Childia curinii, Nilsson, Karin Sara, Wallberg, Andreas & Jondelius, Ulf, 2011

Nilsson, Karin Sara, Wallberg, Andreas & Jondelius, Ulf, 2011, New species of Acoela from the Mediterranean, the Red Sea, and the South Pacific, Zootaxa 2867, pp. 1-31 : 18-20

Childia curinii sp. nov.

( Figs. 15 , 16 , 17 , 18 )

Type Material: Holotype: SMNH Type-8049. Paratype 1: SMNH Type-8050, Paratype 2: SMNH Type-8051.

Type Locality. Formica, Italy (42° 34' 19" N, 10° 53' 5" E), from 37 m water depth, in fine sand.

Other Material examined. Living specimens in squeeze preparations; 3 sets of 4–5 μm serial sagittal sections of paraffin-embedded specimen.

Etymology. Species name honors professor Marco Curini Galletti.

Description. Mature living specimens up to 3000 μm long and 700 μm wide. Body shape cylindric, elongate, widest anteriorly, ends rounded. Body with yellow to green pigment uniformly scattered across body ( Fig. 16 ABD). Epidermis completely ciliated with 5 μm long cilia. Frontal organ well developed. Cell bodies of frontal organ located in the anterior 1/4 of body. Subdermal eosinophilic glands present, sparsely scattered throughout body. Statocyst located 250 μm from anterior end, at U10, 5 μm in diameter. Mouth ventral, at U35.

Body-wall musculature reversed, longitudinal muscles located outside the circular muscles ( Fig. 17 B).

Paired ovaries, each lateral band with up to twelve oocytes, ventral - discernible in sectioned material and partially in live specimens. Ovaries extend anterior to level of mouth and posteriorly to seminal bursa, from U35 to U75. Globular seminal bursa present, at U75, with well-developed bursal wall ( Fig. 17 B). Ciliated female gonopore positioned on ventral side, at level of seminal bursa.

Testes paired, compact, lateral to ovaries, extending anteriorly to level of mouth and posteriorly to male copulatory organ, from U30 to U83. Male gonopore positioned posteriorly on ventral side, U87. Opening immediately to male copulatory organ with sclerotized, conical stylet-like structure, composed of several tightly packed needles ( Figs. 16 C, 17AB). Individual needles of copulatory structure radiating at the proximal end of the stylet.

In squeezed live specimens one can detect about 25 needles up to 75 μm long. Needles weakly stained by eosin. Stylet-like structure surrounded by seminal vesicle ( Fig. 17 AB).

Curved rod-like inclusions present, 30 μm long (up to 60 μm in some cases), and 5–8 μm wide, scattered throughout body in parenchyma, but most visible in posterior ( Fig. 16 BC).

Remarks. The two Childia species can be identified as members of the monotypic Childiidae due to the well developed single copulatory organ built of tightly packed sclerotized needles and the body-wall musculature with longitudinal fibers positioned outside circular fibers. The Bayesian analysis of the nucleotide data places C. aculifera as sister to all other Childia species and Childia curinii is the sister species of the two cryptic species identified as C. submaculatum ( Fig 15 ).

Childia aculifera sp.nov. is easily distinguished from other Childia species by its warm yellow to orange pigmentation, needle-like reflective inclusions, cone shaped stylet-structure with large stylet canal surrounded by seminal vesicle and numerous eosinophilic body glands.

Inclusions are also present in Childia curinii and Childia tranguliferum ( Westblad, 1942) , but with different size, shape and reflectiveness. Inclusions in C. trianguliferum are triangle-shaped and highly reflective. In C.

