Tytthocope fahrbachi, Malyutina, Marina V. & Brandt, Angelika, 2014

Malyutina, Marina V. & Brandt, Angelika, 2014, New species of the deep-sea munnopsid genus Tytthocope (Crustacea, Isopoda, Asellota) from the South Atlantic and the Southern Ocean, Zootaxa 3786 (1), pp. 1-43 : 4-17

Tytthocope fahrbachi sp. nov.

( Figs 1–9 )

Material examined. Holotype ZMH K- 43132: copulatory male 2.45 mm, ANDEEP III, RV Polarstern, EBS, st. 133–2, 16.03.2005, 62°46.73’S, 53°02.57’W, 1584 m. Paratypes ZMH K- 43133: male for dissection 2.55 mm, female for dissection 3.8 mm, juvenile for dissection 1.9 mm, ZMH K- 43134: 74 specimens, 1.8–3.62 mm, from the same station as the holotype.

Additional material: ANDEEP I, RV Polarstern, EBS, st. 46-7, 30.01.2002, 60°38.33’S, 57°57.38’W, 3894 m, 2 females 2.05, 2.9 mm, ANDEEP II, RV Polarstern, EBS, st. 141-10, 23.03.2002, 58°25.07’S, 24°00. 87’W, 2312 m, 3 females 2.45–3.2 mm, male 2.43 mm, ANDEEP III, RV Polarstern, EBS, st. 80-9, 23.02.2005, 70°38.45’S, 14°42.86’W, 3100 m, 7 specimens, 2.2–3.4 mm.

Etymology. The species is named in honor of the expedition leader of ANDEEP III, Dr. Eberhard Fahrbach, who sadly passed away last year.

Diagnosis. Rostrum with serrated lateral keels, anterior margin without setae. Antennula article 1 width more than half of rostrum width and length half of rostrum length. Pleotelson length 0.55 natasome length, narrowly rounded posteriorly. Anteromedial margin of pereonite 5 and pleotelson not raised. Pereonite 5 length 0.25 pleotelson length, 0.6 pereonite 6 length medially, pereonite 7 length 0.1 pleotelson length, 0.25 pereonite 6 length medially, subequal to pereonite 1 in length. Maxilliped palp article 4 distomedial lobe narrow and much shorter than article 5.

Description of copulatory male, holotype. Body ( Fig. 1 ) length 2.53 width of pereonite 5, body height 0.32 of body length. Cephalothorax length 0.65 width, length behind antennula insertion 0.88 antennula article 1 length; rostrum length 0.7 cephalotorax length. Rostrum with serrated lateral keels, anterior margin grooved sloping, length 1.57 antennula article 1 length, width between bases of antennulae slightly more than rostrum length, 2.0 antennula article 1 width. Clypeus 2.0 as wide and 0.5 as long as labrum. Pereonites 1–4 subequal in length, gradually broadened posteriorly, anterolateral margins with small distal seta, coxae of pereopods 1–4 visible in dorsal view, anterolateral margins acute, weakly projected. Natasome length 0.65 body length, width 1.5 cephalon width, dorsum with scattered fine setae, lateral margins with longer setae; pereonites 5 and 6 anterolateral angle with long spine-like UB seta; pereonite 6 length 1.47 pereonite 5 length medially and 0.83 laterally; pereonite 7 length 0.38 pereonite 6 length laterally and 0.25 medially. Pleotelson almost as long wide, length 0.55 natasome length, narrowly rounded posteriorly, preanal ridge small.

Antennula ( Fig. 3 d) length more than 0.35 of body length (tip is broken off); article 1 length 1.25 width, with few fine distal setae, article 2 length 1.2 width, 0.58 length and 0.57 width of article 1 with 2 broom distal setae; article 3 length 0.68 of article 2 length and width 0.77 article 2 width; article 4 length 0.47 article 3 length, with 1 broom distal seta; article 5 and 7 subequal in length to article 3; the following> 23 articles are subequal in length to article 4, articles from 11th onwards with aesthetascs.

Antenna ( Figs 1 a,b, 3e) longer than body (distal part of flagellum broken off); articles 1–4 together equal in length to antennula articles 1–4 length, article 1 small triangular, articles 2–4 subequal in size, scale on article 3 0.3 of article 4 length, with distal seta, article 4 with few distal setae; article 5 subequal in width to articles 1–4, length 2.1 articles 1–4 length together, with 14 stout medial setae, proximal seta largest, and about 10 lateral smaller setae; article 6 length 1.1 article 5 length, width 0.57 article 5 width, dorsal margin with 11 setae: 5 small simple setae proximally and 6 stout setae on distal half, flagellum with more than 11 articles.

