Acanthozoon aranfaibo, Noreña, 2017

Noreña, Carolina, 2017, The Polycladida (Platyhelminthes) of the Canary Islands. New genus, species and records, Zootaxa 4312 (1) : -

Acanthozoon aranfaibo n. sp.

( Fig. 8 and 11 O)

Holotype. One specimen captured in El Salto during the springtime near of town of La Restinga, El Hierro, Canary Archipelago ( Fig. 1 , H2; Table 1 and 2) by Leopoldo Moro and Daniel Cuadrado. 39 slides of sagittal serial sectioned specimen and stained with AZAN; Catalogue number: MNCN 4.01/ 1569-1608.

Type locality and occurrence in the Canary Island . El Salto, El Hierro, Canary Archipelago at depths of 10 metres.

Etymology. The specific name refers to the god of the rain, Aranfaybo, one of the main deities from the El Hierro culture. The delicate and transparent appearance of the species remembers the lightness of the rain.

Occurrence in the Canary Island. This species was observed in intertidal in early spring time.

Description. Body shape oval. Length 2 cm. Dorsal surface with scattered papillae ( Fig. 8 A). Background colour caramel brown, translucent, with dark spots over the entire dorsal surface. Spots are more abundant at the medial line and over the tentacles. Papillae scattered on the dorsal surface with darker tops, gradually decreasing in size towards the body margins. Ventral sucker in the middle of the body. Pseudotentacles as simple folds ( Fig. 8 B). Numerous tentacular eyes in the lower half of and between the tentacles as two separate clusters. Cerebral eyes cluster horseshoe shaped ( Fig. 8 B). Pharynx ruffled and situated in the anterior third of the body with the oral pore posterior to the cerebral ganglion.

The intestine extends backwards and display several lateral branches. The ramifications of the branches anastomose frequently, forming a dense network of orange tones at the margins ( Fig. 8 A and B). Small branches can also be observed within the papillae.

Reproductive system: Male and female reproductive system single and close to each other, both located in the anterior half of the body.

Testes are rounded and ventral located, ovaries near the dorsal side. Vas deferens , swollen and winding, enters into seminal vesicle from posterior end. Seminal vesicle elongated with thick muscular walls, opens into the muscular ejaculatory duct. Prostatic vesicle rounded and smaller than seminal vesicle. Prostatic duct very short and join the ejaculatory duct just before entering the penis. Penis papillae armed with a conical stylet directed slight backwards ( Fig. 8 C). Penial sheath and male atrium ciliated ( Fig. 8 D and E).

Oviducts of the female reproductive organ are connected with small spherical uterine vesicles. The internal vagina turns ventrally and passes through the cement pouch to the vagina externa, which, in this case, serves as the female atrium.

Discussion. The genus Acanthozoon Collingwood, 1876 , is characterized by the presence of scarce generally elongated papillae on the dorsal surface. Acanthozoon also presents a single copulatory organ compared with the two male organs present in Thysanozoon . Both main diagnostic features of Acanthozoon , scarce dorsal papillae and single male copulatory organ, can be recognised in the specimens from the Canary Island.

At present, the genus Acanthozoon consists of 12 valid species distributed mainly in the Indian Ocean or along the American coasts. Acanthozoon aranfaibo n. sp. present a caramel, transparent coloration, shared only with A. allmani (Collingwood, 1876) , A. alderi (Collingwood, 1876) , A. plehni (Laidlaw, 1902) and A. indicum ( Plehn, 1896) , species also having transparent appearance such that intestinal ramifications are visible. All other Acanthozoon species show darker and grey pigmentation.

Dorsal papillae, a conspicuous feature of the genus, can be conical or rounded, white or dark, with yellow, orange, white or black tips. Acanthozoon aranfaibo , together with A. boehmigi ( Stummer-Traunfels, 1895) and A. plehni , have papillae with black tips.

Acanthozoon aranfiabo most closely resembles A. boehmigi . They share several features including body colour, papillae number, shape, pigmentation and the medial bulge. However, clear differences exist between the two species. The cerebral eyes are presented as a rounded cluster in A. boehmigi and a horseshoe-shaped cluster in A. aranfaibo . Tentacular eyes are found within the tentacles in both species, but A. aranfaibo also has rounded clusters of tentacular eyes at the bases of the tentacles. Furthermore, although the medial bulge is darker than the rest of the body in both species, in A. aranfaibo , the bulge also contains a whitish-beige longitudinal band.

Acanthozoon aranfaibo and A. plehni have the same coloration and black-tipped papillae, although the general pigmentation in A. plehni is darker. The most conspicuous differences are found in tentacle and eye features. The tentacles are well separated from each other in A. aranfaibo and closer in A. plehni . The cerebral eyes are grouped in a rounded cluster in A. plehni and a horseshoe-shaped cluster in A. aranfaibo . Another difference is observed in the internal morphology of the papillae: the papillae contain small intestinal branches in A. aranfaibo , whereas in A. plehni , the papillae are filled only with parenchyma.

The genus Acanthozoon is until now known for the Indonesian and Oceanian coasts. This record represents the first for an Acanthozoon species for the European and African coasts.

Figures

FIGURE 1. Sampling station of the Canary Islands (for explanation of legends see Table 1).

FIGURE 8. Acanthozoon aranfaibo n. sp. (MNCN 4.01 / 1569 - 1687). A. In vivo, dorsal view; B. Detail of the anterior region; C. Sagittal section of the male reproductive structures; D. Sagittal section of the reproductive structures; E. Sagittal reconstruction of the reproductive system. af, female atrium; am, male atrium; cg, cement glands; dp, dorsal papilla; e, eyes; i, intestine; ph, pharynx; ps, pseudotentacles; pv, prostatic vesicle; s, stylet; spv, spermiducal vesicle; su, sucker; sv, seminal vesicle; v, vagina.

FIGURE 11. Species located in the Canary archipelago, in vivo. A. Eurylepta guayota n. sp. B. Prostheceraeus giesbrechtii Lang, 1884. C. Prostheceraeus roseus Lang, 1884. D. Enchiridium magec n. sp. E. Anonymus virilis Lang, 1884. F. Anonymus ruber n. sp. G. Pericelis cata Marcus and Marcus, 1986. H. Phrikoceros mopsus (Marcus, 1952) Quiroga, 2008. I. Pseudobiceros wirtzi Bahia and Schrödl, 2016. J. Pseudoceros maximus Lang, 1884. K. Pseudoceros velutinus (Blanchard, 1847) Lang, 1884. L. Pseudoceros mororum n. sp. M. Pseudoceros sp. N. Thysanozoon brocchii (Risso, 1818) Grube 1840. O. Acanthozoon aranfaibo n. sp. P. Yungia aurantiaca (Delle Chiaje, 1822) Lang, 1884. Q. Cestoplana rubrocincta (Grube, 1840) Lang, 1884. R. Multisepta fengari n. sp. S. Planocera pellucida (Mertens, 1833) Örsted, 1844.