Ryocalanus infelix, TANAKA, 1956

RYOCALANUS INFELIX TANAKA, 1956 View in CoL

( FIGS 7–10)

Material: Adult female, dissected, body length 2.65 mm, collection number SMF 37152 About SMF /1–6 (one vial, five slides); Kurile-Kamchatka trench, 46.2333° N, 155.5333° E, station 2–10, project KuramBio, 3 August 2012, above the sea bed at a depth of 4865 m. One adult GoogleMaps female, dissected, body length 2.60 mm, collection number SMF 37153 About SMF /1–4 (one vial, three slides); Kurile-Kamchatka trench, 43.0166° N, 152.9666° E, station 7–10, project KuramBio, 17 August 2012, above the sea bed at a depth of 5223 m. One adult GoogleMaps male, dissected, body length 2.11 mm, collection number SMF 37154 About SMF /1–4 (one vial, three slides); Kurile-Kamchatka trench, 43.5666° N, 153.9666° E, station 5–10, project KuramBio, 11 August 2012, above the sea bed at a depth of 5375 m. One adult GoogleMaps male, dissected, body length 2.11 mm, collection number SMF 37155 About SMF /1–3 (one vial, two slides); Kurile-Kamchatka trench, 46.2333° N, 155.5333° E, station 2–10, project KuramBio, 3 August 2012, above the sea bed at a depth of 4865 m GoogleMaps .

Description: Based on two females and two males.

Adult female: Total length 2.65 mm; prosome 5.1 times as long as urosome ( Fig. 7A, B). Rostrum ( Fig. 7A, C) one-pointed, slender. Cephalosome and pediger 1 separate ( Fig. 7A, B), pedigers 4–5 separate; in dorsal view posterolateral corners of prosome asymmetrical, extended posteriorly into points, extending to distal margin of genital double-somite on right side and to distal margin of second urosomal segment on left side ( Fig. 7A, B, D). Ventral inner surface of pediger 5 with short spinules.

Urosome composed of genital double-somite and three articulated or partly articulated somites ( Fig. 7D–G). Genital double-somite asymmetrical, with lateral swelling on right side or left side and faint line of incomplete fusion on dorsal and ventral surface; in lateral view swollen ventromedially, seminal receptacles in lateral view oval, turned upward. Urosomites 2, 3 and 4 asymmetrical, 3 and 4 partly fused. Urosome covered by viscous mass. Caudal rami asymmetrical with right ramus longer and wider than left; both rami with row of spinules on inner margin and with two lateral setae (II and III), three terminal setae (IV–VI) and one dorsal seta (VII).

Antennule ( Fig. 7H) of 24 free segments, armature as follows:

I – 1s + 1ae, II–IV – 6s + 4ae, V – 2s + 2 ae, VI – 2s + 1ae, VII – 2s + 2ae, VIII – 2s + 2ae, IX – 2s + 2ae; X–XI – 4s + 4ae, XII – 1s, XIII – 2s + 2ae; XIV – 2s, XV – 1s + 1ae, XVI – 2s + 1ae, XVII – 2s + 1ae, XVIII – 2s + 1ae, XIX – 2s, XX – 2s + 1ae, XXI – 2s, XXII – 1s, XXIII – 1s, XXIV – 2s, XXV – 2s, XXVI – 2s, XXVII–XXVIII – 4s + 1ae.

Antenna ( Fig. 8A), coxa with 1, basis with 2 setae; endopod segment 1 with 2 setae and row of spinules, segment 2 with 16 setae; exopod 8-segmented, with 1, 3, 1, 1, 1, 1, 1, 3 setae.

Mandible ( Fig. 8B), gnathobase cutting edge with 8 unequal teeth plus ventral seta; basis with 3 setae; exopodal segments incompletely fused, with 6 setae; first endopod segment with 4 setae (3 setae plus 1 scar), second with 11 setae.

