Fissarcturus Brandt, 1990

Nickel, Judith M. & Brandt, Angelika, 2013, A new species of Fissarcturus Brandt, 1990 (Isopoda, Valvifera, Antarcturidae) from the Southern Ocean, off the South Sandwich Islands, Zootaxa 3692 (1), pp. 136-148 : 138-147

Genus Fissarcturus Brandt, 1990

Fissarcturus: Brandt 1990: 129 ; Wägele, 1991: 174; Poore, 2001: 224. Type species: Fissarcturus emarginatus Brandt, 1990 .

Species composition: Fissarcturus bathyweddellensis Brandt, 2007 , Fissarcturus elongatus (Brandt, 1990) , F. emarginatus Brandt, 1990 , Fissarcturus granulosus (Nordenstam, 1933) , Fissarcturus hirticornis (Monod, 1926) , Fissarcturus mawsoni (Hale, 1946) , Fissarcturus minutus (Brandt, 1990) , Fissarcturus patagonicus (Ohlin, 1901) , Fissarcturus paxillaris (Kussakin & Vasina, 1998) , Fissarcturus poorei (Kussakin & Vasina, 1998) , Fissarcturus robustus (Brandt, 1990) , Fissarcturus rossi Brandt, 2007 , Fissarcturus rugosus (Nordenstam, 1933) , F. sandwichi Brandt, 2007 , Fissarcturus scelerosus (Brandt, 1990) , Fissarcturus stebbingnordenstami (Brandt, 1990) , Fissarcturus stephenseni Wägele, 1991 .

Generic diagnosis. Eyes lateral, rounded or rather oval, sometimes absent; body slender and elongated, dorsally with spines on all segments. Cephalothorax dorsally with two well developed supraocular spines and often a second pair of spines about as long as or shorter than the supraocular ones. Lateral margins of head and pereonite 1 not expanded downwards to cover mouthparts. Pairs of mediodorsal, dorsolateral, lateral, supracoxal and/or coxal spines on each pereonite. All pleonites fused with pleotelson, pleonite 1 defined by suture. Tip of pleotelson cleft, forming two stout, long, diverging caudolateral spines or pleotelson with a pair of caudolateral pronounced spines. Antennula distalmost flagellar article with several pairs of aesthetascs; second flagellar article longer than usual in the family, third flagellar article shorter. Antenna shorter than or as long as body, stout, with short flagellum, a maximum of four flagellar articles and a distal claw-like article. Dactylus of pereopod 1 forming a strong subchela with propodus; dactylus not swollen, propodus long and slender. Dactylus of pereopods 2–4 cylindrical, with a short article and a terminal claw as long as or longer than dactylus itself; without filter setae (Brandt 1990; Wägele 1991).

Fissarcturus dorotheae sp. nov. ( Figs. 2–6 )

Type material. Holotype: SO, South Sandwich Islands: non-ovigerous f# (6.8 mm), station ANDEEP 143-1 (58° 44.69 S, 25° 10.28 W - 58° 44.45 S, 25° 10.66 W), 774 m depth, 25 March 2002, RV Polarstern, EBS (ZMH- K43285 ); Paratypes: SO, South Sandwich Islands: 6f#, 1 non-ovigerous female, 6 mm, ZMH-K43286; 1 juvenile female, 3 mm, ZMH-K43287; 1 juvenile female, 4 mm, ZMH-K43288; 1 juvenile female, 5 mm, ZMH- K43289 ; 1 juvenile female, 5 mm, ZMH-K43290; 1 juvenile female, 5.5 mm, ZMH-K43291. All specimens were collected at the same station as the holotype.

Diagnosis. Spination of pereonites, cephalothorax and pleotelson weak, tubercular-like; only supraocular spines, dorsolateral spines of pereonite 1 and posteriormost lateral spines of pleotelson pronounced; supraocular spines and spines of pereonite 1 long and strong. Preocular spines absent; second cephalic spines little incisive, boss-like structures; supraocular spines equipped with several small spinules. Angular boss-like structures located medially or submedially in front of submedial spines on pereonites 1–3.

