Dendropsyllus kimi, Lee & Huys, 2019

DENDROPSYLLUS KIMI View in CoL SP. NOV.

( FIGS 10–14)

u r n: l s i d: z o o b a n k. o r g: a c t: E C 6 8 4 A C 7 - 0 3 7 5 - 49D6-ABF1-B3AA538FB953

Ty p e l o c a l i t y: S o u t h c o a s t o f K o r e a; S t n A8 (33°59.851′N, 128°30.413′E); fine sand with high silt content; depth 105.7 m ( Fig. 1).

Type material: Holotype ♀ dissected on 12 slides (reg. no. NIBRIV0000829701 ), allotypic paratype ♂ dissected on ten slides (reg. no. NIBRIV0000829702 ), remaining paratypes (two ♀♀, one ♂) preserved in formalin (reg. no. NIBRIV0000829703 ); all type specimens collected on 8 June 2015 from type locality.

* Type species.

a Soyer (1965: fig. 4A) illustrates only four elements on enp-2 but mentions five in the text (albeit erroneously on the proximal segment; p. 335).

b Although the adult male has been reported twice in the literature ( Lang, 1948; Drzycimski, 1969), its swimming leg armature has not been described in any detail.

c George (2006a: 89) describes P1 exp-2 as ‘…with 2 outer bipinnate spines, terminally with 3 bare geniculate setae’. His proposed emendation (on p. 118) [‘P1 exp2 with 2–3 geniculate setae and 2 outer spines (cf. C. tauroides )’] of Conroy-Dalton’s (2003a) generic diagnosis is therefore unjustified and was probably based on his illustration (fig. 4B), which shows only two geniculate setae, with the third one apparently being dislodged as indicated by the dashed lines.

d This seta was absent in the holotype ( George, 2006a: fig. 6A).

e Contrary to Coull’s (1973) original description, the suture between exp-2 and -3 is incomplete ( George, 2006b: fig. 17A).

f Based on damaged specimen, no information available on endopodal armature of P1–P4 ( George & Plum, 2009).

g Based on ♀ copepodid V stage .

h Norman’s (1911) description was based on a composite of two species, making it impossible to decide which of the figured appendages belong to the lectotype illustrated in his habitus drawing ( Conroy-Dalton & Huys, 2000).

Other material examined: Three ♂♂ (reg. no. MInRB-Hr38-L001) preserved in formalin; south coast of Korea; Stn H 12 (32°01.081′N, 126°44.812′E) ( Fig. 1); fine sand with high silt content; depth 110 m; collected on 2 June 2015 GoogleMaps .

Description of female: Body length measured from anterior outer corner of cephalothorax to posterior margin of caudal rami 463–539 μm (mean = 505 μm; N = 3; holotype = 539 μm). Body ( Fig. 10A, B) cylindrical, tapering slightly posteriorly, without clear demarcation between prosome and urosome; integument well chitinized. Somatic hyaline frills weakly developed, plain. Cephalothorax ( Fig. 10A) bilaterally constricted in anterior half; anterior half of dorsal surface with irregular pattern of fine surface wrinkles, as in ♂ (cf. Fig. 14A); anterior corners with sensory triplet consisting of three sensilla and closely associated tube-pore ( Fig. 11A) and a pair of strongly dentate, backwardly recurved frontolateral horns ( Fig. 10A, B); posterior half with a pair of large laterodorsal dendroid processes; lateroventral margins with strongly dentate, upwardly recurved, conical process (CLVPp) and smaller bifid process (CLVPa) proximal to the latter; all processes sensillate, with sensilla positioned apically.

Rostrum: Absorbed into concave anteroventral surface of cephalothorax; with paired widely separated sensilla and midventral tube-pore ( Fig. 11A).

Somites bearing P 2– P 5: Each with paired laterodorsal dendroid processes decreasing in size posteriorly ( Fig. 10A); processes of somites bearing P2–P4 with anterior sensillum halfway along length of process; all somites with middorsal tube-pore.

Original segmentation of genital double-somite ( Figs 10A, B, 13B) indicated by bilateral constriction, dorsal transverse surface ridge and sensillar pattern ( Fig. 10A, B); genital half with two pairs of sensilla and middorsal tube-pore, abdominal half with three pairs of sensilla and two pairs of tube-pores; all sensilla arising from minute tubercles; posterior margin with continuous row of setular extensions. Genital field ( Fig. 13B) positioned far anteriorly, with fused gonopores opening via common midventral slit covered by genital operculum derived from vestigial sixth legs. P6 unarmed. Copulatory pore flanked by paired tube-pores, immediately posterior to each gonopore.

