Spectrarcturus murdochi Stransky & Svavarsson & Poore & Kihara 2020, comb. nov.
Creators: name: Stransky, Bente
name: Svavarsson, Jörundur
name: Poore, Gary C. B.
name: Kihara, Terue Cristina
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Isopoda
Arcturidae
Spectrarcturus
Spectrarcturus murdochi

description: Spectrarcturus murdochi (Benedict, 1898) comb. nov.
(Figs 9–25)
Arcturus murdochi Benedict, 1898: 49–50, fig. 9.
Pleuroprion murdochi.— Richardson, 1899a: 855.— Richardson, 1900: 230.— Richardson, 1905: 342–344, figs 371–372.— Hansen, 1916: 195–196.— Boone, 1920: 30.— Gurjanova, 1936, 198–200, fig. 127.— Gurjanova, 1952: 176.— Schultz,
1969: 52, fig. 53a.— Kussakin & Mezhov, 1979: 149.— Kussakin, 1982: 424–427, figs 315–316. Spectrarcturus multispinatus Schultz, 1981: 67, fig. 2A–I. Syn. nov.
Material examined: Pleuroprion murdochi, holotype, female, 10.5 mm (12 mm according to Richardson 1905) (USNM 7915), Point Barrow Expedition, 31 August 1883, Point Franklin, Alaska.
Spectrarcturus multispinatus, holotype, female, 10 mm length (9 mm according to Schultz 1981) (USNM 181264) (holotype extensively fouled with bacteria), Hero 3-290, Little Nellefiske Bank, Greenland, 64°54´N, 53°38´W, 18 August 1968, 79– 85 m.
New material: Illustrated or dissected specimens. Female, 7.6 mm (ZMH 43165), WH244 Stn 2002-3 (SW station revisited), 60°00.18´N, 46°31.02´W, 167 m, 1 November 2002, sediment as in stn 2001-3, 4.44°C, salinity 34.03, 749 individuals; male, 4.3 mm (ZMH 43166), WH244 Stn 2002-3, same data as before; female, 6.8 mm (ZMH 43167), WH244 Stn 2002-3, same data as before; preparatory female, 6.0 mm (ZMH 43168), WH 233 Stn 2001-3 (SW station), 59°59.99´N, 46°30.83´W, 161 m, 19 October 2001, sandy bottoms, with few small stones and rich in macroinvertebrates (corals, crinoids, ophiuroids, sponges), 5.88°C, salinity 34.53, 847 individuals; preparatory female, 5.9 mm (ZMH 43169), WH244 Stn 2002-3, same data as before; female, 7.6 mm (ZMH 43170), WH 233 Stn 2001-3, same data as before; female, 7.5 mm (ZMH 43171), WH 233 Stn 2001-3, same data as before; juvenile (manca 2), 2.1 mm (ZMH 43172) WH244 Stn 2002-3, same data as before; juvenile (manca 3), 3.3 mm (ZMH 43173), WH244 Stn 2002-3, same data as before; male, 4.1 mm (ZMH 43174), WH244 Stn 2002-3, same data as before; female, 7.2 mm (ZMH 43175), WH244 Stn 2002-3, same data as before.
Further material (not catalogued material, deposited at ZMH, UI and ZMB): WH 233 Stn 1013, 63°36´N, 37°41´W, 237 m, 24 October 2001, sediment consisting mostly of sand, corals, sponges and mussel shells, 4.34°C, salinity 34.86, 13 individuals; WH 233 Stn 1016, 63°34´N, 39°18´W, 219 m, 25 October 2001, sediment as in stn 1013, 4.37°C, salinity 34.81, 4 individuals; WH 233 Stn 1023, 62°28´N, 40°39´W, 251 m, 26 October 2001, sediment as in stn 1013, 4.68°C, salinity 34.48, 1 individual; WH 233 Stn 1047, 60°18´N, 46°35´W, 154 m, 31 October 2001, sediment pure sand, 5.53°C, salinity 34.52, 7 individuals; WH 233 Stn 2001-4 (NW station), 63°07.44´N, 52°17.50´W, 162 m, 6 November 2001, sandy bottoms, with few small stones and rich in macroinvertebrates (corals, crinoids, ophiuroids, sponges), 5.74°C, salinity 34.83, 2 individuals; WH 268 Stn 2004-3 (SW station revisited), 59°59.94´N, 46°31.05´W, 23 October 2004, 160 m, sediment as in stn 2001-3, 6.22°C, salinity 34.67, 349 individuals; WH 268 Stn 2004-4 (NW station revisited), 63°07.22´N, 52°16.84´W, 152 m, 28 October 2004, sediment as in stn 2001-4, 4.48°C, salinity 33.96, 12 individuals. This material was referred to as Spectrarcturus multispinatus in Stransky & Brandt (2010) and Stransky & Svavarsson (2010).
