Ergasilus kimi, Boxshall, Geoffrey A., 2016

Boxshall, Geoffrey A., 2016, A new species of Ergasilus von Nordmann, 1832 (Copepoda: Cyclopoida) from the gills of a dasyatid ray, Himantura oxyrhyncha (Sauvage, 1878) from West Kalimantan, Indonesia, Zootaxa 4174 (1), pp. 93-103 : 94-101

publication ID	https://doi.org/ 10.11646/zootaxa.4174.1.6
publication LSID	lsid:zoobank.org:pub:1F0F6D0F-9D03-43D3-A0E9-7054A6F1001D
DOI	https://doi.org/10.5281/zenodo.5671869
persistent identifier	https://treatment.plazi.org/id/3823883C-FF90-FFB3-FF29-3BAD24E8FD43
treatment provided by	Plazi
scientific name	Ergasilus kimi
status	sp. nov.

Treatment

Ergasilus kimi sp. nov.

( Figs. 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 )

Type material. Holotype ovigerous ♀ from gills of Himantura oxyrhyncha (KA 229) caught in the Java Sea off the coast of West Kalimantan, Indonesia, near Sungai Kakap (00°03’42.38”S, 109°10’37.68”E) on 18 July 2007; registration number MZB Cru Cop 113 GoogleMaps . Paratype ♀ from gills of H. oxyrhyncha (KA 186) caught in the Java Sea off the coast of West Kalimantan, Indonesia, near Jungkat (00°03’46.00”N, 109°12’10.40”E) on 13 July 2007; registration number MZB Cru Cop 114 GoogleMaps . Paratype ♀ from gills of H. oxyrhyncha (KA 236) caught in the Java Sea off the coast of West Kalimantan, Indonesia, near Sungai Kakap (00°03’42.38”S, 109°10’37.68”E) on 18 July 2007; registration number USNM 1266274 View Materials GoogleMaps . Paratype ♀ from gills of H. oxyrhyncha (KA 186) caught in the Java Sea off the coast of West Kalimantan, Indonesia, near Jungkat (00°03’46.00”N, 109°12’10.40”E) on 13 July 2007, partly dissected; registration number NHMUK 2014.661 View Materials . GoogleMaps

Etymology. The species is named in honour of Professor Il-Hoi Kim in recognition of his contributions to our knowledge of the Ergasilidae of the Northern Indo-Pacific.

Description of adult female. Body cyclopiform ( Fig. 1 View FIGURE 1 A), comprising prosome consisting of cephalosome and first pedigerous somite, separated dorsally by functional articulation but fused ventrally, and three free pedigerous somites (bearing legs 2 to 4), and urosome consisting of fifth pedigerous somite, genital double-somite and three free abdominal somites. Cephalosome elongate, covered by dorsal shield; with oral region located ventrally near posterior border and separated from antennary bases by distinct gap. Rostrum ( Fig. 1 View FIGURE 1 C) weakly developed, ornamented with median pore and two pairs of sensillae. First pedigerous somite elongate, narrower than cephalosome. Second pedigerous somite narrower than first, bearing paired, weakly defined integumental windows laterally on tergite (arrowed in Fig. 1 View FIGURE 1 A). Third pedigerous somite narrower than second, and fourth narrower than third; tergite of fourth pedigerous somite completely concealing fifth pedigerous somite in dorsal view ( Fig. 1 View FIGURE 1 A). Fifth pedigerous somite very small, concealed in both dorsal and ventral views. Genital double somite, 1.2 times wider than long, with rounded lateral margins, bearing paired, slit-like genital apertures dorsally, ornamented with transverse rows of spinules on ventral surface ( Fig. 1 View FIGURE 1 B). First and second free abdominal somites broad and short, both ornamented with posterior spinule row along ventral margin. Anal somite deeply incised in midline; about 2.5 times broader than long: ornamented with paired spinule rows on ventral surface ( Fig. 1 View FIGURE 1 B). Caudal rami about 1.4 times longer than wide: armed with four setae, all naked ( Fig. 1 View FIGURE 1 B). Mean body length from anterior margin of cephalothorax to posterior margin of caudal rami 619 µm (range 614–625 µm, based on three specimens). Egg sacs multiseriate, length 575 and 606 µm in holotype.

