Monstrilla ilhoii, Lee, Jimin & Chang, Cheon Young, 2016

Lee, Jimin & Chang, Cheon Young, 2016, A new species of Monstrilla Dana, 1849 (Copepoda: Monstrilloida: Monstrillidae) from Korea, including a key to species from the north-west Pacific, Zootaxa 4174 (1), pp. 396-409 : 397-404

Monstrilla ilhoii sp. nov.

( Figs. 1–5 )

Type locality. Jisepo Harbor (34°49 ' 49.59 '' N, 128°42 ' 21.06 '' E), Geoje Island , south coast of Korea .

Material examined. Holotype ♀ (NHMUK reg. no. 2015.2413), allotype ♂ (NHMUK reg. no. 2015.2414), both undissected, ethanol-preserved, collected from the type locality, 19 Jan. 2014 (C.Y. Chang & J. Lee). Paratypes: one ♀ (DB20042), one ♂ (DB20043), both dissected on slides, from the type locality. Additional material (stored in the junior author’s collection): two ♀♀, Pohang-Yeongil New Port , Pohang , 11 Oct. 2012 (C.Y. Chang & Y.J. Son); one ♀, same locality , 17 Nov. 2012 (C.Y. Chang); eight ♀♀, two ♂♂, Duwon-ri , Janggimyeon, Pohang , 2 Jan. 2014 (C.Y. Chang); two ♀♀, two ♂♂, Gujora Harbor , Geoje Island , 21 Jan. 2014 (C.Y. Chang & J. Lee); two ♀♀, one ♂, Chubong Island, off Tongyeong , 2 Nov. 2013 (C.Y. Chang & Y.J. Son); two ♀♀, Eunjeom , Samdong-myeon, Namhae Island , 19 Oct. 2012 (S.S. Hong); three ♀♀, three ♂♂, Jeju Port , Jeju Island, 11 May 2012 (C.Y. Chang & J. Lee).

Description of female. Body ( Fig. 1 A–B) large, about 3.78 mm long (mean 3.83 mm, standard deviation 0.14, n = 8), measured from anterior end of cephalothorax to posterior margin of caudal rami, excluding antennules and caudal setae. Nearly entire body surface, including antennules, caudal rami and legs 1–4, excluding the wrinkled area around oral papilla, showing polygonal ridge pattern (cuticular reticulation) ( Fig. 5 A). Cephalothorax somewhat large and relatively long, accounting for about 53.1% of total body length. Forehead slightly concave medially between antennulary bases in dorsal view, without rostral protrusion, bearing one pair of small setae near anterior margin; lateral margins abruptly curved inward; middle of dorsal surface ornamented with round patch of 12–13 sensory pores. Nauplius eye not well defined. Transverse striations not clear dorsally and ventrally. Hemispherical, rugged median cuticular process conspicuous on anterior ventral surface between antennulary bases, protruding ventrally ( Figs. 1 C–D, 5B) and flanked by numerous oblique wrinkles between antennulary bases and nipple-like processes. Paired nipple-like processes well-developed, followed by relatively weak transverse wrinkles between nipple-like processes and oral papilla. Oral papilla situated at slightly less than one quarter length of cephalothorax, protruding ventrally, with distal half bent slightly posteriorly. Near posterior margin, three pairs of sensilla arranged in row dorsolaterally. Large, hemispherical protrusion situated mid-ventrally, just anterior to intercoxal sclerite of leg pair 1 ( Fig. 5 B).

Urosome ( Fig. 1 E) consisting of four urosomites, accounting for 22.1% of total body length, excluding caudal setae. Fifth pedigerous somite with two pairs of sensilla medially on dorsal surface. Genital double-somite bearing pair of long ovigerous spines, these being inserted on middle of ventral surface, basally separated, with pointed tips extending far beyond tips of caudal setae, in total equal to about 36% of total body length. Anal somite trapezoidal; lacking wrinkles or striae on both dorsal and ventral surfaces; lateral margins nearly smooth, without apparent notch.

Caudal rami ( Fig. 1 E) stout, about 1.5 times as long as wide; divergent outward; swollen at basal part of inner face and at base of proximal lateral caudal seta. Each ramus armed with six well-developed caudal setae, consisting of two distal, two lateral, one inner distal, and one dorsomedial setae.

Antennule ( Fig. 2 A) equal to about 27% of total body length, close to half (50.1%) as long as cephalothorax; 3- segmented (ratio of lengths of segments from proximal to distal 15.1:15.8:69.1 = 100), with distal segment barely showing traces of fusion of three ancestral segments (purported segments 3–5). Setal armature showing standard arrangement up through purported segment 3. Purported segment 4 with six spinous setae in total (4v 1-3 + 4d1–3) on medial face, accompanied dorsomedially by short, conical spinous projection ( Fig. 2 A, arrow), along with normal armature of three stout, plumose setae and one long aesthetasc. Purported segment 5 with small projection proximally on dorsal surface, spinous seta five medially, three plumose setae (Vd, Vm, Vv), setae b1-3 all dichotomously branched, seta b5 slightly branched, setae b4 and b6 simple; subapical seta 6 1 plumose and hooked; apical spinous seta 6 2 remarkably thicker, dagger-like, with inner hyaline blade, about 55.6% as long as 6 1.