Diagnosis: Body with several large, bluntly pointed spines; 8 spines in transverse row on pereonite 1; pereonite 2 with 6 spines in transverse row, laterodistal margin anterior knob where spines are found on latter pereonites; pereonite 3 with 6 spines in transverse row and small anterolateral and posterolateral spines; pereonite 4 trapezoid, 1.8–2.5 times longer than third pereonite, with anterior transverse spine row with 6 spines, smaller anterolateral spine and small lateral spine or fork spine posterior to spine row; posterior spine row with 6 spines; pereonite 5 with 6 spines in transverse row, small anterolateral and posterolateral spines; pereonite 6 with 6 spines in transverse row, small anterolateral and posterolateral spines; pereonite 7 with 6 spines in transverse row, small posterolateral spine. Pleotelson long, with pair of three spines in row dorsally on anterior part of pleotelson, mid-dorsally pair of dorsal spines; posterior part with smaller spines; spine laterally near anterior margin of pleotelson, pair of large lateral spines near ventral margin; posterior end of female pleotelson bifid and slightly dorsally orientated. All pleonites fused into pleotelson, only one pleonite visible. Antennula short, reaching little beyond distal end of second peduncular segment of antenna. Antenna intermediate in length, about 0.6 of total body length; robust. Spines present on basis of pereopods 5–7. Oostegites present at pereopods 1–5.
Redescription of figured females (Figs 9–17): Body (Figs 9A, B, 10A, B, 11 A–C) length 5.9–10.5 mm; length 4.5 times largest width (excluding spines), increasing in width towards pereonite 4, decreasing in width from pereonite 4 to pereonite 7. Fine setae covering body. Head fused to pereonite 1, suture absent, small ventral notch on lateral margin; small lateral spine near anterior margin, 3 spines dorsally and dorsolaterally between eyes, posterior end of head with 6 spines, dorsal pair largest. Eyes prominent, bulbous.
Pereonite 1 lateral margin deep, convex; 8 spines in transverse row on pereonite 1, dorsal pair largest. Pereonite 2 short, 0.3 times length of pereonite 4, 6 spines in transverse row, dorsal pair largest, laterodistal margin with anterior knob where spines are found on latter pereonites. Pereonite 3 0.4 times length of pereonite 4, with 6 spines in transverse row and small anterolateral and posterolateral spines. Pereonite 4 0.2 times body length; anterior transverse spine row with 6 spines, smaller anterolateral spine and small lateral spine or fork spine (see variation) posterior to spine row; posterior spine row with 6 spines (see variation), dorsal pair largest on body. Pereonite 5 0.4 times length of pereonite 4, with 6 spines in transverse row, small anterolateral and posterolateral spines. Pereonite 6 0.4 times length of pereonite 4, with 6 spines in transverse row, small anterolateral and posterolateral spines. Pereonite 7 0.4 times length of pereonite 4, with 6 spines in transverse row, small posterolateral spine.
All pleonites fused into pleotelson, only one pleonite visible. Pleotelson with different pattern of spines from that of pereonites; pair of three spines in row dorsally on anterior part of pleotelson, mid-dorsally pair of dorsal spines; posterior part with smaller spines; spine laterally near anterior margin of pleotelson, pair of large lateral spines near ventral margin; posterior end of pleotelson bifid and slightly dorsally orientated.
Oostegites on pereopods 1 – 5, largest on pereopod 5 (Figs 9B, 10A, 11A, 17 E–F).
Antennula (Fig. 12A) short, reaching little beyond distal end of second peduncular segment of antenna; peduncle article 1 wide and short, distally with 1 penicillate and 1 slender seta, article 2 0.5 times width of article 1, distally with 4 penicillate setae; flagellum article 1 short, fine seta distally, article 2 2.3 times longer that article 1, 4.4 times longer than wide, with 4–5 aesthetascs (sometimes 3) and 2 penicillate setae (1 broken off in illustration) distally.