Antennule 6-segmented ( Fig. 2 View FIGURE 2 A), setal formula: 3, 12, 5, 4 + ae, 2 + ae, 7 + ae. Antenna 4-segmented ( Fig. 2 View FIGURE 2 B) comprising robust coxobasis armed with short naked seta distally, 3-segmented endopod and curved terminal claw. Second segment (first endopodal segment) unarmed but with small swelling near middle of medial margin carrying tiny sensilla. Third segment (second endopodal segment) shorter and narrower than preceding segment, curved distally and bearing small tooth-like process on medial margin about one third of length from base. Fourth segment (third endopodal segment) reduced, bearing minute seta externally. Claw curved, without fossa on concave margin; length of claw about equal to length of second endopodal segment.

Labrum weakly defined, with slightly concave posterior margin ( Fig. 2 View FIGURE 2 C). Mandible ( Fig. 2 View FIGURE 2 D) with three blades; proximal blade carried on posterior margin, ornamented with 12 blunt teeth increasing in size distally; subapical blade ornamented with row of about 12 large pointed spinules on posterior margin and isolated spinules on anterior margin; apical blade slender, tapering, with fine spinules. Maxillule ( Fig. 2 View FIGURE 2 E) lobate, armed with two unequal distal setae and produced into small process medially. Maxilla ( Fig. 2 View FIGURE 2 F) comprising large tapering syncoxa and basis; syncoxa ornamented with patch of spinules and single pore; basis spatulate and ornamented with dense array of acute spinules. Maxilliped absent, as in all female ergasilids.

Legs 1–4 ( Figs. 3 View FIGURE 3 A–D) biramous, each with 3-segmented endopod and 3-segmented exopod, except for 2- segmented exopod of leg 4. Intercoxal sclerites slender, interpodal plates well developed between legs 1 and 2, legs 2 and 3 and legs 3 and 4; each ornamented with row of large spinules posteriorly ( Fig. 1 View FIGURE 1 D). Spine and seta formula as follows:

Coxa Basis Exopod Endopod Legs 1–4 with outer margins of all endopodal and exopodal segments ornamented with row of spinules; inner margin of first exopodal segment with row of long spinules. Legs 1 to 4 each with row of spinules on basis, near inner posterior margin ( Figs. 3 View FIGURE 3 A–D); leg 1 with additional row of minute spinules adjacent to origin of endopod ( Fig. 3 View FIGURE 3 A).

Fifth leg ( Fig. 1 View FIGURE 1 E) located dorso-laterally and visible in dorsal view; indistinctly 2-segmented; first segment with single (protopodal) seta located and directed dorsally, second (exopodal) segment about 1.4 times longer than wide, ornamented with minute spinules distally, and armed with two long setae; apical seta reaching beyond posterior margin of caudal ramus.

Taxonomic remarks. The new species has 153 congeners and recent studies have shown the genus Ergasilus to be very heterogeneous and in need of revision ( El-Rashidy 1996; Song et al. 2008). The current classification is based almost entirely on characteristics of the adult females, so species such as E. divergens ( Kokubo, 1914) , which is known only from the male ( Ohtsuka et al. 2004), cannot be compared with the new species. The combination of a 3-segmented endopod for leg 1 and the presence of two setae on the free exopodal segment of leg 5, is relatively unusual within the genus, and the new species thus belongs in an assemblage of 28 nominal species of Ergasilus which share these two character states: E. batai Karamchandani, 1952 ; E. borneoensis Yamaguti, 1954 ; E. cochlearius Kuang & Liu, 1991 ; E. flaccidus Fryer, 1965 ; E. genuinus ( Kokubo, 1914) ; E. glyptothoracis Kuang & Qian, 1983 ; E. hemibagri Zhang & Ma, 1994 ; E. iraquensis Amado, in Amado, da Rocha, Piasecki , Al- Daraji & Mhaisen, 2001; E. jiangxiensis Liu, 1998 ; E. lamellifer Fryer, 1961 ; E. leiocassi Xu, 1987 ; E. longicaudatus Kuang & Li, 1984 ; E. manicatus Wilson, 1911 ; E. mendisi Fernando & Hanek, 1973 ; E. mirabilis Oldewage & van As, 1987 ; E. orientalis Yamaguti, 1939 ; E. pararostralis Amado, in Amado, da Rocha, Piasecki, Al-Daraji & Mhaisen, 2001 ; E. peregrinus Heller, 1865 ; E. philippinensis Velasquez, 1951 ; E. rostralis Ho, Jayarajan & Radhakrishnan, 1992 ; E. rotundicorpus Jones & Hine, 1983 ; E. shehyangensis Wang, 1961 ; E. sieboldi von Nordmann, 1832 ; E. sittangenesis El-Rashidy & Boxshall, 2002 ; E. synanceiensis Amado, in Amado, da Rocha, Piasecki, Al-Daraji & Mhaisen, 2001 ; E. uniseriatus Ho, Jayarajan & Radhakrishnan, 1992 ; E. xenomelanirisi Carvalho, 1955 and E. xinjiangensis Kuang & Qian, 1985 .