Second and third abdominal somites ( Figs 10A, B, 13B): With continuous row of setular extensions around posterior margin; with midventral spinule row near hind margin and paired tube-pores ventrally ( Fig. 13B) and dorsally ( Fig. 10A). Anal somite partly cleft midventrally ( Fig. 13B); with few small spinules around ventrolateral hind margin; anal operculum rounded, smooth ( Fig. 13A); paired dorsal sensilla arising from minute tubercles; with ventral pore either side of anal opening.

Caudal rami ( Fig. 13A, B): Divergent and slightly bent inwards, cylindrical; 13 times as long as wide (width measured at insertion point of seta II); with dorsal tube-pore in proximal one-ninth of ramus and ventral tube-pore near seta III; spinules present around ventral hind margin and at base of seta VII; with seven setae. Seta I minute, positioned ventral to seta II; setae II and III minutely pinnate; seta V well developed, spiniform, bipinnate, ~43% of body length ( Fig. 10A); setae IV and VI short and naked; seta VII tri-articulate at base and arising from minute dorsal pedestal, near posterior margin.

Antennule ( Fig. 11A): Three-segmented. Segment 1 compound, longest; posterior margin with long setules in distal third; one dorsal subapical seta arising from spinous projection (arrowed in Fig. 11A). Segment 2 with aesthetasc (length 73 μm) fused at base to long seta. Segment 3 with apical acrothek consisting of aesthetasc (length 32 μm) and two slender setae. Armature formula: 1-[4 + 5 pinnate], 2-[5 + 1 pinnate + (1 + ae)], 3-[9 + acrothek].

Antenna ( Fig. 11B): Coxa represented by well-developed sclerite. Basis and proximal endopod segment fused, forming allobasis; exopod completely absent; membranous insert along outer margin marking original position of exopod (arrowed in Fig. 11B); abexopodal margin with two spinule rows, with one short bipinnate seta in endopodal half. Surface of free endopod with patch of long setules and two distal surface frills; with spinules along medial margin; lateral armature consisting of two bipinnate setae and fine, hair-like seta; distal armature consisting of two pinnate spines and three geniculate setae, longest one fused basally to vestigial seta.

Mandible ( Fig. 11C): Coxa robust, expanding distally to gnathobase bearing two bicuspidate teeth, several incised blades, and one bifid spine plus a pinnate seta at dorsal corner. Palp well developed, one-segmented; with two plumose setae along inner margin (representing basal elements) and three apical plumose setae (representing incorporated endopod); outer margin without armature but with a row of long spinules.

Maxillule ( Fig. 11 D): Praecoxal arthrite subrectangular, with two setae on anterior surface; distal armature consisting of five bare and four pinnate spines. Coxal endite with one unipinnate spine and one unipinnate seta; with few spinules around bases of armature elements. Basis with two closely set endites; proximal endite with one naked spine, and one bare and two unipinnate setae; distal endite with two unipinnate setae. Rami completely incorporated into basis; endopod represented by three unipinnate setae; exopod represented by one bipinnate seta and one tiny seta.

Maxilla ( Fig. 11E): Syncoxa with spinule patches as figured; with two coxal endites; proximal endite with one strong bipinnate spine fused basally to endite and two articulating unipinnate spines; distal endite with three spinulose spines. Allobasis drawn out into unipinnate claw; accessory armature consisting of one unipinnate and two naked setae in addition to one spinulose spine. Endopod tiny, one-segmented, with two unipinnate setae.

Maxilliped ( Fig. 11F): Subchelate, slender. Syncoxa with one strong unipinnate seta; with few spinules along medial margin. Basis with robust, long spinules along palmar margin. Endopod drawn out into long, narrow, curved claw; claw bipinnate with anterior and posterior row of strong pinnules, and with one minute accessory seta at base.

P1 ( Fig. 12A): Intercoxal sclerite moderately wide and narrow; with fine setular extensions along free margin. Praecoxa weakly developed (not shown). Coxa trapezoid, with small, spinulose lobate process on outer margin. Basis transversely elongate, with conspicuous anterior tube-pore near distal margin between rami; both outer and inner element setiform and plumose. Both rami two-segmented; exp-1 outer spine bipinnate; exp-2 with fine spinules along inner margin, with four geniculate setae (two of them with few spinules) and one bipinnate outer seta. Enp-1 small, unarmed; enp-2 3.75 times as long as enp-1, with one plumose seta apically.