Antenna (Fig. 12B) peduncle with 5 articles, articles 4 and 5 longest; flagellum 0.5 times penduncle article 5, flagellum with 3 articles and claw (partly broken off); flagellum with fine setae (mostly broken off); article 2 0.5 length times article 1 length; article 3 0.2 times article 1.
Labrum (Fig. 12C) with fine setae.
Right mandible (Fig. 12D) molar smooth, slightly dentate on anterior edge. Lacinia mobilis with 2 major lobes and 3–4 smaller lobes; spine row comprising 2 dentate spines. Incisor 3-toothed. Left mandible (Fig. 12E) molar smooth, lacinia mobilis 2-lobed; spine row comprising 3 dentate spines, incisor 3-toothed.
Maxillula (Fig. 12F) mesial lobe with 3 long pappose setae distally and mesially one pappose and several fine, slender setae; lateral lobe with 10 cuspidate apical setae and 1 smaller robust apical seta.
Maxilla (Fig. 12G) mesial lobe oblique margin with 9 robust papposerrate setae, 12 – 13 long, simple setae on anterior edge; middle lobe with 3 long pectinate, finely setulate setae; lateral lobe with 2 long pectinate, finely setulate setae.
Maxilliped (Fig. 12H) endite ventrally with 4 slender setae; distally with 7 pappose setae; 3 or 4 large coupling hooks. Palp article 1 short; article 2 with several long simple setae mesiodistally and ventrally; article 3 longest palp article, with long, slender simple setae distally and on ventral surface; articles 4 and 5 distally with several long simple setae. Epipodite distally rounded.
Pereopod 1 (Fig. 13A) held close to mouthparts; basis with several long simple setae distally; ischium short, several long setae on inferior margin and distally on ischium; merus short, 0.88 times longer than wide, several long simple setae and 1 small penicillate seta on inferior margin and distally, superior margin distally with 2 pectinate setae (broken); carpus 2.03 times longer than wide, length 1.7 times merus length, inferior margin with row of clavate distally setulate setae and long slender setae inbetween; propodus length 1.0 times carpus length, 2.1 times longer than wide, several clavate distally setulate setae and slender setae on inferior margin, pectinate and denticulate setae distally on superior margin; dactylus short, 0.2 times propodus length, distally with 3 long setae (2 broken), unguis absent.
Pereopod 2 (Fig. 13B) basis short, superior margin distally forming spine, inferior margin with several slender simple setae; ischium short, inferior margin with several slender simple setae; merus-propodus long and narrow; merus long, 2.7 times longer than wide, groups of long, slender simple setae on inferior margin; carpus long, 4.3 times longer than wide, length 1.2 times merus length, groups of slender, long simple setae on inferior margin; propodus long, 9 times longer than wide, length 1.1 times carpus length, groups of slender, long simple setae on inferior margin; dactylus short, slender, length 0.1 times propodus length, unguis present.
Pereopods 3 and 4 (Fig. 14A, B) similar to pereopod 2; conspicious spine on superior margin of basis; coxa with 2 spines.
Pereopods 5–7 (Fig. 15 A–C) similar in shape, stout, with sparse setae; basis with prominent spine; carpus and merus similar in length, propodus 2.1 to 2.5 times longer than carpus and 1.7 to 2.2 times longer than dactylus. Dactylus with 2 ungui, secondary unguis robust.
Pleopod 1 (Fig. 16A) peduncle 3.5 times longer than wide, with 3 coupling hooks; endopod distally with 5 apical plumose setae; expod as long as endopod, distally with 4 apical plumose setae.
Pleopod 2 (Fig. 16B) with 2 coupling hooks; endopod with 7 apical plumose setae, exopod with 10 apical plumose setae.
Pleopods 3–5 (Fig. 16 C–E) with expanded exo- and endopods; rami apically rounded; 2 plumose setae on endopod of pleopod 3; 1 plumose seta on endopod of pleopods 4 and 5.
Uropod (Fig. 15D) rounded anteriorly, tapering posteriorly with 1 plumose seta; exopod 0.4 times endopod length, 2 apical setae with plumose shaft and short setules on tip; endopod broad, apically rounded, fringed with fine setae.
Description of figured males (Figs 17G, H, 18–23): Body (Fig. 17 G–H, 18A–B) length 4–4.3 mm; length 7.1 times largest width (excluding spines), width of pereonites subparallel. Pattern of spination as in females, spines smaller than in females; spines knob-like. Head fused to pereonite 1, suture absent. Eyes prominent, bulbous.
