Actinocyclus verrucosus Ehrenberg, 1831, by subsequent designation of J. E. Gray (1847)

See Valdés (2002).

Massawa, Eritrea.

AUSTRALIA, Coral Sea, North East Herald Cay, AUS 333868.001, 2 specimens (M. Preker, coll., 24/vi/1997, beach rock, SE side of cay, LT at dusk). Vanuatu, Espiritu Santo Island, Palikulo Peninsula (15°28.90’S 167°15.50’E (DDM)), CAS 179791, 1 specimen (M. Pola-Perez, Y. Camacho-Garcia et al. Coll., 15/ix/2006, intertidal, soft bottom).

Body of grayish color, with some black dots and some tubercles. Anterior border of foot concave and not bilabiate nor longitudinally notched. Presence of m7a odontophore muscles and pleural commissure.

External morphology (Figs 1–9): Size, ~12mm length, ~10mm width. Color grayish with some black dots in preserved specimen. Body rounded, oval, almost as long as wide; elevated dorsum with some several simple dorsal tubercles scattered irregularly (Figs 1–3). Mantle smooth without spicules. Rhinophores with ~17 transverse lamellae (preserved specimen with ~12mm-long CASIZ 179791) (Figs 5–7); rhinophoral sheaths smooth. Gill circle composed of 16–19 unipinnate branchial leaves surrounding anus (preserved specimen with ~12mm-long) (Figs 8–9); branchial sheaths smooth. Mouth opening in anterior ventral region, between anterior region of notum and foot (Fig. 2). Digitiform tentacles very small, one on each side of mouth (Fig. 4). Anterior border of foot concave, not bilabiate, nor longitudinally notched (Fig. 4). Foot not exceeding notum in a preserved specimen (Fig. 2).

Figures 1–4. 

External morphology of Actinocyclus verrucosus. 1. Whole dorsal view, scale: 5 mm. 2. Whole ventral view, scale: 5 mm. 3. Whole right lateral view, scale: 5 mm. 4. Detail of anterior border of foot, ventral view, scale: 2 mm.

Haemocoel organs (Figs 11–12): pericardium and posterior half of visceral mass occupying ~40 % of haemocoel volume. Buccal mass located anteriorly, occupying ~20 % of haemocoel volume. Nervous system dorsal to buccal mass, covered by blood gland, occupying ~10 % of haemocoel volume. Genital system on right side; occupying ~20 % of haemocoel volume. Stomach internal to digestive gland, intestine with small curve at anterior portion, both occupying ~10 % of haemocoel volume.

Figures 5–12. 

Anatomical details of Actinocyclus verrucosus. 5. Rhinophore extracted, ventral view, scale: 0.5 mm. 6. Same dorsal view, scale: 0.5 mm. 7. Same, transverse section, scale: 0.5 mm. 8. Gill circle with retractor muscle, dorsal view, scale: 1 mm. 9. Detail of gill filament, scale: 1 mm. 10. Detail of circulatory system (structures of pericardium), ventral view, scale: 2 mm. 11. Extracted visceral mass, dorsal view, scale: 2 mm. 12. Same, ventral view, scale: 2 mm.

Circulatory and excretory systems (Figs 8–11): pericardial cavity dorsal and posterior to digestive gland, anterior to gill circle. Afferent and efferent veins located at edge of each branchial leaves (Fig. 9). Gill retractor muscle divided in two fibers originating from base of gill circle, running lateral to haemocoel longitudinally up to half of foot level, inserting into dorsal surface of foot (Fig. 8). Auricle funnel-like (wider anteriorly) with thin walls (Fig. 10). Ventricle slightly taller than wide, with thick muscular walls (Fig. 10). Aortic trunk anterior to pericardium, connected to anterior ventricular region (Figs 10–11); posterior artery branched into anterior artery irrigating reproductive system, buccal mass, odontophore and nervous system inserting on blood gland; anterior artery irrigating stomach, caecum and digestive gland (Fig. 11). Auricular vessels connecting lateral cavities of integument to auricle (Fig. 10). Medial sinus connected to afferent branchial ring, irrigating entire digestive gland. Renal vesicle located on right dorsal side of pericardium, near base of auricle, connected to inner surface of pericardium; renal chamber elliptical, with longitudinal folds, ~1/4 of size of ventricle (Fig. 10). Renal chamber extending from dorsal to medial sinus, previously connected to renal vesicle, extending posteriorly to center of gill circle and opening in nephrostome, next to anus pore (Fig. 8). Blood gland undivided (Fig. 11).

