Majimun shirakawai, Uyeno, Daisuke & Nagasawa, Kazuya, 2012

Uyeno, Daisuke & Nagasawa, Kazuya, 2012, Four new species of splanchnotrophid copepods (Poecilostomatoida) parasitic on doridacean nudibranchs (Gastropoda, Opistobranchia) from Japan, with proposition of one new genus, ZooKeys 247, pp. 1-29 : 10-12

Majimun shirakawai gen. et sp. n. Figures 1G, H1012

Type material.

Holotype: female, ex body cavity of Roboastra luteolineata (Baba) ( Nudibranchia : Polyceridae ), off Miyagi Beach, Chatan, Okinawa-jima Island, East China Sea, Japan (26°19'44"N, 127°44'35"E), 6 m depth, 14 June 2010 ( NSMT–Cr 22250). Allotype: male ( NSMT–Cr 22251) collection data same as that of holotype. Paratypes: 1 female and 1 male, ex body cavity of Roboastra gracilis (Bergh), off Cape Maeda, Onna, Okinawa-jima Island, East China Sea, Japan (26°26'41"N, 127°46'20"E), 5 m depth, June 2010 ( NSMT–Cr 22252); 2 females and 1 male, ex body cavity of Roboastra luteolineata (Baba), off Miyagi Beach, Chatan, Okinawa-jima Island, East China Sea, Japan (26°19'44"N, 127°44'35"E), unknown water depth, 14 October 2009 ( RUMF–ZC– 02106).

Type locality.

off Miyagi Beach, Chatan, Okinawa-jima Island, East China Sea, Japan (26°19'44"N, 127°44'35"E).

Description of adult female.

Body length (Figure 10A) 4.99, elongate, composed of elongate prosome with 3 pairs of lateral processes and 3-segmented urosome. Prosome composed of anterior region (cephalosome), middle region (comprising first and second pedigerous somites), and posterior region (comprising third and fourth pedigerous somites). Cephalosome rectangular (Figure 10A, B), bearing protruded rostral area (Figure 10G). Middle region (Figure 10A, B) elongate, about twice as long as wide, bearing constriction at base of first lateral processes and dorsal posterior lobe, without posterolateral processes. Posterior region (Figure 10A, B) elongate, third and fourth pedigerous somites covered with anchor-shaped spinules (Figure 10E) along posterior margin (Figure 10C, D). Lateral processes (Figure 10A) long and slender, about 1.3 times as long as body length. Urosome (Figure 10C, D) small; genital double somite cylindrical, narrower at middle length, bearing paired apertures with slightly prominent posterolateral corners; opercula bearing small shield-like structure with 2 spiniform processes. Caudal ramus (Figure 10F) small, fusiform, about twice as long as wide, bearing 6 setae; apical seta styliform.

Antennule (Figure 11A) 3-segmented bearing spiniform elements; proximal segment subdivided basal part with 4 elements and distal part with 3 elements; middle segment bearing 3 elements; terminal segment bearing 11 elements. Antenna (Figure 11B) 3-segmented; coxo-basis broad, bearing 1 inner spiniform element; proximal segment of endopod bearing 1 inner spiniform element; terminal segment of endopod drawn out into strong apical claw, with 4 and 1 elements along outer and inner margins, respectively. Labrum (Figure 11B) bilobate, bearing paired extra lobes along posterior margin and small central, conical protrusion. Mandible (Figure 11B, C) spatulate, drawn out into blade with pointed tip and 3 dentiform processes. Maxillule not observed. Paragnath (Figure 11B, D) bulbous lobe covered with setules. Maxilla (Figure 11B, E) 2-segmented; syncoxa unarmed; allobasis tapering into curved process, with seta. Maxilliped absent. Labium (Figure 11B) bearing single pointed process, small paired protrusions ornamented with spinules, and posterolateral patch of spinules.

Legs 1 and 2 (Figures 10B, 11F, G) composed of protopod largely incorporated into ventral wall of prosome with exopodal and endopodal lobes; protopod bearing outer basal seta, small protrusion at base of endopodal lobe of leg 1; exopodal lobe indistinctly 2-segmented, tapering into spiniform apical process, bearing 4 and 2 elements in legs 1 and 2, respectively; endopodal lobe cylindrical bearing apical process. Leg 3 (Figures 10C, 11H) represented by conical process with apical seta.

Egg sacs (Figure 10A) cylindrical and spiral; orange in live color (Figure 1G, H).

Variation of female morphology.The morphology of body parts of female paratypes is as in the holotype. The specimens from type series (n = 4) range from 3.31-4.99 (3.99 ± 0.77) BL.

Description of adult male.

Body (Figure 12 A–C) 1.02 long, cyclopiform, composed of cephalothorax and 5 cylindrical somites. Cephalothorax (Figure 12 A–C) large, bulbous, incorporating first and second pedigerous somites, bearing transverse constriction posterior to mouthparts and paired posterolateral outgrowths. Posterior margin of third and fourth pedigerous somites (Figure 12C, D) covered with anchor-shaped spinules (Figure 12E) on both dorsal and ventral surface. Genital somite (Figure 12D) bearing paired apertures; opercula unarmed. Caudal ramus (Figure 12F) conical, about as long as wide, bearing 6 setae; apical seta styliform. No marked sexual dimorphism in antennule and mouthparts. Shape of antenna (Figure 12G) as in female except terminal endopodal segment bearing 5 elements; inner margin bearing 2 of 5 elements. Mandible (Figure 12H) elongate, drawn out into spatulate apical blade with 3 dentiform processes.

Legs 1 and 2 (Figure 12B, I, J) composed of round protopod with outer basal seta, indistinctly 2-segmented exopodal lobe drawn out into pointed process with 4 and 3 elements on legs 1 and 2, respectively, and non-segmented endopodal segment with apical small process. Leg 3 (Figure 12D, K) represented by conical process with apical seta.

Variation of male morphology. The morphology of male paratypes is as in the allotype. The specimens from type series (n = 3) range from 0.50-1.02 (0.75 ± 0.26) in BL.

Site.

All specimens of both sexes were found in the body cavity of the host nudibranchs. The lateral processes on the prosome of females grasped the host’s visceral sac, and their mouthparts were in touch with the host’s gonads. The posterior tip of the urosome and the egg sacs were exposed from the posterior region of the host’s gill circle (Figure 1G). Males were attached to the posterior part of the female prosome (Figure 1H). Both females and males bear patches of hook-like spinules (Figures 10E, 12E) on the posterior margin of the third and fourth pedigerous somites.

Etymology.

The new species is named after Mr. Naoki Shirakawa, an expert diver who finds remarkable animals. He collected the nudibranchs infected by the new species.