Filiform Microtriches Research Articles

Experimental Elucidation of the Life Cycle of Rhinebothrium urobatidium (Cestoda: Rhinebothriidea) from the Round Stingray (Urobatis halleri: Myliobatiformes) to First and Second Intermediate Hosts

The life cycle of the cestode Rhinebothrium urobatidium, whose final host is the round stingray, Urobatis halleri, includes a copepod as the first intermediate host and small benthic fishes as second intermediate hosts. Hexacanth embryos within nonoperculate, untanned eggs collected from round stingray developed in the tidepool copepod Tigriopus californicus into caudate procercoids with an apical organ/sucker and cercomer, and rarely, bothridia. The procercoids, which developed in the body cavity within a membrane, adhered to the copepod intestine, were infective to arrow gobies, Clevelandia ios, within 15 d of exposure at 21°C. When infected copepods were fed to arrow gobies, procercoids developed into nonlacunate plerocercoids each bearing individually retractable bothridia and an apical sucker. Within 10 d of exposure to the second intermediate host, the larvae had migrated up the bile/cystic duct into the gall bladder, where they developed bothridia similar to those of adult worms. Between 30 to 51 d post-infection in the goby, plerocercoids approached the size of larvae found in natural infections, and the scolex became morphologically similar to that of adult worms from round stingrays. Only presumptive filiform microtriches (filitriches) were present on procercoids while both filitrichs and spiniform microtriches (spinitrichs) were present on plerocercoids. Identification of plerocercoids from experimental infections as those of R. urobatidium was confirmed through morphology of the scolex and using cytochrome c oxidase I sequences. The experimental transmission of R. urobatidium to first and second intermediate hosts provides improved understanding of the transmission and ontogeny of shark tapeworms. The biological characteristics of U. halleri, with its diverse parasite fauna, provide significant opportunities to examine the biology of an array of elasmobranch tapeworm taxa.

Ultrastructural observations on the tegumental surface of Polyonchobothrium clarias Woodland, 1925 (Cestoda: Bothriocephalidae), infecting the catfish Clarias gariepinus in Egypt.

The fine structure of the tegument of mature proglottids in Polyonchobothrium clarias, Woodland, 1925, family: Bothriocephalidae, a cestode parasite of the cat fish Clarias gariepinus was studied using transmission electron microscopy.The ultrastructural observations of the tegument revealed that it consists of distal cytoplasm connected with underlying perikarya by cytoplasmic bridges. The distal cytoplasm differs in thickness between the different regions of P. clarias and lies on the basal lamina below which there are two layers of muscles, circular and longitudinal bundles. The main characteristic inclusion in the distal cytoplasm is the presence of electron-dense bodies and vesicles of variable size, shape and density. The tegument perikarya lies beneath the surface musculature.Three different types of microtriches varying in shape and size have been observed on the tegumental surface of the mature proglottids of P. clarias, filiform, blade-like spiniform and digitiform microtriches. Multiple functions of such structures; the amplification of the surface area for digestion, absorption, excretion, movement, attachment to the intestinal mucosa of their hosts and external protection. The types and distribution of microtriches are considered to be of systematic and phylogenetic importance.

A Survey and Morphological Study of Plerocercoidal Nybelinia surmenicola (Cestoda: Tentaculariidae) in the Common Squid from the Korean Coastal Waters

Trypanorhych plerocercoids of Nybelinia surmenicola are described in the common squid, Todarodes pacificus, through the use of light and scanning electron microscopy. Upon dissection, out of 200 common squid from the Korean coastal water, 54 (27%) were found infected with N. surmenicola plerocercoids. Mean N. surmenicola abundance was 2.28 per squid. Body length and width ranged from 6.1-11.1 (8.05) × 2.0-2.2 (2.1) mm. Bothria are broad, bean-shaped, measured 2.4-2.8 × 0.62-0.69 (2.65 × 0.64) mm. The short and long tentacular armatures which are spirally arranged are homeoacanthous and homeomorphous uncinate hooks and consist of compact rose-thorn-shaped tentacular hooks. The tentacle sheaths are coiled in a spiral near the bulbs. Four large bothria are separated by filiform microtriches along the bothridal margins. This is the first description of the plerocercoids of N. surmenicola in the common of squid from the Korean coastal waters.

