Acra Zoologica (Stockholm), Vol. 71, No. I , pp. 3S3.5, 1990 Printed in Great Britain

0001-7272/90$3.oO+ .oO Pergamon Press plc

0 1990 The Royal Swedish Academy of Sciences

The Anatomy of the Circulatory System in the Arminid Nudibranch Armina maculata Rafinesque, 1814 (Gastropoda: Opisthobranchia)

Francisco Jose Garcia and Jose Carlos Garcia-Gomez Laboratorio de Biologia Marina (Zoologia), Departamento de Fisiologia y Biologia Animal, Facultad de Biologia, Apdo. 109.5, Avda. Reina Mercedes s/n, E-41080 Sevilla, Spain

(Accepted for publication 19 June 1989)

Abstract

Introduction

Garcia, F. J . & Garcia-Gomez. J . C. 1990. The anatomy of the circulatory system in the arminid nudibranch Armina macularu Rafinesque, 1814 (Gastropoda: Opisthobranchia).-Acta. zool., Srockh. 71: 33-35,

In Arrnbiu muculum the heart lies anteriorly and has a large muscular ventricle and a delicate auricle running obliquely to the antero-posterior axis. The auriculoventricular valve and the aortic valve are disposed at the anterior end o f the auricle and ventricle respectively. The aortic trunk is located just anterior to the ventricle and gives o f f several arteries. which extend through the wholc body. The main arteries are: the cephalic artery (to the buccal apparatus); the posterior artery (to the notum. digestive glands. ovotestih and renal chamber): the pedal artery (to the foot): and the genital arteries (supplying the different organs of the reproductive system).

These data are compared with thohe of other arminacean species.

Fruncisco JosP Gurciu and Jose Curlor Gurciu-Gdmez. Luboratorio de Biologia Marina (Zoologia). Departamento de Fisiologia y Biologia Animal, Faculrad de Biologia, Apdo. 1095, A vdu. Reitiu Mercedes .slti, E-41080 Sevillu. Spuiti.

Exhaustive anatomical knowledge is necessary to under- stand the complex phylogenetic relationships of the nudi- branch molluscs. With that aim, we decided to carry out a series of anatomical studies (some oriented towards taxonomy) (Garcia & Garcia 1984: Garcia & Cervera 1985; Garcia & Garcia 1985; Garcia et al. 1986, 1988; Cervera & Garcia-Gomez 1988) in order to revise and complete the existing information and/or to describe new aspects of the functional anatomy.

The anatomy -of the suborder Arminacea has been relatively neglected. The scarce data that have been pub- lished are almost exclusively from the last century. Some species are large enough (several centimetres in length) to make dissections, but the disposition of the organs is very complicated. This has led to discrepancies between anatomical descriptions. Therefore, the circulatory system of Armina maculata is described to clarify some differ- ences in the interpretation of the circulatory system in the suborder Arminacea and to expand the knowledge of the anatomy of this suborder.

Material and Methods

The animals were collected off the Strait of Gibraltar, Spain. during the summer of 1980 at 24 m depth (one specimen, 10 cm in length) and Banyuls. France, during the summer of 1984 at 43 m depth (four specimens, 6 7 cm in length), and preserved in 4-S% formaldehyde. Dissections were made under a stereomicroscope using fine forceps and needles. Details of vessels and sinuses were observed by staining the animals with aqueous methylene blue. Some of the small vessels were observed by injection of a bubble of air within the ventricle and biggest arteries and then examining its course into the vessels branching throughout the animal's body.

Results

General anatomical aspects

Armina maculata is an arminid with a large pustuled notum extending in front of the rhinophores as an oral veil (Fig. 1). Beneath the notum along both sides there are gill folds and lamellae containing outgrowths of the digestive gland (Fig. 2). The buccal mass is large, approaching in its form that of Tritonia. The stomach curves to the left side; from here arises a big digestive gland which turns downward and gives off several diges- tive ducts directed toward the notum and lamellae. On the right side the stomach leads into the intestine running on to the anus. The big ovotestis lies above the digestive gland and the other reproductive organs are located in front of that.

