Thordisa rubescens BEHRENS & HENDERSON 1981
Creators: name: Valdés, Ángel
Publisher: name: Zenodo
Year: 2002
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Nudibranchia
Discodorididae
Thordisa
Thordisa rubescens

description: THORDISA RUBESCENSBEHRENS & HENDERSON,
1981(FIGS 4F, 21-23)
Thordisa rubescens Behrens & Henderson, 1981: 120– 124, figs 1-7, 13, 14.
Type material
Big Kelp Reef, Paradise Cove, Los Angeles County, California, USA, 17 October 1979, 67 mm preserved length, leg. R. Henderson (CASIZ 015860).
Additional material
Off Los Angeles, Los Angeles County, California, USA., June 1989, one specimen, 47 mm preserved length, leg. R. Fay (CASIZ 068976).
External morphology
The background colour of the living animals is bright red-orange (Fig. 4F). The dorsum is covered with gold flecks forming a halo around the branchial pit, a middorsal stripe and half crescents posterior to the rhinophores. The intensity of this pattern varies between individuals. In some specimens there are small black and opaque white spots. There is a black spot on top of the largest dorsal papillae. The rhinophores are orange to brown, with several irregular white spots and a white apex. The branchial leaves are the same colour as the dorsum. The whole dorsum is covered with soft and inflated papillae of various shapes and sizes (Fig. 21D). The papillae are contracted when the animal is under stress (Behrens & Henderson, 1981), and are surrounded by irregularly protruding spicules. Some larger papillae are randomly distributed among the others. The rhinophoral and branchial sheaths have papillae similar to those on the rest of the dorsum. There are six tripinnate branchial leaves. The anal papilla is situated in the centre of the branchial circle of leaves. The rhinophores are elongate, having 20 lamellae in a 47-mm preserved length specimen.
Ventrally the anterior border of the foot is grooved and notched (Fig. 22F). The oral tentacles are conical.
Anatomy
The posterior end of the glandular portion of the oral tube has six strong retractor muscles (Fig. 22D) which attach to the body wall. The oval, muscular buccal bulb has two large 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 39 ¥ 40.0. 40 in a 47-mm long specimen. Rachidian teeth are absent. The lateral teeth are hamate and lack denticles (Fig. 21A). The teeth from the middle portion of the half-row are larger than those closer to the medial portion of the radula (Fig. 21B). The outermost teeth are smaller and have a number of small denticles (Fig. 21C). The oesophagus is long and connects directly to the stomach.
The ampulla is long and folded (Fig. 22C). It branches into a short oviduct and the prostate. The oviduct enters the female gland mass near to its centre. The prostate is large and flattened. It has two different portions that are clearly distinguishable in colour and texture. The prostate connects with a long duct that expands into the ejaculatory portion of the deferent duct (Fig. 22B). The penis is armed with a series of large hooks, which have a wide and flat base and a curved cusp (Fig. 23A). The muscular deferent duct opens into a common atrium with the vagina. At the vaginal connection with the atrium there are two small accessory glands attached, and two small sacs each containing a short and irregular hard structure (Fig. 23B). At its proximal end the vagina joins the bursa copulatrix. From the bursa copulatrix leads another duct connecting to the uterine duct and the seminal receptacle. The bursa copulatrix is oval in shape, about 15 times as large as the elongate seminal receptacle.
In the central nervous system (Fig. 22E) the cerebral and pleural ganglia are fused and distinct from the pedal ganglia. There are three 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 long nerves. Gastro-oesophageal, rhinophoral and optical ganglia are present. The pedal ganglia are clearly separated, having two nerves leading from each one. The pedal and parapedal commissures are enveloped together with the visceral loop.
The circulatory system (Fig. 22A) consists of a large heart and two blood glands situated in front of and behind the central nervous system.
Remarks
This is a well-known species of Thordisa described from California by Behrens & Henderson (1981). It was included in the analysis because it is the only species described so far that has penial hooks. Other features of this species agree with the original description of the genus (see Behrens & Henderson, 1981).
description: Published as part of Valdés, Ángel, 2002, A phylogenetic analysis and systematic revision of the cryptobranch dorids (Mollusca, Nudibranchia, Anthobranchia), pp. 535-636 in Zoological Journal of the Linnean Society 136 (4) on pages 575-578, DOI: 10.1046/j.1096-3642.2002.00039.x, http://zenodo.org/record/4634200