Pereopods 1, 3, 4 and 5 broken off.

Pereopod 2 ( Fig. 5 c) length ratios of ischium-dactylus to basis: 0.45, 0.34, 1.24, 1.58, 0.56; basis length 4.18 width, with 1 broom and 3 dorsal small setae and 7 ventral small setae; ischium with 1 dorsal and 2 ventral setae; merus with 1 dorsal and 2 ventral setae; carpus length 7.12 width, with 7 ventral, 4 dorsal small setae and 3 setae distodorsally. Propodus length 9.1 width, with 10 to 11 ventral stout UB setae and 10 dorsal simple setae and 1 broom seta subdistally.

Pereopod 6 ( Fig. 5 d) length ratios of ischium-dactylus to basis: 0.78, 0.26, 1.0, 0.76, 0.34; basis with 2 ventral small setae, ischium with 1 simple ventral seta and distoventral setae, merus with 1 UB distoventral seta; carpus length 1.26 width, with 22 dorsal and 14 ventral plumose setae, propodus length 1.52 width, with 10 dorsal and 11 ventral plumose setae, 1 long stout UB seta distodorsally; dactylus length 3.7 width.

Pereopod 7 ( Fig. 5 e) length 0.64 pereopod 6 length, length ratios of ischium–propodus to basis: 0.5, 0.31, 0.84, 0.50, 0.22; basis with 1 long distoventral seta, ischium with 1 long dorsal seta, carpus length 1.35 width, with 13 dorsal and 7 ventral plumose setae, propodus length 1.77 width with 7 dorsal and 6 ventral plumose setae, dactylus length 3.9 width.

Pleopods ( Fig. 7 ): Pleopod 1 ( Fig. 7 a) tapering distally, length 2.8 proximal width, distal width 0.45 proximal width, distal margin almost straight, with 6 short setae on each lobe, distolateral angles projecting laterally as small acute spines. Pleopod 2 ( Fig. 7 b) protopod length 2.44 width, stylet length 0.6 protopod length; exopod inserted on 0.4 of protopod length from distal margin, hook narrow, 0.5 width of proximal part of exopod. Pleopod 3 ( Fig. 7 c) endopod length 2.1 width, 3 distal plumose setae length about third of endopod length; exopod slightly longer than endopod, width 0.34 endopod width, distal article length 0.5 basal article length, with 2 distal plumose setae, as long as endopod setae. Pleopod 4 ( Fig. 7 d) endopod length 1.87 width, exopod subequal to endopod in length, slightly narrower, distally with 2 plumose setae as long as setae on pleopod 3. Pleopod 5 ( Fig. 7 e) length 1.4 width. Uropod 0.11 pleotelson length.

Adult female. Body ( Fig. 2 ) similar to male body, length 2.48 width of pereonite 6, body height 0.34 of body length. Cephalothorax length 0.54 width, length behind antennula insertion 0.5 antennula article 1 length; rostrum length 0.67 cephalothorax length. Rostrum width between bases of antennulae slightly more than rostrum length, 1.9 antennula width. Natasome length 0.7 body length, width 1.65 cephalon width, lateral margins with scattered fine setae, pereonites 5, 6 and pleotelson with long distolateral seta; pereonite 6 length 1.33 pereonite 5 length medially, subequal to pereonite 5 length laterally; pereonite 7 length 0.43 pereonite 6 length laterally. Pleotelson length 1.08 width, 0.40 body length.

Antennula ( Fig. 3 b) length 0.3 body length; article 1 length 1.3 width, with 4 broom setae dorsally, article 2 length 1.3 width, 0.45 length and 0.46 width of article 1 with 2 broom and 1 simple distal setae; article 3 length 0.63 article 2 length and width 0.47 article 2 width; article 4 length 0.5 article 3 length, with 1 simple distal seta, article 5 2.1 article 3 length, following 8 articles subequal in length to article 3, most of them with aesthetascs.

Antenna ( Fig. 3 c) broken off, articles 1–4 length together equal to antennula articles 1–5 length, article 1 small, triangular; articles 2–4 subequal in size. Scale on article 3 0.3 article 4 length, with 2 distal setae, article 4 with few distal setae.

