Report of the fourth specimen of Amphiorchis solus (Simha & Chattopadhyaya, 1970) Platt, 2002 46 years after the original description

Spirorchiids (family Spirorchiidae Stunkard 1921) are a group of trematodes that inhabit the circulatory and lymphatic system of turtles. The family has approximately 100 species grouped into 19 genera, ten of which are parasites of sea turtles (Smith 1997, Platt, 2002). The genus Amphiorchis Price, 1934 is exclusively reported in sea turtles and six species are currently accepted for this genus: A. amphiorchis Price, 1934; A. lateralis Oguro, 1938; A. indicus Mehrotra, 1973; A. caborojoensis Fischthal & Acholonu, 1976; A. indicum Simha & Chattopadhyaya, 1980; and A. solus (Simha & Chattopadhyaya, 1970) Platt, 2002 (Smith, 1997; Platt, 2002). Amphiorchis solus has exclusively been described in green turtles (Chelonia mydas L.1758). Although the species was first described more than 45 years ago, only three specimens have been reported in the literature (Simha & Chattopadhyaya, 1970; Santoro et al., 2006; Werneck et al., 2011)

The aim of the present note was to report the occurrence of the forth specimen of A. solus, broadening morphometric and morphological information on this species through photographic images.

In August 2015, a juvenile green sea turtle (curved carapace length: 37.0 cm) was discovered in Mangue Seco in the state of Bahia on the northeastern coast of Brazil (11° 31’ 24.924”S and 37° 23’ 57.948”W). The turtle was found dead on the beach with diffuse algae distributed on the carapace as well as eggs from a leech Ozobranchus sp. (Hirudinea: Ozobranchidae) and barnacles on the carapace and plastron. Severe indentation of the plastron and lateral plates of the carapace were found, indicating cachexia. Moreover, skin tumors compatible with fibropapillomatosis were found in the eyes, cervical region, inguinal region and base of the right anterior fin

Necropsy revealed hypotrophy, paleness and a gelatinous consistency of the pectoral muscle as well as blackish spots measuring one mm in diameter with multifocal distribution, concentrated more in the small intestine and to a lesser degree in the large intestine. The heart was examined using the method simplified by Werneck et al. (2006). Twenty three specimens of Learedius learedi Price, 1934 and one specimen of A. solus were found.

The helminths were found dead and fixed in a 70% ethanol, stained with carmine and cleared with eugenol. Morphometric data were acquired with the aid of an image analysis program (ImageJ, National Institutes of Health). Drawings were made using a drawing tube. The helminths were deposited in the Helminthological Collection of the Biosciences Institute (CHIBB), São Paulo State University (UNESP), Botucatu, São Paulo State, Brazil (A. solus number: 7843 and L. learedi number: 7844). A taxonomic key by Platt (2002), the original description (Simha & Chattopadhyaya, 1970) and a study by Werneck et al. (2011) were used for morphological and morphometric comparisons (Table 1).

Description (Fig. 1 and 2): Parasite small, with tapered anterior extremity (Fig. 2A) and slightly rounded posterior extremity (Fig. 2F), marked constriction in equatorial region (Fig. 2B) and small spines covering entire body; Oral sucker subterminal, esophagus long, sinuous and ending in a ceca bifurcation, ceca loop anteriorly then turn posteriorly (Fig. 2A and 2B); Ceca run parallel to side of body curvemediad at level of acetabulum, returning to lateral region of body when approaching anterior testis (Fig. 2C), terminating blindly posterior to posterior testis and anterior to excretory vesicle; Acetabulum rounded (Fig. 2B), positioned in equatorial region, coinciding with body constriction; Two testes, anterior testis larger and sinuous, resembling an S shape (Fig. 2C), posterior testis smaller and slightly oval in shape (Fig. 2D); Ovary lobulate, intercecal and located between cirrus sac and posterior testis (Fig. 2D – E); External seminal vesicle small, oval and intracecal, located posterior to anterior testis, in transverse position in relation to body (Fig. 2F); Cirrus sac elongate and immediately anterior to ovary, diagonal to body and (where visualization was possible) ventral to ovary, terminating in genital pore near posterior edge of ovary (Fig. 2F); Vitelline reservoir easily visible (Fig. 2D), occupying area between ovary and posterior testis; Excretory vesicle V-shaped; Vitellarium (Fig.1 and 2B – F) composed of small follicles that run from cecal bifurcation to region of posterior testis and interrupted in region of ovary, ventral to cecae; Uterus (Fig. 2F – black arrow) with tubular structure occupying area lateroposterior to ovary, with trajectory turned toward medial region of body, at which point increasing in diameter, passing dorsally through the vitelline reservoir and terminating near region of genital pore; no eggs found.

