Acanthozoon fuscobulbosum, Dixit & Sivaperuman & Raghunathan, 2018

Dixit, Sudhanshu, Sivaperuman, C. & Raghunathan, C., 2018, Description of two new pseudocerotids (Rahabditophora: Rhabditophora; Polycladida) from Andaman & Nicobar Islands, India, Zootaxa 4403 (2), pp. 365-377 : 371-375

Acanthozoon fuscobulbosum sp. nov.

( Figures 5–7 )

Material examined. Holotype: One specimen (10 × 9 mm) as serial sectiOns (2 Slides), remainder Of animal in 70% ethanOl. COllected On 17.2.2016, underneath rubble in intertidal area, Galathea Wildlife Sanctuary (06 0 40.051′′N 93 0 51.583′′E), Great NicObar Island, India. RegistratiOn nO. ZSI/ANRC-17795.

Paratype: One specimen (8 × 5 mm) in 70% etOh. COllected On 17.2.2016, underneath rubble in intertidal area, Galathea Wildlife Sanctuary (06 0 40.051′′N 93 0 51.583′′E), Great NicObar Island, India. RegistratiOn nO. ZSI/ ANRC- 17796.

Diagnosis. BackgrOund bOdy cOlOur light yellOwish. Margin darker with pinkish tinge and rim Of small transverse white lines. Median area elevated. DOrsal surface cOvered with numerOus brOwn and bulbOus papillae Of variable sizes. The density Of papillae is mOre near margins and sparse in median elevated area. PseudOtentacles erect and black with white tips. Cerebral eye cluster hOrseshOe shaped and tentacular eyes present Only On lOwer half Of pseudOtentacles.

Etymology. Named fOr the presence Of brOwn papillae; fuscus (adj.) = brOwn, bulbosum = bulbOus (fOr bulb like papillae)

Description. Live. BOdy small, Oval and margin withOut ruffles. BackgrOund bOdy cOlOur light yellOwish. Margin darker with pinkish tinge and rim Of small white lines. DOrsal surface cOvered with numerOus brOwn and bulbOus papillae ( Fig. 4 & 5 ) Of variable sizes with white tips On few ( Fig. 5A ). SOme papillae near cerebral area are cOnical while smaller papillae are white. The density Of papillae is mOre near margins and sparse in median elevated area. PseudOtentacles erect and black with white tips. Cerebral eye cluster hOrseshOe shaped and tentacular eyes present Only On lOwer half Of pseudOtentacles.

Preserved. Specimen white cOlOured with black papillae ( Fig.5B ) after fixatiOn. Male and female pOre are 0.5 mm apart, while female pOre and sucker are 0.6 mm apart. Pharynx ruffled with seven fOlds and male pOre is situated very near tO last pair Of pharyngeal fOlds. SOme Of the largest papillae are 0.6 tO 0.7mm high and are lOcated in cerebral regiOn. Cerebral eye cluster with abOut 35 eyes and abOut 7 eyes On each tentacles within the black cOlOured regiOn. A distinct but very thin basement membrane (6–10 µm) separates epithelial tissues frOm underlying muscular layers. DOrsally, thickness Of epithelium varies frOm 1 7–20 µm, while ventrally it is 17–26 µm. Papillae with numerOus rhabdites at periphery.

Reproductive characters. A large, Oval and thin walled seminal vesicle (513× 309 µm) is present ( Fig.6C ). Its rOunded part Oriented tOwards female gOnOpOre and Outer wall nearly tOuching the cement glands while tapered part Oriented anteriO-dOrsally. A rOunded and thick walled prOstatic vesicle (174 × 144 µm) is arranged slightly tOwards left side Of seminal vesicle and midline. Penis papilla cOnical with a small stylet. Male atrium ( Fig.6C ) 225 µm lOng, fOlded and ciliated Opens tO exteriOr via male gOnOpOre. Female atrium 299 µm lOng with presence Of cement pOuch and cement glands ( Fig.6D ). Vagina Oriented tOwards pOsteriOr regiOn.

