Paracallisoma spinipoda, Hendrycks & Conlan, 2003

Hendrycks, EA & Conlan, KE, 2003, New and unusual abyssal gammaridean Amphipoda from the north-east Pacific, Journal of Natural History 37, pp. 2303-2368 : 2322-2327

Paracallisoma spinipoda sp. nov. (figures 8, 9)

Type material

H  : adult W, 10 mm, (appendages on one slide), CMNC 2002-0029 , Sta. 1216, Cup# 1, 34°47.94∞N, 123°03.80∞W, 3450 m, 24 June 1992. P    : juvenile,

sex unknown, 5.0 mm, CMNC 2002-0030, Sta. 621, Cup# 1, 34°50.88∞N, 122°58.68∞W, 4000 m, date unknown.

Diagnosis

Eye absent; lateral cephalic lobe broad, acute; gnathopod 2, subchelate, palm transverse, indented in the middle, dactyl fitting palm; peraeopods 3–6, subchelate, appearing prehensile, distal three-quarters of propodus margin with stout spines; coxa 4, posteroventral lobe strong, narrowly rounded; peraeopod 5, basis broadly expanded, wider than deep, posterior margin convex, posteroventral lobe broadly rounded, shallow; peraeopods 6–7, posterior margin of basis emarginate ventrally, posteroventral lobe short, rounded; urosomite 1 with a rounded, anterodorsal boss, lateral ridge and slight, posterodorsal carina; telson, lateral margins nearly parallel, cleft 71%, lobes acute with a strong subapical notch.

Description

H  , male, CMNC 2002-0029.

Head: eye absent; rostrum very short; midcephalic margin of head slightly concave below rostrum, produced forwards above upper lip; lateral cephalic lobe broad, acute. Antenna 1: short, length about one-sixth body, callynophore strong, length 0.75×peduncular articles 1–3, densely furnished with aesthetascs medially; accessory flagellum, three-articulate, article 1 length 2.8×remaining articles, with clusters of setae medially; primary flagellum seven-articulate, calceoli present. Antenna 2: long, length about three-fifths body, peduncular articles 4–5 subequal, with brush setae; flagellum about 43-articulate, calceoli present.

Peraeon and pleon: smooth. Urosomite 1: with a rounded anterodorsal boss, lateral ridge and slight, posterodorsal carina. Urosomite 2: very short, dorsally with a round boss, half covered by urosomite 1.

Coxae: 1–4 short, wide, depth less than corresponding peraeon segment.

Mouthparts: prognathous. Upper lip: separated from midcephalic margin, ventral margin narrowly rounded in the middle. Lower lip: outer lobes broad, not widely gaping, mandibular lobes narrow. Mandible: incisors convex, symmetric, anterodorsal corners with a tooth, anteroventral corners with three to four serrations; left lacinia mobilis an asymmetric, stemmed blade, right lacinia absent; accessory spine row with three stout spines; molar long, thorn-like, non-triturative; palp threearticulate, longer than mandible body, palp attached about level with molar, article 2 of palp 1.4×length of article 3, with 13 submarginal, posteroventral setae, article 3 blade-like, with a convex, posterior margin, margin with 20 setae, with three apical setae. Maxilla 1: inner plate triangular, with nine strong plumose setae along medial margin; outer plate with 11 spine teeth in a 7/4 arrangement, distomedial margin with cluster of stiff setae; palp two-articulate, article 1 short, length 0.7×width, article 2 widening distally with six apical, bifurcate spines, one slender distolateral spine, with one subapical seta between second and third bifurcate spine viewed from the distolateral corner. Maxilla 2: inner plate triangular, wider than outer, with 13 mediofacial setae, with terminal spines and setae; outer plate longer than inner, with apicomedial spines and setae. Maxilliped: inner plate widening distally, apical margin emarginate with three nodular spines, with one small, apicomedial spine, oblique facial row with nine plumose setae; outer plate large, reaching two-thirds of palp article 2, semicircular, apically with six plumose setae and one slender spine, medially with 13 small spines and submarginal setae; palp four-articulate, article 2 longest, medial margins setose, articles 1–3 with distolateral setae, dactylus shorter than article 3.

Gnathopod 1: coxa less than 0.5×length of basis; basis with one long posterodistal setae; ischium long, length 2.2×width; carpus length 0.8×propodus, with anterodorsal and anteroventral setae; propodus narrow, simple, tapering distally, dorsal and ventral margins with setae, dactylus minute, complex, shrouded in many rows of plumose setae, posterior margin with four teeth. Gnathopod 2: coxa reaching about two-fifths length of basis; ischium long, length 3×width; carpus long, length 2×propodus, dorsal and ventral medial face covered with very fine setules, distally with long setae; propodus ovate, minutely subchelate, dorsal and ventral medial face covered with very fine setules, margins with long setae, anterodistally with row of strong setae increasing in length dorsally, palm transverse, finely serrated distally, indented in the middle, with one submarginal spine and one strong seta at palm corner, dactylus apically bifurcate, with denticulate posterior margin, reaching palm corner.

