Cristián Ituarte

PARASITES OF THE STOUT RAZOR CLAM TAGELUS PLEBEIUS (PSAMMOBIIDAE) FROM THE SOUTHWESTERN ATLANTIC OCEAN

Abstract This work describes the parasites and their respective pathologies in the stout razor clam, Tagelus plebeius (Lightfoot, 1786) (Psammobiidae) from Argentinean coasts. It represents the first report about a histopathological survey for these species in the Southwestern Atlantic. Specimens of T. plebeius were collected at Mar Chiquita coastal lagoon (37°46′S, 57°27′W) (n = 104 dissected under stereomicroscope, n = 28 histologically sectioned and microscopically examined) and from the mouth of the Quequén Salado River (38°56′S, 60°33′W) (n = 14 dissected under stereomicroscope). Tagelus plebeius was found housing two ciliate species without apparent host reaction and acting as first intermediate host for two digenetic trematode species of the families Fellodistomidae and Gymnophallidae, by hosting sporocysts (mainly in gonad and digestive gland that results in the replacement of host tissues) and as second intermediate host by housing a gymnophallid metacercaria. Likewise, T. plebeius was found parasitized by a larval spirurinae nematode encapsulated by hemocytes. The finding of two ciliate species, the gymnophallid cercaria and metacercaria, and the larval nematode represents the first record for the host. The Southwestern Atlantic populations of this clam seem to be devoid of serious pathogens in the study area.

The fit between parasites and intermediate host population dynamics: larval digeneans affecting the bivalve Neolepton cobbi (Galeommatoidea) from Patagonia

Abstract Temporal variations in prevalence and intensity of infection of larval trematodes in their second intermediate host, the bivalve Neolepton cobbi, were studied relative to the host population dynamics and season in the intertidal zone of Patagonian rocky shores. Two larval gymnophallid metacercariae of Gymnophallidae sp. and of Bartolius sp. were found parasitizing N. cobbi. The parameters of infection were related to the size structure of the host population. The high values of prevalence of Gymnophallidae sp. and Bartolius sp. found between late winter and early austral summer coincided with the dominance of intermediate and larger size classes in the host population. Conversely, the lower prevalence in midsummer coincided with the dominance of small size bivalves (mean size: 0.7±0.1 mm length) after the turnover of the host population. For metacercariae of Gymnophallidae gen. sp., the prevalence was related positively to host size. Mean intensity of infection (mean number of metacercariae per infected individual in a sample) of Gymnophallidae sp. showed no defined seasonal pattern, with more than 60% of bivalves showing low intensities (≤5) on each sampling occasion. Intensity of infection was significantly higher in bivalves ≥1.4 mm length compared to smaller sizes, but showed a tendency to decrease in bivalves ≥2.4 mm length. For metacercariae of Bartolius sp., higher values of prevalence were found in bivalves with lengths between 1.4 and 2.4 mm. Prevalence was lower in larger size classes. Intensity of infection was not related to host size.

Attachment of the Nemertean Malacobdella arrokeana to the Mantle of the Geoduck Panopea abbreviata and Survival Outside the Host

ABSTRACT Results of the histopathological study of mantle tissues of the commercial geoduck Panopea abbreviata hosting the nemertean Malacobdella arrokeana revealed that the normal histology of mantle tissues of the bivalve was not altered by the attachment structure of the nemertean, even when the maximum individuals per clam reached 191 nemerteans. However, the vacuum force generated by the nemertean sucker seems to elicit a slight mechanical stretching of epithelial cells and a negligible infiltration response affecting the connective tissue between inner and outer mantle epithelia beneath the point of attachment. The 99.4% bivalves examined (n = 657) hosted at least 1 specimen of M. arrokeana. Adult nemerteans were able to survive outside the host for up to 3 mo at 13°C. These results suggest that the relationship between M. arrokeana and P. abbreviata should be considered as a commensal rather than a parasitic relationship.

A new species of Haplosporidium Caullery & Mesnil, 1899 in the marine false limpet Siphonaria lessonii (Gastropoda: Siphonariidae) from Patagonia.

A new species of Haplosporidium Caullery & Mesnil, 1899 parasitising the pulmonate gastropod Siphonaria lessonii Blainville in Patagonia, Argentina, is described based on morphological (scanning and transmission electron microscopy) and sequence (small subunit ribosomal RNA gene) data. Different stages of sporulation were observed as infections disseminated in the digestive gland. Haplosporidium patagon n. sp. is characterised by oval or slightly subquadrate spores with an operculum that is ornamented with numerous short digitiform projections of regular height, perpendicular to and covering its outer surface. The operculum diameter is slightly larger than the apical diameter of the spore. Neither the immature nor mature spores showed any kind of projections of the exosporoplasm or of the spore wall. Regarding phylogenetic affinities, the new species was recovered as sister to an undescribed species of Haplosporidium Caullery & Mesnil, 1899 from the polychaete family Syllidae Grube from Japanese waters. The morphological characters (ornamentation of the operculum, spore wall structure, shape and size of spores, and the lack of spore wall projections) corroborate it as an as yet undescribed species of Haplosporidium and the first for the phylum in marine gastropods of South America. Siphonarialessonii is the only known host to date.