Nataliella marcelli n. g., n. sp. (Cestoda: Trypanorhyncha: Rhinoptericolidae) from Hawaiian fishes

A new trypanorhynch cestode from Hawaiian waters is described based on specimens in the collection of the Meguro Parasitological Museum, Tokyo, and newly collected specimens. Nataliella marcelli n. g., n. sp. is characterised by its elongate, craspedote scolex with four small, ear-shaped bothria, an elongate pars vaginalis and long bulbs. The homeoacanthous homeomorphous metabasal armature is comprised of five or six slender, solid hooks per half spiral row. A distinctive basal armature is present, including a combination of six characteristically shaped macrohooks not previously described for trypanorhynchs. The surface ultrastructure consists of gladiate spiniform microtriches that cover the distal and proximal bothrial surface and filiform microtriches on the scolex peduncle. The adults are not known. Nataliella is assigned to the family Rhinoptericolidae Carvajal & Campbell, 1975 based on its possession of four bothria, prebulbar organs and no chainette or intercalary hooks. The family diagnosis is amended to accommodate the new genus. Rhinoptericola megacantha Carvajal & Campbell, 1975 is considered the most closely related species, a position that has been confirmed by molecular analyses of the SSU and LSU rDNA. Nataliella n. g. is intermediate in morphology between the homeoacanth family Tentaculariidae Poche, 1926 (superfamily Tentacularioidea) and the Rhinoptericolidae and other eutetrarhynchid genera (superfamily Eutetrarhynchoidea), sharing characters of both superfamilies.

Luciaella ivanovae n. g., n. sp. (Eucestoda: Proteocephalidea: Peltidocotylinae), a parasite of Ageneiosus inermis (L.) (Siluriformes: Auchenipteridae) in Argentina

Luciaella ivanovae n. g., n. sp. (Proteocephalidea: Peltidocotylinae) is proposed to accommodate a new cestode from a siluroid fish, the manduvé Ageneiosus inermis (Linnaeus) (syn. A. brevifilis Valenciennes) (Auchenipteridae) from the Colastiné River, a tributary of the Paraná River, in Argentina. The new genus is placed in the Peltidocotylinae because it has a medullary ovary with projections into the dorsal cortex, cortical vitelline follicles and testes, a cortical uterine stem, and uterine branches penetrating the medulla and usually as far as the dorsal cortex. Luciaella can be distinguished from all other peltidocotyline genera by the following combination of characters: a quadrangular scolex with four biloculate suckers, each of which has a cap-peak-like structure situated on the anterior margin; the absence of a metascolex; vitelline follicles arranged in two lateral rows which are crescent-shaped in transverse section; testes distributed in two dorsal fields connected anteriorly and sometimes posteriorly; and a vagina which is always anterior to the cirrus-sac and overlaps the convoluted vas deferens. Filiform microtriches are present on all tegumental surfaces, with short filiform microtriches on the scolex and long filiform microtriches on the proliferation zone and on both immature and mature proglottides. The diagnosis of the Peltidocotylinae Woodland, 1934 given by Rego (1994) is amended. L. ivanovae is the fourth proteocephalidean described from A. inermis and the third recorded in this fish host from Argentina.

Ultrastructure of microtriches on the scolex of Cyathocephalus truncatus (Cestoda: Spathe-bothriidea)

The scolex surface of the mature spathebothriidean Cyathocephalus truncatus (Pallas, 1781), a parasite of the brown trout Salmo trutta fario L., was studied using scanning and transmission electron microscopy. A particular attention was paid to microtriches, unique structure on the surface of the Cestoda. The scolex of C. truncatus is covered with two types of filiform microtriches (filitriches): aciculate (approximately 3 microm long) and capillate (approximately 10 microm long). Capillate microtriches, which have never been reported in any other spathebothriideans, are described for the first time using transmission electron microscopy. The tegument covered with filiform microtriches only (no spiniform microtriches are present) is typical of cestode groups supposed to be the most basal, e.g., Gyrocotylidea, Spathebothriidea, and Caryophyllidea.

