Heterozosime tenuis, Kim & Lee, 2021

Kim, Jong Guk & Lee, Jimin, 2021, Proposal of two new genera of the family Zosimeidae Seifried (Copepoda: Harpacticoida): Heterozosime gen. nov. and Acritozosime gen. nov., European Journal of Taxonomy 760, pp. 32-60 : 36-45

Heterozosime tenuis gen. et sp. nov.

urn:lsid:zoobank.org:act:565EFB14-0731-4CD5-AD1E-70A166D5D2FB

Figs 2–8

Etymology

The species epithet reflects the Latin adjective ‘ tenuis ’ (‘thin’ or ‘weak’), referring to the very small seta on the distal margin of P4 enp-3.

Material examined

Holotype

SOUTH KOREA • ♀; the Southern Sea ; 33º59′53.04″ N, 127º29′27.60″ E; stn B4; depth 78.7 m; 8 Jun. 2015; O.H. Yu leg.; MABIK CR00247785 (on 11 slides, unfortunately P5 damaged during mounting process after drawing).

Allotype

SOUTH KOREA • ♂; same collection data as for holotype; MABIK CR00247786 (preserved in 80% ethanol).

Paratypes

SOUTH KOREA • 1 ♀; same collection data as for holotype; MABIK CR00247787 (on 11 slides) • 1 ♀; same collection data as for holotype; MABIK CR00247788 (preserved in 80% ethanol) • 1 ♂; same collection data as for holotype; MABIK CR00247789 (on seven slides, unfortunately, its mouthparts damaged) .

Other material

SOUTH KOREA • 1 ♀; the Southern Sea ; 33º30′11.88″ N, 125º59′48.84″ E; stn E9; depth 96.4 m; 3 Jun. 2015; O.H. Yu leg.; MInRB-Hr60-S001 (on four slides) • 1 ♂; same collection data as for preceding; MInRB-Hr60-S002 (on four slides) • 2 ♀♀, 3 ♂♂; same collection data as for preceding; MInRB-Hr 60-L001 (preserved in 80% ethanol) • 1 ♂; the Southern Sea ; 32º59′49.41″ N, 126º00′04.82″ E; stn F11; depth 82.7 m; 6 Aug. 2016; O.H. Yu leg.; MInRB-Hr60-L002 (preserved in 80% ethanol) • 1 ♀; the Southern Sea ; 35º59′52.62″ N, 127º29′58.19″ E; stn B4; depth 78.7 m; 26 Apr. 2016; T. W. Kang leg.; MInRB-Hr60-L003 (preserved in 80% ethanol) • 2 ♂♂; the Southern Sea ; 33º34′46.66″ N, 126º28′45.12″ E; stn C9; depth 116.3 m; 9 Aug. 2016; O.H. Yu leg.; MInRB-Hr60-L004 (preserved in 80% ethanol) • 8 ♀♀; the Southern Sea ; 33º00′00.84″ N, 125º30′00.72″ E; stn F8; depth 97.0 m; O.H. Yu leg.; 12 Nov. 2015; MInRB-Hr60-L005 (preserved in 80% ethanol) .

Description

Female (based on the holotype, MABIK CR00247785)

MEASUREMENTS. Body length about 473–631 µm (mean = 569 µm, n = 12; holotype 572 µm) measured from anterior tip of rostrum to posterior end of caudal rami in lateral aspect.

HABITUS ( Fig. 2A–B ). Subcylindrical, slightly depressed dorsoventrally, tapering posteriorly, with inconspicuous distinction between prosome and urosome. Rostrum ( Fig. 2C ) large, triangular, fused with cephalothorax basally; anterior tip bifid, with 2 long sensilla; anterior half ornamented with fine setules laterally. Cephalothorax large, with almost parallel lateral margins in dorsal aspect. Second to fourth free pedigerous somites tapering posteriorly. Urosome ( Figs 2A–B , 3A ) comprising P5 bearing-somite, genital double-somite, 3 free abdominal somites, more slender than prosome, tapering posteriorly; urosomites except for penultimate and anal somites with ventrolateral pleural extensions bearing sensillum distally. Genital double-somite ( Figs 2A–B , 3A ) separate dorsally and laterally, but completely fused ventrally; genital field located at anterior half of genital somite, with single genital slit formed by fusion of both gonopores and large mid-ventral copulatory pore posterior to genital slit; genital slit ( Fig. 3A, C ) covered by single large plate, on both sides with 1 stout plumose seta and 2 bare setae (inner one about 3 times as long as outer one), representing P6; each P6 distinguished by deep incision on both sides of distal margin. Penultimate somite with weak pseudoperculum comprising 4 crenate projections ( Fig. 3B ). Anal somite ( Figs 2A–B , 3A–B ) small, with semicircular operculum ornamented with small spinules and 1 pair of small peduncles bearing sensillum dorsally; anal opening wide, armed with 2 diagonal rows of setules.