curinii inclusions are rod-like, much larger (30–60 µm long and 5–8 μm wide), slightly curved and not particularly reflective, while in C. aculifera they are reflective, needle-like and much thinner (2 μm wide). Moreover, the styletlike structure in C. trianguliferum differs from C. aculifera in having a slightly curved distal end and more irregular-shaped and less compact needles. The mouth in C. trianguliferum is located in the anterior end, the seminal bursa is more dorsally positioned, the seminal vesicle does not surround the stylet-like structure and yellow pigmentation is absent. The stylet-like structure of C. aculifera is smaller (50 µm), with fewer needles, than in C. curinii , (75 µm). The female antrum is shorter in C. curinii and the stylet-like structure has a broader shape, compact, and without large stylet canal visible in sections. Both species have yellow pigmentation, but the color is more warm yellow to orange in C. aculifera and yellow to green in C. curinii . C. aculifera also has more intense pigmentation in the middle of body, whereas pigmentation in C. curinii is uniformly scattered across the body. In C. curinii testes extend further anteriorly and the mouth is located in anterior end of body. Furthermore, C. aculifera has less compact eggs, more numerous eosinophilic body glands, and a seminal bursa located closer to the stylet-like structure, than C. curinii and C. trianguliferum .

C. curinii is easily distinguished from other Childia species by its yellow pigmentation, rod-shaped inclusions in the parenchyma, broad cone-shaped stylet-like structure surrounded by the seminal vesicle and relatively large body size, 3 mm. Inclusions are also present in Childia trianguliferum ( Westblad, 1942) and Childia aculifera , but in C. trianguliferum they are triangular and in C. aculifera they are needle-like and reflective in transmitted and reflected light. The inclusions in Childia curinii are rod-shaped, much wider than the inclusions in C. aculifera and not particularly reflective. C. trianguliferum differs from C. curinii in having fewer and less compact visible needles in the stylet-like structure, more numerous and tightly packed eggs, and mouth located closer to statocyst at 25U. The stylet-like structure of C. curinii has more needles and is larger (75 µm) than the stylet like structure in C. aculifera (50 µm). The female antrum is shorter in C. curinii than in C. aculifera . Both species have yellow pigmentation, but the color is yellow to green in C. curinii and more warm yellow to orange in C. aculifera which also has more intense pigmentation in the middle of the body, whereas pigmentation in C. curinii is uniform. In C. curinii testes extend further anteriorly and the mouth is in the anterior end of the body whereas it is located in the mid-body in C. aculifera . C. curinii can appear similar to Childia crassum ( Westblad, 1942) in sagittal sections and drawings because both have paired ovaries and testes, cone-shaped stylet-like copulatory structure, similar position of seminal bursa and large body size. However, there are no inclusions in C. crassum and the pigmentation is orange if present, not yellow. In C. curinii the bursal wall is of uniform thickness, whereas the anterior bursal wall is thicker in C. crassum . The stylet-like copulatory structure in C. curinii is somewhat similar to the stylet like structure in Childia submaculatum ( Westblad, 1942) , but smaller in relation to body size and is surrounded by the seminal vesicle. Live specimens of C. submaculatum are unpigmented, lack inclusions, and have a distinctive pattern formed by sub-epidermal glands that appear white in reflected and dark in transmitted light.

Figures

FIGURE 15. Detail from the majority rule consensus tree summarizing the result of the Bayesian analysis of the combined 18 S rDNA, 28 S rDNA and COI dataset with the GTR + G substitution model after 10 million generations sampled every 1000 generations after a burnin of 5 million generations. C. aculifera is placed as the sister to all other Childia species. Childia curinii is placed as the sister species of the two cryptic species identified as C. submaculatum.

FIGURE 16. Childia curinii sp. nov. Photomicrographs of living specimens. A. Dorsal view of whole specimen. Scale bar: 500 μm. B. View of mid-body. Scale bar: 60 μm. C. Male copulatory organ and inclusions. Scale bar: 30 μm. D. View of posterior end of body. Scale bar: 80 μm.

FIGURE 17. Childia curinii sp. nov. Photomicrographs of sagittal histological sections stained with hematoxylin-eosin. A. Section through length of body. Scale bar: 150 μm. B. Showing section through male and female copulatory organs and circular (double arrowhead) and longitudinal (arrowhead) muscles in body wall. Scale bar: 50 μm.

FIGURE 18. Childia curinii sp. nov. Reconstructions show arrangement of organs. A. Dorsal reconstruction of whole living animal. B. Sagittal reconstruction of the whole animal. Scale bar: 500 μm.