Orygmatobothrium Spp. (Cestoda: Tetraphyllidea) from Triakid Sharks in Argentina: Redescription of Orygmatobothrium schmittii and Description of a New Species

Two species of Orygmatobothrium were found inhabiting triakid sharks collected from the coast of Buenos Aires Province, Argentina. Orygmatobothrium schmittii from Mustelus schmitti is redescribed, including new information on the microtrich pattern. Orygmatobothrium juani n. sp. from Mustelus fasciatus can be distinguished from all other species in the genus using the following combination of characters: worm length, number of proglottids, number of testes, testes distribution, size of eggs, ornamented egg shell, shape of bothridial cleft at level of the marginal accessory sucker, and the extension of vitelline follicles. Species in Orygmatobothrium share a common microtrich pattern with the distal bothridial surface covered with maisiform microtriches interspersed with filiform microtriches, a proximal bothridial surface covered with trifid microtriches, with a medial projection conspicuously larger than the lateral basal projections interspersed with filiform microtriches, an inner and outer surface of the accessory sucker and glandulomuscular organ covered with short filiform microtriches, the scolex proper and cephalic peduncle surface covered with bladelike microtriches, and the germinative zone and entire strobila covered with scutes formed by densely packed filiform microtriches. This general configuration is basically similar to the microtrich pattern described in species of Orectolobicestus and Paraorygmatobothrium.

Surface ultrastructure of the elasmobranchia parasitizing Grillotiella exilis and Pseudonybelinia odontacantha (Trypanorhyncha, Cestoda)

The surface ultrastructure of two monotypic trypanorhynch genera is described based on new material of Grillotiella exilis (Linton, 1909) and type material of Pseudonybelinia odontacantha Dollfus 1966. In G. exilis, spiniform microtriches cover the bothrial surfaces and the anterior part of the pars vaginalis posterior to the bothria. Bifurcate microtriches adorn the bothrial margins, filiform microtriches the scolex peduncle, and capilliform microtriches the posterior scolex end. This microthrix pattern resembles that found in, e.g., Grillotia erinaceus (van Beneden, 1858), with the difference that the anterior part of the pars vaginalis is covered with a collar of multidigitate palmate microtriches. The position of Grillotiella within the Grillotiinae, Lacistorhynchidae is supported based on these data. The bothria and scolex peduncle of P. odontacantha are covered with acerosate and unciniform microtriches on the distal bothrial surface and capilliform microtriches on the scolex peduncle. Short filiform microtriches cover the appendix. The microthrix pattern resembles that of the Tentaculariidae but with unciniform and acerosate microtriches densely covering the entire distal bothrial surface. Tegumental grooves are present on the posterior bothrial margin. They can be distinguished from bothrial pits in otobothrioid trypanorhynchs in having similar unciniform microtriches compared to the other parts of the bothrial surface and in lacking any spiniform microtriches. With the absence of bothrial pits as characteristic for the otobothrioids and its characteristic microthrix pattern, P. odontacantha together with Paranybelinia otobothrioides Dollfus 1966, both belonging to the Paranybeliniidae change their position in the most recent system from the Otobothrioidea into the Tentacularioidea.

Ultrastructure of the proglottid tegument (neodermis) of the cestode Echinophallus wageneri (Pseudophyllidea: Echinophallidae), a parasite of the bathypelagic fish Centrolophus niger

Ultrastructural data are provided on the tegument (or neodermis) of proglottids of the cestode Echinophallus wageneri Monticelli, 1890, the first representative of the family Echinophallidae (Pseudophyllidea), parasites of bathypelagic fish, studied using transmission and scanning electron microscopy. The surface of the ventral concave side of proglottids is covered with filiform microtriches about 1.7 microm long. Their glycocalyx, although very thick, is less extensively developed compared to that on digitiform microtriches localized on the dorsal side of the proglottids, which is also covered with filiform microtriches. The digitiform microtriches of the convex dorsal side are about 0.6 microm long, with a very short, rounded spine and the extraordinarily extensive glycocalyx seen as flocculent material. Short digitiform microtriches of E. wageneri seem to differ from microthrix types previously reported in other cestodes by transmission electron microscopy. The posterodorsal margin of all proglottids is typical in possessing a transverse band of large spiniform, tusk-shaped microtriches with a very long spine (approximately 13 microm in length), merged with filiform microtriches. Marked regional differences found in the morphology and distribution of microtriches on the proglottids of E. wageneri may be related to the different functions of the individual parts of the strobila because of the curling of the tapeworm body within the intestine of its fish host.