P 2–P 4 ( Fig. 12B–D): With moderately wide intercoxal sclerites without ornamentation (as shown for P2; see Fig. 12B). Praecoxae weakly developed (not shown). Coxae trapezoid, with small, spinulose lobate process on outer margin. Bases transversely elongate; with anterior tube-pore near distal outer margin; outer distal seta plumose. Exopods three-segmented, outer spines elongate; P2–P3 exp-3 with anterior tube-pore near distal margin; outer and outer distal setae of P2–P3 exp-3 with defined flexure zone. Endopods absent (P2) or reduced and one-segmented (P3–P4); original position of P2 endopod marked by membranous insert (arrowed in Fig. 12B). Armature formula as follows:

P5 ( Fig.13C): Baseoendopod and exopod fused, without membranous area marking original segmentation; outer basal seta plumose and arising from short setophore, with long tube-pore at base. Endopodal lobe absorbed, represented by tiny pedestal with one minute seta and conspicuous tube-pore at its base. Exopod slender and elongate; with one outer, one apical and one inner pinnate seta; subdistal outer margin with tube-pore.

Description of male: Body length, measured from outer anterior corner of cephalothorax to posterior margin of caudal rami, 474–505 μm (mean = 489 μm; N = 2; dissected paratype = 505 μm). Sexual dimorphism in antennule, P3 endopod, P5, P6, urosomal segmentation and caudal ramus length.

Pattern of dendroid processes, sensilla and pores essentially as in ♀ ( Fig. 14A); cephalothorax with irregular pattern of fine surface wrinkles in anterior half.

Urosome ( Fig. 13E): Slender, six-segmented; sensillar pattern and ornamentation of somites as in ♀ except for additional midventral spinule row on first abdominal somite.

Caudal rami ( Fig. 13D, E): Divergent and slightly bent inwards; shorter and less slender than in ♀; nine times as long as wide (width measured at insertion point of seta II). Armature and ornamentation essentially as in ♀ except for seta V being relatively shorter (~35% of body length) .

Antennule ( Fig. 14B): Six-segmented and subchirocer, geniculation between segments 4 and 5; aesthetasc present on segment 4 (length 75 μm) and as part of apical acrothek on segment 6. Segment 1 compound, longest; posterior margin with few long setules in distal half; one dorsal subapical seta arising from spinous projection as in ♀. Segment 3 represented by a U-shaped sclerite. Segment 4 swollen. Segment 5 with spinous outgrowth representing modified element. Armature formula: 1-[5 + 5 pinnate], 2-[6 + 1 vestigial spine], 3-[1], 4-[3 + 6 pinnate + (1 + ae)], 5-[1 spinous process], 6-[7 + acrothek]. Apical acrothek consisting of two setae and aesthetasc (length 28 μm).

P3 ( Fig. 14C): Protopod and exopod as in ♀. Endopod three-segmented; enp-1 minute, as long as wide, unarmed; enp-2 elongate, anterior distal surface produced into small, recurved spinous apophysis reaching beyond distal margin of enp-3; enp-3 minute, slightly longer than wide, with two apical setae, one of them plumose.

P5 ( Fig. 13F): Baseoendopod and exopod completely separated. Baseoendopod ~1.4 times as long as maximal width; outer basal seta naked and arising from short setophore; outer margin with tube-pore. Endopodal lobe completely absorbed, represented by tiny seta accompanied by tube-pore. Exopod slender and elongate; with one outer, one apical and one inner bipinnate seta; with anterior tube-pores in proximal and distal quarters.

Sixth pair of legs: Asymmetrical ( Fig. 13E), represented by membranous flap (arrowed) covering single functional genital aperture (indicated by dotted line); P6 without armature.

Etymology: The species is named after Professor Il-Hoi Kim (Gangneung-Wonju National University), in recognition of his massive contribution to our knowledge of the Korean copepod fauna.

