Material examined.

Two specimens: one male holotype, 1.4 mm, dissected and mounted in Faure’s liquid on slide MSNVRCr nr. 434; one preparatory female paratype on two slides MSNVRCr nr. 470 in Museo di Storia Naturale di Verona, Italy.

Diagnosis.

Lateral lobes on frontal margin of head developed. Maxillule, basal endite (= outer lobe) left and right with asymmetrical seta. Gnathopods 1 and 2 carpochelate with oblique palm, dactyli with a serrated inner margin with four teeth. Female with extra palmar margin robust seta. Oöstegites on pereiopod 3 and 4, with three regularly placed small button-like processes. Gills present on P3-5. Dactylus of P3 and P4 with slender trifid unguis; P5-7 with thicker bifid unguis, not clearly separated from dactylus. Pleopods 1-3 subtrapezoidal and similar, except first pleopod in male which is flexed and has a broadened tip. Uropod 1 with inner ramus about 1.5 times as long as outer ramus; uropod 2 peduncle without basofacial spine and with two diagonal rows of sturdy rectangular setae, three rows in female, individual setae mostly bifid but with some of them trifid at the tip.

Etymology.

The new species is named after Roberto Argano (University of Rome “la Sapienza”) who collected the specimens and gave them to the Verona Museum for study.

Description.

Body elongate, without coloration, all segments laterally compressed. Head (Fig. 2a) with lateral margin rounded; lateral or ‘ocular lobes’ present on frontal margin, well developed, suboval. Pleonites I-III with diffusely developed posteriorly rounded epimeral plates adorned with simple seta, a superficial marginal edge slightly visible. Urosomite III subcilindrical, slightly longer than deep, enclosing base of telson and uropod III.

Antennule (Fig. 2a), peduncular article slightly shorter than head; article ratio 1:0, 42:0, 42; flagellum of 4 articles, half the length, articles 2-4 with 1 aesthetasc; accessory flagellum slightly shorter than flagellar articles 1+2, three articles.

Antenna (Fig. 2a) subequal in length to antennule; flagellum of 5 articles, slightly shorter than half the length of peduncle, the last article bearing one aesthetasc (antenna drawn by S. Ruffo but not present in mounted slides).

Mandibles with non-triturative molar process, spiniform. Left mandible (Fig. 5d) with broad incisor, right mandible (Fig. 5c) with fine serrations on lacinia and molar process margin.

Maxillule (Figs 5a, e) coxal endite (= inner lobe) with 3 simple setae; basal endite (= outer lobe) with six robust setae of which the second one on the medial side has four teeth in the left maxillule and three teeth in the right one. Endopod (= palp) two-segmented, distal segment with two setae.

Maxilla (Fig. 5b) with short, equally long plates, each bearing four distal setae.

Maxilliped (Fig. 5f) basal endite slender, with one simple seta; ischium with two setae; merus and carpus without setae; propodus with one seta; dactylus with one lateral robust seta and distally two long setae, unguis not discernible.

Oöstegites on pereiopods III-IV (Figs 3d, e), suboval, without setae and with 3 button-like processes.

Coxal gills on pereiopods III-V.

Gnathopod I (Figs 2b, 3b) carpo-subchelate, palm strongly oblique, carpus 2.4 times as long as wide, palm margin smooth, not serrated, and with three short, bifid flagellate setae along lateral side of margin, and one simple seta on palm angle in male. In female two of such setae of which one placed closer to the row of three bifid setae. Just posterior to the palmar angle seta is a broad triangular spine on the medial side in the male, and three spines in the female: two smaller ones and a larger, more pointed one. Dactylus with four long spines along posterior margin and thin setules or grooves at the base of the unguis.

Gnathopod II (Figs 2c, d; 3c) Carpo-subchelate, palm oblique, carpus stronger than in gnathopod I, subtrapezoidal, carpal index = 4.6, palm angle defined by one large seta and one smaller spine in female (Fig. 3c), one seta in male (Figs 2c, d), and with triangular tooth proximal to the palmar angle seta, palm margin with irregular serrations; propodus strong with lobe on lateral side ending in a setule, less pronounced in female; dactylus with four strong teeth enforced with thick margins on lateral side and a groove or bundled setules at the base of the unguis.

Pereipods III-IV (Figs 3d, e) with two distal setae on dactylus at the base of the unguis, and three distal setae on propodus, one of them long and apically bifid, unguis apically trifid. Oöstegites with in both pereiopods regularly placed series of 3 button-like processes.

Pereiopods V – VII (Figs 4a, b, c) progressively longer towards P7; basis of P5 broad, that of P7 slender; carpus of P5 with two long and stout distal setae, others shorter; carpus of P7 with broad, curved and modified comb setae; merus of P7 with long distal seta; dactyli with two small setae distally; unguis bifid.

