Type material. Holotype: adult female (NSMT-Cr 26845), ex body cavity of Sakuraeolis enosimensis (Baba, 1930) (Nudibranchia: Facelinidae), off Irukabana, Nohmi-jima Island, Hiroshima, Seto Inland Sea (34°13′49″N, 132°23′7″E), 10 m, 14 February 2014. Allotype: adult male (NSMT-Cr 26846), collection data same as that for holotype. Paratypes: 1 adult male (NSMT-Cr 26847), collection data same as that for holotype; 2 adult females (NSMT-Cr 26848), ex body cavity of S. enosimensis, off Irukabana, Nohmi-jima Island, Hiroshima, Seto Inland Sea (34°13′49″N, 132°23′7″E), 10 m, 15 February 2014.

Morphology of holotype adult female. Body (Figs. 1D, 2A) 2.26 long. Prosome (Fig. 2A, B) composed of anterior region (cephalosome), middle region (first to second pedigerous somites), and posterior region (third and fourth pedigerous somites). Cephalosome (Fig. 2A, B) broad, not elongate. Middle region (Fig. 2A, B) large, bearing three pairs of long, conical lateral processes and pair of spherical posterolateral processes; lateral processes (Fig. 2A) conical, curved, and as long as or slightly shorter than body; bases of third lateral processes situated on same part of that of second lateral processes. Posterior region (Fig. 2A–C) small, without armature. Urosome (Fig. 2A–C) small, composed of genito-abdomen (Fig. 2D) bearing pair of round lateral lobes, unarmed opercula, and ventral genital apertures. Caudal rami (Fig. 2E) small, almost as long as wide, bearing five setae, single conical element and single spiniform dorsal process; apical seta (seta V) long, setose.

Antennule (Fig. 2H) Two-segmented; proximal segment bearing two blunt spines; terminal segment with transverse constriction, armature consisting of two blunt spines and three setae in proximal part and nine setae and two aesthetascs in distal part. Antenna (Fig. 2I, J) Three-segmented; coxo-basis broad, bearing spine at inner distal corner; proximal segment of endopod bearing inner spine; distal segment of endopod tapering into strong apical claw, with four elements. Labrum (Fig. 2I) bilobate, with flat surface. Mandible (Fig. 2I, K) tapering into single curved, spatulate blade with four dentiform processes. Paragnath (Fig. 2I) represented by pinnate lobe; intermaxillary swelling with two spinular patches. Maxillule not observed. Maxilla (Fig. 2I, L) Two-segmented; syncoxa unarmed; allobasis with spiniform apical element and lateral seta. Maxilliped absent.

Leg 1 (Figs. 2B, 3A) unsegmented, weakly sclerotized and drawn out into protopod fused to elongate exopod and small endopod; protopod bearing outer basal seta; exopod drawn out into elongate lobe bearing multiple constrictions, wrinkly surface, two outer, single long apical, and two small inner elements; endopod represented by small constricted lobe bearing distal setal element. Leg 2 (Figs. 2B, 3B) unsegmented, weakly sclerotized; protopod drawn out into long exopod and small, cylindrical endopod; protopod bearing outer basal seta; exopod tapering into elongate lobe with two small outer, single long apical, and two inner small elements; round endopodal lobe unarmed. Leg 3 (Figs. 2C, 3C) represented by conical robe with apical seta, located near posterolateral corner on ventral side of prosome.

Egg sacs (Fig. 2F, G) bilobate, bearing long curved one side and short swollen other side and attaching at about mid-length to genital apertures; color in life violet (Fig. 1A, B).

Morphology of allotype adult male. Sexual dimorphism clearly prominent in body form. Body (Fig. 3D–F) cyclopiform, 0.86 long. Cephalothorax (Fig. 3D–F) large, incorporating first two pedigerous somites; original boundary between cephalosome and first pedigerous somite marked by bilateral constriction posterior to maxillae. First to second pedigerous somites fused; original boundary marked by faint constriction laterally. Third and fourth pedigerous somites (Fig. 3G) free. Urosome (Fig. 3G) Two-segmented; genital somite bearing paired lateroventral apertures closed off by opercula (Fig. 3H) carrying two processes. Caudal rami (Fig. 3G, I) cylindrical, about three times as long as wide, bearing conical tip, five simple setae, and spiniform terminal seta with pinnate tip. No marked sexual dimorphism in antennule, antenna, and mouthparts (Fig. 3J). Base of antenna located anterior to labrum. Maxilliped absent.

General shape of legs 1 and 2 (Fig. 3K, L) as in female except for protopods bearing small setae; exopods tapering into sharp tip bearing several minute spiniform processes, and endopods represented by elongate, blunt lobes with small apical element. Leg 3 (Fig. 3G, M) represented by simple seta. Legs 4 and 5 absent.

Variation. The morphology of adult female paratypes (n = 2) is as in the holotype. The range of body length of paratypes is 1.81–2.30 (2.05 ± 0.35). Live egg sacs of paratype female pinkish white (Fig. 1C). The morphology of adult male paratypes (n = 1) is as in the allotype. The body length of paratype as 0.93.

Remarks. The new species is concerned to assigned to the genus Lomanoticola based on the following characters of the adult female, i.e., the prosome bears lateral processes which are shorter than the body, the prosome lacks processes on dorsal or ventral sides, the presence of the genito-abdomen, and the mandible represented by a curved blade (Huys, 2001; Uyeno and Nagasawa, 2012). Prior to the discovery of L. nishiharai n. sp. the genus contained two species are known to that are recognized as valid (Huys, 2001). The new species differs from two of these congeners, Lomanoticola brevipes (Hancock and Norman, 1863) and L. insolens Scott and Scott, 1895, by the following combination of the adult female characters: the cephalosome distinctly protruded (vs slightly projected forward); the second and third lateral processes on the body are originated from same bases (vs the third processes attached behind of the bases of the second processes); and the caudal rami bears a seta V which almost the same length as the rami (vs. almost twice as long as the rami) (Hancock and Norman, 1863; Delamare Deboutteville, 1950).

Attachment site. Both adult females and males were found in the body cavity of the host nudibranchs. Only the posterior part of the urosome of the females and their egg sacs protruded from the host's bodies (Fig. 1A–C).

Prevalence and intensity. Three of out of total 17 nudibranchs (17.65%) collected on 14 and 15 February 2014 from the type locality were infested by one female and none or a single male.

Etymology. The specific name of the new species, nishiharai, was chosen in honor of Dr. Naohisa Nishihara, the director of the Satoumi Science Museum, Etajima City as a tribute to his kindness and devoted support for the senior author's fieldwork.

Newly established Japanese name for genus and species. “Ajisai-umiushi-yadori-zoku” is for the genus, and “Ajisai-umiushiyadori” is for the new species. The color of egg sacs of the copepod is reminiscent of that of the flowers of hydrangea, called “Ajisai” in Japanese. “Umiushi-yadori” is the Japanese name for splanchnotrophid copepods.