Description of female holotype (dorsal and lateral views) and paratype (appendages). Habitus of female holotype ( Figs. 2 a–b): Body length 6.8 mm. Eyes rounded, 0.25 of lateral length of cephalothorax. Body long, slender, pereonite 1 fused with cephalothorax; dorsal transverse ridge between cephalothorax and pereonite 1. Preocular spines absent; supraocular spines long, blunt, strongly curved frontally, equipped with spinules, not covering the eyes in dorsal view. Second cephalic spine much shorter than supraocular spine, weakly expressed, a boss-like structure; cephalothorax equipped with small spinules and tubercles. Pereonite 1–3 of about same length and width, pereonite 4 longest, slightly narrower than pereonites 1–3, of about same width as pereonites 6–7, pereonite 5 slightly longer than pereonites 4 and 6–7. Pereonal spination comprising elements in submedial, dorsolateral, supracoxal and coxal positions. Submedial and dorsolateral spines present on pereonites 1–4; submedial spines longest; dorsolateral spines of greater number than submedial ones, smaller and tubercular-like. Pereonites 1–3 with angular boss-like structures located medially or submedially in front of submedial spines. Submedial and dorsolateral spines present on pereonites 5–7, tubercular-like, smaller than dorsolateral spines of pereonites 1–4; dorsolateral spines of pereonites 5–7 of greater number than submedial ones. Pereonite 1 without coxal spination; some small, tubercular-like spines on and above coxae of pereonite 2–6 varying in quantity. Pleon without submedial spines; dorsolateral spines of similar quantity and shape as on pereonites 5–7. All pleonites fused with pleotelson. Pleotelson length about 0.2 times body length, width about 0.5 of total pleotelson length. Position of posteriormost lateral spines at 0.61 of pleotelson length. Spination less prominent, except for the pair of strong spines near apex; several small spines submedially and laterally; partly with small scattered tubercles. Pleotelson apex prominent, triangular and caudally rounded.

Antennula ( Fig. 4 a): length 0.17 times body length, consisting of three peduncular and two flagellar articles; proximalmost peduncular article broadest, 1.5 times longer than wide and shorter than second one, medially and laterally setulated. Second peduncular article longest, 1.2 times longer than first one, with 1 simple seta, seven feather-like setae and another single medial one. Peduncular article 3 smallest, length 0.52 times length of second one, with two simple setae. First flagellar article forming a very short ring with three feather-like setae; terminal article 2.3 times longer than third peduncular article, with several simple setae and six groups of two aesthetascs.

Antenna ( Fig. 4 b): peduncle length 0.8 times body length, with five peduncular and three flagellar articles. Strong lateral spines on articles 2–4, peduncular articles 3–4 with dorsal and ventral short spinules. Third peduncular article length 2 times second peduncular article length and 2.7 times longer than wide. Article 4 long and slender, length 2.3 times article 3 length, with several groups of short bristles and single ones laterally. Article 5 longest, length 2.9 times article 3 length, with several short setules. Flagellar articles with several short setules; first flagellar article longest; second one shortest, 0.52 times length of first flagellar article; article 3 with three terminal setae and a distal claw, 0.72 times length of first flagellar article.

Mandible ( Figs. 3 a–b): mandibles both without palp and asymmetrical. Pars incisiva of rMd with five chitinised cusps; lacinia mobilis of same length as pars incisiva, with four cusps and a row of three setulated setae. Pars molaris stout, broad grinding surface with indented upper margin; setulated dorsally, laterally with eleven simple setae. Pars incisiva of lMd of same length as lacinia mobilis, with four chitinised cusps; lacinia mobilis of lMd with four cusps and four denticulate setae. Pars molaris of lMd stouter than molar process of rMd; setulated dorsally, with four simple setae and one single toothed bristle.

Maxillula ( Fig. 3 c): consisting of two endites, both slightly narrowing distally; medial endite width 0.5 times lateral endite width; lateral endite length 4.1 times width, distally curved medially, with few simple setae and apically ten strong spines, some of them bearing three to four teeth-like structures. Medial endite shorter, length 0.4 times lateral endite length, apically with three roundly setulated long setae.

Maxilla ( Fig. 3 d): consisting of three endites, the inner broad one with four simple setae, six stouter setae roundly covered with long setules and one long and slender seta covered with setules in the proximal and teeth-like structures in the distal part. Medial and lateral endite width 0.5 times inner endite width; medial endite with three simple setae, medially with slender setules and apically with three long and slender setae covered with setules and cusps as the single one of inner endite. Lateral endite with three similar but longer setae, and several similar hairlike setae medially.

Maxilliped ( Fig. 3 e): long-oval epipodite, strong endite and five-segmented palp. Epipodite with three simple setae; covered with setules laterally and medially; endite as long as epipodite, surpassing the second palpal article, distally covered with setules and bearing six spine-like setae, three to four of them surrounded with setules. First palpal article shortest, length 0.4 times length of second article; article 3 longest, 1.4 times longer than article 2; article 4 about as long as article 2, last article 1.3 times longer than first one. First two articles with few setae, dense medial and apical brush of long setulated setae at third to fifths articles.