This list excludes E. cunningtoni Capart, 1944 because of uncertainty about the setation of leg 5. In the original description leg 5 was illustrated as carrying two terminal setae, but Capart (1944: 15) stated that this limb also had a lateral seta which was not figured - “une soie latérale (non figurée)”. Subsequently, after examining new material from the type locality, Fryer (1964, 1965) raised doubts about the existence of this third seta on the free exopodal segment. Irrespective of the form of leg 5, this species differs from the new species in the possession of an outer margin spine on the second exopodal segment of leg 1, and in the form of the second endopodal segment of the antenna, which in E. cunningtoni has a marked indentation proximally on its convex outer margin, and in the very short antennary claw.

This assemblage of 28 species ( Table 1 View TABLE 1 ) can be subdivided by reference to the segmentation pattern of the female antennules. Descriptions of antennule segmentation are generally reliable in the Ergasilidae , although details of antennulary setation are not, particularly in the older literature, because setae are easily broken or overlooked, and the aesthetascs can be difficult to see. The new species possesses a 6-segmented antennule, in common with 24 of the species listed, but the remaining four species, E. flaccidus , E. pararostralis , E. rostralis and E. uniseriatus , all exhibit a 5-segmented antennule and can be eliminated from further comparisons.

Species Body length A1 Antenna P2 CR (L:W) Data source

(mm)

A second group of species can be separated from within the remaining 24 species by the gross morphology of the antenna, which forms the attachment apparatus securing the adult female to the gill filaments of its fish host. In E. glyptothoracis , E. manicatus , E. orientalis and E. rotundicorpus the antenna is a relatively short and compact limb, and the joint between the coxobasis and the first endopodal segment is inflated to form a distinctive lateral swelling ( Table 1 View TABLE 1 ). In the new species and in the remaining 20 species, the antenna is a relatively slender limb and the joint between the two proximal segments is not inflated. One other species, E. lamellifer , also has a distinctive antenna. When first describing this species Fryer (1961) highlighted the presence of a ridge-like lamella along the margin of the first endopodal segment; indeed, this feature was sufficiently remarkable to be alluded to in the name of the species. No other species listed in Table 1 View TABLE 1 has a lamella along the margin of this segment.

The proportions of the caudal rami, as indicated by the length to width ratio (L:W), has proven a useful character for species discrimination in many different copepod families, and there are marked differences between some of the species listed in Table 1 View TABLE 1 . The most elongate ramus is found in E. batai in which the L:W ratio is 7:1 ( Karamchandani 1952), whilst in several species the ramus is about as long as wide ( Table 1 View TABLE 1 ). It is convenient to divide the species into two categories, those with an elongate caudal ramus (i.e., L:W ratio of 3:1 or greater) and those with a relatively short caudal ramus (i.e., a L:W ratio of less than 3:1). The elongate category includes E. batai , E. jiangxiensis , E. longicaudatus , E. mendisi and E. xinjiangensis . Elimination of species listed in Table 1 View TABLE 1 on the basis of gross differences in antennulary segmentation, in the form of the antenna and in the proportions of the caudal rami, leaves 14 species for comparison with the new species in greater detail.