Maxillule ( Fig. 8C), praecoxal arthrite with 9 terminal spines, 3 posterior and 1 anterior setae; posterior surface of praecoxal arthrite with small spinules; coxal endite with 6 setae, coxal epipodite setae broken in all specimens; proximal basal endite with 4 setae, distal basal endite with 5 setae and small surface spinules; endopod with 12 setae and patch of small surface spinules; exopod with 8 setae.

Maxilla ( Fig. 8D), proximal praecoxal endite bearing 3 setae plus attenuation on left limb, 5 setae in right limb, distal praecoxal endite with 3 setae and surface spinules; coxa with 1 outer seta; coxal endites with 3 setae each and surface spinules; proximal basal endite 4 setae; remainig endopod with 9 setae.

Maxilliped ( Fig. 9A), syncoxa with 1 seta on proximal praecoxal endite, 2 setae on middle endite, and 3 setae on distal praecoxal endite; coxal endite with 3 setae; basis with 3 medial setae; endopod 6-segmented with 2, 4, 4, 4, 3 + 1, and 4 setae.

Legs 1–4 biramous ( Fig. 9B–E) with 3-segmented exopods, endopod 1-segmented in leg 1, 2-segmented in leg 2 and 3-segmented in legs 3–4. All endopod and exopod segments with rows of spinules on posterior surface. Coxa of legs 1–3 with inner surface spinules. Leg 2 and 3 with finely serrate terminal spine on exopod segment 3. Seta and spine formula as in Table 4. Leg 1 ( Fig. 9B), endopod lateral lobe with spinules and inner wedge-shaped projection; exopod segment 1 with lateral spine (broken in one specimen) and inner spinules, segment 2 with long lateral spine about the length of exopod segment 2 and 3 together, segment 3 with terminal spine, broken in one specimen.

Leg 2 ( Fig. 9C), coxa with medial seta. Leg 4 ( Fig. 9E, F), coxa with inner surface spinules, 1 strong and 8 short distolateral spines, and patches of spinules on posterior surface.

Adult male: Total length 2.11 mm ( Fig. 10A). Oral limbs and swimming legs as in original description by Tanaka (1956), deviating only in following details:

Left antennule ( Fig. 10B) unmodified, of 24 free segments, extending to first urosome segment; armature as follows: I – 1s + 1ae, II–IV – 5s + 3ae? + 2 short sensillae ( Fig. 10B, see arrows), V – 2s + 2ae + 1 short sensilla, VI – 2s + 1ae, VII – 2s + 2ae + 1 short s in particular position, VIII – 2s + 2ae, IX – 2s + 2ae, X–XI – 4s + 4ae, XII – 1s + 2ae; XIII – 2s + 2ae; XIV – 2s + 1ae, XV – 1s + 1ae, XVI – 2s + 1ae, XVII – 1s + 1ae, XVIII – 2s + 1ae, XIX – 2s + 1ae, XX – 2s + 1ae, XXI – 2s + 1ae, XXII – 1s + 1ae, XXIII – 1s + 1ae, XXIV – 2s + 1ae, XXV – 2s + 1 ae, XXVI – 2s, XXVII– XXVIII – 4s + 1ae.

Right antennule ( Fig. 10C–E) strongly modified for grasping, of 22 free segments; segments XVIII–XXII/ XXIII with surface spinules; segments XIX–XXVI strongly enlarged; segments XX and XXI with 1 proximal spine each, segments XXI–XXII partly fused, segments XXII–XXIII fused, segment XXIV with lateral broad denticulated lamella, segment XXV with small lateral chitinized lamella; hinges occurring between segments XVIII and XIX, XIX and XX, XX and XXI, XXIII and XXIV, XXIV and XXV and XXIV and XXV. Armature as follows: segment I – 1s + 1ae, II–IV – 6s + 4ae, V – 2s + 2ae, VI – 2s + 1ae, VII – 2s + 2ae, VIII – 2s + 2ae, IX – 2s + 1ae; X–XI – 4s + 3ae, XII – 1s + 2ae, XIII – 2s + 2ae, XIV – 2s + 1ae, XV – 1s + 1ae, XVI – 2s + 1ae, XVII – 2s + 1ae, XVIII – 2s + 1 ae, XIX – 2s, XX – 1s+ 1ae +1 spine, XXI – 1s +1 spine, XXII–XXIII – 2s + 1ae, XXIV – 2s + 1ae, XXV – 2s + 1ae, XXVI – 2s, XXVII–XXVIII – 5s + 1ae.

