Tyrinna evelinae ( Marcus, 1958 )

Schrödl, M. & Millen, S. V., 2001, Revision of the nudibranch gastropod genus Tyrinna Bergh, 1898 (Doridoidea: Chromodorididae), Journal of Natural History 35, pp. 1143-1171 : 1160-1165

Tyrinna evelinae ( Marcus, 1958)

(®gures 7±11)

Cadlina evelinae Marcus, 1958: 18 ±21; Collier and Farmer 1964: 380 ±381; Marcus and Marcus 1967: 168 ±169; Thompson 1980: 76 ±77; Edmunds 1981: 176 ±179; 1982: 517.

Tyrinna evelinae: Rudman 1984: 244 ±246; MuniaõÂn et al. 1996: 265±273.

Material examined. Cadlina evelinae det. Thompson, 1980: Three specimens, BMNH, Jamaica. Tyrinna evelinae: Two specimens, ZSM nos 19990006, 19990007, BahõÂa de los Angeles, Gulf of California, Mexico, 5 m depth, 29 June 1996, collected by Sandra Millen, Hans Bertsch, Mike Miller. Two specimens (one ZSM no. 19990005; the other in the Universidad Nacional Mayor de San Marcos , Lima), El Rubio, south of Tumbes, Peru, rocky coast, 20 September 1974, collected by Carlos Paredes.

External morphology. The specimens from the Gulf of California are whitish with orange±red dots all over the notum (®gures 7A,B). There are no data on the living Peruvian specimen; in preserved condition no traces of orange colour can be detected. The specimens from the Gulf have preserved lengths of 18 and 11 mm, and widths of 10 and 6 mm. The preserved Peruvian specimen has 13 mm in length and 7 mm in width. The notal surface is slightly folded in preserved specimens and bears some scattered bosses. These low mammillae are marked by small orange±red dots in the Gulf specimens. Along the notal edge there are about two irregular rows of larger orange markings indicating the position of large subepidermal glands which shine through the translucent notum. The rhinophores and the gill cavity are surrounded by slightly elevated, smooth sheaths. The rhinophores bear 12 leaves in the Peruvian specimen and 14 in the larger specimen from the Gulf. Six bipinnate gills form a circle posteriorly completed by the anal papilla. The long digitiform oral tentacles are deeply grooved longitudinally. The Peruvian specimen has inner, transverse folds due to contraction. Anteriorly the foot corners are elongated, the foot edge is bilabiate, the upper lip is not notched. The tail is long and projects behind the notum.

Mantle structures. There are no spicules within the notal bosses nor in deeper mantle tissue, but this may be due to acid ®xation of the specimens examined. Histological sections do not show obvious empty spaces indicating the positions of dissolved spicules; thus, if spicules were present, they were rare and possibly small.

There are two irregular submarginal rows of spherical MDFs (mantle dermal formations) in all specimens examined. The glands of the outer band have a diameter between 0.2 and 0.3 mm. Inner MDFs of the serially sectioned, small Jamaican specimen ( BMNH, T. evelinae det. Thompson, 1980) reach diameters of up to 0.6 mm, those of the Gulf specimens up to 0.7 mm. The MDF structure of the Jamaican specimen (®gure 8) resembles that described for the small T. nobilis specimen no. 8: MDFs are ®lled with vacuole cells apparently containing a large, central vacuole (15±30 m m in diameter). The vacuoles appear more densely packed than in T. nobilis . The vacuolar cells appear peripherally surrounded by a layer of cells with violet staining particles. In larger MDFs, this layer appears slightly folded and extends somewhat towards the interior. All MDFs are enveloped by a very thin muscular capsule. There is no natural opening to the mantle surface.

Central nervous system. The cerebral and pleural ganglia are fused. There are rhinophoral ganglia separated from the cerebral ganglia. The lens-eyes are shortstalked. A statocyst with several otoconia nestles between cerebropleural and pedal ganglia. In the larger specimen from the Gulf there are two small blood gland lobes, one anterior to the CNS and one above the oesophagus.