Descriptions of swimming leg setation in the family Ergasilidae are sometimes unreliable. In E. jiangxiensis , for example, leg 2 and leg 4 are both described as bearing two inner setae on the second endopodal segment, while leg 3 is shown with only one seta on the equivalent segment ( Liu 1998). Such a pattern is almost certainly incorrect since reductions in leg setation along the leg series in copepods typically follow an antero-posterior sequence. The original description of the legs of E. xenomelanirisi by Carvalho (1955) is similarly problematic, with many setae missing and spines drawn as present where spines never occur in other members of this family. Given such confusion, it is necessary to exercise caution when interpreting some of the older published descriptions of leg setation in small species. However, the recent detailed description of E. sittangenesis by El-Rashidy & Boxshall (2002) revealed an unusual feature of leg setation: the second endopodal segment of leg 2 has only one inner seta while this segment on each of legs 3 and 4 carries two setae. Four other species, all described relatively recently, share this unusual setation pattern, E. hemibagri , E. iraquensis , E. leiocassi and E. mirabilis . The new species differs in the possession of two setae on this segment in leg 2. All five of these species also have markedly larger body size than the new species which, with a mean body length of 0.62 mm, is one of the smallest of those listed ( Table 1 View TABLE 1 ).

The inadequate description of E. xenomelanirisi from Brazil ( Carvalho 1955) also shows a single seta on the second endopodal segment of leg 2, but none on the same segment of leg 3; further evidence that it cannot be considered accurate. For this species comparisons can be restricted to the largest and easiest limb to observe, the antenna, which provides several key differences from the new species. In E. xenomelanirisi the antennary claw is small, only about half the length of the second endopodal segment, whereas in the new species claw and segment are similar in length. The first endopodal segment is about twice as long as wide in E. xenomelanirisi , whereas in the new species it is about 4.2 times longer than wide.

Yamaguti (1954) described E. borneoensis from the gills of “an unknown fish, probably of the Coridae” caught at Bandjermasin, Borneo, close to the type locality of the new species. The Coridae is not a valid family but the genus Coris Lacepède, 1801 is currently included within the actinopterygian family Labridae . The new species can be distinguished by its smaller body size (see Table 1 View TABLE 1 ), relatively long antennary claw (cf. about 60% length of second endopodal segment in E. borneoensis ), and the presence of five setal elements on the distal exopodal segment of leg 4 (cf. 6 in E. borneoensis ). The unusual form of the mandible in E. borneoensis , with four blades, would be unique in the genus and requires confirmation.

Both sexes of E. genuinus were redescribed in detail by Ohtsuka et al. (2004) and it shares the identical leg setation pattern with the new species, but significant differences are found in the antennae. Ergasilus genuinus has a rather robust antenna with the first endopodal segment about 2.2 times longer than wide and bearing two spiniform sensillae in the distal half, whereas in the new species this segment is about 4.2 times longer than wide and carries a knob-like sensilla close to the middle of the medial margin ( Fig. 2 View FIGURE 2 B). The interpodal plates are more heavily ornamented in E. genuinus , with spinules scattered over the entire surface of each plate, not just a single spinule row along its posterior border ( Fig. 1 View FIGURE 1 D).

Kim & Choi (2003) redescribed E. peregrinus , a widespread species reported from China, Korea and Russia (far eastern zone of Siberia). Again, the setation pattern is identical to that of the new species and the main differences can be found in the antennae. Ergasilus peregrinus has a robust antenna with the first endopodal segment about twice longer than wide, bearing a single sensilla in the distal third, and the second endopodal segment lacks sensillae. In contrast, the first endopodal segment is slender in the new species (about 4.2 times longer than wide) and carries a knob-like sensilla close to the middle of the medial margin, while the second segment has a prominent marginal sensilla proximally ( Fig. 2 View FIGURE 2 B).

The type species, E. sieboldi , is one of the largest in the genus, with a body length of between 1 and 2 mm ( Kabata 1979), two to three times larger than the new species. The detailed redescription of this species by Kabata (1979) shows differences in leg setation: leg 1 carries an outer spine on the second exopodal segment (absent in the new species), and legs 2 and 3 each carry an outer spine on the third exopodal segment (absent in the new species). Ergasilus cochlearius (see Kuang & Liu 1991) shares the same leg setation pattern as E. sieboldi , and thus also differs from the new species. In addition the antennary claw is distinctly shorter than the second endopodal segment in both E. sieboldi and E. cochlearius , but about the same length in the new species.

