Histiomena, ORSTED IN MORCH, 1860

Gosliner, Terrence M. & Fahey, Shireen J., 2011, Previously undocumented diversity and abundance of cryptic species: a phylogenetic analysis of Indo-Pacific Arminidae Rafinesque, 1814 (Mollusca: Nudibranchia) with descriptions of 20 new species of Dermatobranchus, Zoological Journal of the Linnean Society 161 (2), pp. 245-356 : 259-261

GENUS HISTIOMENA ÖRSTED IN MÖRCH, 1860

Type species: Pleurophyllidia marginata Örsted in Mörch, 1860 by monotypy.

HISTIOMENA MARGINATA (ÖRSTED IN MÖRCH, 1860)

( FIGS 6 , 7 )

Pleurophyllidia (Histiomena) marginata Örsted in Mörch, 1860.

Camarga marginata Bergh, 1866: 69 , Marcus & Marcus, 1966: 189.

Histiomena marginata Örsted in Mörch, 1860, Marcus & Marcus, 1966: 189.

Armina convolvula Lance, 1962: 51 , figures 1–6. syn. nov.

Histiomena convolvula ( Lance, 1962) Marcus & Marcus, 1966: 189 . syn. nov.

Material examined: CASIZ 074274 , one specimen, 60 mm, dissected, Isla de Salsipuedes , Baja California, Mexico, 25 m depth, collected 15.v.1985 by L. Dunne. CASIZ 020300 , holotype, 25 km south of San Felipe , Baja California, Mexico, intertidal, 1.iv.1962, collected by F. Wolfson.

Geographical distribution: This species is known from the Gulf of California, Costa Rica, and Panama ( Camacho-Garcia et al., 2005).

External morphology: The body is wide, flattened, and ovate with numerous discontinuous longitudinal ridges composed of small rounded tubercles. The wide foot projects beyond the distinct mantle margin. The oral veil is broad, bilobed with an undulating anterior margin. The foot is broad with tentacular anterior corners. Behind the oral veil are the closely spaced rhinophores. The rhinophores have a series of longitudinal lamellae on the rounded club, which has a rounded apex. The stalk widens as it enters the dorsal cavity and there are no lamellae on the stalk. A caruncle is situated just posterior to the rhinophores. Marginal sacs are not visible along the mantle edge. Under the mantle there are at least 30 branchial lamellae at the anterior end of the body and numerous, wavy rows of hyponotal lamellae at the posterior end. The genital opening is situated in the anterior third of the body wall and the anus opening is approximately half way along the body.

The ground colour of the dorsum and foot is deep brown with numerous opaque white spots. The mantle edge is orange with opaque white spots. The rhinophores are brown with a lighter apex. The oral veil has an orange margin and the dorsal surface of the foot has orange marginal and purple submarginal bands.

Buccal armature: The jaws are large and thickly cuticularized ( Fig. 6A ), with a thick masticatory margin and multiple rows of pointed denticles along the basal portion of the margin (the portion opposite the hinged end of the jaws). The radular formula is 49 ¥ 106.1.1.1.106 ( Fig. 6B ). The rachidian teeth ( Fig. 6C ) are narrow with an elongate, rounded central cusp and eight to nine flanking denticles on each side. The flanking denticles are all the same thickness. The inner lateral tooth is posteriorly directed and narrow without denticles. The next several lateral teeth ( Fig. 6D ) are hook-shaped and lack denticles. The middle lateral teeth have a series of fine denticles along their inner face. The outer lateral teeth ( Fig. 6E ) lack denticles.

Reproductive system: The reproductive organ arrangement is androdiaulic. The ovotestis is large and ovoid. The long hermaphroditic duct leads from the ovotestis into the very long and coiled ampulla ( Fig. 7 ). The ampulla bifurcates near the posterior end of the female gland mass into the short, narrow prostate and the short oviduct. The prostate expands into the very large, bulbous, penial sheath. From the large, round bursa copulatrix the narrow vaginal duct emerges, coils once, and continues to a narrow vagina that exits adjacent to the penial opening.

the branchial lamellae are likely to be preservational artefacts and/or differences in observation and description. With the rediscovery of living specimens of Histiomena from Costa Rica (near the type locality of H. marginata ) with coloration identical to specimens from Mexico, the likelihood that these two species are synonymous is greatly increased and we here consider H. convolvula to be a junior synonym of H. marginata .

Figures

Figure 6. Histiomena marginata Örsted in Mörch, 1860, Buccal armature, CASIZ 074274. A, jaw; B, whole radula; C, central portion of radula; D, middle lateral teeth; E, outer lateral teeth.

Figure 7. Histiomena marginata Örsted in Mörch, 1860, Reproductive system, CASIZ 074274. a, ampulla; bc, bursa copulatrix; fg, female gland mass; ot, ovotestis; p, penis; pr, prostate; v, vagina; vd, vaginal duct. Scale bar = 2.0 mm.