Dendrodoris atromaculata ( Alder & Hancock, 1864 )

Brodie, Gilianne D., 2004, An unusual dendrodorid: redescription of the tropical nudibranch Dendrodoris atromaculata (Alder & Hancock, 1864) (Anthobranchia: Doridoidea: Dendrodorididae), Zootaxa 503, pp. 1-13 : 3-11

Dendrodoris atromaculata ( Alder & Hancock, 1864)

( Figures 1 A­F & 2A­D)

Synonymy

Doridopsis atromaculata Alder & Hancock, 1864 , p. 129, Pl. XXXI. figs. 20 ­ 24. Dendrodoris atromaculata (Alder & Hancock) . — Eliot 1906a, p. 662; Willan & Coleman 1984, p. 53.

Dendrodoris sp. 2 Lim & Chou 1970, 96­97, figs. 4N & 9C. Dendrodoris singaporensis Lim & Chou 1970 , p. 104.

Comments on Synonymy

The genus Dendrodoris was created by Ehrenberg (1831) for a dorid from the Red Sea, which was neither adequately described nor dissected, and thus the name was neglected for almost a century ( Gohar & Soliman 1967). Later, Alder and Hancock (1864) founded an equivalent genus Doridopsis on Indian Ocean material. Although Dendrodoris was the first genus name used to collectively describe radula­less dorids, the name Doridopsis was often used because its original description was superior. Pruvot­Fol (1930) provided clarification when she showed that Doridopsis was unequivocally synonymous with Dendrodoris . She then advocated the use of the name Dendrodoris (instead of Doridopsis ) because of its chronological priority.

The original description of D. atromaculata was short, based on preserved material, and contained information about external features only. However, the description was accompanied by excellent drawings that leave no doubt that the material examined in the current study is the same species. Features of particular note in the description, that clearly match it to the current material, are the high convex body, overall colour and markings and the irregular “star­like” surface of the tubercles. The combination of these three features being unique within the Doridoidea.

Dendrodoris atromaculata was redescribed by Eliot (1906a) based on reinvestigation of the preserved type specimen. In this description, mention was made of the “remarkable” gill, in which the branchial plumes were described as “not very ample”( Eliot 1906a: 662).

Lim & Chou (1970) depicted, but did not immediately identify, a dendrodorid from Singapore. Their figure 9C, is instantly recognisable as D. atromaculata and their description (as Dendrodoris sp. 2) confirms this with the words “creamy­yellow with round black patches on the mantle” and “ Gills … consisting of 4 quadripinnate branches arranged at right angles to each other … ” (see Lim & Chou 1970: 96­97). In an addendum to the manuscript, Lim & Chou (1970: 104) state that their Dendrodoris sp. 2 equals Dendrodoris singaporensis sp. nov., and that the type material was lodged in the Singapore National Museum. Unfortunately enquires at this institution did not result in location of this material.

Material Examined

India: HOLOTYPE Madras, Waltair; 1 specimen (35–40 mm living length, unknown date in 1853­4, coll. Sir Walter Elliot, ( NEWHM: 1998. H4379), probably intertidal.

Australia, Queensland: Gulf of Carpentaria, 80 km west of Weipa; 1 specimen (42 mm preserved length), unknown date, coll. M. Gormon & C. Lu, (NMV Reg. No. F86791 ) depth 42 m; Rowes Bay, Townsville; 1 specimen (67 mm long, live), 8 August, 1998, coll. G. Brodie (BC, J1); 1 specimen (85 mm long, live), 27 August, 2000, coll. J. Lariscy, (BC Z1); 1 specimen (54 mm preserved length), 16 September, 2001, coll. F. Chouw (BC K2); Myora Spit, North Stradbroke Island; 1 specimen (85 mm long, live), 4 October 1983, coll. R. Willan & O. Kelly (NTM Reg. No. P625).

Fiji: Viti Levu, Nasese, Suva, 1 specimen (37 mm long live), 26 December 1987, coll. G. & J. Brodie, BC D1 (intertidal).

