Dermatobranchus caesitius Gosliner & Fahey 2011, SP. NOV.
Creators: name: Gosliner, Terrence M.
name: Fahey, Shireen J.
Publisher: name: Zenodo
Year: 2011
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Nudibranchia
Arminidae
Dermatobranchus
Dermatobranchus caesitius

description: DERMATOBRANCHUS CAESITIUS SP. NOV.  (FIGS 30D, 38, 39)  
 Dermatobranchus sp. 2 Gosliner, 1987:110, figure 212. Dermatobranchus sp. 5 Gosliner, Behrens & Valdés,   
2008:309, bottom photo.  
 Type material holotype: CASIZ 174137, 18 mm preserved, Umgazana, Indian Ocean, South Africa, intertidal zone, collected 23.iv.1982 by T. Gosliner. Paratypes: SAM A35750, 14 specimens, 10–20 mm preserved, three dissected, Umgazana, Indian Ocean, South Africa, intertidal zone, collected 23.iv.1982 by T. External morphology: The body shape of the living animal (Fig. 30D) is elongate, flattened, and narrows at the posterior end. The wide foot does not project beyond the distinct mantle margin. There is a series of broken longitudinal dorsal ridges with dorsal tubercles clustered between the ridges. The oral veil extends forward and is pointed at the corners. The rhinophores are situated behind the oral veil. They have a series of longitudinal lamellae on the rounded club. The stalk narrows noticeably. There are no lamellae on the stalk. Marginal sacs are readily visible along the mantle edge. There are no branchial or hyponotal lamellae. The genital opening is situated approximately one-quarter of the way along the body side and the anus is situated about halfway along the body side.   
The ground colour of the dorsum, the dorsal ridges, and the foot is opaque blue with a white mantle margin containing brown regularly spaced spots and an orange edge. The dorsal ridges have a yellowish tint particularly noticeable along the median. The rhinophore stalk is the same blue colour and the club is black. The oral veil is blue with opaque white along the margin.  
 Buccal armature: The jaws are large and thickly cuticularized (Fig. 38A), with a thick masticatory margin and eight to ten rows of simple, triangular, pointed denticles (Fig. 38B). The radular formulae of the two paratypes (SAM A35750) are 27 ¥ 21.1.1.1.21 and 28 ¥ 18.1.1.1.18 (Fig. 38C). The rachidian teeth (Fig. 38D) are moderately broad and laterally directed, with a large, pointed central cusp that is twice as long as the 13–16 flanking denticles on each side. On the outer edge of each rachidian tooth is a broad, rounded cusp that is longer than the adjacent denticles, but shorter than the central cusp. The inner lateral teeth (Fig. 38D) are broad with a pointed first denticle that is longer than the following 10–14 long, pointed denticles. The next 16–19 lateral teeth (Fig. 38E) are elongate hooks with up to 5–11 denticles, the number decreasing on the teeth furthest from the rachidian. The outer two teeth (Fig. 35F) have no denticles and the outermost is smaller than all the other lateral teeth.   
 Reproductive system: The reproductive organ arrangement is androdiaulic. The hermaphroditic duct is long and narrow and leads into the elongate, pear-shaped ampulla (Fig. 39). The ampulla bifurcates near the centre of the female gland mass into a short oviduct and the short, tubular prostate. The prostate expands into the large, bulbous, muscular penial sheath. The round bursa copulatrix is smaller than the ampulla and the same size as the penial sheath. From the bursa, the narrow vaginal duct extends into a slightly wider vagina, which exits into the genital atrium.   
 Remarks: Externally, D. caesitius (Fig. 30D) looks most similar to D. earlei (Fig. 42C). Both species have a pale blue overall appearance with a white mantle margin and white oral veil and have rhinophores with black pigment on the club. However, D. earlei has large brown blotches scattered on the dorsum and along the mantle margin and an orange margin of the oral veil.   
 These two species differ markedly internally, as well. For example, the radular formula of these species is quite different. The formula of D. caesitius is 27–28 ¥ 18–21.1.1.18–21, whereas that of D. earlei is ¥9.1.1.1.9, with an unknown number of radular rows. The rachidian tooth of D. caesitius (Fig. 38D) has a narrower base and is more claw-shaped, with a much longer central cusp than in D. earlei (Fig. 48C).   
 There are reproductive system differences as well. The penial sheath of D. caesitius (Fig. 39) is much shorter and wider than that of D. earlei (Fig. 49). The prostates of D. earlei and D. caesitius are similar in length but slightly longer in D. earlei.   
 The formula and shape of the radular teeth of D. caesitius are similar to those found in D. fasciatus (Figs 50–52). Both species have a wide rachidian tooth with numerous fine denticles and an acutely pointed, elongate central cusp. The inner lateral tooth of D. caestitius is broader and laterally directed whereas that of D. fasciatus is narrower and more posteriorly directed. The middle lateral teeth of D. caesitius have 5–11 denticles whereas those of D. fasciatus have 15–17 denticles.   
 Dermatobranchus caesitius has a blue colour with prominent irregular longitudinal ridges on the notum. In contrast, D. fasciatus is white with a brown transverse saddle and irregular tubercles on the notum. The reproductive anatomy also differs consistently. In D. caesitius, the penial sheath is much wider than the prostate, whereas in D. fasciatus (Fig. 53) they are approximately the same diameter.   
 Several other Dermatobranchus species have reproductive similarities to D. caesitius, such as a large, bulbous penial sheath and slightly expanded vagina. These species include D. albus and D. semilunus. However, neither of these species have similar radular or external morphology.
description: 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 294-296, DOI: 10.1111/j.1096-3642.2010.00649.x, http://zenodo.org/record/5494156