Mandibles ( Fig. 4 ) incisor process with 4 cusps on both mandibles; lacinia mobilis of left mandible length 0.7 incisor process length, with 4 teeth; spine row with 8 and 10 spines on left and right mandibles respectively; molar process slightly shorter and about twice as broad as incisor process, tapering, with 2 main distal teeth and two long setae; condyle length 0.13 mandibular body length, shorter than molar process; palp slender, length 0.81 mandibular body length, article 1 with few fine setae, article 2 length 2.3 article 1 length, with 2 stout distal setae, article 3 tapering distally, with row of marginal short setae, 1 long setulated seta and 2 shorter simple setae distally.

Maxilla 1 ( Fig. 4 d) lateral endite width 1.8 mesial endite width, with small lateral setae and 12 distal spine-like setae, longest distolateral seta subequal in length to endite width, mesial endite with tuft of fine marginal setae, distal margin acute with few more stout long setae.

Maxilla 2 ( Fig. 4 c) middle endite shortest, lateral and mesial endites equal in length, mesial endite with 4 strong setulated and numerous slender distomedial setae, lateral and middle endites with 2 long and 2 shorter distal setae each.

Maxilliped ( Fig. 3 a) basis length 2.6 width, endite slender, width 0.4 basis width, with 5 coupling hooks, distal margin slightly concave, with 4 fan setae and several simple slender setae, lateral margin rounded; palp inserted after 0.45 length of basis, palp length 0.88 basis length, article 1 lateral length 2.8 medial length; article 2 width 1.2 basis width and 2.8 endite width, lateral length 1.82 medial length, lateral margin slightly convex with 8 setae, 1 seta distomedially, distolateral projection slightly longer than article 3 lateral margin; article 3 width 0.8 article 2 width, medial margin serrated with 4 teeth and 5 setae, medial length 1.06 article 2 medial length; article 4 with 4 lateral setae, medial lobe with 1 long distal seta, length 0.3 article 5 length; article 5 subequal to article 4 lateral length, with 1 lateral and 3 distal setae. Epipod length 2.7 width, lateral margin with 4 simple setae.

Pereopods 1–4 ( Figs 5–6 ): basis of pereopod 1 most slender, basis of pereopod 3 broadest, basis 2 slightly longer and basis 3 slightly shorter than basis 1. Pereopod 1 ( Fig. 5 a) length ratios of ischium-dactylus to basis: 0.31, 0.22, 0.86, 0.51, 0.16; basis length 6.6 width, with 15 dorsal and 16 ventral small setae; ischium and merus slightly narrower than basis, ischium with 2 ventral and 4 dorsal setae; merus with 3 ventral and 2 dorsal setae; carpus narrowing distally, length 11.6 width, with 13 dorsal and 10 ventral small setae; propodus as wide as distal part of carpus width, with 7 dorsal and 6 ventral setae; dactylus with 3 thin setae proximally to claws. Pereopods 2 ( Fig. 5 b) length ratios of ischium-dactylus to basis: 0.55, 0.46, 1.42, 1.66, 0.38; basis length 4.35 width, with 4 dorsal small and 2 broom setae and 17 ventral small setae; ischium and merus almost as wide as basis, ischium with 1 dorsal and 5 ventral setae; merus with 1 dorsal and 4 ventral setae; carpus length 8.85 width, with 15 ventral small simple setae, 10 small dorsal UB setae and broom seta subdistally. Propodus length 17.1 width, width 0.6 carpus width, with 12 dorsal simple setae and 17 ventral stout UB setae, distal seta twice as long as others. Dactylus claws broken off. Pereopod 3 ( Fig. 6 a) without propodus and dactylus, length ratios of ischium-carpus to basis: 0.43, 0.42, 1.31; basis length 5.26 width, with 12 small dorsal and 2 broom setae and 14 small ventral setae; ischium and merus slightly narrower than basis, ischium with 4 dorsal and 4 ventral setae; merus dorsal margin with 1 small seta and 1 long seta distally, ventral margin with 4 small setae and UB seta distally; carpus length 9.35 width, with 8 ventral small UB setae, 10 dorsal small UB setae, stout distodorsal seta broken off. Pereopod 4 broken off, basis ( Fig. 6 b) length 5.38 width and 1.1 pereopod 3 basis length.