Peraeopod 3: coxa rectangular, slightly deeper than wide, length about 0.5×basis; basis stout, widening distally; merus length 1.4×carpus, with anterodistal spine and three setae; carpus short, length 0.7×merus, with one anterodistal seta, posterior margin with three setae and two small spines, with two posterodistal spines and one seta; propodus long, length 3×width, prehensile, distal three-quarters of posterior margin with seven spines and two distal locking spines; dactyl long, length 0.6×propodus. Peraeopod 4: coxa wider than deep, width 1.3×depth, posteroventral lobe well developed, narrowly rounded, posterior margin strongly excavated; rest of leg as for peraeopod 3. Peraeopod 5: coxa slightly posterolobate, with a lateral ridge, not covering coxa 6; basis expanded, width 1.3×depth, anterior margin with four spines and two anterodistal spines, posterior margin with two crenations proximally; merus slightly expanded, anterior and posterior margins spinose, posterodistal margin not extended; propodus long, length 3.9×width, prehensile, anterior margin with seven pairs of spines and two distal locking spines, posterior margin with three setae; dactyl long, length 0.6×propodus. Peraeopod 6: coxa wide, width 1.3×depth; basis wide proximally, about equal to depth, anterior margin with two spines and two anterodistal spines, posterior margin with three crenations, ventrally emarginate, with a round, posteroventral lobe; merus as above; carpus long, length 1.2×merus, anterior margin spinose; propodus long, length 4.4×width, prehensile, anterior margin as above, posterior margin with six setae and one long distal seta; dactylus as above. Peraeopod 7: coxa wide, width 1.5×depth; basis wide proximally, about equal to depth, anterior margin with five spines and four anterodistal spines, posterior margin with six crenations, with a strong emargination ventrally, with a round, posteroventral lobe, merus narrower than peraeopod 6 merus; carpus long, length 1.2×merus, anterior margin strongly spinose; propodus slightly narrower than peraeopods 5–6; dactylus as above.

Gills: on peraeopods 2–7. Pleopods: strong. Epimeron 2: posteroventral corner with a small tooth. Epimeron 3: posterior margin straight, posteroventral margin slightly produced to a broad point, ventral margin with four slender spines.

Uropod 1: peduncle length 1.4×inner ramus, with one apicolateral and ten dorsomedial setae; rami lanceolate, slender, outer slightly shorter than inner, with three lateral spines; inner ramus with one lateral and four medial spines. Uropod 2: peduncle about equal to inner ramus, with nine dorsolateral and five dorsomedial spines; rami slender, outer ramus 0.7×inner, with three lateral spines; inner ramus with six lateral and five medial spines. Uropod 3: peduncle about 0.5×outer ramus, with one apicomedial spine; outer ramus slightly longer than inner, two-articulate, article 1 with six lateral and five medial spines; article 2 length 0.5×article 1; inner ramus with three lateral and three medial spines, medial margin lined with plumose setae. Telson: length 1.6×width, dorsolateral margins nearly parallel, with three to four spines, cleft 71%, lobes acute, with a strong, subapical notch and small, immersed spine. Female unknown.

P    , juvenile, 5.0 mm. Similar to adult male, except the following. Antenna 1: callynophore smaller, with fewer aesthetascs, calceoli absent. Antenna 2: short, peduncular articles 4–5 without brush setae; flagellum 18-articulate, calceoli absent. Peraeopods 3–6: margins of propodi with fewer spines. Peraeopod 6: basis, posteroventral emargination very weak. Uropod 3: medial margin of inner ramus lacking plumose setae.

Etymology

The species name is from the Latin spina (spine) and the Greek podos (foot) and refers to the highly spinose condition of the propodus of peraeopods 3–7.

Condition All appendages present.

Variation See description of juvenile above.

Remarks

Paracallisoma spinipoda is clearly distinct from other species in the genus in possessing subchelate peraeopods 3–6, with a somewhat lesser tendency in peraeopod 7. The propodus of these appendages is strongly spined and the dactylus is long, which give the appendage a prehensile appearance. In addition, the telson lobes are not narrowed apically and the strong notch is subapical (vs narrowed apically with a weak to strong, apical notch).

Some closely related, but undescribed species have been found in the Atlantic and Antarctic Oceans (M. H. Thurston and H. G. Andres, personal communication). It will be of interest to compare these species once they are published, to determine the relationships between them. This information will also lead to a better understanding of the biogeography of the genus.

Paracallisoma has historically been a problematic genus and is in need of revision (see Dahl, 1959; Gurjanova, 1962; Hurley, 1963; J. L. Barnard, 1964b; J. K. Lowry and M. H. Thurston, personal communication).

Distribution North-east Pacific off Point Conception, California in 3450–4000 m depth.