Redescription of Cetorhinicola acanthocapax Beveridge & Campbell, 1988 (Cestoda: Trypanorhyncha) from the basking shark Cetorhinus maximus (Gunnerus)

Cetorhinicola acanthocapax Beveridge & Campbell, 1988 is redescribed based on adult specimens collected from a basking shark Cetorhinus maximus (Gunnerus) off the east coast of New Zealand. Both the mature and gravid segments are described for the first time, and the first scanning electron micrographs of the armature and scolex microtriches are provided. Novel features include the opening of the vagina anterior to the cirrus-sac and the extension of the vagina anterior to the cirrus-sac. Pectinate microtriches are present on the anterior quarter of the pars pedunculus scolecis scattered between filiform microtriches; the bothrial margins are covered with tridigitate microtriches, while the adherent surface of the bothria have pectinate microtriches. The additional morphological features described are consistent with a close association between Cetorhinicola Beveridge & Campbell, 1988 and the Eutetrarhynchoidea Guiart, 1927.

Redescription of Cetorhinicola acanthocapax Beveridge & Campbell, 1988 (Cestoda: Trypanorhyncha) from the Basking Shark Cetorhinus maximus (Gunnerus)

Cetorhinicola acanthocapax Beveridge & Campbell, 1988 is redescribed based on adult specimens collected from a basking shark Cetorhinus maximus (Gunnerus) off the east coast of New Zealand. Both the mature and gravid segments are described for the first time, and the first scanning electron micrographs of the armature and scolex microtriches are provided. Novel features include the opening of the vagina anterior to the cirrus-sac and the extension of the vagina anterior to the cirrus-sac. Pectinate microtriches are present on the anterior quarter of the pars pedunculus scolecis scattered between filiform microtriches; the bothrial margins are covered with tridigitate microtriches, while the adherent surface of the bothria have pectinate microtriches. The additional morphological features described are consistent with a close association between Cetorhinicola Beveridge & Campbell, 1988 and the Eutetrarhynchoidea Guiart, 1927.

Comparative study of the microtriches of adult Cestodes (Proteocephalidea: Monticelliidae), and some comments on their systematic value

The surface of the tegument of the scolex and the immature proglottides of Monticellia belavistensis, M. ventrei, Nomimoscolex chubbi, and N. lopesi is described using scanning electron microscopy. Only blade-like spiniform microtriches and filiform microtriches were observed in the species studied. The types, size and density of microtriches on the apical region surface of the scolex, central cavity surface of suckers, marginal ring surface of suckers, non-adherent surface of suckers, proliferation zone surface, and immature proglottis surface were compared among these species. The distribution pattern of the microtriches was not a reliable feature to discriminate among the genera considered in this study. It varied in each of the species of Monticellia examined, and did not permit to split the heterogeneous genus Nomimoscolex. However, the microthrix pattern can be regarded as an additional diagnostic feature to distinguish among species of proteocephalideans. Further comparative research involving other species of proteocephalid taxa is needed to elucidate the systematic value of the tegumental morphology.

Redescription of Monticellia magna (Rego, dos Santos & Silva, 1974) (Eucestoda: Monticelliidae) parasite of Pimelodus spp. (Pisces: Siluriformes) from Argentina, and morphological study of microtriches

Monticellia magna (Rego, dos Santos & Silva, 1974) is redescribed and the microtriches and their distribution are studied for the first time. This species is characterised by the following combination of characters: (1) vagina anterior to cirrus pouch; (2) muscular asymmetrical sphincter present; (3) testes in one layer and in two fields connected anteriorly and posteriorly; (4) vitelline follicles distributed cortical, paramuscular and a few follicles medullary; (5) internal longitudinal musculature strongly developed; and (6) scolex with filiform microtriches in apical region, filiform and spiniform microtriches in central cavity, marginal ring and nonadherent surface of suckers, and spiniform microtriches in neck and immature proglottides. The species parasitised fishes of Pimelodus spp. Strict specificity of South American proteocephalids for their hosts is placed into consideration since recently new host records have been reported, especially for hosts commercially exploited.

Two new species of Litobothrium Dailey, 1969 (Cestoda: Litobothriidea) from thresher sharks in the Gulf of California, Mexico, with redescriptions of two species in the genus.

