Arctopontius adelphus, Kim, 2016

Kim, Il-Hoi, 2016, Siphonostomatoid copepods (Crustacea) mainly associated with marine invertebrates from Korean waters, Journal of Species Research 5 (3), pp. 393-442 : 397-400

publication ID	https://doi.org/ 10.12651/JSR.2016.5.3.393
persistent identifier	https://treatment.plazi.org/id/96353C58-E760-FFA4-FF67-F9AEFF11FC03
treatment provided by	Felipe
scientific name	Arctopontius adelphus
status	sp. nov.

Treatment

Arctopontius adelphus View in CoL n. sp. ( Figs. 3 View Fig , 4 View Fig )

Material examined. Two $$ from washings of a sponge attached to the alcyonacean coral Melithaea japonica (Verrill) , off Sacheon Port (37°50′14″N, 128° 52′32″E) in Gangneung, 18 May 2000. Holotype ($, NI BRIV0000680713 ) has been deposited in the NIBR, Incheon, Korea. Dissected paratype ($) is retained in the collection of the author. GoogleMaps

Female. Body ( Fig. 3A View Fig ) 1.71 mm long, with thick exoskeleton. All prosomal somites with pointed posterolateral corners. Cephalothorax 975 × 900 μm, longer than wide, with slightly produced posterolateral corners. Epimera of 3 metasomal somites markedly extended posteriorly. Urosome ( Fig. 3B View Fig ) 5segmented. Fifth pedigerous somite 223 μm wide. Genital double-somite ( Fig. 3C View Fig ) 195 × 325 μm and consisting of broadened anterior and narrow posterior parts; anterior part markedly expanded, tapering laterally, but with blunt lateral apex; narrower posterior part 185 μm wide. Three abdominal somites 63 × 140, 57 × 117, and 90 × 123 μm, respectively. Caudal ramus 90 × 53 μm, 1.70 times as long as wide, with 6 setae; outer distal and inner distal setae plumose, other 4 setae naked.

Rostrum ( Fig. 1D View Fig ) small, tapering and highly sclerotized. Antennule ( Fig. 3E View Fig ) 417 μm long, 8-segmented; armature formula 1, 14, 6, 2, 2, 2, 2, and 13+ aesthetasc; first segment with 1 minute setule in addition to 1 seta; second segment longest, 1.5 times as long as first segment. Antenna ( Fig. 3F View Fig ), syncoxa unarmed; basis slightly longer than syncoxa and unarmed. Exopod small, 1 segmented, 12 × 5 μm, armed with 1 minute lateral and 2 longer distal setae. First endopodal segment unarmed, 35 × 20 μm; second endopodal segment 47 × 19 μm, armed with 1 seta laterally and 2 setae plus 1 long spine distally.

Oral siphon 740 μm long, extending to posterior margin of cephalothorx. Mandible represented by long, threadlike stylet bearing denticulate distal part ( Fig. 3G View Fig ). Maxillule ( Fig. 3H View Fig ) bilobed; inner lobe 155 μm long and setulose, with 1 small and 1 longer apical setae; outer lobe 77 μm long, with setules on distal part of outer margin and armed with 2 long and 1 small, apical setae. Maxilla ( Fig. 3I View Fig ), syncoxa unarmed; basis slender, with 1 spiniform seta subdistally and spinules distally; terminal claw distinctly articulated from basis. Maxilliped ( Fig. 4A View Fig ) 6segmented; syncoxa distally with 1 inner seta and outer tuft of setules; basis with setules on outer margin, 1 seta at distal 2/5 of inner margin, and minute spinules on distal part of inner margin; 4 endopodal segments with 2, 0, 1, and 1 setae, repectively; terminal claw twice as long as terminal endopodal segment, with minute spinules along concave inner margin.

Legs 13 with 3segmented exopod and endopod, but leg 4 with 3segmented exopod and 2segmented small endopod. Leg 1 ( Fig. 4B View Fig ) with 3 spines and 4 setae (formula III, 1, 3) on third exopodal segment, otherwise as in A. minutus n. sp. Leg 2 ( Fig. 4C View Fig ) and leg 3 with same armature formula, but leg 3 with smaller inner seta on coxa and less pronounced inner distal protrusion of basis. Leg 4 ( Fig. 4D View Fig ) as in A. minutus n. sp., but both setae on endopod plumose ( Fig. 4E View Fig ). Armature formula of legs 24 as in A. minutus n. sp.

Leg 5 ( Fig. 4F View Fig ) rudimentary, represented by 2 papillae bearing 1 and 2 naked setae, respectively. Leg 6 represented by 1 spiniform seta and 1 large, plumose seta on genital operculum ( Fig. 4G View Fig ).

Male. Unknown.

Etymology. The specific name adelphus is a Greek, meaning “brother”. It alludes to similarity of the new species to A. minutus n. sp. in having a similar body length, the same type locality, and other similar morphological features.

Remarks. Arctopontius adelphus n. sp. is easily differentiated from its congeners by the characteristic armature condition (3 spines and 4 setae, formula III, 1, 3) of the third exopodal segment of leg 1. On the same segment in other species of the genus there are 2 spines and 5 setae (formula II, 1, 5) in A. expansus G.O. Sars, 1915 or 3 spines and 5 setae (formula III, 1, 4) in A. hanseni Eiselt, 1986 , A. novenarius Johnsson, 2002 and A. minutus n. sp. (G.O. Sars, 1915; Eiselt, 1986; Johnsson and da Rocha, 2002; and this paper, respectively). Arctopontius adelphus n. sp. and A. minutus n. sp. are collected from the same locality and similar to each other in several respects. Noticeable differences between them, in addition to the difference in the armature condition of the third exopodal segment of leg 1, are as follows: the inner seta on the first endopodal segment of leg 4 is naked in A. minutus n. sp., but plumose in A. adelphus n. sp.; and the exopod of leg 5 is small but distinct and armed with 3 setae in A. minutus n. sp., while it is rudimentary, represented only by a papilla bearing 2 setae in A. adelphus n. sp.