Chamicola nagasawai, Ohtsuka & Boxshall & Torigoe, 2000

Ohtsuka, Susumu, Boxshall, Geoffrey A. & Torigoe, Kenji, 2000, A new genus and species of the family Mantridae (Copepoda: Cyclopoida) infesting the bivalve Pseudochama retroversa from the Seto Inland Sea, western Japan, Journal of Natural History 34 (10), pp. 1967-1976 : 1970-1975

publication ID	https://doi.org/10.1080/00222930050144800
DOI	https://doi.org/10.5281/zenodo.4757040
persistent identifier	https://treatment.plazi.org/id/C9401A44-FFA0-FFD2-FEA5-FE3A7DA4FE20
treatment provided by	Carolina
scientific name	Chamicola nagasawai
status	n. gen., n. sp.

Treatment

Chamicola nagasawai n. gen., n. sp.

( figures 2- 5 View FIG View FIG View FIG View FIG )

Material examined. Nine adult females and four adult males.

Types. HOLOTYPE: 1♀, Yasuura , 7 January 1999, dissected, CBM-ZC 4942 . PARATYPES: 2♀♀, Shiju Islands , 20 August 1998, dissected, CBM-ZC 4943 ; 1♀ and 2 ♂♂, Kokuno Island , 19 August 1998, dissected, CBM-ZC 4944 ; 1♀, Kokuno Island , 19 August 1998, whole specimen, CBM-ZC 4945 ; 1♀ and 1, ♂ Shiju Island , 20 August 1998, whole specimens, CBM-ZC 4946 ; 3♀♀ and 1, ♂ Kokuno Island , 19 August 1998, whole specimens, BM(NH) 1999.748-751 .

Body length. ♀: mean ± SD, 2.29 ± 0.25 mm ( n = 8), range 1.99-2.76 mm.: ♂ 1.52 ± 0.11 mm ( n = 4), 1.42-1.67 mm.

Description. Female ( holotype). Body (figure 2A) 2.47 mm in length, more or less depressed; cephalosome separate from fi rst pedigerous somite; cephalosome expanded laterally, with distinct naupliar eyes present; maximum width measured at its posterior end. Rostrum (figure 2B) separate at base, weakly bifurcate at tip.

First pedigerous somite narrow. Urosome consisting of fi fth pedigerous somite, genital double-somite and three-segmented abdomen; fi fth pedigerous somite expanded laterally. Genital double-somite (figure 2A, C) wider than long; gonopores located laterally at about one-third length, covered with vestigial leg 6 (figure 2D); single copulatory pore located ventro-medially at about one-third length, connected via paired copulatory ducts to seminal receptacles; transverse rows of minute spinules posteriorly on ventral surface. Anal somite (figure 2E) with serrated posterior margin ventrally; caudal ramus approximately fi ve times longer than wide; seta V longest.

Antennule ( figure 2F View FIG , G) 15-segmented. Segmentation pattern and armature elements as follows: 1(I - II)━ 3, 2( III - V)━ 5, 3 ( VI - IX)━ 8, 4 (X)━2, 5(XI)━ 2, 6( XII - XIV)━6, 7 ( XV - XVII)━ 5, 8(XVIII)━ 1, 9(XIX)━ 2, 10 (XX)━ 1, 11(XXI)━ 2, 12 ( XXII - XXIII)━ 2 + aesthetasc, 13 (XXIV)━1 + 1, 14(XXV)━ 1 + 1 + aesthetasc, 15 ( XXVI - XXVIII)━ 7 + aesthetasc. Antenna (figure 2H) foursegmented; basis separate from endopod; exopod represented by two setae of unequal length; fi rst endopodal segment with vestigial seta at midlength; distal compound segment representing second to fourth ancestral segments, with three setae and one rudimentary seta at one-third length, and one robust claw, two curved spiniform setae, and two long and two short setae terminally; distal endopodal segment bearing two oblique rows of spinules along outer margin. Labrum (figure 3A, B) with strong paired processes laterally.

