Pseudocallisoma coecum ( Holmes, 1908 ) Holmes, 1908

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 : 122-127

Pseudocallisoma coecum ( Holmes, 1908) comb. nov.

Figs 19–21

Scopelocheirus coecus Holmes 1908: 500 , figs 10–12. — Shoemaker 1945: 186 (in part, part? P. platepistomum ).—J.L Barnard 1954: 54, figs 4, 5.— Gurjanova 1951: 241 (key).

Paracallisoma coecum .— Hurley 1963: 61, fig. 18.—Andres 1977, 60. — Barnard & Karaman 1991: 511.— Thurston 2001: 685 (table 2).

Paracallisoma coecus .— J.L. Barnard 1958: 97 (list).— J.L. Barnard 1964: 319, fig. 3.— Brusca 1967a: 384, 385, table 4.— Brusca 1967b: 450.— Childress & Nygaard 1974: 228, table 1(physiology).— Childress 1975: 788 (table 1a) (physiology).— Quetin, Ross & Uchio 1980: table 1(physiology).— Smith & Baldwin 1982: 292 (table 3).— Austin 1985: 601.— Vermeer & Devito 1988: 65, 67, table 2 (ecology).— Ikeda 2013: 342 (table 1).

Paracallisoma alberti .— Birstein & Vinogradov 1955: 223, 279 (in part).—Birstein & Vinogradov 1958: 228.—Birstein & Vinogradov 1960: 176, fig. 5, 233, fig. 33.— Gurjanova 1962: 309, fig. 102.— Nagata 1963: 1.—Birstein & Vinogradov 1970: table 1, table 3.— Hatch 1983: 194, 195, table 3 (ecology).— Nysewander 1983: 328, table 7 (ecology).— Sanger & Ainley 1988: 182 (ecology).— Hatch 2013: 275 (ecology).

Not Paracallisoma coecum = Paracallisoma platepistomum .— Shoemaker 1945:186.

Material examined. Holotype —female, 20.8 mm, specimen and four slides, USNM, 38538. Bureau of Fisheries, Station 4405, 1196– 1287 m, off San Clemente Island, California, 0 9 April 1904.

Description. Holotype, female, 20.8 mm USNM, 38538.

Antenna 1 peduncle article 1 short, length 0.9 x breadth, without posterodistal spine or lobe; peduncle article 2 short, 0.5 x article 1; peduncle article 3 short, 0.26 x article 1; flagellum seven-articulate, without posterodistal setae, callynophore present, calceoli absent; accessory flagellum long, 0.63 x primary flagellum, five-articulate, article 1 short, 0.6 x article 2. Antenna 2 length 1.2 x antenna 1; peduncle without brush setae; peduncle article 1 greatly enlarged, not covering article 2; article 3 short, 0.6 x article 4; peduncle articles 4 and 5 not enlarged; flagellum well-developed, nine-articulate, calceoli absent.

Mouthpart bundle—Right mandible incisor symmetrical, large, slightly convex margin with tooth-like projection at either end; lacinia absent; accessory setal row with three robust setae, lacking distal setal tuft; molar an acute conical structure, mandibular palp attached midway; article 1 short, length 0.64 x breadth, without setae; article 2 slender, length 3.25 x breadth, with 24 submarginal posterodistal A2-setae; article 3 slender, oval, with 19 D3 setae along distal two thirds of the margin, and 3 E3 setae.

