Paracallisoma idioxenos, Horton, Tammy & Thurston, Michael H., 2015

Horton, Tammy & Thurston, Michael H., 2015, A revision of the genus Paracallisoma Chevreux, 1903 (Crustacea: Amphipoda: Scopelocheiridae: Paracallisominae) with a redescription of the type species of the genus Paracallisoma and the description of two new genera and two new species from the Atlantic Ocean, Zootaxa 3995 (1), pp. 91-132 : 101-106

Paracallisoma idioxenos sp. nov.

Figs 6–8

Not Paracallisoma alberti — Lampitt et al. 1983: 76, table 1.— Thurston 1990: 266.

Material examined. Holotype —Pre-adult female, 15.4 mm; carcass and seven slides, ( NHMUK 2015.2853), Station 52216#5, 23–25 June 1985, 48°50.02'N 16°29.51'W, AmphT, 4842 m.

Allotype —Adult male, 11.0 mm ( NHMUK 2015.2854), station data as above.

Paratypes — 20 specimens ( NHMUK 2015.2855-2864), station data as above.

Additional material. Porcupine Seabight and Porcupine Abyssal Plain, Station 9756#8, 13–15 April 1978, 49°53.6'N 13°57.9'W, TRAP B, 3852 m, one specimen. Station 50812#1, 3 August 1980, 49°45.4'N 14°10.3'W, BN 1.5/3M, 4080–4100 m, one specimen. Station 50909, 10–11 November 1980, 49°53.83'N 14°00.36'W, TAmph, 3918 m, one specimen. Station 52403#20, 8–9 December 1986, 49°10.9'N 16°16.7'W, AmphT, 4850 m, one specimen. Station 52701#1, 16–21 May 1991, 48°48.2'N 16°24.9'W, BSNACK, 4840 m, one specimen. Station 52701#35, 22–23 May 1991, 48°48.5'N 16°23.6'W, DEMAR, 4843 m, 29 specimens. Station 52806, 2–3 August 1992, 50°11.8'N 14°41.1'W, Aberdeen pop-up fish trap, 3976 m, one specimen. Station 13077#4, 14–18 March 1997, 48°55.82'N 16°35.25'W, trap on NIOZ Lander, 4844 m, one specimen. Station 13077#35, 19–23 March 1997, 48°58.10'N 16°24.93'W, trap on NIOZ Lander, 4845 m, one specimen. Station 13077#71, 24–27 March 1997, 48°50.01'N 16°17.97'W, traps on NIOZ Lander, 4840 m, eight specimens. Station 13077#92, 27–28 March 1997, 48°49.50'N 16°20.97'W; DEMAR, 4844 m, twelve specimens. Station 13078#3 29–31 March 1997, 48°46.99'N 16°22.09'W; DEMAR, 4842 m, one specimen. Station 13078#14, 1–2 April 1997, 48°55.12'N 16°25.06'W; DEMAR, 4845 m, seven specimens. Station 13078#22, 3 April 1997, 48°43.02'N 16°38.18'W; DEMAR, 4842 m, one specimen. Station 13200#31, 7 July 1997, 48°48.79'N 16°23.43'W; DEMAR, 4842 m, six specimens. Station 13200#42, 13–15 July 1997, 48°54.81'N 16°34.93'W; DEMAR, 4844 m, 34 specimens. Station 13200#55, 16 July 1997, 48°49.02'N 16°21.59'W; DEMAR, 4844 m, two specimens.

Iberian Margin. Station 15741#1, 4–5 August 2005, 39°34.95'N 10°16.50'W, Trap, 4286 m, one specimen. Station 56839#1, 4–5 May 2006, 38°06.59’N 09°58.18'W, Trap, 4445 m, two specimens. Station 56847#1, 7–8 May 2006, 39°35.50'N 10°19.00'W, Trap, 4403 m, five specimens.

