Racovella birramea, Jaume & Gràcia & Boxshall, 2007

Jaume, Damià, Gràcia, Francesc & Boxshall, Geoff A., 2007, New genera of Bogidiellidae (Amphipoda: Gammaridea) from SW Pacific and Mediterranean marine caves, Journal of Natural History 41 (5 - 8), pp. 419-444 : 433-443

publication ID	https://doi.org/ 10.1080/00222930701228835
persistent identifier	https://treatment.plazi.org/id/03BD87FC-707A-FFC5-FE68-FA8F0C2DF9F1
treatment provided by	Felipe
scientific name	Racovella birramea
status	sp. nov.

Treatment

Racovella birramea View in CoL sp. nov.

( Figures 8–14 View Figure 8 View Figure 9 View Figure 10 View Figure 11 View Figure 12 View Figure 13 View Figure 14 )

Material examined

Cova des Coll (Portocolom, Mallorca , Balearic Islands). UTM coordinates ( Datum Europe 50): 4364500/31 522770. Anchialine cave with submarine entrance comprising 6294 m of flooded plus 726 m terrestrial passages. Topography and description of fauna from the cavity published in Gràcia et al. (2005). Holotype: single specimen 1.47 mm, sex unknown, captured 400 m inland in waters of 33‰ salinity; completely dissected and mounted in lactophenol on two slides; slides sealed with nail varnish ( BMNH reg. no. 2006-1126). Collected by authors, 21 December 2004.

Description

Eyeless and unpigmented. Head ( Figure 8A View Figure 8 ) about as long as wide, with hardly developed rostrum, lateral lobe, and postantennal sinus (terms sensu Lincoln 1979, p 15). Body tergites with sparsely set long sensillae as figured. Slender seta present at posteroventral corner of each of fifth to seventh pereonites ( Figure 8C View Figure 8 ). Epimeral plates ( Figure 8D View Figure 8 ) with rounded posterodistal corners; seta present on posterior margin of plates 2 and 3.

Antennule ( Figure 12A View Figure 12 ) about 43% of body length. Proximal peduncle segment 2.7 times longer than wide, with strong flagellate spine on posterior margin. Second peduncle segment about 3.3 times longer than wide, attaining 77% length of proximal segment. Third peduncle segment 58% length of preceding segment. Main flagellum longer than peduncle, seven-articulate, with aesthetascs on articles 5 and 6. Accessory flagellum twoarticulate, hardly reaching distal margin of proximal article of main flagellum; proximal article three times longer than distal article.

Antenna ( Figure 12B View Figure 12 ) slightly shorter than antennule, peduncle segment 3 with flagellate spine on anterior margin; segment 4 longest, 3.3 times longer than wide; fifth segment 80% length of preceding segment, 3.8 times longer than wide. Flagellum five-articulate, shorter than two distal segments of peduncle combined, apparently lacking aesthetascs.

Labrum ( Figure 9A View Figure 9 ) globose with setulose distal margin. Paragnaths ( Figure 9B View Figure 9 ) bilobed, outer lobes hardly setulose distally, inner lobes densely setulose.

Left mandible ( Figure 9C View Figure 9 ) with subrectangular, similar coarsely six-denticulate incisor and lacinia ( Figure 9A, D View Figure 9 ). Spine row comprising three elements serrated distally along one margin only. Molar triturative, columnar, with patch of stiff coarse setules basally close to spine row ( Figure 9D View Figure 9 ); molar seta apparently absent. Palp three-segmented, proximal two segments naked, distal segment with three apical and one subapical seta; segments 2 and 3 sparsely setulose.

Right mandible ( Figure 9E View Figure 9 ) similar to left counterpart except for incisor (fivedenticulate), lacinia, and spine row. Presumed lacinia with finely serrated, expanded distal margin, similar to distal element of spine row. Spine row composed of three elements, two more proximal serrated along one margin only.

Maxillules ( Figure 9F View Figure 9 ) symmetrical. Coxal endite with three setae. Basal endite with six dentate spines. Distal segment of two-segmented endopod carrying three distal setae.

Maxilla ( Figure 9G View Figure 9 ) reduced, both endites similar in length. Coxal endite with eight unequal setae; basal endite with six setae.