Gnathopod 1 simple; coxa large, shorter than coxa 2, tapering, rounded distally, anterior margin slightly concave; basis long, expanded distally, length 2.7 x breadth, anterior margin smooth, with 14 simple setae; ischium short, length 1.2 x breadth, anterior margin smooth; merus, posterior margin without distal setae; carpus subrectangular, long, length 3.3 x breadth, longer than propodus; propodus tapering distally, posterior margin with a few groups of simple, slender setae, apex with numerous distally pappose robust setae; dactylus minute, complex, covered in sensory setae. Gnathopod 2 subchelate; coxa large, tapering slightly; ischium long, length 2.8 x breadth; carpus long, length 3.75 x breadth, posterior margin straight; propodus subrectangular, narrow, length 2.4 x breadth with numerous pappose robust setae distally; posterior margin with seven groups of slender robust setae, apically with row of distally plumose setae; palm very short, acute, with short setules, palmar corner with one long and one short robust seta; dactylus inserted in anterior third of propodus apex, curved, just longer than palm, posterior margin with three setae. Pereopods simple. Pereopod 3 missing. Pereopod 4 coxa wider than deep, posterior lobe well-developed, broadly rounded, posterior margin sloping anteriorly, breadth 1.1 x depth; basis slender, straight; merus not expanded anteriorly; carpus slender, posterior margin strongly setose; propodus slender, posterior margin with five robust setae and two distal locking setae; dactylus long, straight. Pereopod 5 coxa large, deep, width 1.4 x depth weakly lobate posteriorly with a lateral ridge, twelve simple setae along posterodistal margin; basis weakly expanded proximally, strongly widening distally, posterodistal lobe large, reaching a quarter of the way along the merus, anterior margin with four robust setae distally; merus very slightly expanded posteriorly with robust setae on both posterior and anterior margins; carpus slender, posterior margin strongly setose; propodus very long, slender, tapering, length 6.3 x breadth, anterior margin with three robust setae and one pair of distal locking setae; dactylus slender, tip broken. Pereopod 6 coxa small, not lobate posteriorly; basis anterior margin evenly convex, posterior margin expanded, straight, with eleven simple setae, rounded posterodistal lobe reaching merus; merus as in pereopod 5; carpus 1.1 x propodus; propodus very long, tapering, length 7.4 x breadth, anterior margin with nine robust setae and one pair of distal locking setae, posterior margin with 13 long slender simple setae; dactylus, slender, tip broken. Pereopod 7 coxa small, posterior lobate; basis, anterior margin weakly convex, proximal posterior margin expanded, rounded, convex, then sloping slightly anteriorly and excavate posterodistally, posterodistal lobe narrow, reaching almost halfway along merus; merus anterior and posterior margins subparallel; carpus 1.07 x propodus; propodus long, slender, length 6.1 x breadth, anterior margin with seven groups of robust setae, and one pair of distal locking setae; dactylus, slender, tip broken.

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

Uropod 1 peduncle long, 1.9 x inner ramus, with five lateral robust setae, one dorsal robust seta, and eleven dorsomedial robust setae; rami subequal; inner ramus, with seven medial robust setae, and five lateral robust setae; outer ramus, with three lateral robust setae and 2 medial robust setae. Uropod 2 missing. Uropod 3 peduncle short, length 0.8 x inner ramus, with one apicolateral robust seta, one simple seta, two dorsal slender simple setae, and five medial slender simple setae; inner ramus, with six medial robust setae and 13 medial slender plumose setae, with a microsetose distomedial margin; outer ramus, 2-articulate, article 2 short, with a microsetose distomedial margin; article 1 with six medial robust setae, six slender plumose setae, and one robust seta apicolaterally.

Telson longer than broad, slender and strongly tapering distally, length 1.65 x breadth, cleft 62%, with a pair of dorsolateral robust setae, lobes subacute, lacking apical incision.

Supplementary description from Barnard (1954) illustrations & material. Head exposed, deeper than long, lateral cephalic lobe large, narrow, subacute; rostrum absent; eyes apparently absent. Maxilla 1 inner plate tapering distally, inner margin fully setose, with>20 pappose setae; outer plate narrow with eleven setal teeth in 7/ 4 arrangement; palp large, two-articulate, article 1 short, article 2 narrow, with six terminal robust setae, one robust flag seta; Maxilla 2 inner plate broad, rounded apically, with pappose setae in oblique mediofacial setal row; outer plate slightly longer than inner. Maxilliped inner plate large, subrectangular, emarginate distally with three apical nodular setae, oblique facial setal row strong with 16 pappose setae; outer plate medium size, subrectangular with apical plumose setae and small nodular setae medially; palp large, 4-articulate, article 2 broad, article 3 long, slender, length 3.3 x breadth; dactylus well-developed.