Remarks on Type Material

As stated by Eliot (1906a), the holotype described by Alder & Hancock (1864) was originally collected by Walter Elliot in 1853­4. This specimen is lodged in the Hancock Museum at Newcastle­on­Tyne and registered under the system described by Eliot (1906b). When the material was re­examined by Eliot (1906a: 662) he stated that, although many of the Alder & Hancock specimens were in very poor condition, the holotype of D. atromaculata was “rather well preserved.” This holotype was examined in the current study. The specimen is indeed well preserved and the characteristic black notal markings can be clearly seen despite 150 years of preservation. The specimen has previously been dissected by an anterior dorsal incision. The internal organs are intact and appear in reasonable condition. Although the holotype is small (only 15 mm preserved length) compared with the material examined in the current study, I have no doubt that they belong to the same species because of the distinct external features and markings.

Redescription

The following description is based on the examination of four live specimens [BC ­ D1, J1, Z1 & K2], preserved material (including three specimens dissected and selectively sectioned [BC – J1, Z1 & K2] and two additional specimens [NTM P625, NMV F86791 ] used to supplement the histological investigation of the notum.

Dendrodoris atromaculata is tuberculate, possesses a relatively high body profile and is large and broad in comparison to several other members of the genus that are relatively smooth and elongate e.g. D. nigra (Stimpson, 1855) . The extended crawling length of living adults is up to 85 mm. The body is soft but firm. The dorsum is covered in irregular “star­like” compound tubercules, each consisting of a cluster of finger­like papillae of different heights that taper to rounded apices ( Figure 2A ). The apex of these subsidiary papillae is often pinkish in formalin­preserved material and the central papilla is generally larger than the rest. A microscopic inspection of the remainder of the notum, between the tubercules and along the mantle edge, reveals a covering of simple papillae.

The notum is pale yellow, sometimes darkening to orange centrally. In the Fijian specimen, irregular ginger­brown patches were present, primarily around the notal margin ( Figure 1B). These were not observed in the Australian material but replaced by a more even spread of large, irregularly­shaped black patches ( Figure 1A). When these dark patches occurred close to a compound tubercle the pale apices of the papilla became even more obvious (because of the dark background), thus giving a distorted impression of an uneven distribution of tubercules over the notum.

In one specimen examined from Rowes Bay, small black spots were scattered across the ventral underside of the pale orange notum, but these markings were absent in the remaining specimens. Some dark markings from the dorsal surface were visible ventrally in some preserved material because of the translucent nature of the body tissue.

The fully retractable rhinophores are small and relatively inconspicuous for the size of the animal. The clavus is orange, diagonally lamellate, and quite long proportionally. The stalk is translucent and there is no change in width or angle where the claval lamellae begin.

In all of the material examined, the cream and grey gill consists of four, large branchiae. When the living animal is at rest, these branchiae form a large equilateral cross over the rear of the body (see Figure 1A). The edge of the gill pocket is simple, without a raised rim. The anal papilla is not large or prominent and there is no sign of a gap between the posterior gill branchiae as seen in some other Dendrodoris species. Internally, large gill retractor muscles are found at the gill base and, as documented for D. nigra (see Wägele et al. 1999), these extend down between the posterior lobes of digestive gland before running along the ventral surface of the body cavity.

The notum overlaps the vivid orange foot by a considerable margin. However, the foot itself is large and quite wide (18 mm wide in 37 mm long animal), sometimes with small brown spots on the dorsal surface. The mouth is ventral, within a notch in the antero­ventral surface of the foot. No oral tentacles were observed in either live or preserved material.

General Histology

The large size of specimens precluded serial sectioning of the whole animal. However, sections of the notal tissue were examined from three specimens (two collected fresh at Rowes Bay one year apart, and another from North Stradbroke Island). Bundles of large (~0.3 x 0.04 mm), elongate spicules ( Figure 1C) were located in the notal connective tissue. The notal tissue of all three specimens also contained unusual, microscopic, darkstaining structures forming thin, irregular lines ( Figure 1D). At first these structures were thought to be fungi or bacteria. However, further analysis (using wax histology) gave a negative result for fungi (PAS stain, see methods section) and an inconclusive result for bacteria (Gram stain). In light of these results, I believe these structures to be black pigment within the connective tissue. However, this arrangement of pigment is quite different (very wide­spread throughout the tissue rather than concentrated along the notal epithelial boundary) to that seen in other members of Dendrodoris (e.g. see D. nigra in Wägele et al. 1999: Figures 1A & B).