BODY ORNAMENTATIONS. Integument of cephalothorax ornamented with several paired sensilla; posterior and ventrolateral margins armed with crenate processes, forming weak pseudoperculum, and small peduncles bearing sensillum. Posterior margins of somites except for penultimate and anal somites dorsally ornamented with crenate or pointed processes and small peduncles bearing sensillum; genital double-somite and second abdominal somite ventrally serrate, with 1 pair of small peduncles bearing sensillum; penultimate somite with 3 crenate protrusions laterally and row of spinules ventrally; anal somite ventrally with row of spinules at base of caudal rami. Epimera of free pedigerous somites with 1 (in P3–P4) or 2 (in P2) crenate processes, 2 small peduncles bearing sensillum and 1 row of anterior minute spinules. Pleural extensions on urosomites armed with spinules. Dorsal surface of genital doublesomite, second and third abdominal somites ornamented with minute spinules posteriorly. Anal somite with 1 pair of dorsolateral pores and 3 pairs of ventrolateral pores.

CAUDAL RAMI ( Figs 2A–B , 3A–B ). About 2.8 times as long as greatest width, about 1.5 times as long as anal somite, with 1 pore on ventrolateral surface; with 7 setae: ventrolateral seta I bare, short, slightly shorter than half length of ramus, inserted in mid-length of outer margin; dorsolateral seta II bare, shorter than seta I; seta III ventrally arising from outer distal corner, slightly shorter than caudal ramus, with weakly pinnate outer margin; principal setae IV and V well-developed, covered with minute spinules distally, with internal fracture plane proximally; seta IV about 2.7 times as long as ramus; seta V about twice as long as seta IV; seta VI located at inner distal corner, slightly longer than seta I; seta VII triarticulate basally, arising from small peduncle located on dorsal surface subdistally.

ANTENNULE ( Fig. 4A ). Robust, short, 6-segmented. First segment ornamented with 2 rows of spinules along inner margin, with 1 long pinnate seta subdistally. Second segment largest, subdivided by incomplete suture, with 1 bare seta, 7 plumose setae (1 bi-articulate basally and 6 non-articulate), 6 spinulose setae, 5 stout tri-spinulose setae and 1 ae, which is basally fused to adjacent tri-spinulose seta. Third segment small, with 1 weakly pinnate seta and 1 stout tri-spinulose seta. Fourth segment with 1 small spinulose seta, 2 plumose setae and 3 tri-spinulose setae; outer margin produced, with 1 bare bi-articulate seta distally. Fifth segment smallest, with 1 weakly pinnate seta. Distal segment small, with 1 stout tri-spinulose, 2 weakly pinnate and 4 bi-articulated bare setae and 1 ae, which is basally fused to adjacent tri-spinulose seta. Setal armature formula as: 1-[1], 2-[18 + (1 + ae)], 3-[2], 4-[7], 5-[1], 6-[6 + (1 + ae)].

ANTENNA ( Fig. 4B ). Coxa small, unornamented. Basis elongate, ornamented with 1 row of spinules on lateral surface and 2 short rows of spinules along abexopodal margin, with 1 spinulose abexopodal seta. Exopod 3-segmented; proximal segment elongate, with 1 plumose seta; middle segment smallest, with 1 spinulose seta; distal segment longer than first and middle segments combined, with 1 spinulose seta on lateral margin proximally and 1 serrate and 2 spinulose setae on distal margin. Endopod 2-segmented; proximal segment with 1 long spinulose seta on abexopodal margin; distal segment about 1.8 times as long as preceding segment, ornamented with 1 group of lateral spinules and 1 row of subdistal spinules; lateral armature comprising 1 small bare and 2 stout spinulose setae; distal armature comprising 1 stout spinulose spine, 1 stout spinulose seta, 3 pinnate geniculate setae and 1 slender seta, which is fused basally with adjacent spinulose seta.

MANDIBLE ( Fig. 4C ). Coxa with bulge medially; gnathobase armed with 1 small and 3 multicuspidate teeth and 1 pinnate dorsal seta. Palp composed of basis, endopod and exopod; basis elongate, with 3 plumose setae distally; exopod 1-segmented, slightly smaller than endopod, with 1 plumose and 2 pinnate setae; endopod 1-segmented, with 4 plumose setae.

