Dermatobranchus arminus, Gosliner & Fahey, 2011

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 : 288-290

publication ID	https://doi.org/ 10.1111/j.1096-3642.2010.00649.x
persistent identifier	https://treatment.plazi.org/id/761B2D60-485D-E27F-099B-FC8DFE3D3BFE
treatment provided by	Valdenar
scientific name	Dermatobranchus arminus
status	sp. nov.

Treatment

DERMATOBRANCHUS ARMINUS View in CoL SP. NOV.

( FIGS 30C View Figure 30 , 33 View Figure 33 , 34 View Figure 34 )

Dermatobranchus sp. 4 Gosliner, 1987: 11 , figure 214.

Type material: Holotype. SAM A35755, dissected, 14 mm preserved, The Mill, Bakoven, Atlantic coast, Western Cape Province, South Africa, no depth recorded, collected 16.ix.982 by W. Liltved.

Geographical distribution: This species has only been reported from the Atlantic coast of South Africa (present study).

Etymology: The specific name arminus is in reference to the decidedly Armina -like body form of this Dermatobranchus species.

External morphology: The body shape of the living animal ( Fig. 30C View Figure 30 ) is broad, flattened, and narrows at the posterior end. The anterior end of the notum does not form a distinct ridge that separates the notum from the rhinophores and the rest of the oral veil. The foot does not project beyond the distinct mantle margin. There is a series of 27 longitudinal dorsal ridges. The oral veil extends forward and has blunt extensions at the corners. The wide-spaced rhinophores are behind the oral veil. They have a series of longitudinal lamellae on the rounded club. The stalk narrows noticeably. There are up to nine longitudinal hyponotal lamellae under the mantle. There are visible marginal sacs along the mantle edge. The genital opening is situated approximately one quarter of the distance along the body on the right side. The Reproductive system: The reproductive organ arrangement is androdiaulic. The wide hermaphroditic duct leads into the thinner, elongate, tubular ampulla ( Fig. 34 View Figure 34 ). The ampulla bifurcates into the female gland mass via a short oviduct and into the short, narrow prostate. The prostate expands into the long, tubular, yet bulbous penial sheath that is as long as the prostate. The round bursa copulatrix is larger than the ampulla and smaller than the penial sheath. From the bursa, the narrow vaginal duct extends into the equally narrow vagina, which exits into the genital aperture.

anus is situated approximately halfway towards the posterior end of the body. There are hyponotal lamellae at the anterior of the body.

The ground colour of the dorsum and foot is opaque white with a pale tan tint. The dorsal ridges are opaque white and there are dark markings between the ridges that are arranged in a band on the anterior dorsum, almost at the midline. The rhinophore stalk and club are both the same opaque white colour as the body. The oral veil is opaque white with a white margin.

Buccal armature: The jaws are large and thickly cuticularized, with a thick masticatory margin and four rows of triangular, pointed denticles. Part of the radula is shown in Figure 33A View Figure 33 , and the remainder is mounted on a permanent microscope slide. The radular formula of the holotype is 32 ¥ 40.1.1.1.40 ( Fig. 33B View Figure 33 ). The rachidian teeth ( Fig. 33C View Figure 33 ) have a broad base with a large, thick, and pointed central cusp that is substantially wider than the eight flanking denticles on each side. The next two lateral teeth ( Fig. 33D, E View Figure 33 ) have a flat base with a large hookshaped first denticle with four, much shorter and narrower, pointed denticles. The next several lateral teeth are long hooks with at least five pointed denticles. The outer 9–12 teeth ( Fig. 33F View Figure 33 ) are pointed and needle-like.

Remarks: Externally, D. arminus has some features in common with species of Armina , including longitudinal ridges, the wide oral veil, and hyponotal lamellae. This species also has several characteristics in common with species of Dermatobranchus . There is no anterior notal margin and there are no branchial lamellae in D. arminus . In the subsequent phylogenetic analysis, D. arminus is clearly a member of the clade of Dermatobranchus species rather than a member of the Armina clade. The coloration of the new species also has some similarities to described Armina species. For example, several Armina have opaque white longitudinal dorsal ridges, such as A. californica ( Cooper, 1863) , but in that species, the ground colour is pinkish brown and there are no dark markings in between the ridges or arranged in a band on the anterior third of the dorsum. The oral veil of A. californica is narrower and has more greatly pointed corners than the wide, more blunt edged veil of D. arminus . Armina loveni ( Bergh, 1860) has a yellowtan ground colour and Armina juliana Ardila & Diaz, 2002 has a red background colour. Both of these species have different oral veil morphology (anvilshaped) as compared to D. arminus .

Dermatobranchus albineus also has an opaque white ground colour with opaque white longitudinal ridges, but there are no dark markings on the dorsum. That species does not have hyponotal lamellae, whereas D. arminus has these lamellae.

These species also differ in their radular structure. Dermatobranchus albineus has a radular formula of 37–39 ¥ 11–17.1.1. 1. 11–17, whereas the formula of D. arminus is 32 ¥ 40.1.1.1. 40 in a 14 mm specimen. Not only does the number of radular teeth differ markedly, but so does the form of the teeth. Dermatobranchus albineus has wide inner lateral teeth whereas they are narrow in D. arminus . The outer lateral teeth are curved in D. albineus and are much straighter in D. arminus .

These two species have reproductive differences as well. Although both have a bulbous penial sheath, the sheath of D. arminus is longer and more tubular than the wide, more rounded penial sheath of D. albineus . The vagina of D. arminus is much narrower than the bulbous vagina of D. albineus .