Description. Holotype, pre-adult female, 15.4 mm. Head exposed, deeper than long, lateral cephalic lobe large, narrow, subacute; rostrum absent. Eyes apparently absent in preserved material. Antenna 1 short, length 0.12 x body; peduncular article 1 short, length 0.95 x breadth, without posterodistal spine or lobe; peduncular article 2 short, 0.28 x article 1; peduncular article 3 short, 0.14 x article 1; flagellum 5-articulate, without posterodistal setae, calceoli absent, accessory flagellum long, 0.61 x primary flagellum, 3-articulate, article 1 long, 3.5 x article 2, forming partial cap over callynophore. Antenna 2 2.1 x antenna 1; peduncle without brush setae; peduncular article 1 greatly enlarged, not covering article 2; weakly geniculate between peduncular articles 3–4, article 3 short, 0.7 x article 4; peduncular articles 4 and 5 not enlarged; flagellum well developed, 21-articulate, calceoli absent. Mouthpart bundle subquadrate. Epistome and upper lip separate; epistome produced, rounded; upper lip not produced, slightly rounded. Mandible incisors symmetrical, large, with convex margins; left lacinia mobilis a stemmed asymmetric blade; accessory setal rows without distal setal tuft, each with three robust simple setae; molar an acute conical structure, mandibular palp attached midway; article 1 short, length 0.65 x breadth, without setae; article 2 slender, length 4.2 x breadth, with 15 submarginal posterodistal A2-setae; article 3 slender, bladelike, with 18 D3 setae along distal two thirds of the margin, and three E3 setae. Maxilla 1 inner plate tapering distally, inner margin fully setose, with eleven pappose setae; outer plate broad with eleven setal teeth in 7/4 arrangement; outer row with ST1 large, slender, four-cuspidate, ST2–7 large, slender, ST2 four-cuspidate, ST3 sixcuspidate, ST4 six-cuspidate, ST5 five-cuspidate, ST6 seven-cuspidate, ST7, seven-cuspidate, inner row with STA–D slender, STA bifurcate, STB weakly one-cuspidate, STC four-cuspidate, STD three-cuspidate distally; palp large, 2-articulate, article 1 short, article 2 with seven terminal robust setae, one robust flag seta present on distolateral corner and one subterminal seta. Maxilla 2 inner plate broad, tapering distally, with 21 pappose setae, with terminal robust setae; outer plate slightly longer than inner with apicomedial dentate and plumose setae. Maxilliped inner plate large, subrectangular, slightly emarginate distally with four apical nodular setae, oblique facial setal row strong with 14 pappose setae and a submarginal row of four pappose setae; outer plate medium size, subrectangular with ten apical plumose setae, with ten small nodular setae medially and two longer robust setae on the distomedial corner; palp large, four-articulate, article 2 broad, length 1.8 x breadth, 1.8 x article 3; article 3 long, slender, length 2.2 x breadth; dactylus well-developed, with one sub-terminal seta, unguis present.

Gnathopod 1 simple; coxa large, slightly shorter than coxa 2, basis long, slender, length 3.6 x breadth, anterior margin smooth, with simple setae; ischium length 1.6 x breadth, anterior margin smooth with one seta posterodistally; merus, posterior margin with a few simple setae distally; carpus subrectangular, long, length three x breadth, subequal to propodus; propodus large, margins subparallel, posterior margin with a few groups of simple, slender setae, apex densely furnished with pappose robust setae; dactylus minute, complex, covered in sensory setae, posterior margin with one small tooth. Gnathopod 2 subchelate; coxa large, subequal in size to coxa 3; ischium long, length 3.0 x breadth; carpus long, length 3.1 x breadth, posterior margin straight; propodus subrectangular, margins sub-parallel, not expanded distally, long, length 2.1 x breadth, posterior margin with five groups of slender robust setae, apically with row of distally plumose setae decreasing in size towards palm; palm acute, straight, with serrate margin; dactylus inserted near middle of distal margin of propodus, curved, and reaching almost to palmar angle, corner defined by two teeth. Pereopod 3 coxa large, subrectangular; basis robust, sinuous and slightly expanded distally; merus slightly expanded anteriorly; propodus posterior margin with eight robust setae and two distal locking setae; dactylus short, slightly curved. Pereopod 4 as pereopod 3 except coxa wider than deep with well-developed posteroventral lobe, subacutely produced, posterior and ventral margins confluent, breadth 1.4 x depth. Pereopod 5 coxa very large, posterior lobate with a lateral ridge, eleven simple setae along ventral margin; basis weakly expanded proximally, widening distally with strong posterodistal lobe extending to 0.3 x length of merus, posterior margin concave with six short robust setae, anterior margin with two robust seta distally; merus weakly expanded posteriorly with robust setae on posterior and anterior margins; propodus long, length 4.4 x breadth, anterior margin with five groups of one or two robust setae and one pair of distal locking setae, posterior margin with 4–5 simple setae; dactylus slightly curved. Pereopod 6 coxa small, weakly lobate posteriorly; basis anterior margin smooth, strongly convex with four short robust setae anterodistally, posteroproximal margin expanded, rounded, forming lobe with five simple setae on margin, posterior margin slightly concave with three short simple marginal setae, narrowly rounded posterodistal lobe reaching merus; merus weakly expanded posteriorly; propodus long, longer than propodus of pereopods 5 and 7, length 5.5 x breadth, anterior margin with six groups of one or two robust setae and one pair of distal locking setae, posterior margin with ten–eleven slender simple setae; dactylus slightly curved. Pereopod 7 coxa small, lobate posteriorly with five simple slender setae on posteroventral margin and about ten simple setae on anterior margin; basis anterior margin slightly sinuous with five short robust setae anterodistally, proximal posterior margin broadly expanded, rounded, convex with six short simple setae along margin, excavate posterodistally with a round posterodistal lobe extending to 0.25 x merus; merus weakly expanded posteriorly; propodus long, length 3.3 x breadth, anterior margin with four pairs of robust setae, and one pair of distal locking setae, posterior margin with four slender simple setae; dactylus slightly curved.

