Aldisa zetlandica, (ALDER & HANCOCK, 1854)

Valdés, Ángel, 2002, A phylogenetic analysis and systematic revision of the cryptobranch dorids (Mollusca, Nudibranchia, Anthobranchia), Zoological Journal of the Linnean Society 136 (4), pp. 535-636 : 579

ALDISA ZETLANDICA ( ALDER & HANCOCK, 1854)

( FIGS 24 , 25 )

Doris zetlandica Alder & Hancock, 1854: 102 .

Type material

SYNTYPE: Shetland Islands, Scotland, one specimen, 11 mm preserved length, leg. J. Alder ( BMNH 1858.5.28.210) .

Additional material

Sixten Bocks , Skagerakexpedition 1937, stn. 24.7B (58∞56¢N, 9∞55¢W), Norway, 50–100 m depth, one specimen, 12 mm preserved length ( SMNHI 1759 ) . North of Hassen , Trondheimsfjord, Norway, 250 m depth, 19 June 1936, two specimens, 3–10 mm preserved length ( SMNHI 1691 ) . Trondheimsfjord , Norway, date unknown, one specimen, 15 mm preserved length ( SMNHI 1540 ) . Trondheimsfjord , Norway, 4 July 1924, one specimen, 14 mm preserved length, leg. B. Hamstrom ( SMNHI 1503 ) .

External morphology

The external morphology of this species has been described in detail by Thompson & Brown (1984). My specimens were preserved, so no data on the living animals were available.

The general colour of the living animals is white to grey-green. The rhinophores and gill are pale yellow. The whole dorsum is covered with conical and elongate tubercles varying in size and shape ( Fig. 24C ). The largest tubercles are situated in the central region of the body. The rhinophoral and branchial sheaths are surrounded by tubercles similar to the rest of the dorsal tubercles. There are six bipinnate branchial leaves, forming a circle. The anal papilla is prominent, situated in the centre of the branchial circle of leaves. The rhinophores are elongate, having 11 lamellae in a 15- mm preserved length specimen.

Ventrally there are two short, blunt and grooved oral tentacles on each side of the mouth opening ( Fig. 25F ). The anterior border of the foot is grooved but not notched.

Anatomy

The posterior end of the glandular portion of the oral tube has six strong retractor muscles ( Fig. 25E ) which attach to the body wall. The oval, muscular buccal bulb has two additional muscles attached. Two short salivary glands connect with the buccal bulb at each side of the oesophageal junction. The buccal bulb is as long as the glandular portion of the oral tube. The labial cuticle is smooth. The radular formula is undeterminable owing to the thin, elongate and overlapping teeth. The radular teeth are very thin and long, having a wide triangular base and a rounded upper edge ( Fig. 24A ). The teeth have a series of 19–22 elongated denticles on their outer and upper edges ( Fig. 24B ).

The ampulla is very short and convoluted, and branches into a short oviduct and the prostate ( Fig. 25C ). The oviduct enters the female gland mass near to its centre. The prostate is tubular, short, folded and granular. It connects with a long duct that narrows and expands again into the ejaculatory portion of the deferent duct. The muscular deferent duct opens into a common atrium with the vagina ( Fig. 25B ). The vagina is long. Near to its proximal end it joins the bursa copulatrix. From the bursa copulatrix leads another duct that connects to the seminal receptacle and the uterine duct. The bursa copulatrix is oval in shape, about three times as large as the seminal receptacle.

In the central nervous system ( Fig. 25D ) the cerebral and pleural ganglia are fused and distinct from the pedal ganglia. There are four cerebral nerves leading from each cerebral ganglion and three pleural nerves leading from each pleural ganglion. There is no separate abdominal ganglion on the right side of the visceral loop. The buccal ganglia are near to the rest of the central nervous system, joined to the cerebral ganglia by two relatively short nerves. Rhinophoral and optical ganglia are present. The pedal ganglia are clearly separated, having three nerves leading from each one. The pedal and parapedal commissures are enveloped together with the visceral loop.

The circulatory system ( Fig. 25A ) consists of a large heart and a small blood gland situated in front of the central nervous system.

Remarks

Aldisa zetlandica ( Alder & Hancock, 1854) was redescribed by Millen & Gosliner (1985) in the framework of a revision of the genus Aldisa . They compared its anatomy and external morphology with that of other members of this genus and concluded that it constitutes a valid species.

Figures

Figure 24. Aldisa zetlandica (SMNHI 1540), SEM images of the radula and dorsal tubercles. A, general view of the lateral teeth; scale bar = 43 Mm. B, detail of the lateral tooth cusps; scale bar = 15 Mm. C, dorsal tubercles; scale bar = 250 Mm.

Figure 25. Aldisa zetlandica (SMNHI 1540). A, general view of the anatomy; scale bar = 1 mm. B, reproductive system; scale bar = 1 mm. C, detail of the ampulla and prostate; scale bar = 1 mm. D, central nervous system; scale bar = 1 mm. E, lateral view of the buccal bulb; scale bar = 1 mm. F, ventral view of the mouth area; scale bar = 0.5 mm.