Pericardium

The pericardium is a spacious cavity lying anteriorly on the reproductive system, oesophagus and stomach (Fig. 3). The heart has a big and muscular ventricle and delicate auricle running obliquely to the antero-posterior axis. The auricle connects to the ventricle through the auriculoventricular valve, which has two flaps projecting into the ventricle from the auricle. Another valve is located at the anterior end of the ventricle (aortic valve), projecting as a dorsal flap into the aortic trunk (Fig. 7).

Blood flows from the branchial lamellae to the auricle through the lateral pallial vessels.

33

I I olio an ne I ad I ed

Circulatory System of Armina 35

Arterial circulation

The ventricle is just behind a large aortic trunk which continues obliquely forward and dips toward the vaginal duct. From the aortic trunk several arteries arise:

(1) The cephalic artery (Fig. 7, ca.). This arises from the left side of the aortic trunk and extends to the pos- terior surface of the buccal apparatus. At this point it plunges downward and passes ventrally along the buccal mass (buccal artery, Fig. 5, ba). This artery gives off two branches to the odontophoral sinus and one branch to the buccal sinus. At the level of the outer lips the cephalic artery bifurcates (oral arteries, oa), one branch running to the right and the other to the left on the oral tube (Figs 5, 6, oa).

(2) The posterior artery (Figs 3 .7 pa). This passes from the aortic trunk to the anterior end of the ovotestis. I t continues posteriorly as a median longitudinal vessel along the dorsal surface of the visceral mass. At the level of the posterior end of the ovotestis the posterior artery turns upward to the dorsal surface of the posterior diges- tive chamber (Fig. 3) where it branches out. Also, many branches arise from the posterior artery to cover nearly the whole surface of the ovotestis; several branches con- nect with the renal chamber (Figs 3, 8) and others go into the lateral notum and ramify between the digestive ducts and the lamellae.

(3) The pedal arteries (Figs 3, 4). Two pairs originate from the posterior lateral branches of the posterior artery [indicated as ( I ) and (2) in Figs 3 and 41. They plunge ventrally toward the foot. The anterior pedal arteries (apa) extend forward and branch out. The posterior pedal arteries @pa) continue backward and give off several lateral branches; the two posterior pedal arteries are con- nected by three transverse vessels (Fig. 4).

(4) The genital arteries (Fig. 7). Several vessels orig- inate from the aortic trunk, supplying the different organs of the reproductive system.

Discussion

The circulatory system of the arminaceans is almost unknown. Only Bergh (1866) has given some data for several arminid species. In Armina tigrina Bergh (1866) described five or six veins connecting laterally to the auricle, which come from the dorsal and lateral dermis, and also two dorsal veins which connect to the posterior end of the auricle. In A . maculata we have seen only one pair of veins, coming from the lamellae and connecting laterally to the auricle.

Although the size of A . tigrina and A . maculata speci- mens are large enough to make dissections, the anatom- ical study of their circulatory system is not easy. This could explain the very different anatomical interpret- ations. Ballesteros (1983) described the heart in A . tigrina

and A . maculata as being located at the posterior end of the visceral cavity, from which originates the cephalic artery. This artery turns right connecting to the renal chamber. This is neither in accordance with the obser- vations of Bergh (1866) nor with our own observations. What Ballesteros described as the kidney is identical to the structure identified as the ventricle by Bergh and us; our study shows that the structure Ballesteros called the heart is a posterior digestive chamber. Hence, the cephalic artery and its connection to the renal chamber described by Ballesteros are the posterior artery and its origin from the aortic trunk.

Compared to other genera of arminaceans, A . maculata presents some marked differences. Thus, in the genus Jarzolus, Trinchese (1881) described a big posterior dorsal vein and two anterior dorsal veins connecting to the aur- icle. In Telarma arztarctica, Odhner (1934) described a big sinus in front of the ventricle that gives off an aortic trunk to the right and left. These aortic trunks give rise to the anterior and posterior aorta respectively. This arrange- ment is somewhat similar to the aeolidacean nudibranchs.

Acknowledgement

We would like to thank Dr. Philippc Bouchet of the Musi.um National d'Histoire Naturelle dc Paris who provided the specimens collected in Banyuls.

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