Remarks. Pseudocallisoma coecum ( Holmes, 1908) , the type species of this genus is described here from the holotype, a carcass and slides in poor condition supplemented by the material figured by Barnard (1954). Pseudocallisoma coecum , originally placed in Scopelocheirus by Holmes (1908), and then Paracallisoma by Schellenberg (1926a), is known from the Pacific Ocean at depths down to 4023 m. A single male specimen was illustrated by Barnard (1954) from bathypelagic material collected by the Vel ero IV off the coast of California. The male differs only in the longer second antennae which are about three times as long as in the female and with the presence of calceoli on both antennae ( Barnard 1954). A juvenile specimen (6 mm) was figured by Barnard (1964), and differs in the less setose mouthparts, the outer plate of the maxilliped having only four lateral setae instead of 14. Pseudocallisoma coecum has also been recorded frequently at high northern latitudes in the Pacific under the name Paracallisoma alberti by Birstein and Vinogradov (1955, 1958, 1960, 1962, 1964, 1970) and Gurjanova (1962). This species is closely related to P. platepistomum (see remarks section for P. platepistomum ).

Depth range. 500–4023 m ( Holmes 1908; Shoemaker 1945; Barnard 1964; Brusca 1967; Childress & Nygaard 1974). Records from hauls fished with open nets (e.g. 0–9000 m, Birstein and Vinogradov (1958)) are uninformative and have been excluded. Although the shallowest depth of occurrence for net-caught material is ca. 500 m, this species is reported as a constituent of seabird stomach contents ( Hatch 1983, 2013; Nysewander 1983; Vermeer & Devito 1988; Sanger & Ainley 1988). P. c o ec u m has been found in stomach contents of six widely divergent species of seabird ( Sanger & Ainley 1988) and forms an important part of the diet of two storm petrel species ( Vermeer & Devito 1988). Storm petrels do not dive and feed by picking food items from the surface while airborne. P. coecum is positively buoyant and may have to swim to stay down ( Childress & Nygaard 1974) but it seems improbable that the storm petrel diet consists entirely of dead or moribund individuals.

Distribution. Pacific Ocean: off San Clemente Island, California, United States ( Holmes 1908); Pacific City, Oregon, United States (from the stomach of a duck*) ( Shoemaker 1945); San Nicolas Basin and off Santa Barbara Island, California, United States ( Barnard 1954); outer Santa Barbara Passage, California, United States ( Hurley 1963); off Kamchatka, Russia ( Shoemaker 1945; Gurjanova 1962); Gulf of Alaska ( Barnard 1964); Kuril- Kamchatka Trench (Birstein & Vinogradov 1958); near the Tenji Seamount, south-south-west of the Aleutian Trench (Birstein & Vinogradov 1958); near the Makarov Seamount (Birstein & Vinogradov 1960); Japan Trench ( Nagata 1963) (from Kilgallen & Lowry 2015). [*This material was collected from the stomach of a storm petrel, not a duck.]

Figures

FIGURE 19. Pseudocallisoma coecum (Holmes, 1908). Holotype, Pacific Ocean, off California, 1196 – 1287 m, 20.8 mm, antennae, uropods 1, 3, telson, right mandible.

FIGURE 20. Pseudocallisoma coecum (Holmes, 1908). Holotype, Pacific Ocean, off California, 1196 – 1287 m, 20.8 mm, gnathopods, pereopods 4 – 7.

FIGURE 21. Pseudocallisoma coecum (Holmes, 1908). Figures from Barnard (1954), male, 15 mm, Velero IV specimen, Pacific Ocean, off California, antenna 2, lower lip, maxilliped, maxilla 1 and maxilla 2.