Digestive system (Figs 8, 13–21, 28–31): Oral tube composed of outer lip, with pleats lengthwise; inner lip with transverse fold; mt, two pairs of retractor muscles of buccal mass, originating on oral tube, running dorsally and ventrally to oral tube, inserting on body side, about three times as wide and twice as long as m10 (Fig. 15). Odontophore oval, connected to oral tube by several fine longitudinal dorsal and ventrolateral protractors muscles of buccal sphincter, originating in anterior region of odontophore, inserting in posterior region of integument, close to oral tube (m10) (Fig. 14); Buccal sphincter surrounding chitinous part of oral tube. Odontophore muscles: m2, pair of strong retractor muscles of buccal mass, six times longer than wide, originating on anterior dorsal odontophore, running laterally to m4 and inserting ventrally on dorsal portion of foot; m3, two times wider than long, transverse fibers between esophagus and odontophore (Figs 15–16); m4, pair of dorsal tensor muscles of radula, strong and broad, 1/2 winder than long, covering externally 2/3 of cartilage, inserting on ventral portion of subradular membrane; m5, pair of dorsal auxiliary tensor muscles of radula, twice as long as wide, originating on most posterior region of odontophore cartilages, covering ~1/3 of posterior cavity of odontophore, as long as, but with ~1/3 of m4 width, inserting on ventral side of subradular membrane, around radular sac; m6, unpaired horizontal muscle, with transverse fibers connecting anterior surfaces of left and right odontophore cartilages, as long as wide, about same length and half as wide as m4 (Fig. 20); m7, pair of thin muscles originating each into an odontophore cartilages and inserting on m7a passing ventrally by m5, and on radular sac (Fig. 19); m7a, originating on posterior region of odontophore cartilage and inserting on radular sac, m7’ auxiliary (Fig. 19). Pair of odontophore cartilages slender, elliptical. Subradular membrane thin, strong, translucent (Fig. 18). Radular sac ~1/6 of odontophore (Fig. 16). Jaw elements not analyzed. Radular teeth (Figs 28–31): rachidian teeth absent; formula 50 x 17.0.17 (preserved specimen, ~15 mm-long, AUS C333868001). Innermost lateral teeth broad and thick, with large and rounded cusp and about six to eight cusps along inner edge (Fig. 31). Mid-lateral teeth narrow basally and elongated, with apical cusp larger than other, twenty-one lateral cusps (Fig. 30). Outermost teeth shorter than middles laterals, about sixteen to eighteen cusps (Fig. 29). Pair of salivary glands long, tubular, about same length as esophagus; duct inserting in anterior region of esophagus, extending posteriorly to anterior region of digestive gland (Fig. 14). Esophagus simple, originating dorsally to odontophore, inserting directly in anterior region of stomach, internal longitudinal folds with same diameter along entire length (Figs 14–15). Stomach internal to digestive gland, oval, close to anterior region of intestine, with distinct digestive ducts (Fig. 21). Intestine with longitudinal folds along its entire length, diameter same as esophagus diameter. Caecum as an elongated sac, located ventrally to stomach, opening on anterior portion of stomach (Fig. 21), close to esophageal insertion, ~½ length and ~1/2 of width of stomach. Digestive gland dark brown, internal to hermaphrodite gland, cone-shaped; inner face of gland sponge-like, bearing three ducts (Fig. 21). Anus opening into pore at center of gill circle (Fig. 8); anal papilla absent.

Figures 13–21. 

