Ceratosomicola japonica, 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 : 2-5

Ceratosomicola japonica sp. n. Figures 1A, B24

Type material.

Holotype: female, ex body cavity of Hypselodoris festiva (A. Adams) ( Nudibranchia : Chromodorididae ), off Irukabana, Nohmi-jima Island, Hiroshima, Seto Inland Sea, Japan (34°13'49"N, 132°23'7"E), 5 m depth, 11 December 2010 ( NSMT–Cr 22240). Allotype: male ( NSMT–Cr 22241), collection data same as that of holotype. Paratypes: 1 female and 3 males ( NSMT–Cr 22242), collection data same as that of holotype; 1 female and 2 males ex body cavity of Hypselodoris festiva , off Irukabana, Nohmi-jima Island, Hiroshima, Seto Inland Sea, Japan (34°13'49"N, 132°23'7"E), 3 m depth, 12 December 2010 ( NSMT–Cr 22243).

Type locality.

Off Irukabana, Nohmi-jima Island, Hiroshima, Seto Inland Sea, Japan (34°13'49"N, 132°23'7"E).

Description of holotype female.

Body length from rostrum to posterior margin of anal somite: 4.27. Body (Figure 2A) composed of large prosome with 3 pairs of ventrolateral processes and small 3-segmented urosome. Prosome indistinctly 3-segmented, composed of anterior region, cephalosome, middle region comprising first to second pedigerous somites, and posterior region as third and fourth pedigerous somites. Cephalosome (Figures 2A, B, 3A) ellipsoid bearing rostrum with round margin, wider than long, bearing single apical lobe and 1 paired lateral lobes. Middle region large, bearing two transverse dorsal bulges and 5 ventral protrusions; anterodorsal bulge ornamented by 2 paired anterior and 1 paired lateral protrusions; posterior dorsal bulge carrying 2 pairs of lateral protrusions. Posterior region (Figure 2 A–C) bearing two ventral protrusions on third pedigerous somite and constriction at border between third and fourth pedigerous somites. Ventrolateral processes (Figure 2A) long and slender, distinctly longer than body. Urosome (Figure 2D) onion-like shaped, comprising genital double somite and two free postgenital somites ornamented with pattern of small scales on ventral surface. Genital double somite bearing paired ventral genital apertures. Caudal rami (Figure 2E) globular bearing two and three spiniform elements on outer margin and tip, respectively; one element on tip serrated.

Antennule (Figure 3A, B) 4-segmented; proximal segment rectangular bearing 4 spines on anterior margin; second segment with 3 anterior spiniform and 1 posterior setiform elements; third segment bearing 2 anterior and 1 posterior elements; terminal segment bearing 6 spiniform and 1 setiform elements. Antenna (Figure 3A, C) 3-segmented, conical with large sclerite at base, comprising coxobasis and 2-segmented endopod; coxobasis unarmed; proximal endopodal segment bearing 1 seta; terminal endopodal segment claw-like bearing 7 small elements. Labrum (Figure 3A) bilobate, unarmed. Labium (Figure 3A) bearing two paired spinulose lobes. Mandible (Figure 3A, D) represented by single recurved blade covered with numerous spinules along both anterior and posterior margin. Maxillule absent. Maxilla (Figure 3A, E) weakly sclerotized globular tapering into lanceolate tip. Maxilliped absent.

Swimming legs rudimentary; protopod largely incorporated into ventral wall of prosome. Leg 1 (Figures 2B, 3F) represented by outer basal seta, small exopodal lobe with seta and conical process along outer margin and 2 processes on tip, and spiniform endopodal element. Leg 2 (Figures 2B, 3G) bearing basal seta, elongate exopod indistinctly 2-segmented, tapering into apical process with 4 elements and single process, and endopodal lobe elongate, unarmed with intermedial constriction. Leg 3 on holotype indistinct.

Egg sacs (Figure 2F) curved, semicircle; color in life crimson.

Variation of female morphology. The morphology of female paratypes is as in the holotype, except leg 2 shows variability. Leg 3 is distinctly visible on the paratype females. Paratype female (NSMT-Cr 22243) has the exopod of leg 2 (Figure 3H) tapering into apical process with constriction and 2 elements. Paratype female (NSMT-Cr 22242) possesses a vestigial leg 3 (Figure 3I), represented by a blunt element on a protrusion. The specimens from type series (n = 3) range from 3.11-4.27 (3.76 ± 0.59) in body length (BL).

Description of allotype male.