MAXILLULE ( Fig. 5A ). Praecoxal arthrite well-developed, with 2 juxtaposed setae on anterior surface; distal margin armed with 8 stout spines and 1 delicate seta. Coxa ornamented with 1 row of spinules on anterior surface distally; epipodite represented by 1 plumose seta; endite with 3 bare setae distally and 1 bare seta subdistally. Basis armed with 1 row of spinules on dorsal margin and 1 row of spinules on anterior surface subdistally; with 2 endites: dorsal endite with 1 plumose and 2 bare setae distally and 2 bare setae subdistally; ventral endite weak, with 2 bare setae distally. Exopod 1-segmented, with 3 plumose setae. Endopod 1-segmented, larger than exopod, with 3 plumose and 3 bare setae.

MAXILLA ( Fig. 5B ). Syncoxa large, ornamented with 2 short rows of spinules along outer margin; two praecoxal endites fused basally, proximal one with 3 setae (1 plumose, 1 bare and 1 spinulose) and distal one with 3 setae (1 bare and 2 spinulose); proximal coxal endite elongate, with 3 setae (1 bare, 1 pinnate and 1 spinulose); distal coxal endite with 1 stout serrate spine and 2 setae (1 slender bare and 1 stout spinulose). Allobasis with 1 seta near base of endopod; endite with 2 stout serrate spines distally and 2 bare setae subdistally. Endopod small, 2-segmented; proximal segment with 3 bare setae laterally; distal segment with 3 bare setae distally.

MAXILLIPED ( Fig. 5C ). Maxilliped 3-segmented, comprising syncoxa, basis and 1-segmented endopod. Syncoxa trapezoidal, ornamented with 1 row of long inner spinules proximally. Basis elongate, as long as preceding segment, ornamented with 1 row of inner spinules subdistally, with 1 stout spinulose seta distally. Endopod small, rectangular, with 2 plumose setae on distal margin, of which inner one about twice as long as outer one and 2 bare setae on lateral margin.

P1 ( Fig. 5D ). Praecoxa lacking in the figure. Intercoxal sclerite wide, unornamented. Coxa large, ornamented with 3 rows of spinules on anterior surface, 1 row of minute spinules on distal margin and 1 row of posterior spinules near outer distal corner. Basis ornamented with 2 groups of spinules on anterior surface, 1 row of spinules on distal margin of pedestal of inner ramus and 1 row of long setules along inner margin; outer setophore small, with a few anterior spinules and 1 spinulose spine; inner spine spinulose, reaching to mid-length of enp-2, arising from small peduncle bearing few anterior spinules. Both rami 2-segmented; exopod reaching to mid-length of enp-2; exp-1 ornamented with outer spinules and inner setules, with 1 spinulose outer spine; exp-2 ornamented with outer spinules, with 3 spinulose spines along outer margin, 1 small spinulose spine and 1 long spinulose seta on distal margin and 2 plumose setae on inner margin; all outer spines on exopod with gradually enlarged outer spines toward distal tip; enp-1 slightly longer than wide, ornamented with 1 row of setules on outer margin and 1 row of spinules near outer distal corner, with 1 plumose seta on inner margin; enp-2 elongate, about 1.2 times as long as enp-1, ornamented with outer spinules along outer margin, with 1 small spinulose outer spine, 1 long spinulose distal spine and 2 plumose inner setae ( Table 2 ).

P2–P4 ( Figs 6A–B , 7A ). Praecoxae short but wide, ornamented with 1 row of minute spinules on distal margin (praecoxa of P3 lost during dissection). Intercoxal sclerite pentagonal, with concave rear edge. Coxae large, ornamented with 3 rows of spinules on anterior margin, 1 row of spinules at outer distal corner and 1 row of posterior setules (absent in P4) near lateral margin. Bases ornamented with 1 row of distal spinules on pedestal of inner ramus and 1 row of long setules on inner margin; anterior surface with 2 groups of spinules in P2; outer seta stout, plumose, arising from outer setophore bearing 1 row of anterior spinules; length of outer setae gradually increasing from P2 to P4. Both rami 3-segmented; exopod longer than endopod; endopod reaching to mid-length of exp- 3 in P2, slightly exceeding end of exp- 2 in P3, and reaching to distal fourth of exp- 2 in P4; each exopodal segment ornamented with outer and distal spinules and inner setules; exp-1 elongate and exp-2 shortest, each with 1 pinnate outer spine and 1 plumose inner seta; exp-3 with 2 pinnate outer spines, 1 pinnate outer distal spine (with plumose inner margin), 1 plumose inner distal seta and 2 plumose inner setae; enp-1 and enp-2 ornamented with outer setules, distal spinules and a few inner spinules, with 1 plumose inner seta, respectively; enp-3 ornamented with outer spinules, minute distal spinules, a few fine inner setules and 1 or 2 posterior spinules; P2–P3 enp-3 with 1 pinnate outer spine, 2 plumose distal setae and 1 inner plumose seta; P4 enp-3 with 1 long pinnate outer spine, 1 delicate outer distal seta, 1 plumose inner distal seta and 1 plumose inner seta; length of outer spines on enp-2 gradually increasing from P2 to P4 ( Table 2 ).