Mandible (figure 2I -K) with small protuberance between two ventral-most teeth; fi rst endopodal segment bearing four setae, second segment with four lateral and two terminal setae in addition to three setae on subterminal process which is not found in opposite palp; exopod four-segmented, setal formula 1, 1, 1, 2. Maxillule (figure 3C) with stout praecoxal arthrite, bearing two spinulose setae and seven spines, distal-most of which heavily sclerotized; coxal endite with single plumose seta; coxal epipodite bearing two plumose setae of unequal length; proximal and distal basal endites rudimentary, two and fi ve setae, respectively; endopod unisegmented, with four lateral and fi ve terminal setae; exopod quadrate, with four long plumose setae terminally. Maxilla ( figure 3D, E View FIG ) well developed; praecoxa incompletely fused with coxa, fi rst and second endites bearing four and one seta, respectively; coxal endites with two and three setae, respectively; basis fused with heavily sclerotized claw bearing two setae of unequal size; endopod three-segmented, fi rst to third segments bearing 1, 1, 4 setae, respectively. Maxilliped (figure 3F) bearing 1, 2, 2 setae on syncoxal endites; syncoxa also with three rows of minute spinules; basis with subterminal spinulose seta; endopod unisegmented, with fi ve pinnate setae and one naked seta.

Legs 1-4 (figure 4A -D) with both rami three-segmented. Spine and seta formula of these legs as in diagnosis of the family given by Huys (1990, p. 284), except for the presence of only one inner seta on the second endopodal segment of leg 1. Coxae of legs 1-4 each with inner seta; basis of leg 1 with inner spine and outer seta; outer basal seta present in legs 2-4. Terminal spines of legs 2-4 curved inwards.

Leg 5 (figure 2A, C) two-segmented; proximal segment bearing outer seta; distal segment with two terminal setae of unequal length, one outer and one inner subterminal seta; inner subterminal seta shortest, at base of which row of minute spinules present. Leg 6 (figure 2D) lamelliform, bearing short outer spine and inner setule at dorso-posterio r corner.

Male ( paratypes). Body (figure 5A) similar to that of female, but more slender. Rostrum (figure 5B) separate at base as in female. Urosome consisting of fi fth pedigerous somite, genital somite, and four-segmented abdomen. Antennule (figure 5B) 14-segmented, unigeniculate between 12 (XX) and 13 ( XXI - XXIII). Segmentation pattern and armature elements as follows: 1(I - II) ━ 3 , 2 ( III - V) ━ 5 , 3 ( VI - IX) ━ 8 , 4 (X)━ 2, 5(XI)━ 2, 6 (XII)━ 2, 7(XIII)━ 2, 8(XIV)━ 2, 9( XV - XVII) ━ 4 + aesthetasc, 10 (XVIII)━1, 11(XIX)━ 2, 12 (XX)━ 1 modi fi ed spine-like fused element + 1, 13 ( XXI - XXIII) ━1 modi fi ed spine-like fused element + 1, 14 ( XXIV - XXVIII) ━ 10 (elements indisguishable). Antenna as in female. Mandible ( figure 5E View FIG ) as in female; fi rst endopodal segment bearing four or fi ve setae; subterminal protuberance absent on second endopodal segments on either side. Maxilla as in female. Maxilliped (figure 5F) without distinct sexual dimorphism.

Legs 1-4 as in female, but outer spines on third exopodal segment not as strongly curved inward as in female. Leg 5 (figure 5C) as in female. Leg 6 (figure 5D) lamelliform, with two setae at outer posterior corner.

Variation. The terminal prominence on the second endopodal segment of the mandibular palp on one side only of the holotype (figure 2I) was not found in other type specimens. It is therefore interpreted as an abnormal condition. The dissected paratypes ( 4♀♀, 2 ♂♂) bear four setae on the fi rst endopodal segment in the female and either four or fi ve in the male. The presence of fi ve setae in one male paratype is interpreted here as abnormal.

The degree of inward curvature of outer spines on the second and third exopodal segments of legs 1-4 varies between the dissected types. In one paratype female an inner seta is present on the right basis of leg 1 instead of a spine.

Etymology. The new speci fi c name is named in honour of Dr Kazuya Nagasawa (National Institute of Far Seas Fisheries Research).

Ecological notes

The prevalence and intensity of Chamicola nagasawai in Pseudochama retroversa collected in the Seto Inland Sea, western Japan ranged from 11.3 to 25.0%, and from 1.0 to 2.6, respectively. No other parasitic copepods were found in P. retroversa . This copepod appears to be relatively host-speci fi c since it was not found in the sympatric bivalve Chama japonica (Lamarck) , belonging to the same family, Chamidae , although only small samples were available for examination ( table 2 View Table 2 ).

Ovigerous females were found on 19- 20 August 1998 in Shiju and Kukuno Islands, and 7 January 1999 in Yasuura. Surface water temperature in the central part of the Seto Inland Sea, where the new species was collected, widely ranged from 9-12°C (January) to 27-29°C (August) ( Hirota, 1961, 1979; present study). The species seems to be in reproductive condition throughout the year. The holotype female of C. nagasawai carries a pair of egg-sacs on the genital double-somite, each of which contains 17 or 18 eggs.