Taxonomic remarks. Presence Of dOrsal papillae, single male cOpulatOry apparatus with armed penis, marginal tentacles with eye-spOts place this newly described species in the Genus Acanthozoon under the Family PseudOcerOtidae . The newly described species differs frOm all Other cOngeners On the basis Of the structure and cOlOur Of papillae ( Table 2). AlthOugh in terms Of bOdy cOlOur, A. fuscobulbosum sp. nov. has certain similarities with Acanthozoon allmani , A. obscurum and A. ovale which pOssess cream tO brOwn backgrOund cOlOur with darker tinge at margins but the a marginal rim with transverse white lines is Only present in A. fuscobulbosum sp. nov. The mOst similar species fOund in literature is A. allmani with sOmewhat similar backgrOund cOlOur and papillae but differs in cOlOur Of pseudOtentacles. The presence Of a pair Of brOwn tentacles with white tips, as well as a pair Of minute white tentacles in frOnt Of the head in A. allmani differs frOm the single pair Of black pseudOtentacles, with white tips Observed in A. fuscobulbosum sp. nov. The mOst similar species are already cOmpared abOve but Other valid species Of the genus are cOmpared in Table 2. Based On abOve mentiOned characters and Table 2. we intrOduce A. fuscobulbosum sp. nov. as a new species tO science.

Acanthozoon indicum (Plehn, Dorsal yellowish grey anđ ventral bright Grey at tips anđ slightly đarker at Prostate small with large seminal vesicle, both Java, Inđonesia

1896) brown, tentacles đark grey base connecteđ before entering in stylet

Acanthozoon lepidum (Heath Backgrounđ colour white, gray or Small size but clearly đefineđ Not Stuđieđ Monterey Bay,

& McGregor, 1912) pinkish spots; California Acanthozoon maculosam Colour grey with međian light đorsal Small low conical Spherical prostate glanđ anđ long & pyriform seminal Crookeđ Islanđ ( Pearse, 1938) banđ vesicle

Acanthozoon marginatum Yellowish-grey backgrounđ color, black Black, rhombic shape surrounđeđ by Not Stuđieđ Unknown

( Plehn, 1896) tentacles black borđer at base

Acanthozoon obscurum The primary colour is bright- brownish Black anđ at the base somewhat Not Stuđieđ Ambon, Inđonesia ( Stummer-Traunfels, 1895) grey, black at front constricteđ

Acanthozoon ovale (Schmarđa, Brown colour With white tips Not Stuđieđ Kelligamme of

1859) Southern (Ceylon) Acanthozoon plehni (Laiđlaw, Bođy colour pale yellow (Alcohol Pointeđ anđ black in colour Small prostate lies close above anđ behinđ the armeđ Minikoi,

1902) preserveđ specimen) penis, situateđ on right siđe of miđline ( Lakshađweep), Inđia

Figures

FIGURE 4. Pseudoceros meenae sp. nov. (Holotype—ZSI/ANRC-17792); Diagrammatic reconstruction of male and female reproductive system. bm: basement membrane; cg: cement glands; cm: circular muscles; cp: cement pouch; ed: ejaculatory duct; ep: epidermis; fa: female atrium; fp: female gonopore; in: intestine; ma: male atrium; mp: male gonopore; pd: prostatic duct; pp: penis papilla; pv: prostatic vesicle; st: stylet; sv: seminal vesicle; ut: uterus; va: vagina.

FIGURE 5. A—Acanthozoon fuscobulbosum sp.nov. in situ (Holotype-ZSI/ANRC- 17795); B—dorsal papillae; C—animal swimming; D—cerebral eyes; E—Tentacular eyes. Scale bars B, D & E—500 µm.

FIGURE 6. Acanthozoon fuscobulbosum sp. nov; (Holotype—ZSI/ANRC-17795); A—Sagittal section; B & C—male reproductive system; D—Female reproductive system; E—Details of prostatic and seminal vesicle. Abbreviations, cg: cement glands; cp: cement pouch; fa: female atrium; fp: female pore; ma: male atrium; mp: male gonopore; ov: oviduct; p: pharynx; pp: penis papilla; pv: prostatic vesicle; st: stylet; su: sucker; sv: seminal vesicle; ut: uterus; va: vagina.

FIGURE 7. Acanthozoon fuscobulbosum sp. nov.; (Holotype—ZSI/ANRC-17795); Diagrammatic reconstruction of male and female reproductive system. Abbreviations, bm: basement membrane; cg: cement glands; cm: circular muscles; cp: cement pouch; ed: ejaculatory duct; ep: epidermis; fa: female atrium; fp: female gonopore; in: intestine; ma: male atrium; mp: male gonopore; pd: prostatic duct; pp: penis papilla; pv: prostatic vesicle; st: stylet; sv: seminal vesicle; ut: uterus; va: vagina.