Pereopods 5–7 ( Fig. 6 ): Pereopod 5 ( Fig. 6 c) length 1.12 pereopod 1 length, with shorter basis, length ratios of ischium–dactylus to basis: 0.89, 0.3, 1.14, 0.83, 0.3; basis with 11 ventral small setae and 1 dorsal long UB seta, ischium with 4 dorsal plumose setae and 8 simple ventral setae with longest distally, merus with ventral UB setae; carpus length 1.31 width, with 28 dorsal and 10 ventral plumose setae, distodorsally with broom seta, propodus length 1.6 width, with 14 dorsal and 14 ventral plumose setae, distodorsal margin with 1 long stout UB seta and one broom seta and 1 small UB seta distoventrally, dactylus length 3.28 width, 2 small setae distally. Pereopod 6 ( Fig. 6 d) length 1.03 pereopod 5 length, basis longer (1.22), ischium slightly shorter (0.88) than these articles of pereopod 5, length ratios of ischium-dactylus to basis: 0.64, 0.26, 0.97, 0.67, 0.21; basis with 14 ventral small setae and 3 distoventral UB setae, ischium with 11 simple ventral setae and 2 plumose dorsal setae, merus with 2 UB setae and 7 small setae ventrally and 1 dorsal set; carpus length 1.3 width, with 30 dorsal and 11 ventral plumose setae, propodus length 1.57 width, with 14 dorsal and 15 ventral plumose setae, distodorsal margin with 1 long stout UB seta, dactylus length 3.33 width, with serrate dorsal margin, 2 small distal setae. Pereopod 7 ( Fig. 6 e) length 0.64 pereopod 6 length, length ratios of ischium–propodus to basis: 0.6, 0.25, 1.0, 0.55, 0.20; basis with simple small setae proximally and 1 plumose distoventral seta, ischium with 1 dorsal and 2 ventral plumose setae, merus with dorsal plumose seta, carpus length 1.2 width, with 26 dorsal and 8 ventral plumose setae, propodus length 2.05 width with 8 dorsal and 8 ventral plumose setae, dorsal margin with serrate fringe of setulae; dactylus as long as distodorsal seta of propodus.

Pleopod 2 ( Fig. 2 d) length 1.17 width, height 0.38 length.

Uropod ( Fig. 5 f) 0.11 pleotelson length. Protopod length 0.8 width, slightly broadened distally, with 3 distal setae; endopod length 1.8 protopod length, with 2 small medial setae, 3 UB and 2 broom distal setae; exopod 0.6 of endopod length and 0.5 width, with 1 broom and 1 simple distal setae.

Juvenile. Although the specimen has an operculum, the stout antennula indicates the juvenile is male. Body ( Fig. 2 d) length 2.5 width of pereonite 5. Rostrum length 0.55 cephalon length. Rostrum with weak lateral keels, anterior margin sloping, with two setae, width between bases of antennulae subequal to rostrum length, width 1.35 antennula width. Pleotelson length 1.18 width, 0.35 body length.

Antennula ( Fig. 9 b) article 1 length 1.26 width, with 2 dorsal setae; article 2 0.55 length and 0.5 width of article 1, with 4 distal broom setae; article 3 length 0.4 of article 2; article 4 length 0.75 following growth zone weakly differentiated on segments, thicker than articles 3 and 4, next 6 articles subequal in length to article 4, last with aesthetasc.

Antenna ( Figs 2 d, 9a) subequal to body in length; article 5 length 1.6 articles 1–4 together; article 6 1.2 article 5; flagellar articles not less than 11 (tip broken off).

Pereopods 1–4 ( Fig. 8 ): Pereopod 1 ( Fig. 8 a) length ratios of ischium-dactylus to basis: 0.38, 0.26, 1.05, 0.70, 0.33; basis length 4.5 width, with 1 dorsal broom and few small setae; ischium and merus with 2 small simple setae each; carpus with 4 dorsal and 4 small ventral setae; propodus with 4 dorsal and 3 ventral setae; dactylus with 3 thin setae proximal to claws.

Pereopods 2–4 bases with 1 or a few dorsal broom setae and a few small setae; ischii and meri with a few small simple setae, meri 2–4 with 1 distodorsal and 1 distoventral UB setae; carpi with few dorsal and ventral UB setae, ventral margin with serrated transparent fringe; propodi with ventral stout UB setae, distal seta twice as long as the others, dorsally simple and UB setae and 1 broom seta subdistally; dactyli elongate with slender claws. Pereopod 2 ( Fig. 8 b) length 1.59 pereopod 1 length, length ratios of ischium–dactylus to basis: 0.50, 0.43, 1.09, 1.31, 0.53; basis length 3.47 width, ischium with 1 dorsal and 4 ventral setae; merus with 2 distodorsal and 2 ventral setae; carpus with 4 ventral UB setae, 5 dorsal and 2 distodorsal setae. Propodus with 7 simple setae and 1 subdistal broom seta dorsally and 6 ventral stout UB setae, distal seta twice longer than others. Pereopod 3 ( Fig. 8 c) of the same length as pereopod 2, length ratios of ischium–dactylus to basis: 0.46, 0.49, 1.20, 1.4, 0.45. Pereopod 4 ( Fig. 8 d) length 1.15 pereopod 2 length, ratios of ischium–dactylus to basis: 0.46, 0.38, 1.26, 1.5, 0.48.

