Arcantitanais, Sanchez-Garcia & Penalver & Bird & Perrichot & Delclos, 2016
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publication ID |
https://doi.org/ 10.1111/zoj.12427 |
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persistent identifier |
https://treatment.plazi.org/id/5824AB77-FF8A-DB2B-FF0B-FA98FCE75569 |
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treatment provided by |
Marcus |
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scientific name |
Arcantitanais |
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GENUS ARCANTITANAIS View in CoL SANCHEZ- GARCIA,
PE NALVER ~ & PERRICHOT GEN. NOV
Type species
Arcantitanais turpis Sanchez-Garcıa, Pe nalver ~ & Perrichot sp. nov. by monotypy.
Etymology
The generic name derives from Arcantiatum, the former Latin name of the Archingeay locality from which the fossil comes, combined with Tanais , a genus name used widely as a suffix in the Tanaidomorpha .
Diagnosis
Male. Unknown. Female. Body relatively slender, about five times as long as wide. Cephalothorax suboval when viewed dorsally (much longer than wide). Eyes large (<9% of cephalothorax surface). Pereon rather short (about 0.5 times the body length). Pleon rather short (less than 0.3 times the body length). Antennule with four articles. Functional mouthparts retained; maxilliped article 2 with very long thick inner seta. Cheliped not robust; fixed finger and dactylus subequally developed, not widely separated at base, without forming a distinct gap between them (i.e. nonforcipate); carpus fairly elongated and slender (ratio length/ width close to 3). Pereopod coxa present in all pereopods, bearing one long seta; pereopod 1 much longer than following pereopods, with very long dactylus plus unguis (clearly longer than propodus); pereopods 2 – 3 with dactylus plus unguis much shorter than in pereopod 1; pereopods 4 – 6 heavily armed with curved spines, with dactylus plus unguis as long as in pereopods 2 – 3 but stouter, claw-like but not fused. Uropod biramous, relatively long and slender, endopod about 1.9 times the length of exopod; endopod and exopod with two articles; exopod not reaching half the length of distal endopodal article.
ARCANTITANAIS TURPIS SANCHEZ- GARCIA, PE NALVER ~ & PERRICHOT SP. NOV. ( FIGS 9 – 12 View Figure 9 View Figure 10 View Figure 11 View Figure 12 )
Etymology
Named after the ugly appearance of this species (from the Latin adjective turpis meaning ‘ugly’).
Occurrence
Font-de-Benon quarry, 1 km east of Archingeay-Les Nouillers (Charente-Maritime, south-west France); uppermost Albian – lowermost Cenomanian (amber level A1sl-A; Neraudeau et al., 2002; Dejax & Masure, 2005; Batten et al., 2010).
Type material
Holotype IGR.ARC-40, ♀. Largely intact, but preserved in a clear-yellow brittle piece of amber with multiple bubbles and internal fractures that hinder examination. The specimen is observed in dorsoventral view, and thus, some chelipedal characters are not currently visible. The cephalothorax dorsal surface is partially missing, eroded from the amber surface. An amber fracture runs along the pleon obscuring the third and fourth pleonites. Paratype IGR.ARC-283.10, ♀ (see Material and methods above).
Diagnosis
As the genus is monotypic so far, the diagnosis is identical to that of the genus.
Description (based largely on the holotype IGR.ARC- 40, Figs 9 View Figure 9 , 10 View Figure 10 ).
Body ( Figs 9A View Figure 9 , 10A View Figure 10 , 11 View Figure 11 , 12 View Figure 12 ) small, total length 0.78 mm; relatively slender, 5.27 times longer than wide; subcylindrical, slightly flattened dorsoventrally. All observed setae simple.
Cephalothorax suboval when viewed dorsally, gradually narrowing anteriorly (i.e. without a lateral constriction), 1.58 times longer than its maximum width; about 0.27 times total body length, longer than combined length of pereonites 1 – 3; lateral mar- gins convex, posterior margin rounded. Rostrum absent. Eyes well developed, large, diameter 0.21 times the cephalothorax length, slightly bulging, anterolaterally placed on cephalothorax.
Pereon rather short, about 0.47 times total body length. All pereonites wider than long, with fairly convex lateral margins when viewed dorsally, rectangular when viewed laterally (visible laterally in the paratype); pereonites 1 – 3 subequal in size, about 2.50 times wider than long; pereonites 4 – 5 the longest, subequal in size, each about 1.50 times the length of each of pereonites 1 – 3, about 1.67 times wider than long; pereonite 6 just slightly shorter than each of pereonites 1 – 3, about 2.17 times wider than long.
Pleon ( Fig. 11 View Figure 11 ) rather short, about 0.26 times total body length, with five free subequal pleonites each bearing pairs of pleopods; pleonites as wide as pereonites but much shorter (each about 0.36 times the length of each of pereonites 4 – 6), about 4.43 times wider than long. Pleotelson short, not reaching the length of two pleonites together, gradually tapering distally, with broadly rounded posterior margin bearing one very long ventral seta (most likely paired).
Antennule ( Figs 11 View Figure 11 , 12 View Figure 12 ) four-articled, fairly slen- der, tapering distally, relatively short, 0.66 times the length of cephalothorax; article 1 about 0.37 times the length of antennule, not reaching the length of articles 2 and 3 combined, 1.65 times longer than thick, slightly expanded laterally at cephalothorax insertion, with one short outer seta distally; article 2 about half the length of article 1 (0.58 times), 1.13 times longer than thick, with one very long and one short outer setae plus one short inner seta distally; article 3 about 0.80 times the length of article 2, 1.20 times longer than thick, with two short inner setae distally; terminal article (article 4) 1.36 times the length of preceding article, 3.10 times longer than thick, bearing two short setae plus four long unequal setae apically.
