Armina magna Baba 1955

ARMINA MAGNA BABA, 1955 (FIGS 1A, 2, 3) Armina magna Baba, 1955:22, text figures 31, 32, pl. 11, figures 29, 30. Material examined: CASIZ 173357, one specimen dissected, 60 mm preserved, station (stn) T39, muddy sand 100–138 m, Cervera Shoal, west of Pamilacan Island, Bohol, Philippines, collected 6.vii.2004 by T. Gosliner, Y. Camacho, J. Templado, M. Malaquias, M. Poddubetskaia. CASIZ 174127, OT 607, one specimen, 130 mm alive, off San Isidro, Panglao Island Philippines, 9°33.4′N, 123°49.6′E – 9°33.8′N, 123°51.5′E, mud and fine sand, stn T10, 117– 124 m depth, collected 15.vi.2004 by T. Gosliner, Y. Camacho, J. Templado, M. Malaquias, M. Poddubetskaia. Geographical distribution: This species is known only from Sagami Bay, Japan (Baba, 1955) and Panglao, Bohol Island, and Cervera Shoal, Philippine Islands (present study). External morphology: The body shape of the living animal (Fig. 1A) is broad, flattened, and narrows at the posterior end. The wide foot projects beyond the distinct mantle margin and has a large ovoid pedal gland on its posteroventral surface in the larger specimen examined. The pedal gland is absent in the smaller specimen. There are up to 22 prominent longitudinal dorsal ridges with some additional shorter ridges in between, over the surface of the notum. The blunt oral veil extends forward and is rounded at the sides. Behind the oral veil are the closely spaced rhinophores. The rhinophores have a series of longitudinal lamellae on the rounded club. 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 36–56 branchial lamellae at the anterior end of the body and at least 52–60 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 black and the dorsal ridge crests are pale yellow to opaque white. The mantle edge is bright yellow. The rhinophore lamellae are black and the stalk has black stripes perpendicular to the lamellae. The anterior hyponotal lamellae have dark spots and the hyponotal respiratory leaves have dark edges. The ventral surface of the oral veil, the foot sides, and the foot sole has dark mottled blotches and the anterior foot edge is white. Buccal armature: The jaws are large and thickly cuticularized (Fig. 2A), with a thick masticatory margin and approximately seven rows of pointed denticles along the entire margin of each jaw (Fig. 2B). The radular formula (CASIZ 173357) is 40 ¥ 8.36.1.1.1.36.8 (Fig. 2C). The rachidian teeth (Fig. 2D) are broad with a large, spear-shaped central cusp and four to five flanking denticles on each side. The flanking denticles are all of the same thickness. The inner lateral teeth have a narrow base and a cusp that is posteriorly directed. The cusp has three to four triangular denticles and two to three smaller secondary denticles along its outer side. The next 36 lateral teeth (Fig. 2E) are hook-shaped with up to three pointed denticles on the under side. The number of denticles decreases to one denticle on the teeth towards the outer edge of the radula. The outer approximately eight lateral teeth (Fig. 2F) are also hook-shaped, with no denticles and the outermost tooth is smaller than the other teeth. Reproductive system: The reproductive organ arrangement is androdiaulic. The long hermaphroditic duct leads from the ovotestis into the tubular ampulla (Fig. 3). The ampulla bifurcates near the distal end of the female gland mass into the well-defined albumen gland and into the very long, multi-coiled prostate. The prostate expands into the long, bulbous penial sheath. From the large, ovoid bursa copulatrix the very long, narrow vaginal duct emerges and continues to a wider vagina that exits adjacent to the penial opening. At the distal end of the vagina is a muscular collar. Remarks: Armina magna is known only from the original description (Baba, 1955) from Japan. The external morphology, radula, and jaws were described but the reproductive system was not. One of its most distinctive features, in addition to its colour pattern, is the large ovoid pedal gland that is also present in the larger specimen of the Philippine material examined here. The incomplete orange margin of the oral veil is consistent between Baba’s and the present material. The rachidian teeth of the Japanese material had six to seven denticles that extended well onto the median cusp, whereas the present material has five to six denticles that do not extend on to the cusp. The other radular teeth are very similar in their denticulation in specimens from both localities. The differences between Baba’s and the present material are relatively minor, and there is little doubt that they are conspecific. Externally, A. magna closely resembles A. californica (Cooper, 1863) and Armina paucifoliata Baba, 1955. All of these species have a very dark background colour and light coloured dorsal ridge crests and mantle margin. The dorsal ridges of A. californica are white, whereas those of A. magna are white to yellow and the ridges of A. paucifoliata are light yellow. The white mantle edge of A. californica is much wider with more solid pigmentation than the narrow, uneven white pigment along the edge of A. paucifoliata. Armina magna has a yellow to orange mantle edge. For further morphological details of A. californica see the Remarks section of A. paucifoliata. The oral veil of A. magna and A. paucifoliata differs (Fig. 1A, B). That of A. magna has blunt, rounded front corners, whereas the veil of A. paucifoliata is anvil-shaped and pointed. The caruncle of A. magna is wider than that of A. paucifoliata. Furthermore, A. magna has an ovoid pedal gland whereas A. paucifoliata has a linear one. The radular morphology differs between these species. The lateral teeth of A. magna (Fig. 2D) have long, pointed denticles that protrude from under each hook-shaped tooth. In contrast, the denticles of A. paucifoliata (Fig. 4D) are shorter and are attached at the outer sides of each lateral tooth. There are up to 15 smooth outer lateral teeth in A. paucifoliata and up to eight smooth teeth in A. magna. The major reproductive system difference between these two species is the presence of the muscular collar on the vagina of A. magna. Armina magna (Fig. 3) also has a shorter, wider penis than the elongate slender penis of A. paucifoliata (Fig. 5).Published as part of 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, pp. 245-356 in Zoological Journal of the Linnean Society 161 (2) on pages 253-256, DOI: 10.1111/j.1096-3642.2010.00649.x, http://zenodo.org/record/549415