Pereonite 1 lateral margin deep, convex. Pereonite 2 short, 0.4 times length of pereonite 4. Pereonite 3 short, 0.4 times length of pereonite 4. Pereonite 4 0.2 time body length; mid- and anterior parts constricted, anterior transverse spine row absent. Pereonite 5 0.4 times length of pereonite 4. Pereonite 6 0.39 times length of pereonite 4. Pereonite 7 0.3 times length of pereonite 4.
All pleonites fused into pleotelson, only one pleonite barely visible. Pleotelson with different pattern of spines from that of pereonites; pair of three spines in row dorsally on anterior part of pleotelson, mid-dorsally pair of dorsal spines; posterior part with few small spines; spine laterally near anterior margin of pleotelson, pair of large lateral spines near ventral margin; posterior end of pleotelson flat tipped and slightly dorsally orientated.
Antennula (Figs 18C, D, 19A) flagellum article 1 short, fine seta distally, article 2 4.3 times longer that article 1, 4.5 times longer than wide, with 14 aesthetascs on distal and lateral margin.
Antenna (Fig. 19B) peduncle with 5 articles, articles 4 and 5 longest; flagellum 0.5 times penduncle article 5, flagellum with 3 articles and claw; flagellum with fine setae. Article 2 0.6 length times article 1 length; article 3 0.5 times article 1; claw 1.1 times article 3.
Labrum (Fig. 19C) with fine setae.
Right mandible (Fig. 19D) molar smooth, lacinia mobilis with 3 major lobes and several irregular smaller lobes. Spine row comprising 2 dentate spines. Incisor 3-lobed. Left mandible (Fig. 19E) molar smooth, but slightly dentate on anterior edge. Lacinia mobilis 3-lobed. Spine row comprising 3 dentate spines. Incisor 2-lobed.
Maxillula (Fig. 19F) lateral lobe with 11 cuspidate apical setae and 1 pappose seta (mesial lobe got lost during disection).
Maxilla (Fig. 19G) mesial lobe oblique margin with 5 robust pappose setae, 5 long, simple setae on anterior edge; middle lobe with 2 long papposerrate setae; lateral lobe with 2 long papposerrate setae.
Maxilliped (Figs 19H, 20A) endite ventrally with 1 slender setulate seta; distally with several pappose setae; 2 coupling hooks. Palp article 1 short; article 2 with several long setulate setae mesiodistally and ventrally; article 3 longest palp article, with long, slender setulate setae distally and on ventral surface; articles 4 and 5 distally with several long setulate setae. Epipodite distally rounded.
Pereopod 1 (Fig. 20B) held close to mouthparts; ischium short, several long simple setae on inferior margin and distally on ischium; merus short, 1.2 times longer than wide, several long simple setae on inferior margin, 2 pectinate setae distally on superior margin; carpus 1.9 times longer than wide, length 1.6 times merus length, inferior margin with long slender papposerrate setae; propodus length 1.1 times carpus length, 2 times longer than wide, several slender papposerrate setae on inferior margin, denticulate setae distally on superior margin; dactylus short, 0.2 times propodus length, distally with 4 long simple setae, unguis absent.
Pereopod 2 (Fig. 21A) basis short, inferior margin with several slender setae and 3 penicillate setae on superior margin; ischium short, inferior margin with several slender simple setae; merus-propodus long and narrow; merus long, 2.5 times longer than wide, groups of long, slender simple setae on inferior margin; carpus long, 3.9 times longer than wide, length 1.4 times merus length, groups of long, slender simple setae on inferior margin; propodus long, 4.4 times longer than wide, length 0.9 times carpus length, groups of long, slender simple setae on inferior margin; dactylus short, slender, length 0.1 times propodus length, unguis present, but broken.
Pereopods 3 and 4 (Fig. 21B, C) similar to pereopod 2.
Pereopods 5–7 (Fig. 22 A–C) similar in shape, stout, with sparse setae; basis of pereopods 5 to 6 with prominent spine and 3 penicillate setae. Pereopod 7 basis without spine, with 4 penicillate setae; carpus and merus similar in length, propodus 1.9 to 2.3 times longer than carpus, 1.8–1.9 times longer than dactylus. Dactylus with 2 ungui, secondary unguis robust (Fig. 18E).