Fig. 1

Fig. 2

Previous records: Ventricle of heart in C. mydas from Gulf of Ma-nar, India (Simha & Chattopadhyaya, 1970) and Brazil (Werneck et al., 2011 and present report) as well as intestine of C. mydas in Costa Rica (Santoro et al., 2006)

Amphiorchis solus was originally described as Squaroacetabulum solus by Simha & Chattopadhyaya (1970) based on a single specimen collected from the heart of a green sea turtle from the Gulf of Manar, India. The acetabulum (“…whitish, situated anterior to the equatorial plane, is nearly square and the corners are slightly drawn outwards...”) and position of the pre-ovarian and post-ovarian vitelline follicles were what most piqued the interest of the authors and led them to institute the genus.

Platt (2002) considered the genus Squaroacetabulum to be synonymous with the Amphiorchis. Moreover, the author suggested that A. solus could be synonymous with A. caborojoensis, due to structural similarities and the shape of the acetabulum (“slightly squared ventral sucker”), but stressed that specimens of S. solus (A. solus n. comb.) were not available for evaluation and validation. Forty adult female turtles were evaluated during the nesting season in Costa Rica by Santoro et al. (2006), with the occurrence of only one specimen of A. solus (prevalence: 2.5%), which was collected from the intestine, but no morphological or morphometric data were provided.

Amphiorchis solus was again reported in the heart of a green sea turtle on the coast of Brazil, where only one specimen was found (Werneck et al., 2011). The authors compared this specimen with specimens of A. caborojoensis and determined that the species are distinct and valid.

The morphometric analysis of the specimen revealed that the width of the acetabulum, dimensions of the oral sucker and external seminal vesicle, width of the anterior testis, length of the posterior testis and length of the cirrus sac were larger in comparison to previously published data (Table 1). Moreover, new data are presented herein on the width of the esophagus and cirrus sac as well as the distances from the genial pore and intestinal ceca to the posterior extremity and from the cecal bifurcation to the anterior extremity. However, such differences are not surprising, as this is only the third specimen of the species with known morphometric data and the findings merely reflect possible individual variation.

One of the most striking differences is the circular shape of the acetabulum, as also reported by Werneck et al. (2011), which differs from the original description of a square shape, explaining why the genus originally received the name Squaroacetabulum (Simha & Chattopadhyaya, 1970). Another interesting point regards the vitelline follicles, which are less dense in the present specimen and very different from those reported by the authors of the original description of the species. Moreover, a relatively voluminous tubular structure was found in the specimen described herein, which occupied the left side of the lateroposterior region of the ovary (Fig. 2F – black arrow). In our opinion, this is the uterine loop, which is described for the first time for the species. Unfortunately, no eggs were found in the current specimen.

Based on the present findings, A. solus may be considered a rare species with low prevalence and intensity rates. Such information is supported by the few studies on this species (Simha & Chattopadhyaya, 1970; Santoro et al., 2006; Werneck et al., 2011; present report). The lack of specimens impedes broader morphological knowledge on the species and only reports of further individuals will contribute to a better understanding of the internal and surface structures of this parasite.