Hypopharynx ( Fig. 3 f): consisting of two outer and two inner lobes. Outer lobes three times bigger than inner lobes.

Pereopod 1 ( Fig. 4 c): more robust than pereopods 2–7. Basis longer than propodus, 2.9 times longer than wide; distoventrally with five long and slender simple setae, laterally and medially equipped partly with row of setules. Ischium length 0.6 times basis length, 1.8 times longer than wide; ventrally with five long and slender simple setae, one of them covered with setules, and with very few setules dorsally. Merus length 0.6 times ischium length, 1.3 times wider than long, with four simple setae ventrally, two of them setulated, one simple seta laterally, another one distodorsally as well as few setules distodorsally. Carpus trapezoidal, 1.1 times wider than long, about as long as merus; ventrally with one small and eight long and slender simple setae, four to five of them covered with setules, one similar simple seta laterally and a row of setules distoventrally. Propodus subchelate and slender, length 2.6 times carpus length, twice as long as wide; propodus and dactylus densely setose, propodus ventrally and partly laterally with small and long, slender simple setae, many of them covered with setules, some long and slender, feather-like setae distodorsally and laterally. Dactylus shorter than propodus, 4.5 times longer than wide, with two short distal claws and between bearing a seta; with several long and slender simple and feather-like setae.

Pereopod 2 ( Fig. 4 d): basis 2.1 times longer than wide; with two small simple setae dorsally, one long, slender and two small simple setae distoventrally and a row of setules distodorsally. Ischium length 0.8 times basis length, 1.8 times longer than wide; with three small simple setae distodorsally, another three ventrally and another one distoventrally; with few setules proximodorsally and distoventrally. Merus length 1.4 times ischium length, 2.3 times longer than wide; with two small simple setae dorsally and another five ventrally, very few setules proximoventrally and one long filter seta ventrally. Carpus length 2.4 times merus length, 6.6 times longer than wide; with seven small simple setae dorsally, another ten ventrally and eight strong and long filter setae ventrally. Propodus length about 0.9 times carpus length, 9.5 times longer than wide; with ten small simple setae dorsally, ventrally and laterally and nine long filter setae distoventrally. Dactylus length 0.4 times propodus length, 12.5 times longer than wide; with four small simple setae distally. Unguis longer than dactylus.

Pereopod 3 ( Fig. 5 a): basis 3.6 times longer than wide; with one long filter seta distolaterally and two small simple setae distoventrally. Ischium length 0.7 times basis length, 2.7 times longer than wide; with one long spinelike seta proximoventrally, three small simple setae ventrally and few setules distodorsally. Merus 1.2 times longer than ischium, 2.9 times longer than wide; with three long filter setae and five small simple setae ventrally. Carpus length 2.1 times merus length, 7.2 times longer than wide; with five small simple setae dorsally, another eight ventrally and six long filter setae ventrally. Propodus about 0.8 times carpus length, 8.8 times longer than wide; with eight small simple setae dorsally, another eight ventrally and eleven long spine-like setae spread laterally and ventrally. Dactylus length about 0.5 times propodus length, 9 times longer than wide; with two small and slender simple setae distally. Unguis length 1.25 times dactylus length.

Pereopod 4 ( Fig. 5 b): basis 6 times longer than wide; with four small simple setae dorsally, another seven ventrally, two distally, two small rows of setules distodorsally and –ventrally and three long filter setae distally; bearing one small single feather-like seta dorsally. Ischium about 0.5 times basis length, 2.8 times longer than wide; with two small simple setae and three long spine-like setae laterally. Merus length about 1.1 times ischium length, 3 times longer than wide; with five long filter and six small simple setae ventrally. Carpus 2.2 times longer than merus, 7.8 times longer than wide; with fourteen small simple setae arranged dorsally and ventrally and nine long filter setae laterally and ventrally. Propodus length 0.6 times carpus length, 5.8 times longer than wide; with five simple setae dorsally, four simple setae ventrally, a single one distally and eight long filter setae lateroventrally and distally. Dactylus about 0.6 times propodus length, 10.7 times longer than wide; with two simple setae distally. Unguis length about 0.8 times dactylus length.

Pereopods 5–7 ( Figs. 5 c–e): shorter and stronger than P2–4; two distal claws, stouter and much shorter than unguis of P2–4.