Actinocyclus verrucosus details of digestive system. 13. Foregut and nerve ring, ventral view, some adjacent structures also shown as in situ, scale: 1 mm. 14. Same dorsal view, scale: 1 mm. 15. Same, longitudinally sectioned, showing internal oral tube, dorsal view, scale: 1 mm. 16–20. Odontophore anatomy, scales: 1 mm. 16. Whole ventral view, sphincter removed. 17. Whole dorsal view, esophagus removed. 18. Dorsal view, radula removed, each cartilage slightly deflected. 19. Whole right view. 20. Ventral view, m4 and m5 folded down to expose odontophore cartilage; m7 and m7a removed. 21. Midgut as in situ, dorsal view, scale: 2 mm.

Genital system (Figs 2, 11–12, 22–24): located between buccal mass and digestive gland, mainly on right and dorsal sides. Hermaphrodite gland around digestive gland, dark beige in color (Figs 11–12). Hermaphrodite duct thin, long located posterior end of ampulla (Figs 22–23). Ampulla located on female gland, elongated and tubular, about same length as oviduct, inserting distally at junction of oviduct and prostate (Fig. 23). Prostate glandular, connected to female gland, ~1/2 of ampulla’s length. Vas deferens and penis muscular, cylindrical, elongated, ~1/2 of prostate’s width (Fig. 22). Female gland well-developed, rounded, occupying ~40% of reproductive system volume, about same length and twice width as oviduct (Figs 22–23). Oviduct occupying ~1/3 of female gland volume (Figs 22–23). Uterine duct located at base of bursa copulatrix and seminal receptacle, inserted in female gland near oviduct, relatively short, ~1/10 of vagina’s length and same diameter as vagina (Figs 22, 24). Seminal receptacle pyriform, as large as bursa copulatrix, connected to vagina near uterine duct through short stalk (Figs 22, 24). Bursa copulatrix rounded, connected to vagina after seminal receptacle, length ~1/6 of vagina’s length, also through stalk three times longer than uterine duct (Figs 22, 24). Vagina cylindrical, elongated, same width and four times longer than penis, followed ventrally by prostate and located parallel to penis on gonopore (Fig. 24). Gonopore on right side, located in anterior fifth of length of animal from head, between foot and notum (Fig. 2).

Figures 22–27. 

Actinocyclus verrucosus reproductive system. 22. Dorsal whole view, most structures uncoiled, scale: 1 mm. 23. Same, ventral view, scale: 1 mm. 24. Detail of uncoiled female structures, dorsal view, scale: 1 mm. 25–27. Central nervous system. 25. Dorsal view, scale: 1 mm. 26. Ventral view, scale: 1 mm. 27. Detail of buccal and gastroesophageal ganglia, ventral view, scale: 0.5 mm.

Central nervous system (Figs 25–27): located dorsally to odontophore, mostly covered by blood gland. Pair of cerebral and pleural ganglia fused with each other dorsally and ventrally. Pedal ganglia fused with cerebral and pleural ganglia ventrally, not fused among themselves, connected by long and thin pleural commissure. Pedal commissure simple, ½ of length of pleural commissure, both surrounding esophagus and salivary glands (Fig. 26). Buccal ganglia short, located ventrally to odontophore, between radular sac and anterior portion of esophagus, connected to cerebral ganglia through long and slender connective tissue, united to gastro-esophageal ganglia by short connective tissue. Gastro-esophageal ganglia with length ~1/4 of buccal ganglia length, spherical (Fig. 27). Rhinophoral ganglia bulb-shaped, connected to anterior portion of cerebral ganglia (Fig. 25). Dorsal eyes located on cerebral ganglia with short stalk, pedunculated. Statocysts small and iridescent, located ventrally between pedal and pleural ganglia (Fig. 25).

West and Central Indo Pacific [Red Sea (Ehrenberg 1831), Philippines, and Indonesia (Bergh 1878, 1890), East Africa, Malaysia and Japan (Eliot 1904, 1913), Vietnam (Risbec 1956), Hawaii (Kay and Young 1969), Queensland (Willan and Coleman 1984), Western Australia (Wells and Bryce 1993), Madagascar and Marshall Island (Valdés 2002)].

Figures 28–31. 

Actinocyclus verrucosus, radula in SEM. 28. Panoramic view, scale: 100 µm. 29. higher magnification in central region, scale: 40 µm. 30. Outer lateral teeth, scale: 10 µm. 31. Detail of marginal teeth tip, scale: 10 µm.