Splanchnotrophus helianthus, 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 : 5-7

Splanchnotrophus helianthus sp. n. Figures 1C, D57

Type material.

Holotype: female, ex body cavity of Thecacera pennigera (Montagu) ( Nudibranchia : Polyceridae ), off Matoba Beach, Takehara, Hiroshima, Seto Inland Sea, Japan (34°19'29"N, 132°55'21"E), 15 m depth, 17 February 2009 ( NSMT–Cr 22244). Allotype: male ( NSMT–Cr 22245), collection data same as that of holotype. Paratypes: 1 female and 9 males ( NSMT–Cr 22246), collection data same as that of holotype; 1 female ex body cavity of Thecacera pennigera , off Matoba Beach, Takehara, H iroshima, Seto Inland Sea, Japan (34°19'29"N, 132°55'21"E), 15 m depth, 15 January 2009 ( NSMT–Cr 22247); 1 female and 1 male ex body cavity of Thecacera pennigera , off Izaki, Yashiro-jima Island, Yamaguchi, Seto Inland Sea, Japan (33°51'49"N, 132°19'29"E), unknown water depth, 27 April 2008 ( NSMT–Cr 22248).

Type locality.

Off Matoba Beach, Takehara, Hiroshima, Seto Inland Sea, Japan (34°19'29"N, 132°55'21"E).

Description of holotype female.

Body (Figure 5A) 3.44 long, composed of elongate, slender prosome with 3 pairs of long lateral processes and small 2-segmented urosome. Prosome (Figure 5A, B) composed of anterior region, cephalosome, middle region comprising first to second pedigerous somites, and posterior region as third pedigerous somite. Cephalosome (Figure 5B, F) elongate, bent ventrally, with projecting rostral area. Middle region (Figure 5A, B) large, constricted posterior to base of anterior lateral processes with paired and single dorsal protrusions. Posterior region (Figure 5 A–C) broad, without armature. Lateral processes (Figure 5A) long and slender, distinctly longer than body length. Urosome (Figure 5C, D) small; genito-abdomen narrower posteriorly with paired posterolateral lobes; unarmed opercula and genital aperture located on ventral. Caudal rami (Figure 5E) small, about twice as long as wide, bearing 6 setae and 1 dorsal spiniform process; apical seta long, styliform.

Antennule (Figures 5F, 6A) 2-segmented; terminal segment bearing 2 constrictions making it appearing as original segmentation; proximal segment bearing 2 blunt spines; terminal segment bearing 2 blunt spines and 1 seta in proximal part, 3 setae and 1 aesthetasc in middle part, and 9 setae and 2 aesthetascs in distal part. Antenna (Figures 5F, 6B) 3-segmented; coxo-basis broad, bearing 1 inner spine with spiniform tip; proximal segment of endopod bearing 1 inner spine; terminal segment of endopod tapering into strong apical claw, with 2 spines and 2 setal elements. Labrum (Figure 6B) bilobate, bearing flat surface. Mandible (Figure 6C) spatulate, tapering into single curved blade with 2 dentiform processes giving trifid appearance. Labium (Figure 6B) developed with paired spinulose patches. Maxillule not observed. Paragnath (Figure 6B) developed, represented by pinnate lobe. Maxilla (Figure 6B, D) 2-segmented; syncoxa unarmed; allobasis tapering into spiniform element, with seta. Maxilliped absent.

Leg 1(Figures 5B, 6E) unsegmented, weakly sclerotized and drawn out into elongate exopod and small endopod; protopod bearing outer basal seta; exopod drawn out into spiniform lobe bearing multiple constrictions, wrinkly surface, 3 outer and 1 inner setal elements; endopod a small lobe tipped with seta. Leg 2 (Figures 5B, 6F) unsegmented, weakly sclerotized; protopod drawn out into long exopod and small, cylindrical endopod; protopod bearing outer basal seta; exopod tapering into a pointed process with three outer and 1 inner small element; endopodal lobe bearing small apical seta. Leg 3 (Figures 5C, 6G) represented by conical process with apical seta, located near posterolateral corner on ventral side of prosome.

Egg sacs (Figure 5A) bilobate, bearing curved side and swollen side; color in life cream (Figure 1C, D).

Variation of female morphology. The morphology of female paratypes is as in the holotype. The specimens from type series (n = 3) range from 2.81-4.47 (3.57 ± 0.83) BL.

Description of allotype male.

Sexual dimorphism prominent in body form. Body (Figure 7 A–C) cyclopiform, 0.63 long, composed of cephalothorax and 5 cylindrical somites. Cephalothorax (Figure 7 A–C) large, incorporating first and second pedigerous somites, with constriction posterior to mouthparts. Urosome 3-segmented (Figure 7D); genital somite scarcely discernible in dorsal view, bearing paired apertures; opercula carrying 2 processes along posterior margin. Anal somite (Figure 7D) nearly completely withdrawn into genital somite. Caudal rami (Figure 7E) cylindrical, about three times as long as wide, bearing 5 setae, styliform terminal seta bipinnate toward tip, and 2 dorsal spiniform spines.

No marked sexual dimorphism in antennule, antenna, and mouth parts, except location of antenna. The base of antenna located anterior to labrum (Figure 7F).

Leg 1 (Figure 7G) biramous; protopod narrower than that of female, with minute basal outer seta; exopodal lobe elongate, tapering into pointed process, carrying 4 outer and 1 inner elements; endopodal lobe small, tipped with minute apical element. Leg 2 (Figure 7H) longer than leg 1; protopod bearing minute basal outer seta; exopodal lobe elongate, tapering into pointed process, bearing 3 outer and 1 inner elements; endopodal lobe tipped with minute element, bearing 1 small outer element. Leg 3 (Figure 7D) represented by single seta. Legs 4 and 5 absent.

Variation of male morphology. The morphology of male paratypes is as in the allotype. The specimens from type series (n = 11) range from 0.32-0.63 (0.53 ± 0.12) in BL.

Site.

Both female and male specimens were found in the body cavity of host nudibranchs. The females grasped the host’s visceral sac by the lateral processes on the prosome (Figure 1D). Only the posterior tip of the urosome and the egg sacs were exposed from the host’s gill circle (Figure 1C).

Etymology.

The specific name “helianthus” is from the Latin meaning sunflower. The live body color of this new species is yellowish, and the egg sacs attached on the host nudibranch look like flowers.

Remarks.

Four species of Splanchnotrophus are currently recognized as valid ( Huys 2001). Splanchnotrophus helianthus sp. n. differs from Splanchnotrophus angulatus Hecht, 1893, Splanchnotrophus dellachiajei Delamare Deboutteville, 1950, Splanchnotrophus gracilis Hancock & Norman, 1863 in the absence of paired posterolateral processes on the prosome and the genito-abdomen bearing lateral lobes in females (vs. the presence of posterolateral processes on the prosome and the genito-abdomen without paired lateral lobes, Hancock and Norman 1863; Delamare Deboutteville 1950; Huys 2001). Huys (2001) claimed that, in Splanchnotrophus angulatus , the shape of the female’s genito-abdomen is constant, irrespective of prosome valiability, and the size and shape of the posterolateral lobe of the prosome certainly shows variability. Nevertheless, this species always possesses the posterolateral lobe, which is regarded as a useful identification character. The original description of Splanchnotrophus willemi by Canu (1891) has no illustration and includes only a minimum amount of information. However, the presence of pleural wings on the third pedigerous somite in Splanchnotrophus willemi is not shared with the new species ( Canu 1891).