Pleonites 1–3 dorsally smooth. Epimeron 1 anterior margin setose, slightly concave, lateral face with angled ridge; posteriorly rounded, with a slight posteroventral tooth. Epimeron 2 anterior margin sinuous, rounded; lateral face with angled ridge, posterior margin convex, posteroventral corner with small tooth. Epimeron 3 posteroventral corner with small tooth, ventral margin with 15 small robust setae.

Gills on pereopods 2–7. Brood plates on pereopods 2–5.

Urosomite 1 concave anteriorly with a rounded smooth boss posteriorly. Uropod 1 peduncle long, 1.46 x inner ramus length, with one apicolateral robust seta, one apicomedial robust seta, and 14 dorsomedial setae; rami subequal; inner ramus, with three medial and two lateral robust setae, and a microsetose lateral margin; outer ramus, with three lateral robust setae and a microsetose medial margin. Uropod 2 peduncle long, 1.2 x inner ramus, with one apicolateral robust seta, one apicomedial robust seta, ten dorsomedial setae, and two dorsolateral robust setae; inner ramus, length 1.1 x outer ramus, with five medial robust setae and three lateral robust setae; outer ramus, with two lateral robust setae and a microsetose medial margin. Uropod 3 peduncle short, with two apicolateral robust setae, one apicomedial robust seta and two simple setae, and five slender simple medial setae; inner ramus slightly shorter than outer, with four medial robust setae and 14 medial slender plumose setae; outer ramus, 2-articulate, article 2 short, with a microsetose medial margin; article 1, medial margin with six medial robust setae and six slender plumose setae, and one lateral slender robust seta.

Telson sub-triangular, length 1.6 x breadth, deeply cleft (68%), with two lateral robust setae per lobe, distal margins incised with subapical notch and one small immersed seta per lobe.

Sexual dimorphism. Male antenna 2 length 2.1 x antenna 1, 24-articulate, with brush setae, calceoli present on both antennae, lateral cephalic lobe narrower than in female.

Etymology. Derived from the Greek, idioxenos— friend, in honour of the friendship between the authors and Roger Bamber, dedicatee of the special issue in which this paper appears.

Remarks. Paracallisoma idioxenos sp. nov. is very closely allied to Paracallisoma alberti Chevreux, 1903 , and has been recorded as this species in recent literature ( Lampitt et al. 1983; Thurston 1990). The differences are subtle and were only recognised when material of P. alberti from the region of the type locality was obtained for study. The species can be distinguished by the variation in the insertion of the gnathopod 2 dactylus and the shape of the propodus: in the type species P. al b er t i, the dactyl is inserted at the anterodistal angle of article 6, and does not reach the palmar corner (only reaching about halfway down the palm) and the propodus is broadened distally. However, in P. idioxenos the dactylus is inserted around the middle of the apex of article 6 and nearly reaches the palmar corner, and the margins of the propodus are subparallel. The new species has a more nearly triangular telson with narrower lobes than does P. alberti and among subtle differences in setation has more dorsomedial robust setae on the peduncles of uropods 1 and 2 (14 and ten respectively compared to nine and five).

Depth range. 3852–4850 m.

Distribution. North-east Atlantic Ocean. Porcupine Seabight (3852–4850 m), Iberian Margin (4286–4445 m).

Paracallisoma zivianii Kilgallen & Lowry, 2015

Paracallisoma zivianii Kilgallen & Lowry, 2015: 29 .

Type material. Holotype —male, 12.0 mm, AM P.69091, east of Flynn Reef, Queensland, Australia (16°37.82'S 146°23.08'E), 1000 m, baited trap, 7–8 June 1993, collected by J.K. Lowry, P. Freewater & W. Vader, RV Sunbird [QLD-950/ SEAS].

Paratype— one specimen, 10.8 mm, AM P.69092, east of Flynn Reef, Queensland, Australia (16°37.82'S 146°23.08'E), 1000 m, baited trap, 6–7 June 1993, collected by J.K. Lowry, P. Freewater & W. Vader, RV Sunbird [QLD-931/ SEAS].

Remarks. This species is most similar to P. alberti . It differs from both P. alberti and P. idioxenos in the shape of the gnathopod 2 palm, which is transverse. It also differs in the length of the dactyl of gnathopod 2 which is as long as the palm but shorter in the other two species. The latter character must be used with caution as it is an ontogenetic character for both species, with smaller specimens having relatively longer dactyli.

Depth range. 963–1000 m.

Distribution. Australia —east of Flynn Reef, Queensland, to north-east of Coffs Harbour, New South Wales.

Figures

FIGURE 6. Paracallisoma idioxenos sp. nov. Holotype, pre-adult female, 15.4 mm, habitus.

FIGURE 7. Paracallisoma idioxenos sp. nov. Holotype, pre-adult female, 15.4 mm, head, antennae, mouthparts, epimera and uropods. Allotype, adult male, 11 mm, head and antennae.

FIGURE 8. Paracallisoma idioxenos sp. nov. Holotype, pre-adult female, 15.4 mm, gnathopods, pereopods and telson.