Sexual dimorphism present in body form, and swimming legs. Body (Figure 4 A–C) 2.81 long, composed of cephalothorax and 5 cylindrical somites. Cephalothorax large, bulbous, incorporating first and second pedigerous somites, bearing transverse constriction and paired lateral and single dorsal protrusions posterior to mouthparts, paired posterolateral outgrowth, and paired and single ventral protrusions. Genital somite (Figure 4D) incompletely segmented, bearing transverse dorsal folding and paired apertures; opercula unarmed. Caudal rami (Figure 4E) globular, 2 and 3 elements along outer margin and on tip, respectively. No marked sexual dimorphism in antennule, antenna, and mouthparts. Tip of maxilla (Figure 4F) slightly sharper than that of female.

Leg 1 (Figure 4B, G) represented by outer basal seta, lobate exdopod with 2 elements, and spiniform endopodal element. Leg 2 (Figure 4B, H) represented by outer basal, serrated seta, elongate exopodal lobe with single element, and elongate endopodal lobe with single blunt element on tip. Leg 3 (Figure 4D, I) represented by spiniform element.

Variation of male morphology. The morphology of male paratypes is as in the allotype. The specimens from type series (n = 6) range from 2.16-2.81 (2.42 ± 0.43) in BL.

Site.

Female and male specimens were found in the body cavity of the host nudibranchs. Only the posterior tip of the urosome and the egg sacs were exposed from the host’s gill circle (Figure 1A, B). The mantle around the gill circle of the infected nudibranch was malformed into elongate tubes which obscured the host’s gills and the egg sacs of the copepod (Figure 1B).

Etymology.

The specific name of the new species “japonica” refers to Japan, where it was collected. Hypselodoris festiva , the type host of this new species, is widely distributed around the Japanese archipelago and is one of the common nudibranchs of Japan. Ceratosomicola japonica sp. n. is the first species of parasitic copepods to have been described from Japan ( Fujita 1895).

Remarks.

Ceratosomicola sacculata ( O’Donoghue, 1924) was originally described as Splanchnotrophus sacculatus . Huys (2001) redescribed this species based on a female and established a new genus Ceratosomicola. Three species, Ceratosomicola coia Salmen, Wilson & Schrödl, 2008; Ceratosomicola delicata Salmen, Wilson & Schrödl, 2008; Ceratosomicola mammilata Salmen, Wilson & Schrödl, 2008, were subsequently described based on specimens of both sexes, and this genus is now composed of four species ( Salmen et al. 2008b). The new species clearly differs from Ceratosomicola coia and Ceratosomicola delicata in having 7 ventral protrusions on the prosome of the female (vs. without ventral protorusions on Ceratosomicola coia and Ceratosomicola delicata ; Salmen et al. 2008b). Although the female of Ceratosomicola mammilata shares 7 protrusions, this species can be differentiated from the new species by having 2 pairs of lateral lobes on the anterior region of the prosome and a posterior pair of ventral protrusions located anterior to the base of third ventrolateral processes, i.e. on the second pedigerous somite (vs. 1 pair of lateral lobes on the anterior region of the prosome and a posterior pair of ventral lobes located posterior to the base of third ventrolateral processes, i.e. on the third pedigerous somite). In Huys’ (2001) redescription of Ceratosomicola sacculata , the ventral protrusions on the prosome was not described, while in the original description, O’Donoghue (1924) referred to the presence of at least 2 paired ventral lobes on the prosome. However, Ceratosomicola sacculata is distinguishable from the new species by the following characters in females: the anterior region of the prosome is trilobate (vs. ellipsoidal and bearing a pair of lateral lobes in the new species) and the middle region of the prosome bears 3 transverse dorsal bulges (vs. 2 transverse dorsal bulges in the new species).

In the course of dissection to describe Hypselodoris festiva (as Chromodoris marenzalleri ) ( Nudibranchia : Chromodorididae ) from the western North Pacific Ocean off Misaki, Kanagawa Japan ( Fujita 1893), one female specimen of splanchnotrophid was discovered by Fujita (1895) from the body cavity of the host. Although Fujita (1895) recognized some differences between this copepod and other splanchnotrophids, he did not describe it as a new species nor deposit it in any museum because of the incomplete specimen. The species was subsequently recognized as a member of Ceratosomicola by Huys (2001). Ceratosomicola japonica sp. n. was collected from the same host species ( Hypselodoris festiva ) in the Seto Inland Sea off Nohmi-jima Island, Hiroshima, Japan and shares important characters as follows: the anterior region of the prosome is wider than long, bearing a pair of lateral lobes ( Fujita 1895, figure 2) and middle region of the prosome bears a paired anterior and single posterior ventral protrusions with the latter being larger than the others ( Fujita 1895, figure 1). Fujita (1895, figure 2) also described the middle region of the prosome as bearing a cross-shaped concavity. This corresponds to the transverse dorsal bulges with 4 bulbous protrusions on each corner of Ceratosomicola japonica sp. n. Therefore, the Fujita’s splanchnotrophid is apparently conspecific with Ceratosomicola japonica sp. n.