Pereopods 5 and 6 ( Fig. 9 ) same length, 1.16 pereopod 1 length. Pereopod 5 ( Fig. 9 c) length ratios of ischium– dactylus to basis: 0.78, 0.35, 1.0, 0.69, 0.35, basis length 2.8 width, with 1 UB, 1 plumose and 2 dorsal broom setae; ischium with 3 dorsal plumose setae; merus with 1 UB and 2 ventral simple setae; carpus length 1.14 width, with 19 dorsal plumose setae, 7 ventral plumose setae. Pereopod 6 ( Fig. 9 d) length ratios of ischium–dactylus to basis: 0.72, 0.29, 0.90, 0.62, 0.31; carpus length 1.3 width.

Uropod ( Fig. 9 e) 0.12 pleotelson length. Protopod length 1.0 width, 2 setae distally; endopod length 1.66 protopod length, with 2 simple medial, 1 broom, 3 simple and 2 UB distal setae; exopod 0.6 of endopod length and 0.44 width, with 1 UB and 1 distal simple seta.

Remarks. In possessing denticles on the rostral margins, and with regard to the short pereonite 7, the new species resembles the type species of the genus, T. megalura . The maxillipeds of both species have a similar shape: palp article 2 has a long distolateral projection, article 3 is visibly narrower than article 2: its width is just 0.8 of article 2 width. The differences to T. megalura are: medial margin of article 3 is serrate in the new species and smooth in T. megalura , article 5 is more slender than that of the latter, the endite of the new species has 5 coupling hooks instead of 3 in T. megalura . In contrast to T. megalura the male pleopod 1of the new species has a broader distal margin with acute lateral projections; the male pleopod 2 has a longer, more slender stylet, the exopod of pleopod 4 has 2 distal plumose setae instead of 1 in T. megalura .

The following new species described herein also belongs to this group of species. When Wilson & Hessler (1981) redescribed T. megalura they mentioned three undescribed species from the Atlantic deep sea with a similar serrate rostrum, but these species are still undescribed.

Distribution. The Weddell Sea, at depths between 1584 and 3894m.

Figures

FIGURE 1. Tytthocope fahrbachi sp. nov. Holotype male (ZMH K- 43132). A, body, dorsal view. B, body, lateral view. C, cephalon frontal oblique view. D, pleotelson, ventral view.

FIGURE 2. Tytthocope fahrbachi sp. nov. Paratype female (ZMH K- 43133). A, body, dorsal view. B, body, lateral view. C, pleotelson, ventral view. D, juvenile, body, dorsal view.

FIGURE 3. Tytthocope fahrbachi sp. nov. Paratypes male and female (ZMH K- 43133). A, maxilliped, with details of endite distal margin. B, female antennula. C, basal part of female antenna. D, male antennula. E, male antenna.

FIGURE 4. Tytthocope fahrbachi sp. nov. Paratype female (ZMH K- 43133). A, left mandible with details of palp distal article and incisor. B, right mandible with details of palp distal article and incisor. C, maxilla 2 with details of distal margins of lobes. D, maxilla 1 with details of distal margins of lobes.

FIGURE 5. Tytthocope fahrbachi sp. nov. Paratypes male and female (ZMH K- 43133). A, female pereopod 1. B, female pereopod 2. C, male pereopod 2. D, male pereopod 6. E, male pereopod 7. F, female uropod.

FIGURE 6. Tytthocope fahrbachi sp. nov. Paratypes female (ZMH K- 43133). A, pereopod 3. B, basis of pereopod 4. C, pereopod 5. D, pereopod 6, E, pereopod 7.

FIGURE 7. Tytthocope fahrbachi sp. nov. Paratype male (ZMH K- 43133). A, pleopod 1. B, pleopod 2. C, pleopod 3. D, pleopod 4. E, pleopod 5.

FIGURE 8. Tytthocope fahrbachi sp. nov. Paratype, juvenile (ZMH K- 42970) A, pereopod 1. B, pereopod 2. C, pereopod 3. D, pereopod 4.

FIGURE 9. Tytthocope fahrbachi sp. nov. Paratype, juvenile (ZMH K- 42970). A, antenna. B, antennula. C, pereopod 5. D, pereopod 6. E, uropod.