P5 ( Fig. 3D ). Left and right legs connected by small intercoxal sclerite. Baseoendopod short, wide; outer setophore well-developed, bearing 1 long pinnate seta; endopodal lobe elongate, reaching to distal third of exopod, with 2 long plumose distal setae, of which inner one about 1.4 times as long as outer one; ornamented with a few spinules on outer margin. Exopod basally fused to baseoendopod, with 3 marginal setae, of which inner most one about 1.8 times as long as two other elements and 1 small seta arising from small peduncle on anterior surface near outer margin.

Male (based on the paratype MABIK CR00247789)

MEASUREMENTS. Body ( Fig. 8A ) length smaller than in female, 406–474 µm (mean 446 µm, n = 9; allotype 406 µm). Sexual dimorphisms shown in urosome, antennule, P2 endopod, P5 and P6.

UROSOME ( Figs 7B , 8A ). Urosome 6-segmented; genital somite and first abdominal somite separated; pleural extensions less developed than those of female; ventral surfaces of first and second abdominal somites ( Fig. 7B ) with 1 row of medial spinules posteriorly.

ANTENNULE ( Fig. 8B ). Subchirocer, 8-segmented. First segment ornamented with 3 groups of spinules along inner margin, with 1 long pinnate seta. Second segment with 1 long pinnate seta. Third segment with 1 bare bi-articulate, 1 tri-spinulose and 6 pinnate setae. Fourth segment with 1 bare bi-articulate, 1 stout tri-spinulose, 1 bare, 2 small pinnate and 3 long spinulose setae. Fifth segment smallest, with 1 bare seta and 1 pinnate seta. Sixth segment stout, with 1 bare seta, 3 plumose setae, 4 small pinnate setae, 3 tri-spinulose setae and 1 ae, which is basally fused to adjacent long tri-spinulose seta. Seventh segment with 1 bare bi-articulate seta. Distal segment with 1 stout tri-spinulose, 3 plumose and 6 triarticulate setae and 1 ae, being basally fused to adjacent plumose seta. Setal armature formula as: 1-[1], 2-[1], 3-[8], 4-[8], 5-[2], 6-[10 + (1 + ae)], 7-[1], 8-[9 + (1 + ae)].

P2 ENDOPOD ( Fig. 6C ). P2 endopod 2-segmented by fusion of original enp-2 and enp-3; enp-1 as in female except for presence of anterior pore subdistally; distal segment elongate ornamented with long outer spinules proximally, small outer spinules distally, a few spinules on anterior surface and 1 anterior tube pore subdistally; with 1 plumose inner seta proximally, 1 plumose distal seta and 1 stout outer apophysis.

P5 ( Fig. 7B ). Basally fused with somite. Left and right baseoendopod confluent medially; with welldeveloped outer setophore bearing 1 long weakly pinnate seta; endopodal lobe rudimentary, represented by 2 bare setae. Exopod small, basally fused with baseoendopod, with 1 weakly pinnate and 2 bare setae on distal and subdistal margins and 1 small seta arising from anterior surface of baseoendopod between outer setophore and exopod.

P6 ( Fig. 7B ). Symmetrical, represented by well-developed plate; each plate with 2 lobes distally; outer one with 1 weakly pinnate spine; inner one ornamented with few anterior spinules, with 1 weakly pinnate outer spine and 1 small bare inner seta.

Variability

Holotype female specimen (MABIK CR00247785) displays an abnormal condition in the P1 enp-2 of the right ramus, lacking a proximal inner seta ( Fig. 5E ; arrowhead).

