagnosis of Stenosoma (see above), noting that the taxonomy behind Leptosoma Risso, 1826 made it "a better established genus". Hence, he retained the name Stenosoma Leach, 1814 based on precedence, but explicitly used the diagnosis proposed by Risso (1826) to set Stenosoma apart from Idotea .

In his revision of the British idoteids, Collinge (1917) took a different approach. Based on the wrong assumption that Leptosoma Risso, 1826 was preoccupied, and that the name Stenosoma had "been used with so many varied conceptions that, with Miers, I agree that it cannot be employed for any section or division of the family" ( Collinge 1917: 727), he proposed the replacement name Synisoma , together with an emended diagnosis of the genus. Collinge (1917) included two nominal species in Synisoma ( Idotea acuminata lancifer Miers, 1881 and Stenosoma acuminatum Leach, 1814) but did not designate a type species for the genus name.

Kussakin (1982) designated Stenosoma acuminatum Leach, 1814 (under Article 67.7, cited as " Stenosoma acuminatum Leach, 1815") as type species of Synisoma Collinge, 1917. Since that was one of the originally included nominal species, Kussakin’s is a valid subsequent designation. Moreover, because Synisoma Collinge, 1917 is a replacement name for Stenosoma Leach, 1814 and, as discussed above, Stenosoma acuminatum Leach, 1814 is also one of the nominal species originally included in Stenosoma Leach, 1814, under Article 67.8 Kussakin’s is also a valid subsequent designation of Stenosoma acuminatum Leach, 1814 as the type species of Stenosoma Leach, 1814. As for Leptosoma Risso, 1826, as far as we can ascertain, no type species has yet been designated, and there is no indication on the present whereabouts of Risso’s type material.

Synisoma Collinge, 1917 is currently in prevailing usage, as it has been used virtually in all works published after 1917. To promote nomenclatural stability, the ICZN allows for a reversal of precedence (Article 23.9) whenever a junior synonym is in prevailing usage provided that the two conditions defined in Articles 23.9.1.1 and 23.9.1.2 are both met. In this case, however, the first condition, that the senior synonym has not been used as a valid name after 1899, is not met. In fact, Stenosoma Leach, 1814 was used as a valid name in at least six works posterior to 1899: Nobre (1903), Norman (1904), Norman and Scott (1906), Tattersall (1911), Issel (1912), and Stephensen (1915).

Given the complex taxonomic history of the genus Stenosoma and its synonyms, their diagnoses have been modified on an ad-hoc basis to accommodate each new species described. For example, both Dollfus’ (1894) diagnosis of Stenosoma and Collinge’s (1917) diagnosis of Synisoma exclude species with an antennal flagellum reduced to a single clavate article. The most recent revision of the genus made by Rezig (1989) did not account for the two Pacific species, Stenosoma pacificum (Nunomura, 1974) and Stenosoma wetzerae (Ormsby, 1991). Recently, Hedo and Junoy (1999) and Castellanos and Junoy (2005) concluded that the two most important characters distinguishing Synisoma (= Stenosoma ) from the other Idoteidae are a pleon lacking distinct somites and a maxillipedal palp composed of four articles. According to these authors, all other characters display a high degree of intra-generic variability. We hereby present an updated diagnosis for the genus, which is broadened from that given by Rezig (1989).

Diagnosis.

Body elongate, lateral margins parallel or sub-parallel, sometimes widening slightly towards pereonites III–IV. Cephalon with pronounced anterolateral lobes, smooth or with a pronounced dorsal tubercle; eyes lateral, small. Antennulae with first article expanded, flagellum composed of a single article. Antenna articles 3-4 longer, flagellum multiarticulated or composed of a single clavate article. Maxillipedal palp with 4 articles. Pereonites smooth, frequently with a shallow dorsal keel, seldom developing into a dorsal triangular tooth; pereonites I–III often with a pair of lateral tubercles. Coxal plates small, round, rarely medium sized and triangular, invisible in dorsal view, or visible dorsally on perionites II–VII or V–VII. Pereopods ambulatory, slender and sub-equal, terminating in a biungulate dactyl with simple setae. Pleon without articulating pleonites (pleotelson), pleonites I–III frequently indicated by incomplete sutures visible ventrolaterally or dorsally (pleotelsonic formula 0+3); pleotelson long, not less than one third of body length, terminally pointed; dorsal surface smooth or with a shallow keel. Penes attached to posterior ventral margin of pleonite 1, fused basally as a penial plate divided over most of its length. Uropod uniramous, endopodite more or less triangular in shape.

Species included.

Stenosoma acuminatum Leach, 1814; Stenosoma appendiculatum (Risso, 1826); Stenosoma capito (Rathke, 1837); Stenosoma carinatum (Lucas, 1849); Stenosoma lancifer (Miers, 1881); Stenosoma spinosum (Amar, 1957); Stenosoma bellonae (Daguerre de Hureaux, 1968); Stenosoma pacificum (Nunomura, 1974); Stenosoma nadejda (Rezig, 1989); Stenosoma mediterraneum (Rezig, 1989); Stenosoma wetzerae (Ormsby, 1991); Stenosoma raquelae (Hedo & Junoy, 1999); Stenosoma albertoi (Castellanos & Junoy, 2005); Stenosoma stephenseni sp. n.