Aeolidiella drusilla Bergh, 1900

Miller, M. C., 2001, Aeolid nudibranchs (Gastropoda: Opisthobranchia) of the family Aeolidiidae from New Zealand waters, Journal of Natural History 35 (5), pp. 629-662 : 647-652

Aeolidiella drusilla Bergh, 1900

(®gures 6±9)

Aeolidiella drusilla Bergh, 1900: 233 ±235; Bergh, 1905: 222 ±223; Suter, 1913: 581 ±582.

Morphology (®gure 7A,B)

Extended length up to 34 mm. Body long, broad, depressed, with a low pericardial swelling, wide head, and very short tail. Foot broader than visceral part of body, curved in front, anterior corners extended as slender, tapered processes in length approximately one-third of maximum width of foot (®gure 7A); foot tapers gradually then abruptly to a point. Orals short, stout at base, tapering to a rounded tip, approximately one-thirteenth of body length, jutting sideways from head. Rhinophores simple, slightly shorter than orals, wide at base, broadly rounded at apex: eyes visible immediately behind them. When extended largest cerata long, cylindrical with a short bulbous basal section and tall conical apex; at rest shorter, slightly ¯attened towards base; cnidosacs large (®gure 7C). Cerata completely cover body except middle region behind rhinophores which extends approximately onequarter of body length; in up to 27 single rows, maximum of 17 in a row (rows 5 and 6), rows curving forwards, strongly so, anteriorly, ®rst two rows continuing forwards beyond rhinophores (®gure 7B). Anus and renal pore lie between rows 4 and 5, former near top of space, latter approximately one-third of way down. Reproductive apertures just below and between lower ends of rows 5 and 6.

Colour

Body wall translucent: head, body, basal third of oral tentacles (upper surface only), rhinophores speckled lightly with purple pigment. Opaque white on distal two-thirds of orals (upper surface only) extending as a line to base and continuing across front of head, on distal two-thirds of rhinophores and anterior face of cerata from just below cnidosac to base. Digestive gland diverticula apricot, visible through posterior face of cerata.

Alimentary system (®gure 7C±F)

Oral tube short, wide leads into long, ovate (from above) buccal bulb. Oral glands paired, long, wide, cylindrical, regularly looped (®gure 7E), lying at sides of buccal bulb. Salivary glands, lying about middle of stomach, large, weakly lobed and sacculate (®gure 7F); a narrow duct runs forward to enter buccal bulb at sides of oesophagus. Stomach large. Lateral pre-cardiac stomachal ducts of digestive gland fork and two prongs run obliquely forwards to base of oral tentacles. Median post-cardiac duct very wide. First pairs of lateral ducts fork like pre-cardiacs but prongs do not reach as far forwards. Rest of ducts single. Ventral and forward curvature of secondary lateral ducts lessens towards tailÐanterior pairs of primary ducts opposite in origin but gradually become alternate posteriorly. Diverticula producing secondary lateral ducts project a short distance mesially: digestive (ceratal) diverticula arise in a single row. Intestine arises immediately behind right pre-cardiac duct curving around in an arc to open dorso-laterally.

Buccal armature

Radula formula of a 34 mm specimen 19 (including 2 developing teeth) Ö 0.1 .0. Teeth broad, curved, pectinate, widely notched in centre, large median cusp present (®gure 8A). Denticles lying in notch short, those on lateral lobes tall at summit reducing in size to each side. Jaws large, ovate, highly convex, thickened in front with low, curved articulatory ridge at hinge (®gure 8C). Masticatory process fairly broad, tip extending as a fairly long process; posterior margin uneven, cutting edge thickened and smooth.

Kidney (®gure 7D)

Broad, dorso-ventrally compressed though still fairly deep; complexly rami®ed dorso-laterally. Extends forwards as a lobe on each side of pericardium, left side to left pre-cardiac duct of digestive gland, right almost to where oesophagus joins stomach. Renopericardial duct lies level with centre of pericardium, renal duct a little behind it.

Reproductive system (®gure 9A)

Gonad extends rearwards to approximately thirteenth pair of lateral ducts of digestive gland. Gonad lobed, each lobe consisting of many follicles. Each follicle consists of a proximal sac (male) with one to ®ve distal acini (female); follicular ducts, as many as 40, join to form each lateral duct, latter in turn joining median hermaphrodite duct. At anterior end of gonad hermaphrodite duct widens to become ampulla, very long, irregularly looped and coiled. Ampulla narrows at anterior to form common duct which soon bifurcates. Upper branch of common duct vas deferens, lower oviduct, latter widening (fertilization chamber), then constricting and dividing as a T-junction, left arm leading to large bursa copulatrix, right to female glands: vas deferens soon enlarges into a prostatic section, ends of this smooth, middle region sacculate on one side. Penis long, tongue-like, tapering quite abruptly to rounded tip; unarmed (®gure 9B).