Pereopod 5 ( Fig. 5 c): basis longest article, 5.8 times longer than wide; with two simple setae each ventrally and dorsally, few setules dorsally and several setules ventrally; bearing five feather-like setae dorsally; dorsally partly serrated. Ischium length about 0.6 times basis length, 4.4 times longer than wide; with few small simple setae dorsally and ventrally, a single longer one distally, setulated ventrally and distodorsally. Merus 0.5 times ischium length, twice as long as wide; with three simple setae ventrally, a single hemiplumose, spine-like seta; densely setulated ventrally and distodorsally. Carpus length 2.1 times merus length, 2.5 times longer than wide; with two simple setae distodorsally, a single one dorsally and another one distoventrally; with four hemiplumose, spine-like setae ventrally; densely setulated ventrally and with few setules distodorsally. Propodus 1.8 times longer than carpus, 4.8 times longer than wide; with two setulated spine-like setae as on merus and carpus and two simple setae ventrally, two simple setae distodorsally, one of them long and slender, a dense row of setules ventrally, few setules dorsally; bearing a single feather-like seta dorsally. Dactylus length about 0.5 times propodus length, 3.7 times longer than wide; with few simple setae and setules dorsally and ventrally, three simple and slender setae distally and two short distal claws, dorsal one much longer and stouter than ventral one.

Pereopod 6 ( Fig. 5 d): basis longest article, 4.3 times longer than wide; with several simple setae dorsally and ventrally and two feather-like setae dorsally. Ischium length 0.6 times basis length, 4.1 times longer than wide; with few simple setae ventrally, densely setulated ventrally, with few setules distodorsally. Merus length 0.6 times ischium length, twice as long as wide; with one simple seta dorsally, three spinulated setae ventrally, with few setules distodorsally, densely setulated ventrally. Carpus about as long as merus, 2.4 times longer than wide; similar in setation to merus but instead of few setules, two long spine-like setae distodorsally. Propodus 1.8 times longer than carpus, 4.6 times longer than wide; with three setulated setae and a dense row of setules ventrally, three long spine-like setae, several simple setae and a single feather-like seta dorsally. Dactylus length 0.4 times propodus length, 3.7 times longer than wide; with few simple setae and several setules dorsally and ventrally, one simple seta and two claws distally, shape similar to P5.

Pereopod 7 ( Fig. 5 e): basis 2.6 times longer than wide; with four simple setae ventrally, another one dorsally, a single feather-like seta and very few setules dorsally. Ischium length about same as basis length, 3.5 times longer than wide; with few simple setae ventrally and dorsally, few setules distodorsally and a dense row of setules distoventrally. Merus length 0.6 times ischium length, 2.1 times longer than wide; with three simple setae dorsally, few setules distodorsally, a single setulated seta and a dense row of setules ventrally. Carpus length 0.7 times merus length, 1.7 times longer than wide; with two long setae distodorsally; setation ventrally similar to merus. Propodus longest article, length 2.4 times carpus length, 4.4 times longer than wide; with three setulated setae and densely setulated ventrally, five simple setae, three of them dorsally, one laterally, one ventrally, few setules and a single feather-like seta dorsally. Dactylus length about 0.4 times propodus length, 2.5 times longer than wide; with several setae of varying length dorsally and ventrally and another two distally in between two distal claws with same shape as the ones of P5–6.

Pleopod 1 ( Fig. 6 a): sympodite 0.6 as long as rami, with four coupling setae and a lateral row of five to six teeth-like structures. Exopodite of about same length as endopodite, width 1.3 times width endopodite; terminally and medially equipped with setae, ten distal and five lateral long and slender setae, ten of them plumose; endopodite with ten distal long and slender setae, three of them plumose.

Pleopod 2 ( Fig. 6 b): of about same size and shape as Plp1; a tooth-like structure visible laterally on sympodite; exopodite length about 1.5 times endopodite length, width 1.2 times endopodite width; exopodite and endopodite terminally and medially equipped with setae; exopodite with eleven distal long and slender plumose setae; endopodite with two lateral and nine distal long and slender plumose setae.

Pleopod 3 ( Fig. 6 c): sympodite length about 0.2 times rami length; with one simple seta. Endopodite with several small simple setae laterally and medially, two lateral simple setae and four medial plumose setae; exopodite with eight lateral groups of three to four simple setae, shorter than setae of endopodite.