As part of a survey of the metazoan parasites of elasmobranchs of the Gulf of California, Mexico, the spiral intestines of 10 pelagic thresher sharks Alopias pelagicus and one bigeye thresher shark A. superciliosus were examined for tapeworms. Eight of the A. pelagicus specimens examined were found to host Litobothrium amplifica and L. daileyi. Both tapeworm species are redescribed based on examination of this new material with light and scanning electron microscopy, and the ranges of most of the measurements for these species are expanded; scanning electron micrographs and detailed illustrations and measurements of their segment anatomy are presented for the first time. An argument is made that the identification of the original host specimens of these species was in error and that A. pelagicus is likely to be the correct original host. In addition, L. nickoli n. sp., a third species in the genus hosted by A. pelagicus, was found in three of the 10 individual hosts examined. This species differs from all six known Litobothrium species in the form of the pseudosegments of the scolex, the anterior two being essentially non-cruciform, while the latter three are distinctly cruciform. All other species possess either no non-cruciform or at most one non-cruciform segment anteriorly. The single specimen of A. superciliosus examined was found to host the new species, L. janovyi. This species differs from L. coniformis, L. gracile and L. amsichensis in its possession of four rather than three, three and five cruciform pseudosegments, respectively. It lacks the modificiations of the fourth pseudosegment seen in L. amplifica and lacks the anterior non-cruciform fifth pseudosegment found in L. daileyi. It most closely resembles L. alopias but differs among other features in its greater total length, greater number of segments and longer mature segments. SEM of the four species collected from the Gulf of California as well as material of L. amsichensis from the goblin shark Mitsukurina owstoni that hosted the type-specimens of this species show that all surfaces of the body of all five species bear a dense covering of long filiform microtriches. L. amplifica bears a single row of large spine-like structures throughout most of the posterior margins of the first and second cruciform pseudosegment only. L. daileyi possesses one to two rows of overlapping spine-like structures on the posterior margins of the first four pseudosegments with the exception of the medial projections. The fifth pseudosegment lacks these structures. L. janovyi n. sp. bears spine-like structures on the lateral margins of only the third and fourth pseudosegments. L. nickoli n. sp. bears spine-like structures throughout the posterior margins of the first and second pseudosegments, and throughout the posterior margins of the third and fourth pseudosegments with the exception of the medial projections; the fifth pseudosegment lacks these structures. L. amsichensis bears no structures that could be considered to be spine-like on any of its pseuosegments, but possesses a border of densely arranged larger microtriches on the posterior margin of all five pseudosegments. A key to the species is included.

Two New Species of Echinobothrium (Cestoidea: Diphyllidea) from Myliobatiform Elasmobranchs in the Gulf of California, Mexico

Two new species of diphyllidean cestodes, Echinobothrium mexicanum n. sp., and Echinobothrium fautleyae n. sp., are described, the former from the spiral intestines of the bat rays Myliobatis californicus and Myliobatis longirostris and the latter from the spiral intestine of the cownose ray Rhinoptera steindachneri, all caught in the Gulf of California, México. Echinobothrium mexicanum is most easily distinguished from the majority of the species of the genus by the number of large apical hooks in each dorsoventral group (23) and from the remainder in the number of lateral hooklets in each group on the scolex. Echinobothrium fautleyae differs conspicuously from all other members of the genus in that the first and last lateral hooklets in each group are distinctly larger than the other hooklets in each group. Serial sections of the scoleces of these 2 new species confirm that the attachment structures on the scolex are bothria, rather than bothridia, as has been described in other species in the genus, suggesting that the attachment structures of the scolex should be examined in more detail in the genus in general. Palmate microtriches of various forms cover the proximal bothrial surfaces of both new species and are also found on the dorsal bothrial surfaces of E. fautleyae. The distal bothrial surfaces of E. mexicanum are covered with slender spiniform and short filiform microtriches. The cephalic peduncles of both species possess short filiform microtriches only. Comparison of these 2 new species with the other 3 species in this genus that have been examined with SEM suggests that the various forms and distributions of these microtriches is unique in each of these 2 species. We believe these features will prove to be taxonomically useful.

Scolex morphology of the cestode Silurotaenia siluri (Batsch, 1786) (Proteocephalidae: Gangesiinae), a parasite of European wels (Silurus glanis).