Maxilliped ( Figure 9H View Figure 9 ) with short endites. Basal endite with single stout spine and four smooth setae on distal margin, and with single smooth seta subdistally on posterior surface of segment. Endite of ischium with three stout spines distally, two smooth setae on posterior surface, and two others along inner margin. Merus and carpus with one and six smooth setae, respectively. Propodus with distal portion of anterior surface densely spinulose; seven smooth setae, two of them with rounded tip, subdistally on segment as figured. Dactylus with row of lamellar spinules along posteromedial margin and with patch of slender spinules proximally on anterior surface. Unguis with row of rounded denticles on proximal half.

Coxal plates ( Figure 8A–C View Figure 8 ) wider than long, plates 2–5 with anterior margin overlapping one in front, plates 5–6 with posterior margin overlapping one to rear. Coxal gills ( Figure 8A–C View Figure 8 ) on pereopods 3–6, stalked.

Coxa of first gnathopod ( Figure 8B View Figure 8 ) 1.8 times wider than long, with evenly rounded, convex anterior margin and oblique, slightly concave posterior margin; distal margin convex, with seta on anterodistal corner and about midway along margin. Basis ( Figure 10A View Figure 10 ) 3.1 times longer than wide, with posterodistal corner projecting into lobe with stout seta. Ischium and merus with posterior margin finely spinulose. Carpus with posterodistal corner protruding, but not finger-like as in preceding taxon, with stout spinulose seta subsdistally on lobe ( Figure 10B View Figure 10 ); posterior margin of segment spinulose. Propodus ( Figure 10A View Figure 10 ) larger than second gnathopod counterpart, about 2.2 times longer than wide, with oblique, slightly concave, smooth palm margin; palm angle at 45% of maximum length of segment, with single flagellate spine on medial margin; distal portion of posterior margin of segment serrate. Nail long, overreaching palm angle, with single subterminal indentation harbouring three setae.

Coxa of second gnathopod ( Figure 8B View Figure 8 ) 1.4 times wider than long, similar to that of preceding pereopod but with more convex anterior margin, oblique posterior margin, and with seta located at posterodistal corner of segment instead of midway along distal margin. Basis ( Figure 10C View Figure 10 ) slender, 2.8 times longer than wide and as long as basis of first gnathopod. Merus with hardly developed posterodistal lobe. Carpus about 1.7 times longer than wide, with oblique posterior margin; patch of spinules on posteromedial surface. Propodus about 2.3 times longer than wide and 1.4 times longer than carpus, with parallel anterior and posterior margins; palm angle positioned at 55% maximum length of segment, with one long and slender flagellate spine at each side; palm margin straight, almost devoid of armature, smooth; patch of spinules submarginally on medial surface of segment close to anterior margin; posterior margin spinulose midway, serrate distally. Nail bearing two deep indentations subdistally on posterior margin.

Pereopods 3–4 ( Figure 11A, B View Figure 11 ) similar, pereopod 3 longer due to proportionally longer basis and propodus. Coxae of both limbs ( Figure 8B View Figure 8 ) similar, roughly rectangular, 1.6 times wider than long, with convex anterior margin, oblique, slightly concave posterior margin, and straight distal margin with seta at anterodistal and posterodistal corners; plate 4 with comparatively more rounded anterior margin.

Pereopods 5–7 ( Figure 11C–E View Figure 11 ) slender, pereopod 5 shorter than others, pereopods 6–7 similar in length. All with slender basis, although that of pereopod 7 comparatively more expanded (2.3 times longer than wide). One flagellate spine at anterodistal corner of propodus of pereopods 5 and 6 elongate, surpassing tip of respective nail. Coxae 5–7 similar ( Figure 8C View Figure 8 ), with anterodistal lobe progressively shorter towards posterior, posterodistal lobe wanting; all coxae with seta at posterodistal corner; coxa 5 with one seta at anterodistal corner.

Relative length of nail (dactylus + unguis) of pereopods 4–7 as follows: 40:60:90:100 ( Figure 12C–F View Figure 12 ). Pereopods lacking lenticular organs.

Pleopods 1–3 ( Figure 13A, C, D View Figure 13 ) biramous, similar except for somewhat shorter third pleopod, all lacking secondary sexual characters. Protopod with two retinacles ( Figure 13B View Figure 13 ) subdistally on medial margin. Exopod three-articulate, with pair of plumose setae per article; endopod unisegmented, shorter than proximal article of corresponding exopod, with two short, unequal terminal setae, single seta subdistally on outer margin, and two setae along inner margin.

