Sphaerobathytropa, VERHOEFF, 1908

Schmidt, Christian, 2007, Revision of the Neotropical Scleropactidae (Crustacea: Oniscidea), Zoological Journal of the Linnean Society 151, pp. 1-339 : 77-78

SPHAEROBATHYTROPA VERHOEFF, 1908

Includes only the type species; a second nominal species is synonymized below. The phylogenetic affinities of this species have been enigmatic since its discovery,

so a review of the published opinions is given and discussed here.

Discussion of the phylogenetic position of Sphaerobathytropa

Concerning the genus Sphaerobathytropa , the aim of the cladistic analysis included in the present article was only to assess whether or not this genus belongs to the Scleropactidae . The various hypotheses on the systematic position of Sphaerobathytropa are discussed here. Sphaerobathytropa was originally placed in the Eubelidae . As the Eubelidae were redefined and several taxa removed from this family, this needs reconsideration. The Eubelidae , as defined by Taiti et al. (1991), are characterized by two apomorphies: the sulcus arcuatus, a deep furrow along the lateral margin of the first coxal plate, and the shape of the uropods. The sulcus arcuatus is absent only in species that secondarily gave up the conglobational ability. Sphaerobathytropa does not show these apomorphies, and also lacks apomorphies of subordinate taxa of the Eubelidae , e.g. number of penicils on inner endite of first maxilla greater than two, or pleopodal lungs of some complexity. Therefore, placement of Sphaerobathytropa in the Eubelidae is not supported. Vandel (1963) included Sphaerobathytropa in the subfamily Sphaeroniscinae of the family Eubelidae , together with Sphaeroniscus , Scleropactes and Circoniscus . This subfamily was elevated to family rank by Vandel (1968). Later, Holdich et al. (1984) replaced the name Sphaeroniscidae by Scleropactidae , because the latter has priority. The Scleropactidae are most closely related to some South American Philosciidae , with which they share an apomorphic, long antennal cone ( Schmalfuss, 1980) with a pair of short lateral sensilla; also, on the maxilliped palp, the setae of the distal tuft of the second article are inserted on a common socket ( Leistikow, 2001; Schmidt, 2002, 2003). The antennal cone of Sphaerobathytropa is only half as long as the distal flagellar article, but the lateral sensilla are short, approx. 0.25 of the length of the apical cone. This condition can be said to be intermediate, and does not clearly favour a close relationship with the Neotropical Scleropactidae or Philosciidae . The maxilliped palp does not exhibit the apomorphy of the above-mentioned groups.

A third hypothesis suggests a relationship of Sphaerobathytropa with the Armadillidae . No phylogenetic system of the Armadillidae has existed before now. The discussion concerning the groundpattern of the Armadillidae has only recently been opened ( Taiti et al. 1998). Sphaerobathytropa does not have the hourglass shape of the pleotelson that is characteristic of the great majority of the Armadillidae , but there are also some (putative) members of the Armadillidae with a differently shaped pleotelson. Probably, the molar penicil, which consists of several hairy seta on an elongate socket, could support a relationship with the Armadillidae .

The dorsal tricorns are similar to those found in the non-conglobating genera Trichorhina and Calycuoniscus, Neotropical representatives of Platyarthridae or closely related to these. They are also similar to the tricorns of the west Mediterranean Spelaeoniscidae . The species of that taxon are of a similar size but leave the second antennae outside when conglobating. Furthermore, they have the uropods specialized in a completely different way than Sphaerobathytropa . In contrast to all these forms, the noduli of Sphaerobathytropa are large and prominent.

Recently, some enigmatic species were described from Greece and tentatively placed in the Scleropactidae ( Schmalfuss, 1995) . One of them, Xeroporcellio pandazisi Strouhal, 1954 , has exoantennal conglobation ability, small lateral lobes of the cephalothorax, a three-jointed flagellum of the second antenna, and a long apical cone. In these characters, as well as in the shape of the pleotelson and uropods, it closely resembles the South American genus Scleropactes , and the same arguments can be used for rejecting a close relationship with Sphaerobathytropa . The other species, Kithironiscus paragamiani Schmalfuss,1995 , is an endoantennal conglobator with a schisma on the posterior corners of the first coxal plates. The noduli laterales are small, but distant from the posterior margins of the tergites, as in Sphaerobathytropa . In contrast, the conformation of the uropods of Kithironiscus resembles more the condition found in the Spelaeoniscidae .

The conclusion of these considerations is that the sister group of Sphaerobathytropa cannot be identified at present, because the taxa that need to be considered are still insufficiently known, their monophyly is not supported, or their groundpattern is not yet reconstructed. It is also possible that Sphaerobathytropa separated from its sister group early in the evolutionary history of the Crinocheta, and numerous characters were transformed during its own evolution, a circumstance that does not facilitate comparison with other taxa.

For the time being, it is proposed to retain Sphaerobathytropa as ‘incertae sedis’, until new data allow its phylogenetic position to be revised.