Lobomolgus foveolatus, Kim & Boxshall, 2021

Kim, Il-Hoi & Boxshall, Geoff A., 2021, Copepods associated with Ascidian hosts (Tunicata): Intramolgidae and Lichomolgidae, with descriptions of four new genera and 13 new species, Zootaxa 5013 (1), pp. 1-75 : 64-70

Lobomolgus foveolatus sp. nov.

( Figs. 40–42 )

Type material. Holotype ♀ (MNHN-IU-2014-21608, body with appendages of right side), and paratype (♂ (MNHN-IU-2014-21494, dissected) from aẚdemnum molle (Herdmann, 1886) MNHN-IT-2008-3125 (= MNHN A2 /DID.C/226): 13 miles West of Murex Resort, West of Manado town, North Sulawesi, Indonesia, OCDN 1260 -F, Site MANADO 5, depth 43 m, CRRF coll. 17 May 1993.

Etymology. The specific name is derived from the Latin fove (=a pit), referring to the presence of numerous pits on the exoskeleton of the new species.

Description of female. Body ( Fig. 40A, B ) large, body length 3.48 mm; gradually narrowing from anterior to posterior; body surface ornamented with numerous small pits. Prosome expanded dorsally ( Fig. 40B ); maximum width 1.26 mm (across first pedigerous somite). Prosomal somites each with well-developed dorsal tergite. Cephalosome and first pedigerous somite clearly defined from each other by dorsal suture. First to fourth pedigerous somites well-separated from one another by broad arthrodial membrane. Second to fourth pedigerous somites with posterolateral extensions, short in second and third pedigerous somites, but elongate, digitiform in fourth pedigerous somite. Urosome 5-segmented; fifth pedigerous somite 409 μm wide; genital double-somite 382×555 μm, with expanded anterior half and narrower posterior half; genital apertures positioned dorsolaterally in anterior region. Three free abdominal somites 227×318, 145×255, and 136×236 μm, respectively. Caudal ramus ( Fig. 40C ) about 2.7 times longer than wide (263×98 μm), gradually narrowing distally; armed with 5 thin, naked setae; setae I and II absent.

Rostrum ( Fig. 41A ) small, directed ventrally, sub-globular in ventral view. Antennule ( Fig. 40D ) 590 μm long, gradually narrowing, 7-segmented; armature formula 4, 8, 4, 3, 4+aesthetasc, 2+aesthetasc, and 7+aesthetasc; all setae small and naked. Antenna ( Fig. 40E ) 4-segmented; armature formula 1, 1, 2, 2+2 claws; 2 distal segments (second and third endopodal segments) distinctly narrower than proximal segments; terminal segment about 2.5 times longer than wide (68×27 μm); 2 terminal claws very unequal in length, 50 μm (inner) and 18 μm (outer).

Labrum ( Fig. 40F ) broad, with broad median incision separating semicircular posterolateral lobes; with 1 transverse row of minute spinules in middle. Mandible ( Fig. 40G ) with elongate distal lash, distinct inner proximal notch; inner margin of blade with densely arranged broad spinules; convex outer margin of lash with 3 rows of denticles, inner margin with spinules distally. Maxillule ( Fig. 40I ) with 1 minute seta on inner margin and 2 apical spatulate setae. Maxilla ( Fig. 40J, K ) consisting of syncoxa and basis; syncoxa large but unarmed; basis strongly recurved, with globular structure (transformed inner seta) and pale, leaf-like scale (transformed anterior seta); distal lash directed proximally, with more than 10 leaf-like scales proximally on convex margin. Maxilliped ( Fig. 41B ) 3-segmented; first segment unarmed; second segment with 2 small setae and irregularly wavy outer margin; third segment tapering, with 1 minute spinule in middle, and terminating in digitiform process.

Legs 1–3 ( Fig. 41C–E ) with 3-segmented rami. Outer side of coxa of legs 1-3 markedly protruded. Inner coxal seta absent in legs 1–4. First and second endopodal segments in legs 1 and 2 and first endopodal segment of leg 3 lacking inner seta. Leg 4 ( Fig. 41F ) with 3-segmented exopod; endopod lacking. Inner seta on second exopodal segment of legs 1-4 minute. Spines and setae on legs thin and naked. Armature formula for legs 1–4 as follows:

Coxa Basis Exopod Endopod

Leg 1: 0-0 1-0 I-0; I-1; II, 5 0-0; 0-0; 1, 2, 2

Leg 2: 0-0 1-0 I-0; I-1; II, 6 0-0; 0-0; 1, 2, 3

Leg 3: 0-0 1-0 I-0; I-1; II, 6 0-0; 0-1; 1, 2, 3

Leg 4: 0-0 1-0 I-0; I-1; III, 4 (absent)

Leg 5 ( Fig. 41G ) consisting of dorsolateral seta on somite and small, lobate exopod fused to somite; armed with 1 small and 1 minute seta apically. Leg 6 ( Fig. 41G ) represented by 1 seta, 1 setule, and 1 small spinule on genital operculum.

Description of male. Body ( Fig. 42A ) narrower and much smaller than that of female; body length 1.53 mm; prosome 864×477 μm. Body lacking surface ornamentation of pits present in female. Cephalothorax circular in dorsal outline. Fourth pedigerous somite with digitiform lateral processes. Urosome 6-segmented; fifth pedigerous somite 220 μm wide; genital somite 167×237 μm, with convex lateral margins. Four abdominal somites 79×133, 76×118, 52×103, and 67×121 μm, respectively. Caudal rami widely divergent, about 4.1 times longer than wide (197×48 μm), armed with 5 setae as in female.