Ciliated cells were not detected along the notal epithelium, nor were copiously vacuolated epithelial cells, as defined by ( Wägele 1998), visible in the notal epithelium.

notal epithelium, pg = pigment, ps = penial spines, sp = spicule.

Digestive System

A diagram of the anterior part of the digestive system is given in Figure 2B . The ptyaline gland is not distinctly bilobed and the ptyaline duct is relatively long and thin, becoming very narrow distally. Distally, the ptyaline duct and the oral tube are both surrounded by a muscular bulb. The smooth pharynx is relatively long and a pair of rounded, compact salivary glands is present, at the junction of the pharynx and oesophagus, one on either side. The salivary glands are difficult to find in preserved material because their coloration is very similar to the pharynx on which they sit. The oesophagus is broad and bumpy in external appearance, particularly distally. It curves around on itself several times before entering the stomach within the pale brown digestive gland. As is typical of the genus, the stomach is indistinct and totally embedded within the digestive gland. The digestive gland is by far the largest organ in the body cavity, and very distinctly bilobed posteriorly.

The posterior part of the digestive system is simple with the intestine arising from the embedded stomach to emerge from the posterior half of the digestive gland. In only one of the three animals dissected, a pyloric bulb with several folds could be seen proximally ( Figure 2C ). No bulb or folds were seen in the two other specimens. The intestine is narrow, dorso­ventrally flattened and thin walled, it extends over the digestive gland before terminating at the anus. The anal papilla is not swollen and lying among the large gill branchiae remains inconspicuous.

Reproductive System

The vivid orange gonad was well developed in all three specimens dissected and covers most of the digestive gland. The post­gonadial reproductive system is shown in Figure 2D . The system is triaulic with the rounded bursa copulatrix (= gametolytic gland) and elongate receptaculum seminis leading from the vaginal duct. The ampulla is simple and pyriform. The prostate gland is tubular and uniform in appearance. A rounded vestibular gland (~ 2 mm in diameter) is present within the body cavity and attached close to the base of the distal oviduct. The vas deferens is smooth and uniform in width; while the penis is armed with numerous rows of closely packed, elongate spines ( Figure 1E).

Histology of Vestibular Gland

The vestibular gland contains large, rounded acini ( Figure 1F) and the lumen has no epithelial fringe of deep staining microvili known to house bacteria in some other Dendrodoris species (see Klussmann­Kolb & Brodie 1999). Additional wax sections of the vestibular gland were examined for bacteria, but none were detected by the Gram stain technique.

Nervous System

The nervous system is well developed with a ring of fused ganglia surrounding the distal pharynx. The smooth surfaced pharynx can move freely backwards and forwards through this ring. A separate pair of small, cream ganglia is also located well behind this principal ring, very close to the salivary glands. Without close inspection, it is possible that these ganglia could be confused with the salivary glands.

Circulatory & Excretory Systems

The blood gland is irregular in shape and flattened dorso­ventrally. In situ, it lies dorsally over the anterior section of the oesophagus, just posterior to the ring of ganglia described above. A rounded renal syrinx is present and located on the right side, in the posterior­most section of the body cavity.

Occurrence and Habitat

Dendrodoris atromaculata appears to be relatively rare, a fact also noted by Alder and Hancock (1864). The type locality is Waltair, India. The field guide of Willan & Coleman (1984) records D. atromaculata as occurring in Queensland and Western Australia, however, the current study documents for the first time the presence of D. atromaculata in tropical Australia, Fiji and Singapore. The four living specimens observed in the current study were found in very shallow water at the lower section of the intertidal zone, either out in the open within sponge­gardens or under rocks on sheltered muddy reefal areas.

Natural History

No details of egg masses or developmental biology are currently known for this species. The Townsville specimens were found in consecutive years during the month of August. This may well suggest a seasonal occurrence, particularly since the large size and conspicuous appearance of this species should make it relatively easy to find. However, these collections may also be the result of increased accessibility to intertidal sponge gardens during the very low tides at this time of year. One individual found in Rowes Bay was observed to excrete orange faeces, strongly suggesting it had been feeding on an orange sponge. Compared with several other dendrodorids (e.g., D. fumata Rüppell & Leuckart, 1828 ) D. atromaculata is relatively inactive in captivity.

