Deioneus sandizelli Dworschak, Anker & Abed-Navandi, 2000

Anker, Arthur, 2020, Two new species and new records in the alpheid shrimp genera Salmoneus Holthuis 1955 and Deioneus Dworschak, Anker & Abed-Navandi, 2000 in theAtlantic Ocean (Malacostraca: Decapoda), Zootaxa 4786 (3), pp. 345-368 : 362-365

Deioneus sandizelli Dworschak, Anker & Abed-Navandi, 2000

Figs. 11 , 12

Deioneus sandizelli Dworschak, Anker & Abed-Navandi 2000: 304 , figs. 1–26.

Material examined. 1 ovigerous specimen (cl 4.4 mm, missing minor cheliped), OUMNH. ZC. 2015-08-029, Gulf of Guinea, São Tomé and Príncipe, São Tomé Island, Praia das Conchas, shallow subtidal flat with large rocks covered with silt or mud, deep under rock on fine sand or mud, depth at low tide: 0–1 m, leg. A. Anker, 15.02.2006 [fcn 06-230] .

Remarks. Deioneus sandizelli sp. nov. was described based on two specimens from São Tiago, Cape Verde Islands, both collected with a suction pump from burrows of callianassid ghost shrimps ( Dworschak et al. 2000). The holotype inhabited the burrow of Corallianassa intesi (de Saint-Laurent & Le Loeuff, 1979) , whilst the paratype was found inside the burrow of Neocallichirus pachydactylus (A. Milne-Edwards, 1870) .

The present specimen of D. sandizelli is the first record of the species for São Tomé and Príncipe, significantly extending its previously known distribution (type locality only) from the Cape Verde Archipelago to the Gulf of Guinea. It was neither collected using a suction pump nor found together with a ghost shrimp. However, there were traces of burrowing activity near and under large, mud-covered, subtidal rocks, under which the present specimen of D. sandizelli was found, suggesting that it was possibly associated with some callinassid host.

The monotypic genus Deioneus was separated by Dworschak et al. (2000) from the closely related Salmoneus using the following criteria: (1) presence of an articulated subtriangular flap at the posterolateral angle of the sixth pleonite (absent in Salmoneus ); (2) presence of a prominent tooth on the cutting edge of the fixed finger of the minor cheliped (absent in Salmoneus ); (3) lateral plate of the third maxilliped coxa acutely produced (rounded in Salmoneus ); and (4) absence of an appendix masculina in females.With an almost threefold increase of species in the genus Salmoneus after the publication of Dworschak et al. (2000), some of the above-listed differences are blurred. For instance, in S. degravei Anker, 2010 , the lateral plate of the third maxilliped coxa is strongly produced posteriorly, protecting the hypertrophied arthrobranch, just like in D. sandizelli (cf. Dworschak et al. 2000: fig. 12; Anker 2010a: fig. 8c). Also in S. degravei , the minor cheliped pollex possesses a very stout subdistal tooth at the same location as the one of D. sandizelli (cf. Dworschak et al. 2000: fig. 18; Anker 2010a: fig. 9c). In the non-related S. brucei Komai, 2009 and S. yoyo Anker, Firdaus & Pratama, 2014 , the minor cheliped is also armed with prominent teeth, but these seem to be at a different position and thus may not be homologous to that of D. sandizelli and S. degravei (cf. Komai 2009: fig. 4C, D; Anker et al. 2014: fig. 2H). Most importantly, a re-examination of the ovigerous “female” holotype of D. sandizelli (NHMW 18796) by Dr. P.C. Dworschak (pers. comm.) revealed that the specimen actually possesses a short appendix masculina, similar to that of the São Tomean specimen, which also appears to be either pre- or post-ovigerous, judging from the long oviferous setae on the protopod ( Fig. 11c, d ).

In addition, several species of Salmoneus , including S. saotomensis sp. nov. and S. yoyo , have an incomplete suture at the posterolateral angle of the sixth pleonite ( Fig. 8c ; see also Anker et al. 2014: fig. 1C), in the exact position of a well-developed, subtriangular, articulated flap in Deioneus ( Fig. 11b ; see also Dworschak et al. 2000: fig. 1) and numerous other alpheid genera. However, none of the species currently assigned to Salmoneus possesses a completely formed, i.e. articulated (= separated from the rest of the somite) subtriangular flap. This includes all species with the more or less enlarged minor cheliped, such as S. erasimorum , S. caboverdensis , S. saotomensis sp. nov., S. degravei , S. camaroncito , S. jarli , S. brucei and S. yoyo .

In summary, from the four characters that were used to distinguish Deioneus from Salmoneus by Dworschak et al. (2000), the characters (2), (3) and (4) cannot be considered as valid. The character (1), i.e. the presence / absence of an articulated flap on the sixth pleonite, is the only character that can be used to distinguish the two genera. Since this character appears to be of great importance in alpheid taxonomy since Coutière (1899), Deioneus can be retained as a genus distinct from Salmoneus . However, it must be noted that at least in Nennalpheus Banner & Banner, 1981 , the development of the articulated flap appears to be variable, with only two out of three species having it ( Banner & Banner 1981b; Anker 2019). The presently available evidence suggests that at least S. degravei is more closely related to D. sandizelli than to other species of Salmoneus , based on the above-mentioned characters (2) and (3), as well as numerous other morphological similarities, e.g. in the frontal margin of the carapace, telson, pereiopods, etc. ( Fig. 11a ; see also Anker 2010a: figs. 7–9). The morphological diversity of Salmoneus substantially increased over the past decade, making the last major taxonomic reassessment of the genus by Anker & Marin (2006) rather obsolete, although at least some of the informal species groups established therein certainly have both taxonomic and phylogenetic importance. Therefore, the present author prefers to await a comprehensive phylogenetic analysis of Salmoneus and several allied genera (in addition to Deioneus , the American Triacanthoneus Anker, 2010 and the western Pacific Caligoneus Komai & Fujita, 2018 ; see Anker 2010b; Komai & Fujita 2018) to formally transfer S. degravei to Deioneus since such an action will make necessary important emendations in the generic diagnoses of both genera.

Figures

FIGURE 8. Salmoneus saotomensis sp. nov.: holotype, ovigerous specimen (cl 3.8 mm) from São Tomé (MZUSP 34071); a—frontal region, dorsal view; b—same, lateral view; c—posterior pleonites, lateral view; d—telson, dorsal view; e—first article of antennular peduncle, tooth on mesioventral carina, lateral view; f—third maxilliped, lateral view; g—same, tip of ultimate article, dorsolateral view; h—second pereiopod, lateral view; i—third pereiopod, lateral view; j—same, distal portion of propodus and dactylus, mesial view; k—fourth pereiopod, lateral view; l—fifth pereiopod, lateral view; m—same, propodus and dactylus, mesial view; n—second pleopod, appendix interna and appendix masculina, lateral view; o—uropod, dorsal view.

FIGURE 11. Deioneus sandizelli Dworschak, Anker & Abed-Navandi, 2000: ovigerous specimen (cl 4.4 mm) from São Tomé (OUMNH.ZC. 2015-08-029); a—rostro-orbital region of carapace and right eye, lateral view; b—posterior pleonites, lateral view; c—second pleopod, lateral view; d—same, appendix interna and appendix masculina.

FIGURE 12. Deioneus sandizelli Dworschak, Anker & Abed-Navandi, 2000: ovigerous specimen (cl 4.4 mm) from São Tomé (OUMNH.ZC. 2015-08-029), living shrimp (missing left = minor cheliped) in dorsal [a] and lateral [b, c] views. Photographs by the author.