Antenna ( Fig. 10D View Figure 10 ) six-articled, about 0.88 times the length of antennule (length cannot be easily measured because of its foreshortened position) and much thinner, although it is relatively stout; articles 1 – 3 subequal in length, square (ratio length/width close to 1), the shortest, combined length about 0.44 times the length of antenna, the first article without visible setae, the second and third with one outer and one inner distal seta, respectively; articles 4 – 6 subequal in length, each about 1.25 times the length of each of articles 1 – 3, article 4 with one outer distal seta, article 5 with one outer and one inner distal setae; terminal article (article 6) the thinnest, highly setose, bearing up to four short plus four long unequal setae apically.
Maxilliped ( Figs 9B View Figure 9 , 10B View Figure 10 ) endites and basis poorly visible. Endites unfused, reaching half length of palp article 3, without visible setae. Maxilliped palp fourarticled, with stout articles 1 – 3; article 1 without visible setae; article 2 with one very long thick seta and two thick short setae on inner margin; article 3 with three thick short setae on inner margin and one fine short seta on outer margin; article 4 thinner, with four thick short setae distally.
Cheliped ( Figs 10A View Figure 10 , 11 View Figure 11 ) not robust; sclerite not visible; basis widening distally, about 1.66 times longer than thick, 0.77 times the length of carpus, with one long outer seta distally; merus subtriangular, with one long ventral seta; carpus fairly elongated and slender, widening distally, about 3.03 times longer than thick, 1.30 times the length of propodus, with one very long ventral seta subdistally; propodus delicate, with up to two long ventral setae distally; fixed finger and dactylus subequal in length (visible laterally in the paratype), relatively short and small, without forming a distinct gap between them at their base (i.e. nonforcipate), with several setae although the exact pattern cannot be determined as preserved, terminating in unguis.
Pereopod 1 ( Figs 9C View Figure 9 , 10E View Figure 10 ) much longer than following pereopods; coxa present, bearing one long seta; basis fairly slender, cylindrical, about 7.06 times longer than thick, longer than combined length of merus and carpus, with two long thin setae proximally; ischium short, bearing one thin seta; merus and carpus subequal in length, not widening distally, without visible setae; propodus longer than carpus, tapering distally, with one dorsal and one ventral long seta subdistally plus one dorsal long seta distally; dactylus plus unguis curved and very long, about 1.26 times the length of propodus; unguis not distinguishable. Pereopods 2 – 3 ( Figs 9E View Figure 9 , 10E View Figure 10 ) as pereopod 1 but shorter; ischium without visible seta; merus together with carpus shorter than combined length of merus and carpus 1 (angle of view probably reducing this measurement slightly); merus with up to one distal seta; carpus with up to three minute setae plus one long distal seta; propodus about half the length of propodus 1 (0.51 times), with one minute ventral seta plus one long dorsal seta distally; dactylus plus unguis about 0.38 times the length of dactylus plus unguis 1, nearly as long as propodus (0.96 times); unguis not distinguishable.
Pereopods 4 – 6 ( Figs 9E, F View Figure 9 , 10E View Figure 10 ) similar in length to pereopods 2 and 3 but sturdier; coxa present, bearing one long seta; basis fairly robust, more inflated than in pereopods 1 – 3, longer than combined length of merus and carpus (exact ratio measurements not possible as preserved), with two long thin setae proximally; ischium short, bearing one thin seta; merus and carpus subequal in size, widening distally, with two and up to four strong curved spines distally, respectively, not showing basal protuberances; propodus longer than carpus, tapering distally, with up to four strong curved spines distally plus one thin dorsal seta subdistally; dactylus and unguis not fused, clawlike, strongly curved, as long as dactylus plus unguis of pereopods 2 and 3 but stouter, combined length about 0.67 times the length of propodus.
Pleopods (visible in the paratype, Fig. 11 View Figure 11 ) all alike, basal article rounded; with long setae bundled together under the pleon.
Uropod ( Figs 9D View Figure 9 , 10C View Figure 10 , 12 View Figure 12 ) biramous, the endopod about 1.88 times the length of exopod; basal article subrectangular, widening distally, fairly short and stout, about as long as thick, slightly shorter than exopod article 1, without visible setae. Endopod relatively long and slender, with two subequal articles; article 1 with two long setae distally, article 2 with one outer long seta subdistally and three long plus two short setae distally. Exopod not reaching half the length of distal endopodal article, much thinner than endopod, with two subequal articles; article 1 with one outer long seta distally, and article 2 ending with two long setae.
Remarks
Arcantitanais turpis gen. et sp. nov. is mainly distinguished from the other taxa described herein by its body shape, antennular articulation, cheliped morphology, pereopod 1 with very long dactylus, pereopods 4 – 6 heavily armed with curved spines, and uropods with both rami elongated and slender.
Pereopodal ischial setation can be diagnostic ( Bird & Holdich, 1984) and the setae in Arc. turpis seem to be a suitable taxonomic character for species description. However, in general terms when observing tanaidaceans preserved in amber, these setae are fragile and it is often not possible to determine whether they have been broken off or were never present. Although not included in the diagnosis, it is notable that Arm. rara gen. et sp. nov. has a welldeveloped ischium on pereopods 4 – 6 bearing up to two short and thin setae, whereas Arc. turpis has a shorter ischium on pereopods 4 – 6 bearing up to one seta.
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