Digestive system. The oral tube is covered by a thick cuticle which laterally and ventrally bears mostly bi®d jaw rodlets (®gure9A). The radula formula is 87 Ö 88.1. 88 in the Peruvian specimen, 78 Ö 86.1. 86 in the larger specimen from the Gulf. The rhachidian teeth are generally smaller than the laterals. It has a medially elongated apex and bears one to three pairs of irregular, ridge-like lateral denticles without forming a projecting central cusp. The innermost lateral tooth has two or three inner and outer denticles beside the main cusp in the Peruvian specimen (®gure 9B). The following, hook-shaped laterals only have up to three outer denticles. In the larger specimen from the Gulf the ®rst right lateral has up to three inner and four outer denticles beside the main cusp (®gure 9C). In contrast, the ®rst left lateral has no inner denticles and up to three outer denticles. The following, hookshaped laterals only have outer denticles. Their number decreases successively to one posterolateral denticle below the main cusp (®gure 9D). Outer laterals are more erect, the outermost teeth are reduced in size, irregular in shape and bear up to four denticles. An outline of the digestive system of the Peruvian specimen is illustrated in ®gure 10. In all specimens examined, there is one pair of tube-like salivary glands. The stomach lies medially or to the left, embedded within the digestive gland. A bulbous caecum may or may not reach its dorsal surface. The broad, longitudinally folded intestine leaves the digestive gland, runs along its anterior border and curves backwards to the anal papilla adjacent to the dorsal surface of the digestive gland.

Reproductive system. The genital systems of the specimens examined (see ®gure 11) are similar and agree well with the original description of T. evelinae by Marcus (1958). After its junction with the ampulla, the vas deferens begins as a rather short prostatic portion. It passes into a strongly curved portion which is sheathed by a muscular layer. The distal portion of the vas deferens is muscular and straight, passing into a tubular papilla which protrudes into the vestibule. No genital armature has been detected. A pair of large dendritic accessory glands covers the distal genitalia and opens at the aperture of the common male and female vestibule. These glands were not detected within the still juvenile, serially sectioned specimen from Jamaica; the ampulla, male and female ducts with allosperm receptacles were already present, but there were only traces of female glands and the atrium and genital openings were not yet developed. The vagina is a long, thin and convoluted duct. It divides into a straight insemination duct which opens distally into the nidamental gland and a duct running to the rounded, almost sessile bursa copulatrix. The receptaculum seminis is oval, somewhat smaller than the bursa and inserts close to the bursa with a short stalk. The nidamental duct possesses a distally swollen bulb at the junction of the accessory glands.

Geographic distribution. Tyrinna evelinae has been reported from northern Peru (this study) to Baja California ( Collier and Farmer, 1964) and the Gulf of California ( Marcus and Marcus, 1967; this study), as well as from Atlantic waters: Ilhabela and Guaruja near Santos, Brazil ( Marcus, 1958), Jamaica ( Thompson, 1980; Edmunds, 1981) and Ghana ( Edmunds, 1981, 1982). A record from Puerto Rico was listed by Marcus (1977).

Remarks. The specimens from Peru and the Gulf of California described herein externally and anatomically agree well with the original descriptions of Brazilian T. evelinae by Marcus (1958) and subsequent ones of material from Baja California and the Gulf of California by Collier and Farmer (1964) and Marcus and Marcus (1967). Therefore, they are identi®ed as T. evelinae .

Apparent diOEerences in tentacle shape was the main reason for Ortea’s (1988) questioning the conspeci®ty of specimens assigned to T. evelinae . In contrast to all other known T. evelinae which have long oral tentacles with a deep longitudinal groove, Thompson (1980) pointed out that specimens of T. evelinae from Jamaica were described as having digitiform, but ungrooved oral tentacles. Edmunds (1981) described specimens from Ghana which possessed longitudinally grooved tentacles but gave no detailed information on the tentacle shape of his two specimens from Jamaica. Re-examination of Thompson’ s single undissected Jamaican specimen from the BMNH con®rms the presence of digitiform, longitudinally grooved (`enrolled’) oral tentacles.

Edmunds (1981) noted slight colour diOEerences within his material but found no evident diOEerences between the specimens from Ghana, Jamaica and the Paci®c. Collier and Farmer (1964) described considerable variation of radular teeth shape within a single specimen of T. evelinae . Edmunds regarded diOEerences in the radular teeth morphology of his specimens to be caused by intraspeci®c variation rather than by speci®c separation. In order to reconstruct major organ systems, the only entire specimen of Thompson’ s Jamaican material has been serially sectioned during this study: the CNS, mantle glands and digestive system agree with other T. evelinae as described herein. The reproductive system was immature and therefore di cult to compare with those of mature specimens. The arrangement of the allosperm receptacles agrees with other T. evelinae but vestibular glands are absent. Since the reproductive organs are not fully developed and, especially, the whole vestibular region is not yet developed, this is certainly due to its immature state. There are no relevant morphological features which argue against the conspeci®ty of the Brazilian, and the northern and southern Paci®c specimens with those from Jamaica and Ghana.

Edmunds (1982) discussed possibilities leading to a tropical amphiatlantic distribution, such as steady gene ¯ow via drifting larvae, or adults carried by boats. Slow divergence rates in certain nudibranchs may explain the presence of T. evelinae within both tropical Paci®c and Atlantic waters which were isolated from each other during at least the last 1.5 million years, since the closing of the Isthmus of Panama.