Ergasilus synaceiensis has the same leg setation pattern as the new species (see Amado et al. 2001) but differs in having a much more swollen prosome than the new species, and its genital double-somite is just longer than wide whereas in the new species it is wider than long. In addition, the antennary claw is only half the length of the second endopodal segment in E. synaceiensis and bears two sensillae (one at mid-length, the other distally), while in the new species the claw and segment are similar in length and only a single, proximally-located sensilla is present.

The antenna of E. philippinensis is long and slender but the claw is only about half the length of the second endopodal segment ( Velasquez 1951) whereas in the new species the claw and segment are about equal in length. The caudal rami are also more elongate in E. philippinensis than in the new species ( Table 1 View TABLE 1 ).

Finally, the new species can be distinguished from E. shehyangensis (see Wang 1961) by differences in the antenna and there are also apparent differences in leg setation. The antenna of E. shehyangensis has sensillae located in the distal third of the first endopodal segment and in the middle of the second, whereas in the new species the former is located mid-segment and the latter is located in the proximal third. Also the claw is only half the length of the second endopodal segment in E. shehyangensis , but about the same length in the new species. Outer spines are shown as present on the terminal exopod segment of legs 2 and 4 of E. shehyangensis by Wang (1961). No such spines are present in the new species but the lack of this spine on Wang’s figure of leg 3 raises some concern over the accuracy of the description.

References

Figures

Tables

TABLE 1. Comparisons of character states exhibited by species of Ergasilus with a 3 - segmented endopod of leg 1, plus 2 setae on the free exopodal segment of leg 5. Abbreviations: A 1 = number of antennule segments; P 2 = number of inner setae on second endopodal segment of leg 2; CR (L: W) = length to width ratio of caudal rami.

E. batai	09–1.25	6	slender	2	7:1	Karamchandani (1952)
E. borneoensis	0.9–1.1	6	slender	2	1.3:1	Yamaguti (1954)
E. cochlearius	0.54–0.65	6	slender	2	1.5:1	Kuang & Liu (1991)
E. flaccidus	0.6–0.9	5	slender	1	1:1	Fryer (1965)
E. genuinus	0.72–0.84	6	slender	2	1.3:1	Ohtsuka et al. (2004)
E. glyptothoracis	0.85–1.01	6	inflated	2	1.2:1	Kuang & Qian (1983)
E. hemibagri	0.66–0.93	6	slender	1	1.3:1	Zhang & Ma (1994)
E. iraquensis	1.08	6	slender	1	1:1	Amado et al. (2001)
E. jiangxiensis	0.55	6	slender	2	6:1	Liu (1998)
E. kimi sp. nov.	0.61–0.63	6	slender	2	1.4:1	present account
E. lamellifer	0.85	6	lamella	2	1.6:1	Fryer (1961)
E. leiocassi	0.78–0.96	6	slender	1	1.1:1	Xu (1987)
E. longicaudatus	0.95–0.99	6	slender	2	6:1	Kuang & Li (1984)
E. manicatus	0.75	6	inflated	?	1:1	Wilson (1911)
E. mendisi	0.8–0.9	6	slender	2	3.5:1	Fernando & Hanek (1973)
E. mirabilis	0.93	6	slender	1	2:1	Oldewage & van As (1987)
E. orientalis	0.7	6	inflated	2	1.2:1	Yamaguti (1939)
E. pararostralis	0.71	5	slender	1	1:1	Amado et al. (2001)
E. peregrinus	0.79	6	slender	2	1.2:1	Kim & Choi (2003)
E. philippinensis	0.86	6	slender	2	2.7:1	Velasquez (1951)
E. rostralis	0.80–0.86	5	slender	2	1.5:1	Ho et al. (1992)
E. rotundicorpus	0.60	6	inflated	2	1:1	Jones & Hine (1983)
E. shehyangensis	0.91–1.15	6	slender	2	1.5:1	Wang (1961)
E. sieboldi	1.0–2.0	6	slender	2	2.1:1	Kabata (1979)
E. sittangenesis	0.78	6	slender	1	1.7:1	El-Rashidy & Boxshall (2002)
E. synanceiensis	0.89	6	slender	2	1.3:1	Amado et al. (2001)
E. uniseriatus	0.56–0.60	5	slender	2	1.2:1	Ho et al. (1992)
E. xenomelanirisi	0.6–0.7	6	slender	1?	1:1	Carvalho (1955)
E. xinjiangensis	0.89–0.98	6	slender	2	3:1	Kuang & Qian (1985)