Pleopod 4 ( Fig. 6 d): sympodite short; endopodite length 0.9 times exopodite length, both of same width; endopodite laterally and medially equipped with small simple setae, four long and slender plumose setae, two lateral and two medial ones. Exopodite medially with row of small simple setae.

Pleopod 5 ( Fig. 6 e): sympodite short, length about 0.1 times exopodite length; with one simple seta; exopodite 1.3 times longer than endopodite, bare; endopodite of about same width as exopodite, with few simple setae distally and two long and slender plumose seta laterally.

Uropods ( Fig. 6 f): exopodite length 1.1 times endopodite length; rami equipped roundly with small setules; endopodite with three distal setae.

Etymology. The new species is named in honour of the first author’s grandmother Dorothea Stelzer.

Distribution. Only known from type locality.

Remarks. Only the female of Fissarcturus dorotheae is known. F. d o ro t h e a e can easily be distinguished from other species of the genus by the dorsal spination of the body. Only the supraocular spines, the dorsolateral spines of the first pereonite and the most proximal caudolateral spines of the pleotelson are pronounced, the remaining spines are very small, weak or tubercular-like. On the first three pereonites there are angular, boss-like structures located medially or submedially in front of the submedial dorsal spines which are not present in this form in other species of this genus.

The new species is most similar to Fissarcturus sandwichi Brandt, 2007 , but does not bear the typical cauliflower-like dorsal spination. Furthermore, the coxal spination differs from the one of F. sandwichi : the new species bears no spines on the first coxa, but in F. s a n d w i c h i there are several frontally directed marginal spines on coxa 1. In contrast to F. s a n d w i c h i there are neither tubercles on the ischium or carpus of pereopods 2–4 nor tubercles or denticulate spines on the bases of pereopods 2–7 in F. d o ro t h e a e. F. sandwichi does not bear any further spines on the cephalothorax besides the supraocular spines and the second cephalic spines. The new species, however, is equipped with several small spinules and tubercles dorsally on the cephalothorax. There is also a difference in the number of articles of the antennal flagellum: there are four articles present in F. sandwichi , in comparison to only three in case of F. dorotheae . The caudolateral pleotelsonic spines insert less caudally in the new species. In F. dorotheae they are inserted at 0.4 pleotelsonic length from the caudal tip in contrast to F. sandwichi where they insert at 0.3 pleotelsonic length from the caudal tip. The pleotelsonic spines and tubercles are less numerous in F. dorotheae . The supraocular spines of F. d o ro t h e a e are strong and frontally bent like in F. sandwichi , but contrary to this species they are equipped with several small spinules. Spinulated spines are otherwise only present in Fissarcturus rossi Brandt, 2007 from which the new species can easily be distinguished by the less prominent dorsal spination in case of F. dorotheae and the caudolateral pleotelsonic spines which insert more apically and are longer in F. rossi . As in Fissarcturus mawsoni (Hale, 1946) the supraocular spines of F. dorotheae are the longest spines of the body and the bodies of both species bear many small and blunt spines, but in contrast to F. mawsoni the new species has smaller caudolateral pleotelsonic spines which insert more anteriorly. The supraocular spines are acute and rather straight in F. mawsoni but apically rounded and strongly bent frontally in the new species. Furthermore, the second cephalic spines differ in these species; in F. dorotheae these spines are very weakly pronounced and resemble boss-like structures similar to the ones of F. sandwichi .

Figures

FIGURE 2. Fissarcturus dorotheae sp. nov.; a – b, holotype female (ZMH-K 43285). a, lateral view. b, dorsal view. Scale bar = 1 mm.

FIGURE 3. Fissarcturus dorotheae sp. nov.; a – f, paratype female (ZMH-K 43286). a, rMd. b, lMd. c, Mx 1. d, Mx 2. e, Mxp. f, Hyp. Scale bar = 0.1 mm.

FIGURE 4. Fissarcturus dorotheae sp. nov.; a – d, paratype female (ZMH-K 43286). a, A 1. b, A 2. c, P 1. d, P 2. Scale bar: a, c – d = 0.1 mm, b = 0.5 mm.

FIGURE 5. Fissarcturus dorotheae sp. nov.; a – e, paratype female (ZMH-K 43286). a, P 3. b, P 4. c, P 5. d, P 6. e, P 7. Scale bar = 0.1 mm.

FIGURE 6. Fissarcturus dorotheae sp. nov.; a – f, paratype female (ZMH-K 43286). a, Plp 1. b, Plp 2. c, Plp 3. d, Plp 4. e, Plp 5. f, Urp. Scale bar = 0.1 mm.