Two new species of Waldo Nicol, 1966 from sub-Antarctic waters (Bivalvia: Galeommatoidea)

Abstract Two new sub-Antarctic Waldo species (Bivalvia) are described: Waldo digitatus and W. paucitentaculatus. Waldo digitatus has a large, elongate–oval shell, with a short, horizontal dorsal margin, the valves showing a wide ventral gape, well separated from the anterior gape, and faint radial sculpture, fading toward shell margin. In addition, in this species the inhalant-pedal aperture is flanked by 5–15 pairs of tentacles. Waldo paucitentaculatus has a small, triangular–oval shell, with anterior and posterior half of dorsal margin long, sloping gently at similar angles, the anterior and ventral shell gapes coalesce to form a single, narrow and elongated gape, and radial sculpture well-marked and visible from beaks to ventral margin. Another distinctive character is the presence of only 1 or 2 pairs of tentacles bordering the siphonal-pedal aperture. Both species were found living as epibionts on the heart sea urchin Abatus cavernosus: W. digitatus is restricted to the perioral area and W. paucitentaculatus is more widely distributed, mainly on the oral surface.

Tellimya Tehuelcha, New Species: First Record of Tellimya Brown, 1827, In South America (Bivalvia: Lasaeidae), with Notes on Life History and Reproduction

Galeommatoids are small bivalves usually living as epibionts on other invertebrates. Among them, a number of genera, such as Waldo Nicol, 1966, Scioberetia F. Bernard, 1895, Montacuta Turton, 1822, Tellimya Brown, 1827, Brachiomya Jespersen, Lützen & Nielsen, 2004, and Montacutella Jespersen, Lützen & Nielsen, 2004, are associated with sea urchins. Only Scioberetia and Waldo were reported from the southern tip of South America (F. Bernard, 1895a–c; Zelaya & Ituarte, 2002). Tellimya was proposed to include Mya suborbicularis Montagu, 1803, Ligula substriata Montagu, 1808, Mya ferruginosa Montagu, 1808, Tellimya lactea Brown, 1827, T. tenuis Brown, 1827, T. elliptica Brown, 1827 (based on Mya ferruginosa Montagu, 1808, and an objective synonym thereof), T. glabrum Brown, 1827, and T. ovata Brown, 1827. Subsequently, Gray (1847) designated Mya ferruginosa as its type species. Pérès (1937), Pophan (1940), Deroux (1961) and Oldfied (1961) provided information on the gross anatomy and functional morphology of the type species, and Kamenev (2008) clarified the details of the hinge morphology of the genus. Tellimya has sometimes been regarded as a subgenus of Montacuta (e.g., Pelseneer, 1925; Ponder, 1968), but currently regarded as a full genus (e.g., Chavan, 1969; Aartsen, 1997; Marshall, 2002; Kamenev, 2008). In the present paper, a new species of Tellimya from the Magellan Region, which constitutes the first record of the genus in South America, is described.

Tissue reaction of Tagelus plebeius (Bivalvia: Psammobiidae) against larval digeneans in mixohaline habitats connected to the south-western Atlantic.

This paper describes the organism–organism relationship between a bivalve host and larval digeneans. The studied population of the stout razor clam Tagelus plebeius from the mixohaline Mar Chiquita lagoon (37° 32′S 57° 19′W) showed 100% of prevalence of infection by a larval digenean (metacercaria) of the family Gymnophallidae. The larvae occupied the extrapallial space just below the hinge of the bivalve. The tissue reaction against larval digeneans by T. plebeius consisted of hyperplasia and metaplasia of the outer layer of the mantle epithelium adjacent to parasites, forming an invagination to generate a sac that surrounded gymnophallid larvae. According to the intensity of infection, each sac progressively enlarged to harbour a variable number of larvae. In highly infected clams, a great number of sacs are formed. Eventually, the older sacs containing larvae may become closed, losing their communication with the extrapallial space and sinking into the dorsal part of the visceral mass. Larvae within sacs grow and remain alive until they reach an appropriate definitive bird vertebrate host. Older lesions commonly showed remains of dead larvae which had undergone resorption. As a result, an orange to brownish amorphous material accumulated in the space once occupied by the larvae leaving conspicuous orange marks on the inner surface of the valves. In some cases, calcifications in the form of pearls or blisters were observed.