Legs 1–4 ( Figs. 2 B, 3A–C), all with both endopod and exopod 3-segmented. Intercoxal sclerite subquadrate, about 1.5 times as long as wide, lacking setule or spinule row on medial face and along posterior margin. Coxa without setae and also lacking marginal rows of setules or spinules. Basis not fully divided from coxa medially; all outer basal setae on legs 1–4 slender, naked; seta on leg 3 relatively much longer. Outer margin of first exopodal segments of legs 1–4 undulate; outer margins of all endopodal segments hirsute. Outer spine on all first exopodal segments short, less than half as long as segment; outer spine on all third exopodal segments curved, long, about 70% as long as segment; distal spinous seta of all exopods extremely long, heterogeneously ornamented with setules on inner side basally and numerous fine spinules along most of inner side. Seta/spine armature of swimming legs 1–4 as follows (Roman numerals indicate numbers of spines, and Arabic numerals indicate numbers of setae):

Leg 5 ( Fig. 1 E) bilobed, both lobes confluent basally and not fully divided distally. Exopodal lobe including fused part elongate, armed with three long, plumose setae apically or subapically, all of subequal length. Endopodal lobe including fused part also elongate, its tip nearly reaching to distal end of exopodal lobe, armed with one short subapical seta.

Description of male. Body ( Fig. 4 A) large, but much smaller than that of female, allotype about 2.76 mm long (mean 2.83 mm, standard deviation 0.09, n = 5), showing polygonal ridge pattern on nearly whole body surface, excluding genital apparatus. Cephalothorax ( Figs. 4 B–C, 5B) relatively short, representing about 43.3% of total body length; constricted at about anterior quarter, then slightly swollen near middle. Nauplius eye big; three eye cups subequal in size; median ventral one circular, its diameter about 1/3 of cephalothorax width at eye level ( Fig. 4 A). Band of transverse striations situated 42–48% of way from anterior end of cephalothorax: about 20–24 obvious striations on dorsal surface, about ten faint striations on ventral surface ( Fig. 4 A–C). Median cuticular process, two nipple-like processes, and oral papilla similar to those of female. Sensory pores on dorsal surface of prosomites as shown in Fig. 4 A.

Urosome ( Fig. 4 A, D) 5-segmented, comprising fifth pedigerous somite, genital somite, two postgenital somites, and anal somite. Fifth pedigerous somite with two sensory pores anteriorly and two sensilla posteriorly on middle of dorsal surface, showing subrectangular arrangement; ventral surface with scattered oblique wrinkles. Anal somite ( Figs. 2 D, 4D) trapezoidal; lateral margin smooth, without notch or wrinkles; posterolateral corners round, with thickened cuticle. Caudal rami ( Fig. 2 D) divergent, about 1.3 times as long as wide, with distal part of inner margin slightly undulate; each ramus furnished with six setae, comprising two lateral, two terminal with bulbous bases, one inner distal, and one dorsal.

Antennule ( Fig. 2 C) long, a little shorter (87.9%) than cephalothorax, equal to 38.1% of total body length; 5- segmented (length ratio of segments from proximal to distal 19.8:16.7:14.4:25.7:23.4 = 100); geniculate between fourth and fifth segments. Segment 4 armed with five spinous setae in total (4v 1-3 + 4d1-2) on medial face, accompanied by short, conical, spinous projection dorsomedially ( Fig. 2 C, arrow), along with one stout plumose seta (IVv) and one long aesthetasc. Apical segment with four dichotomously branched setae (A–D) and two slender, unbranched setae (elements 3–4) laterally on posterior margin; element 1 subapical, plumose and slightly hooked; element 2 apical, markedly thicker, dagger-shaped, about half as long as element 1.

Legs 1–4 as in female. Leg 5 completely lacking, its site evident only as small wrinkles at posteromedial edge of fifth pedigerous somite ( Fig. 4 D).

Genital apparatus ( Figs. 4 D–E, 5D) comprising long, ventrally protruding shaft and small distal lappets. Pair of lappets well separated from each other by slightly concave and undulating distal margin of shaft, entire complex horseshoe-shaped, with tips of lappets slightly overreaching anterior margin of next postgenital somite. Lappets narrowing distally and gently curving inwards, ornamented with deep indentations. Genital openings covered with paired, subtriangular, membranous opercular flaps, each flap bearing numerous minute hairs along its distomedial face. Spermatophores not observed.

Etymology. The new species is named in honor of Professor Il-Hoi Kim, the great and most exhaustive taxonomist of parasitic copepods.

Figures

FIGURE 1. Monstrilla ilhoii sp. nov. (female). A, habitus, dorsal; B, habitus, lateral; C, anterior part of cephalothorax in ventral view, showing median cuticular process, paired nipple-like processes, and oral papilla; D, anterior part of cephalothorax in lateral view, showing antennulary base, median cuticular process (arrow), and nipple-like process; E, urosome, ventral, with leg 5 and proximal part of ovigerous spine. Scale bars: A – B = 500 µm; C – E = 100 µm.

FIGURE 2. Monstrilla ilhoii sp. nov. (female, A – B; male, C – D). A, right antennule, ventral; B, leg 1; C, left antennule, dorsal; D, postgenital urosomites and caudal rami, ventral. Arrows indicate the additional spinous projections on the fourth segment of antennules. Scale bars = 100 µm.

FIGURE 3. Monstrilla ilhoii sp. nov. (female). A, leg 2; B, leg 3; C, leg 4. Scale bar = 100 µm.

FIGURE 4. Monstrilla ilhoii sp. nov. (male). A, habitus, dorsal; B, anterior half of cephalothorax, lateral; C, anterior part of cephalothorax in ventral view, showing median cuticular process, paired nipple-like processes and oral papilla, band of transverse striations, and sensory pores; D, urosome, lateral; E, genital apparatus, ventral. Scale bars: A = 500 µm; B – D = 100 µm; E = 50 µm.

FIGURE 5. Monstrilla ilhoii sp. nov. (SEM photographs; female, A; male, B – D). A, female cephalothorax, lateral; B, anterior part of cephalothorax in ventral view, showing median cuticular process, paired nipple-like processes, and oral papilla; C, antennules, dorsal; D, genital apparatus, ventral. Scale bars = 100 µm.