Penial plate (Fig. 23G) slightly turned, simple.
Pleopod 1 (Fig. 23B) peduncle 2.5 times longer than wide, with 3 coupling hooks; endopod distally with 6 apical plumose setae; expod as long as endopod, distally with 6 apical plumose setae.
Pleopod 2 (Fig. 23C) with 2 coupling hooks; endopod with 4 apical plumose setae, exopod with 7 apical plumose setae; appendix masculina styliform, straight, 1.7 times longer than endopod.
Pleopods 3–5 (Fig. 23 D–F) with expanded exo- and endopods; rami apically rounded; 2 plumose setae on endopod of pleopod 3; 1 plumose seta on endopod of pleopods 4 and 5.
Uropod (Fig. 23A) rounded anteriorly, tapering posteriorly; exopod 0.3 times endopod length, 2 apical setae with plumose shaft and short setules on tip; endopod broad, apically rounded, fringed with fine setae.
Remarks: Schultz (1981) erected Spectrarcturus Schultz, 1981 for a new species, Spectrarcturus multispinatus. The holotype is damaged, which according to Schultz, referencing Richardson (1905), looked much like Pleuroprion murdochi (Benedict, 1898). The description of Spectrarcturus multispinatus is somewhat inaccurate. Schultz (1981: fig. 2A, C) showed a single transverse row of spines on pereonite 4, whereas our re-examination demonstrated that pereonite 4 is actually longer and has two rows of spines (Fig. 25). This inaccuracy could be because the only available specimen was damaged on the left side, as stated by Schultz (1981). No characters used in Schultz´s (1981) description of S. multispinatus separate this species convincingly from P. murdochi. We therefore treat S. multispinatus as a subjective junior synonym and transfer both names to Spectrarcturus.
Spectrarcturus murdochi comb. nov. shows pronounced sexual dimorphism in body shape and in size. Males are considerably smaller than females, and with fewer spines on the body. Pereonite 4 has similar proportion of the total body length in both sexes, but the length ratio between pereonite 4 and pereonites 3–5 differs between sexes. The pleotelson of females is posteriorly bifid, while it is flat tipped in the males.
Females vary in the pattern of the mesial spines in the second row of spines on pereonite 4. Females have either one pair of simple, large posteromesial spines (Fig. 17A, B), a pair of forked spines (Fig. 17C, D), or a forked spine on one side but simple spine on the other side (Fig. 17A, B). Kussakin (1982) observed variations in the numbers of spines on the pleotelson, not only between specimens in the same sample, but also in the numbers on each side of the same individual.
Kussakin (1982) found specimens of Spectrarcturus murdochi from the Bering Sea to be more similar to Benedict’s (1898) description and figures of specimens from Alaska, than to specimens found near the North Kurile Islands. The latter differed in having stronger and denser setae on the dorsal surface of the body and smaller dorsal spines. Furthermore, Kussakin (1982) observed fewer dorsal spines, i.e. two pairs, on the pereonites than shown by Benedict (1898), but these differences may result from inaccuracies in the illustration of Benedict (1898).
Already at the second manca stage (Fig. 24A, B) pereonite 4 has become elongated. The body is though without spines. During the third manca stage (Fig. 24C, D) the spines have developed, although being still knob-like.
Distribution: Northern Alaska (Point Franklin); South and West Greenland; Bering Sea, Anadyr estuary, northern part of the sea near eastern Kamchatka; Northern part the Okhotsk Sea and near Shelikhov Bay; North Kurile Islands. Hansen (1916) had a single specimen, labelled “ Iceland and the Faeroes”. The species has, however, not been found there since, despite extensive sampling. The species is recorded at depths between 40 and 200 m.
Habitat: In Greenlandic waters the habitat of the species is sandy bottoms, with few small stones and was rich in macro-invertebrates (corals, crinoids, ophiuroids and sponges).
description: Published as part of Stransky, Bente, Svavarsson, Jörundur, Poore, Gary C. B. & Kihara, Terue Cristina, 2020, Revision of Pleuroprion zur Strassen, 1903 (Holidoteidae) and re-evaluation of Spectrarcturus Schultz, 1981 (Arcturidae) (Crustacea, Isopoda, Valvifera), pp. 1-52 in Zootaxa 4894 (1) on pages 15-35, DOI: 10.11646/zootaxa.4894.1.1, http://zenodo.org/record/4315364