A new species of gymnophallid (Digenea) and an amended diagnosis of the genus Gymnophalloides fujita, 1925.

Abstract:  Morphological and molecular evidence suggest that specimens formerly described as Lacunovermis sp. from Nacella (Patinigera) spp. (Patellogastropoda: Patellidae) belong to a new species of Gymnophalloides Fujita, 1925. Based on the new information, they are identified as Gymnophalloides nacellae n. sp. The new species differs from Gymnophalloides tokiensis, Gymnophalloides seoi, and Gymnophalloides heardi mainly through the presence of a group of papillae located on the ventral surface between oral and ventral suckers. A detailed morphological study revealed the lack of pars prostatica, a character previously reported in G. seoi, which is why it was formerly placed in the Gymnophallinae. Molecular information proved that G. nacellae is close to G. seoi, being nestled together with Parvatrema representatives. This molecular information, along with the absence of pars prostatica, allows these 2 genera to be placed in Parvatrematinae. An amended diagnosis of Gymnophalloides is provided. Histological sections of mantle epithelium of the limpet show metacercariae attached by their oral and ventral suckers in a similar manner to G. seoi in its host, the oyster Crassostrea gigas. Tissue reaction includes cells of outer mantle epithelium being stretched by sucker attachment, hemocyte infiltration of connective tissue between mantle epitheliums, and abnormal calcareous deposition on the inner surface of the shell.

Revision of the family Gymnophallidae Odhner, 1905 (Digenea) based on morphological and molecular data

This paper reviews the family Gymnophallidae, recognizing as valid seven genera; four within the subfamily Gymnophallinae: Gymnophallus Odhner, 1900 (syn. Meiogymnophallus Ching, 1965), Paragymnophallus Ching, 1973, Pseudogymnophallus Hoberg, 1981, and Bartolius Cremonte, 2001, and three in the Parvatrematinae: Parvatrema Cable, 1953, Lacunovermis Ching, 1965, and Gymnophalloides Fujita, 1925. Specimens representing one species of each available genus were chosen from those well-described and non controversial species, for which strong morphological information was available, and used for molecular studies (ITS1-5.8S-ITS2-28S rDNA strands were sequenced). The presence or absence of a pars prostatica differentiates between the 2 subfamilies, Gymnophallinae and Parvatrematinae. The characters used to differentiate genera are: location of the ovary (pre-, post- or inter-testicular), size and location of the genital pore (inconspicuous and located at the anterior margin of the ventral sucker, or conspicuous and located at some distance from the anterior margin of ventral sucker), presence of caecal pockets, and presence or absence of ventral pit (a muscular structure which can be either well-developed, similar in size and musculature to the ventral sucker, or be poorly developed). The characters previously used to distinguish among genera that actually should be considered to separate species include: shape of tegument spines (broad, sharp or serrated), presence of lateral projections on the oral sucker (also called papillae or lips), shape of the seminal vesicle (unipartite or bipartite), shape of the prostatic duct (elongate or oval), presence of papillae on the genital pore, shape of the genital atrium (tubular, wide, oval), shape of the vitellaria (follicular in a variable degree, paired or single), shape of the excretory vesicle (V or Y), and extension of uterus (restricted to forebody, at hindbody or extending in both). Additionally, some of these characters may vary with the age of worm. The morphological and molecular information obtained in this study provided strong support for recognizing seven valid genera in the family Gymnophallidae.

Neactaeonina argentina, New Species, and Family Placement of the Genus Neactaeonina Thiele, 1912 (Mollusca: Gastropoda)

ABSTRACT Neactaeonina argentina, a new species from the outer Argentine shelf off Buenos Aires province, is described. The species is characterized by the elongate, low-spired shell, with shouldered, nearly straight whorls, deep suture, and sculpture composed of numerous, broad, flat spiral cords. The radula is similar to that previously described for the type species, Neactaeonina cingulata Thiele, 1912, except in having a greater number of teeth. The present study provides the first information on the anatomy and histology of the genital system, and details of the radula anatomy of Neactaeonina, both unknown to date. The study of anatomical characters demonstrates that Neactaeonina has clear similarities with other Acteonidae, with a combination of features present in Acteon (such as the presence of a strongly calcified shell, with well-developed operculum; mantle cavity opening anteriorly; nervous system with only the cerebropleural ganglia fused; a single allosperm sac associated with the female system; radula without cardinal tooth; and oral cuticle with rod-like processes); and some characters present in acteonid genera other than Acteon (e.g., the number and morphology of teeth, and processes of the oral cuticle). However, Neactaeonina shows some characters thus far not reported for any other genus currently placed into the Acteonidae: salivary glands with laminar structure, male genital system with an open portion, a single allosperm sac opening distally, and a flat and triangular copulatory organ.