Rostrum ( Fig. 42B ) semicircular. Antennule ( Fig. 42C ) 7-segmented, with armature formula 4, 12, 6, 3, 4+aesthetasc, 2+aesthetasc, and 7+aesthetasc; setae small. Antenna with 3 setae on third segment (second endopodal segment), otherwise as in female.

Labrum, mandible, maxillule and maxilla as in female. Maxilliped ( Fig. 42D ) 4-segmented; first and third segments unarmed; second segment with 2 small setae; fourth segment as long claw bearing 1 seta and 1 setule proximally.

Legs 1-4 ( Figs 42 E-H) segmented as in female; outer side of coxa not inflated. Inner seta on first endopodal segment of legs 1-3 minute. Armature formula for legs 1-4 differing from that of female as follows (third endopodal segment of leg 3 damaged):

Coxa Basis Exopod Endopod

Leg 1: 0-0 1-0 I-0; I-1; III, I, 3 0-1; 0-1; I, 2, 2

Leg 2: 0-0 1-0 I-0; I-1; III, I, 4 0-1; 0-1; I, II, 3

Leg 3: 0-0 1-0 I-0; I-1; III, I, 4 0-1; 0-1; (? I, II, 2)

Leg 4: 0-0 1-0 I-0; I-1; II, I, 4 (Absent)

Leg 5 as in female. Leg 6 represented by 2 small setae on genital operculum.

Remarks. iobomolgus okẚnawaensẚs and i. foveolatus sp. nov. are no doubt congeneric. They share the characteristic antenna, labrum, mandible, and maxilla. Nevertheless, they exhibit various differences, mainly in the leg armature, as summarised in Table 1.

Genus Zygomolgus Humes & Stock, 1972

Diagnosis. Body cyclopiform. Urosome 5-segmented in both sexes. Caudal ramus typically elongate, with 6 setae. Rostrum well-developed. Antennule 7-segmented, with armature formula 4, 13, 6, 3, 4+aesthetasc, 2+aesthetasc, and 7+aesthetasc in female; in male second segment with 2 additional aesthetascs so far as known. Antenna 4-segmented, with armature 1, 1, 2+claw, and 3+4 claws. Labrum with broad median incision and tapering posterolateral lobes. Mandible with elongate distal lash and 1 to 4 digitiform processes (scales) on outer side of blade. Maxillule distally with 2 setae or 3 setae plus 1 setiform process. Maxilla consisting of unarmed syncoxa and basis; basis with 3 setae and elongate distal lash; inner seta (seta I) large, spinulose; distal lash spinulose, with 3 to 5 thick spinules proximally on outer margin. Maxilliped 3-segmented, third segment claw-like. Legs 1-3 with 3-segmented rami. Leg 1 lacking sexual dimorphism. Third exopodal segment of leg 3 armed with 4 spines and 5 setae (formula III, I, 5) or 3 spines and 5 setae (formula II, I, 5); third endopodal segment armed with 3 spines and 2 setae (formula I, II, 2) or 2 spines and 2 setae (formula I, I, 2). Leg 4 with 3-segmented exopod and 2-segmented endopod; third exopodal segment armed with 3 spines and 5 setae (formula II, I, 5) or 3 spines and 4 setae (formula II, I, 4); endopod armed with 1 inner seta on proximal segment and 2 spines distally on distal segment (formula 0-1; 0, II, 0). Leg 5 consisting of dorsolateral seta on surface of somite and free exopodal segment armed distally with 2 setae, or 1 spine plus 1 seta. Leg 6 represented by 2 setae and 1 denticle on genital operculum. Associated with compound ascidians, algae, or holothurians.

Type species. Zygomolgus tenu ẚfurcatus (Sars G.O., 1917) by original designation.

Remarks. The genus Zygomolgus currently consists of six species. As differential features of this genus, the antenna has one claw on the third segment (the second endopodal segment) and 4 claws on the terminal segment, and the mandible has 1 to 4 digitiform processes (scales) on the outer side of the blade. The male is known only in Z. cuanens ẚs ( Gotto, 1954).

Figures

FIGURE 40. iobomolgus foveolatus sp. nov., female. A, habitus, dorsal; B, habitus, right; C, left caudal ramus, dorsal; D, antennule; E, antenna; F, labrum; G, mandible; H, paragnath; I, maxillule; J, maxilla; K, basis of maxilla. Scale bars: A, B, 0.5 mm; C, D, 0.1 mm; E, G, J, 0.05 mm; F, H, I, K, 0.02 mm.

FIGURE 41. iobomolgus foveolatus sp. nov., female. A, rostral area, ventral; B, maxilliped; C, leg 1; D, leg 2; E, leg 3; F, leg 4; G, right leg 5 and genital aperture, dorsal. Scale bars: A, C–G, 0.1 mm; B, 0.05 mm.

FIGURE 42. iobomolgus foveolatus sp. nov., male.A, habitus, dorsal; B, rostrum; C, antennule; D, maxilliped; E, leg 1; F, leg 2; G, leg 3; H, exopod of leg 4. Scale bars: A, 0.2 mm; B–H, 0.05 mm.