Remarks

There is no doubt in allocating Heterozosime tenuis gen. et sp. nov. to the Zosimeidae on account of morphological features of the antenna, mouthpart appendages, P1 and P 5 in both sexes, which are identical with autapomorphies given by Seifried (2003). Significantly, this new species is morphologically similar to the typica -group of Zosime , as defined by Kim et al. (2016), on the basis of certain features such as the mandibular endopod with four setae; the maxillulary free endopod with six elements; the outer spines of the P1 exopod with gradually increasing outer spinules toward the distal end; the typical female P5 with a deep incision between the exopod and endopodal lobe and a well-developed cylindrical outer setophore; and the outermost seta of the P5 exopod displaced by a small peduncle toward the surface in both sexes. However, it is identified by a two-segmented exopod in the P1. All known zosimeid copepods exhibit constant P1 segmentation with a three-segmented exopod.

The two-segmented exopod in P1 is not common within the Harpacticoida ( Moura & Martínez Arbizu 2003) ; we could not assign this Korean species to any well-defined genus in the family. We thus postulate that the two-segmented exopod of P1 is a significant autapomorphy of H. tenuis gen. et sp. nov. within the family and that our proposal of a new genus, Heterozosime gen. nov., for H. tenuis gen. et sp. nov. is reasonable. In the Idyanthidimorpha, proposed by Seifried (2003), which comprises only the two families Idyanthidae and Zosimeidae , this striking feature is evident in three idyanthid genera – Styracothorax Huys, 1993 , Aspinothorax Moura & Martínez Arbizu, 2003 and Meteorina George, 2004 – but also in the new zosimeid genus Acritozosime gen. nov. proposed in the present study ( Huys 1993; Moura & Martínez Arbizu 2003; George 2004).

Notably, this new species shares the presence of two outer spines on the P2–P4 exp-3 with four Zosime species: Z. bathyalis Por, 1967 , Z. changi , Z. comata and Z. gymnokosmosa . The latter three species were reported from the Southern Sea of Korea, which includes the type locality of H. tenuis gen. et sp. nov. Nevertheless, H. tenuis gen. et sp. nov. displays an additional noteworthy characteristic: fine setules on the lateral margins of the rostrum in both sexes.

The shape of the H. tenuis gen. et sp. nov. male P2 is very similar to that of Z. changi , which also has a two-segmented endopod. As suggested by the position of the setal armature in the P2 endopod, this is the result of the fusion of the original middle and distal segments in both species.

Figures

Fig. 2. Heterozosime tenuis gen. et sp. nov. Holotype, ♀ (MABIK CR00247785). A. Habitus, dorsal view, inserts show details of surface at high magnification (×1000). B. Habitus, lateral view. C. Rostrum, dorsal view.

Fig. 3. Heterozosime tenuis gen. et sp. nov. Holotype, ♀ (MABIK CR00247785). A. Urosome excluding P5-bearing somite, ventral view. B. Posterior end of penultimate somite, anal somite, and caudal rami, dorsal view. C. Genital field, ventral view. D. P5.

Fig. 4. Heterozosime tenuis gen. et sp. nov. Holotype, ♀ (MABIK CR00247785). A. Antennule. A'. Antennule without ornamentation. B. Antenna. C. Mandible.

Fig. 5. Heterozosime tenuis gen. et sp. nov. Holotype, ♀ (MABIK CR00247785). A. Maxillule. B. Maxilla. C. Maxilliped. D. P1. E. Abnormal condition of P1 endopod; arrowhead indicates the absence of the proximal seta on enp-2.

Fig. 6. Heterozosime tenuis gen. et sp. nov. A–B. Holotype, ♀ (MABIK CR00247785). A. P2. B. P3. C. Paratype, ♂ (MABIK CR00247789). P2 endopod.

Fig. 7. Heterozosime tenuis gen. et sp. nov. A. Holotype, ♀ (MABIK CR00247785). P4. B. Paratype, ♂ (MABIK CR00247789). Urosome, ventral view.

Fig. 8. Heterozosime tenuis gen. et sp. nov. Paratype, ♂ (MABIK CR00247789). A. Habitus, dorsal view. B. Antennule. B’. Antennule without ornamentation.

Tables

Table 2. Setal formula of thoracic legs of two zosimeid species described in the present study. The notation of the setal formula follows Huys et al. (1996).

	P1			P2	P3		P4
	Exopod Endopod		Exopod	Endopod	Exopod	Endopod	Exopod Endopod
Heterozosime tenuis gen. et sp. nov.	0.223	1.211	1.1.222	1.1.121 (1.11apo in ♂)	1.1.222	1.1.121	1.1.222	1.1.121
Acritozosime spinesco gen. et sp. nov.	0.123	0.011	1.1.122	0.011	1.1.222	0.120	1.1.222	1.120