Diagnostic Features

Dendrodoris atromaculata is unique among described members of Dendrodoris being the only member of the genus known to possess finger­like notal papillae, large dense notal spicules and a gill plume that is cross­like. The distinguishing external features of D. atromaculata are its: (a) large size, (b) high body profile, (c) yellow ground colour (generally with black patches), (d) lack of oral tentacles, (e) finger­like papillae distributed over the notum, (f) “star­like” dorsal tubercles and (g) large cross­like gill plume. Internally, the distinctive features are: (h) an unusual distribution of black pigment within the connective tissue, (i) large, dense notal spicules, and (j) distinctive rounded acini within the reproductive vestibular gland.

Discussion of some important and previously used generic features and phylogenetic characters

Ptyaline Glands & Notal Spicules

Possession of ptyaline glands, unique digestive structures found in all members of Dendrodoris , confirmed the generic placement of D. atromaculata . However, the discovery of prominent notal spicules was unexpected since Valdés & Gosliner (1999) and Valdés (2002) found “integumentary” spicules were absent in all species of Dendrodoris included in their phylogenetic analyses of radula­less dorids and cryptobranch dorids respectively. An absence of such spicules can therefore no longer be considered as a generic feature for Dendrodoris .

Pyloric Bulb or Sac

In only one of the three animals dissected was a pyloric bulb (as defined by Wägele et al. 1999: 92) present (see Figure 2C ). These findings confirm the intraspecific variation of this intestinal structure, as previously found by Brodie et al. (1997) [described under the incorrect term pyloric gland], and confirms that the presence and form of a pyloric bulb (or sac) is unsuitable for separating species and for use in phylogenetic analyses.

Vestibular Glands

The vestibular gland microstructure found in D. atromaculata has, to date, been found only in an unnamed species of Dendrodoris from Japan (see Brodie 2002). Relatively few Dendrodoris are known to possess a vestibular gland (e.g., D. nigra , D. goani Rao & Kumary, 1973 ; D. elongata Baba, 1936 ). However, vaginal glands sometimes also called vestibular glands (see Gosliner 1994) are reported from many dorid nudibranchs. Description of these reproductive accessory organs has largely been undertaken at the gross morphological level ( Gosliner 1994) with little description of ultrastructural detail or microanatomy. This fact makes the collective usage of “presence or absence” of such glands, at the gross morphological level in phylogenetic studies, inadvisable because ultrastructural or microanatomical investigation is required to determine their similarity. This conclusion is reinforced by the vestibular gland investigations of D. nigra (see Klussmann­Kolb & Brodie 1999), where an unusual microstructure was found to house symbiotic bacteria, and in similar investigations of D. coronata Kay & Young, 1969 (see Brodie & Klussmann­Kolb 2000) and D. fumata (Rüppell & Leuckart, 1828) (see Brodie 2001). In the latter two species, the vestibular gland is embedded within the body wall making it non­observable by gross dissection. In future comparative studies it is essential that microstructural investigations of these organs, and the surrounding body wall tissues, be undertaken.

Figures

FIGURE 2 A – D. 0 0 Composite drawings of Dendrodoris atromaculata (preserved material) showing: A. compound dorsal tubercule. B. anterior part of the digestive system. C. posterior part of the digestive system. D. arrangement of the post­gonadial reproductive system. amp = ampulla, an = anus, bc = bursa copulatrix, bw = body wall, es = exit to stomach, hd = hermaphroditic duct, int = intestine, mb = muscular bulb, mo = mouth, ng = nidamental gland, np = notal papilla, oes = oesophagus, ot = oral tube, ov = oviduct, pg = prostate gland, ph = pharynx, pb = pyloric bulb (not present in all individuals), ptd = ptyaline duct, ptg = ptyaline gland, rm = retractor muscle, rs = receptaculum seminis, sg = salivary gland, va = vagina, vd = vas deferens, vg = vestibular gland. Scale bars = 2 mm.