Pleopods I-III (Fig. 2a) subtrapezoidal, without setae. Pleopod I in male deformed or broadened distally.

Uropod I (Figs 2e, 4e) male: protopod with one seta and a row of fine setules on anterolateral margin; exopod with very feeble segment suture and one seta placed at two-thirds the length; endopod with terminal row of spines and four long setae laterally. In female protopod with three setae; endopod with six long setae laterally.

Uropod II (Figs 3a, 4d), protopod with two oblique comb rows in male, and three in female; setae of rows more or less rectangular with bifid or trifid, or even comb-like tips; endopod slightly longer than exopod, sharper, and with four setae.

Uropod III (Fig. 2a) short, 2 segmented, with one ramus, protopod with 2 distal setae, ramus short with 1 distal seta.

Telson (Fig. 2a) globose, with 1 pair of long dorsal setae.

Differences between male and female: gnathopods without extra palmar seta in male, and uropod II without a third comb row in male. Pleopod I in the male has a broadened tip.

Remarks.

Ingolfiella arganoi sp. n. shares most morphological character states with a species found 2500 km southeastward across the Indian Ocean, on the Maldives, namely Ingolfiella xarifae (Ruffo, 1966), from washed-out broken coral pieces (Favites sp.). Species ranges of stygobionts have not been reported to exceed such large distances in the past and molecular work on cryptic lineage diversity of populations of groundwater crustaceans have even diminished existing ranges to distances of less than 1000 km (Trontelj et al. 2009).

For now, five clear morphological differences justify the designation of a new species that also is geographically quite far away from its nearest congeners. These differences can be observed in the four spines on the medial margin of the propodus of gnathopod I – three spines in Ingolfiella xarifae; subtrapezoidal carpus of gnathopod 2 – elongate oval in xarifae; palmar index of gnathopod 2 is 4.6 – against 6.4 in xarifae; palm of gnathopod 2 strongly serrate – almost smooth in xarifae; pereiopod VII with specialized, combed, robust setae distally on carpus – not present in xarifae.

The differences in the placement, form and number of setae have shown to be quite consistent in the case of the poorly setose ingolfiellids (Vonk and Sanchez 1991). The spines and setae that have remained, are perhaps critically functional due to selective reductive factors in the underground environment.

The oöstegites have 3 small button-like processes. The same character was described in Ingolfiella alba Iannilli et al., 2008, where also three small button-like processes are present, but here from P3 to P5. Re-examination of Ingolfiella xarifae typus by Sandro Ruffo and V.I. allowed them to observe also on the oöstegites of this species the button-like processes, as described for Ingolfiella alba.Something similar was described in Metaingolfiella mirabilis Ruffo, 1969, although the processes were smaller and more numerous. These structures are probably present in other Ingolfiella species but have yet to be observed and described (Iannilli et al., 2008). Stock (1979) observed in Ingolfiella quadridentata Stock, 1979, that oöstegites found on P3 and P4 were: “curved, truncate at tip, provided with 3 apical teeth, but without setae.”

In other amphipods with preparatory females (females in a moult stage in between two brooding periods), these structures are sometimes present on the oöstegites (pers. comm. D. Jaume). Slattery (1985) mentions the development of oöstegites in infaunal amphipod families of Phoxocephalidae and Haustoriidae undergoing three stages of development: buds (of the oostegite itself), preparatory (moderately long oöstegites with some setae), and mature (long oöstegites, curved, and setose to form a brood-carrying pouch or marsupium). If the buttons, that occur in threesomes on the oöstegites of pereiopods III and IV in Ingolfiella arganoi, can be observed in other ingolfiellids as being present at the same time with setae this might prove their precursory role. On the other hand, in contradiction to these observations, are our studies of abundant material of Ingolfiella alba, that shows this character. The material consists of several individuals collected in different years (from 1992 to 2004) and in different months of the year. We could verify that the structure is always the same, namely the presence of only three button-like processes, and we did not find setae on the oöstegites. So an interpretation of these structures being preparatory setae seems not convincing for Ingolfiella species.

In agreement with Ruffo and Vigna Taglianti 1989 the new species could be placed in the subgenus Tethydiella, although Vonk and Schram (2003), basing their phylogeny on more characters, did not use the splitting of Ingolfiella into genus and subgenera as several taxa are poorly described when compared to recent taxonomic descriptions and only few species have both sexes well known.

However, the species-groups in sensu Ruffo (1970) and Ruffo and Vigna Taglianti (1989) may still be of practical taxonomic use and the geographical location as well as the morphological diagnosis fits the Tethydiella group. Of course, more detailed biogeographic data are required to reconstruct the history of the actual distribution of Ingolfiellidae (Iannilli et al. 2008).