Remarks: Ryocalanus infelix was so far only known from a male specimen. Together with female specimens, also males of this species were present in the samples. COI sequence analysis verified the assignment of females and males to the same species (see below).

The urosome of all female specimens was covered by a viscous mass (as indicated in Fig. 7A, B) that was only removable by placing the urosome into lactic acid for at least 24 h. We hypothesize that this viscous mass-like structure is either connected to the mating process or might be remnants of egg sacs. The antennule of one female did show a quadrithek arrangement of appendages with segments V, VII, VIII, IX and XIII bearing two small, slender aesthetascs in addition to two setae. While the doubling of aesthetascs is unusual in female calanoid copepods, it has previously been observed in a few genera within the Calanidae by Fleminger (1985). He postulated that quadrithek females derive from genotypic males in which the gonad develops as an ovary and suggested that environmental factors or internal factors affect the final, phenotypic sex.

The morphology of the male specimens is mostly as in the original description of Tanaka (1956), except for: the basis of leg 1 carries 1 medial seta that is missing in the original description; the maxillule coxal endite carries 6 setae (vs. 5 setae in the original description); and the maxillary endopodite carries 9 setae (vs. 8 setae in the original description). The setation of the left male antennule, which was missing in the original description, is given here. Segmental fusions in the right male antennule are not absolutely unambiguous in Ryocalanus infelix and R. squamatus sp. nov. due to the significant Ryocalanus male morphological transformations in the ancestral antennule segments distal to the segment XXI. More specifically, a fusion of segment XXV–XXVI, observed for R. infelix ( Tanaka, 1956) , could not be observed here. Instead, based on the morphology of the male antennules of Ryocalanus squamatus sp. nov. and R. infelix from the Kurile-Kamchatka trench, ancestral segments XXII and XXIII are apparently fused. This compund segment (XXII–XXIII) is distally followed by segments that are each supplied by two setae (both distoanterior and distoposterior), which is a marker for the ancestral segments XXIV, XXV, XXVI and XXVII (e.g. Huys & Boxshall, 1991). This interpretation can also be applied to R. brasilianus ( Renz et al., 2013) , for which the earlier interpretation of antennule segmental fusions was left for discussion. The right antennule of R. infelix differs from other Ryocalanus species in the shape of the denticulated and chitinized lamella on segments XXIV and XXVI, which is of a different structure in R. brasilianus ( Renz et al., 2013) and absent in R. squamatus sp. nov. and R. bowmani ( Markhaseva & Ferrari, 1996) .

The length of males discovered from the Kurile-Kamchatka trench varied between 1.95 and 2.15 mm.

Females and males differed in the number of setae in the mandible endopod segment 2 (10 in males, 11 in females), the maxilla basal distal endite setation (four in females, three in males) and the maxilliped endopod setation (endopod 6-segmented with 2, 4, 4, 4, 3 + 1, and 4 setae in females, endopod 6-segmented, with 2, 4, 3, 2, 2 + 1, and 4 setae in males). The maxilla praecoxal endite showed variations in setation between left and right limbs of both, female and male individuals with the armament being 3 setae plus attenuation or 5 setae.

GENUS YROCALANUS RENZ, MARKHASEVA & SCHULZ, 2013 View in CoL