Localities and habitats

New Zealand, the North Island. East Coast: Parengarenga Harbour , Paua, 30 1 specimens amongst growth on wharf piles, 20 October 1992 (M. S. Morley); Bay of Islands, NW Okahu (or Redhead) Island, one specimen at 10.5 m, 8 December 1985 (S. de Clive Cook); Whangamumu Harbour, whaling station, two specimens under rocks 1 m below low tide, 11 December 1991 (M. S. Morley); Leigh, Goat Island Bay , Waterfall Reef, one specimen on coarse gravel beneath a stone at 9 m, 29 December 1976 (collected by R. C. Willan); Waiwera , south side of Mahurangi Island , one specimen on under surface of a rock at low water, 27 January 1960; Great Barrier Island , Sandy Bay near Tryphena , two specimens on rock at 4.5 m, 4 January 1986; Wellington, Lyall Bay , four specimens under stones at extreme low tide `Ecklonia ’ zone, 27 December 1947 ( Museum of New Zealand collection). West Coast: South Taranaki Bight , 33 km SW of Oaonui, Maui `A’ Platform , on braces at level 4, 57±58 m, 1977±79. The South Island , East Coast : Kaikoura , one specimen, August 1962 ( Pilgrim collection); Christchurch , Heathcote Estuary , one specimen on Ulva , 24 August 1954 ( Pilgrim collection E.I); Banks Peninsula , Menzies Bay , one specimen, 1946 ( Pilgrim collection M.B.I); Otago Harbour , Portobello reef, one specimen, November 1952 ( Museum of New Zealand collection), Aquarium Point , under stones and rocks in the sublittoral fringe, two specimens on 16, one on 17 August 1962. Chatham Island , Port Hutt , headland to East (Napper Point), two specimens under a rock 0.5 m below low tide, 5 February 1989 (M. S. Morley) .

Breeding

One spawn band, eggs pink, near specimens collected at Aquarium Point, Portobello on 16 August 1962; spawn laid in captivity by one of the specimens collected near Port Hutt on 5 February 1989 (M. S. Morley).

Types

Not designated: one specimen from French Pass , opposite d’Urville Island, the South Island, New Zealand ( Bergh, 1900) .

Remarks

There is little doubt that the specimens examined by me belong to Aeolidiella drusilla Bergh. As far as Bergh’s original description allows there is much agreement on size and form of the body, cerata and the arrangement of them, oral and salivary glands, radula and jaws. The only marked diOEerence is the position of the anus and renal pore, along, not down, the side of the body. Bergh (1900) states that they lie between ceratal rows 5 and 6 whereas in the specimens described here they lie between rows 4 and 5. However, this diOEerence can be explained as intraspeci®c variation. The position of the anus does vary in this species. The specimen collected at Kaikoura seemingly has the anus within row 5; in fact it is con®ned between rows 4 and 5, the lower part of what seems to be 5 is an additional posterior branch of row 4, the true lower part of 5 bending rearwards behind the anus. Bergh (1905) tentatively named three specimens collected at Waru Bay, Ceram as A. drusilla . There is only one feature which could be used to connect these specimens with the one originally describedÐthe presence of elongate oral glands. Engel (1925) pointed out that the description of the radular teeth is unclear, and I agree, a detailed account and ®gures of the teeth (the one provided could be of any tooth) being vital when the soft parts have been spoilt by preservation. Aeolidiella drusilla occurs in Australia having been found at Westernport, Victoria, in May and June, 1983 (reported by Bob Burn in a letter to me dated 16 February, 1985). Unfortunately, the New Zealand and Australian specimens cannot be compared as the latter have yet to be described.

Specimens from Auckland ± Northland appear somewhat diOEerent externally from those taken from southern North Island and further south. When crawling the northern animals have a much neater bearing, the cerata all being held in the same curved shape (see Powell, 1979, pl. 51, ®g. 7); also, the cerata are shorter, the digestive diverticula are grey, and there is dense yellowish brown pigment on the cerata of the ®rst four or ®ve rows giving the impression of a light coloured ruOE (as in Aeolidiella alderi Cocks , but in this species it is due to the lack of surface pigment on the cerata of the ®rst two rows). The larger southern animals are often untidy looking in that the cerata are held in all sorts of attitudes even when crawling, and they have apricot coloured ceratal diverticula and no ruOE. There are no obvious diOEerences in morphology and anatomy.

Comparing Aeolidiella drusilla with other congeneric species, it is closest in external appearance to Aeolidiella glauca (Alder and Hancock, 1845) . However, A. drusilla has shorter oral tentacles and rhinophores and the opaque white surface pigment is scattered evenly where it occurs, unlike A. glauca in which it is present as spots, mottling or blotches. In A. drusilla the radular teeth have a wide as well as deep median notch with shorter denticles on each side of the cusp, and the cerata in single rows: A. glauca has teeth with a narrower notch and two lines of cerata distally in the anterior, longer rows. Since its original description, A. drusilla has been recognized as a distinct species ( Engel, 1925; Marcus, 1955; Marcus and Marcus, 1970; Gosliner and Gri ths, 1981; Gosliner, 1985). However, because of the incomplete description, very few attempts have been made to compare A. drusilla with related species. Marcus and Marcus (1970) mentioned some features of it when discussing the determination of a specimen of A. indica from Madagascar. It is puzzling why this match was made as the two species are easily distinguished from each other.