Uropod 1 ( Figure 14A View Figure 14 ) biramous, exopod shorter than endopod, and both rami shorter than protopod (65 and 81% of protopod length, respectively). Protopod elongate, about 3.9 times longer than wide, lacking basofacial spine and with flagellate spine on dorsolateral and dorsomedial corner; distal corners of segment serrate. Tips of rami serrate, with three spines around tip. Uropod 2 ( Figure 14B View Figure 14 ) similar to preceding limb except for proportionately shorter protopod and endopod. Uropod 3 ( Figure 14C View Figure 14 ) longest, with unisegmented rami subequal in length. Protopod 66% length of rami, with stout flagellate spine at lateral corner and short smooth seta proximally on medial margin. Exopod with smooth tip bearing four unequal spines, and single spine about midway along lateral margin. Endopod with terminal serrations and two unequal setae on tip; single spine located at two-fifths of distance along medial margin of segment.

Telson ( Figure 14D, E View Figure 14 ) wider than long, with deeply excavate distal margin and single flagellate spine on tip of each lobe; two short and smooth setae placed subdistally on outer margin of each lobe.

Etymology

Species named after the biramous condition of the pleopods, a feature unrecorded to date in Balearic bogidiellids.

Remarks

This new taxon is remarkable among the Bogidiellidae sensu stricto (see Koenemann and Holsinger 1999 for a restricted diagnosis of the family) in exhibiting a combination of only six distal spines on the basal endite (5outer lobe) of the maxillule, plus coxal gills on pereopods 3–6. The former feature is shared only with Mexigidiella Stock, 1981 , since all other bogidiellids display seven spines at this position. The condition of the coxal gills is shared with Aequigidiella Botosaneanu and Stock, 1989 , Aurobogidiella Karaman, 1988 , Marinobogidiella Karaman, 1982 , and Nubigidiella Karaman, 1988 . Of these five genera, only Aurobogidiella and Marinobogidiella share with the new taxon the reduced endopod of pleopods 1–3 (non-articulate and about equal in length to the proximal article of the corresponding exopod). Both genera are monotypic and restricted to the Western Mediterranean (Bay of Naples), where they inhabit the interstices of coarse marine sand at depths of 1– 6 m. Irrespective of the close geographical and phenetic affinity, both of these taxa differ markedly from the new taxon in many respects. Aurobogidiella —known from the female only—displays a four-articulate exopod of pleopod 2, lacks a strong spine on the carpal lobe of gnathopod 1, and bears one seta on the second segment of the mandibular palp ( Karaman 1979, 1988). Marinobogidiella is known from the male only, and displays a unisegmented endopod (5palp) on the maxillule, a hardly excavated telson and, as in the preceding species, one seta on the second segment of the mandibular palp ( Schiecke 1978; Karaman 1982). Neither of these two taxa displays the characteristic array of serrations present terminally on both rami of uropods 1–2, and on the endopod of uropod 3 of the new taxon.

Other genera of bogidiellids are known to occur in the peri-Mediterranean area (namely Bogidiella , Hebraegidiella Karaman, 1988 , Maghrebidiella Diviacco and Ruffo, 1985 , and Medigidiella Stock, 1981 ) or in islands of the NE Atlantic (namely Bogidiella , Cabogidiella , Stygogidiella Stock, 1981 , and Xystriogidiella ). Of them, only Hebraegidiella , Stygogidiella , and some Bogidiella species display a non-articulate endopod on pleopods 1–3 which is shorter than the proximal article of the exopod. These three genera differ from the new taxon in having a different number of coxal gills and seven distal spines (instead of six) on the basal endite of the maxillule, among other features.

Apart from the new taxon described above, two other bogidiellids are known to occur in Balearic groundwaters. Bogidiella balearica Dancau, 1973 is a cave-dwelling anchialine species distributed along the SE coast of Mallorca and the neighbouring Cabrera archipelago. Bogidiella torrenticola Pretus and Stock, 1990 is an interstitial species known only from the type locality, the hyporheic zone of a stream on the west coast of Mallorca. Both species clearly differ from the new taxon in the display of lenticular organs on the pereopods and of a basofacial spine on the protopod of uropod 1, among many other features (see Stock and Iliffe 1987; Jaume 1990; Pretus and Stock 1990). In addition, Pretus (1991) reported the occurrence of at least three other bogidiellid taxa in Balearic groundwaters, which remain undescribed.