Remarks: Conroy-Dalton (2003a) proposed the genus Dendropsyllus to accommodate a species, De. thomasi , described from the San Diego Trough, northeastern Pacific. The genus was characterized by the distinctive pattern of dendroid body processes (lacking on abdominal somites), the presence of a well-developed conical process on the lateroventral margins of the cephalothorax, P1 exp-2 with four geniculate setae, P1 enp-2 with one apical seta, the complete absence of P2 endopod, P3 exp-3 with one inner seta and the loss of the inner seta on P4 exp- 3. She transferred the Southern Hemisphere species Ceratonotus magellanicus George & Schminke, 1998 (Straits of Magellan, Chile) and Ce. antarcticus George & Schminke, 1998 (Halley Bay, Weddell Sea, Antarctic) to Dendropsyllus , because they deviate significantly from her revised diagnosis for Ceratonotus . George (2006a) re-examined De. magellanicus ( George & Schminke, 1998) based on new material from the Chilean Pacific continental slope off Chiloé Island and provided the first description of a male in the genus. Gómez & Díaz (2017) recently added a fourth species, De. californiensis , from the Southern Trough of the Guaymas Basin in the Gulf of California.

The morphology of De. kimi is in complete accordance with the characters summarized in Conroy-Dalton’s (2003a) generic diagnosis. It exhibits a number of unique characters not found in any of its congeners ( Table 3): (1) dorsalsensillatetuberclesonabdominalsomites1–2 absent (but note that the condition in De. antarcticus is unclear); (2) P3 endopod ♀ one-segmented with armature formula 020 instead of two-segmented with formula 0.020 or 0.021; and (3) inner spine on P5 exopod ♀ longer than outer seta (ratio 0.75) instead of being shorter. The female antennule of the new species also displays a first segment that is more elongate than in most of its congeners, being 1.1 times the length of segments 2 and 3 combined (measured along the posterior margin). The one-segmented condition of the P4 endopod in the female is shared with De. antarcticus .

Males of Dendropsyllus spp. appear to be very rare. George (2006a) reported a single one of De. magellanicus , and De. kimi is the first species to be known from more than one male. Comparison of male characters will therefore have to be confined to these two species. Dendropsyllus kimi shows sexual dimorphism in the ventral spinule patterns on the abdominal somites, with the male exhibiting an additional transverse row near the posterior margin of the first abdominal somite (absent on the genital double-somite of the female; Fig. 13B, E). Unfortunately, George (2006a) figured the male of De. magellanicus only in dorsal aspect and did not mention any sex-related differences in abdominal spinulation in the text; the potential significance of this character at generic level therefore remains unconfirmed. George (2006a) reported slight sexual dimorphism in the size of the P4 endopod in De. magellanicus , but this was not observed in the new species. Relative differences in caudal ramus length have been discerned between sexes of both species. In De. magellanicus , the caudal ramus is longer in the female (length:width ratio 16.0) than in the male (10.5); likewise, in De. kimi it is shorter in the male (9.1) than in the female (13.7). Males of both species show an identical modification of the P3 endopod, being three-segmented with an apophysis arising from the middle

* George & Schminke (1998) mention the presence of ‘sensilla raised on small knobs’, but it is unclear how they compare with the sensillate tubercles reported in other members of the genus.

†Outer seta broken in the only available female. Abbreviation: benp, baseoendopod.

segment and displaying two apical setae on the terminal segment. Females of both species exhibit two apical setae on the (only or) distal endopodal segment of P3 ( Table 3) and lack an outer spine/seta as in most members of the Ceratonotus group ( Table 2). Recently, Gómez & Díaz (2017) reported an outer spine-like element on the female P3 enp-2 of De. californiensis , a condition observed so far only in Touphapleura schminkei ( George, 1998) . Despite the male being unknown, they considered this element as novel and autapomorphic for De. californiensis and not homologous to the inner apophysis observed for the male of De. magellanicus . This supposition is unlikely, because in every species of the Ancorabolinae that shows this seta in the female, it is suppressed in the male ( T. schminkei and all species of the Ancorabolus group) and takes part in the formation of the apophysis. Unlike the great majority of species in the Laophontidae and related families, where an apophysis becomes expressed in the male only when an outer spine is present in the female ( Huys, 1990), the presence of such a spine is not necessarily required for the formation of an apophysis in the Ancorabolinae , suggesting different ontogenetic pathways in males and females.

Based on the records published so far, the genus essentially assumes a Pacific distribution, with De. antarcticus the only, albeit neighbouring, outlier from the Weddell Sea in the Southern Ocean.