The morphology of the scolex of the tapeworm Silurotaenica siluri (Batsch, 1786) (Proteocephalidae: Gangesiinae), a specific parasite of European wels (Silurus glanis L.), was studied using light, scanning (SEM), and transmission electron (TEM) microscopy. The scolex of S. siluri is rather uniform in shape and size; it is globular, and has four prominent, anteriorly directed suckers and a spherical, muscular apical organ corresponding to the rostellum of cyclophyllidean cestodes. The rostellum-like apical organ is armed with five to six irregular rows of small hooklets with a wide, oval basal plate and a short, posteriorly curved blade. The excretory system of the scolex is formed by sinuous secondary canals ending blindly beneath the distal layer of the tegument, not opening outside. The surface of the scolex is covered with filiform microtriches; giant spine-like and blade-like microtriches, incorrectly interpreted as spines or hooklets in previous descriptions of S. siluri, are present on the neck region and posterior margins and internal cavities of the suckers. It is assumed that tegumental spines reported in the scolices of other proteocephalideans (subfamilies Acanthotaeniinae and Gangesiinae, genera Spasskyellina and Nomimoscolex) could indeed be spiniform microtriches.

Tegumental topography of the plerocercoid of Gymnorhynchus gigas (Cestoda : Trypanorhyncha).

The tegumental topography of the plerocercoid of Gymnorhynchus gigas is described for the first time. The surface features were examined by scanning electron microscopy. Eight different types of microthrix pattern were found. Differences in the shape and density of microtriches depend on their location. A unique morphological feature is reported herein, namely, filamentous microtriches that were arranged in clusters with a dome-shaped pattern when the bothridial surface was relaxed but sunk into a crater when the bothridial surface was contracted. In contrast to other trypanorhynchan cestodes, palmate microtriches are not found on the tegument of this plerocercoid. The microtriches on the caudal extension gradually increased in length with growing distance from the blastocyst, which showed short knob-like structures. These structures developed into elongated filiform microtriches on the posterior region of the caudal extension.

On the Status of the Genus Pinguicollum (Tetraphyllidea: Onchobothriidae) with a Redescription of P. pinguicollum

Material of the poorly known Pinguicollum pinguicollum from Raja spp. in California from the personal collections of Nathan Riser and Mike Moser was examined by light and scanning electron microscopy. The presence of unusual triloculated bothridia covered with a layer of tissue, but capable of protruding through an aperture in this tissue, was confirmed. The species is also unusual in its lack of a muscular pad and apical sucker on each bothridium and in its possession of bifid hooks in which the axial prongs are conspicuously shorter than the abaxial prongs. The scolex was interpreted to consist of a short bothridial region and an elongate cephalic peduncle containing 4 pairs of robust longitudinal muscle bundles. The segment morphology is described in detail and figured for the first time. The ovary is bilobed in cross section; the testes are arranged in multiple rows in cross section. The apex of the scolex was found to possess elongate, filiform microtriches. The distal surfaces of the protrusible regions of the bothridia were covered with short filiform microtriches in the anterior and both short filiform microtriches and spiniform microtriches on the posterior bothridial surfaces. The remainder of the scolex and cephalic peduncle were covered with densely packed, spiniform microtriches of varying sizes. Based on the unusual bothridia, robust cephalic peduncle, and lack of muscular pad and apical sucker on the bothridia, it is recommended that the genus be considered to be valid. As all attempts to locate the type material of the species failed, a neotype is designated to facilitate future study of the genus.

A comparison of scolex morphology between the plerocercoid and the adult of Calliobothrium verticillatum (Tetraphyllidea: Onchobothriidae)

The morphological changes associated with the ontogenetic transformation of the scolex from larva to adult were investigated in the tapeworm Calliobothrium verticillatum (Rudolphi, 1819) van Beneden, 1850 by comparing the morphology of plerocercoids collected from the hermit crab Pagurus pollicaris Say, 1817 with that of adult worms collected from the shark Mustelus canis (Mitchell, 1815), using scanning electron microscopy. The apex of the scolex in young plerocercoids bore a conspicuous sucker. Each bothridium was flat and divided into four regions: an anterior oval region with two marginal bumps, and three posterior loculi clearly marked by two costae. The microthrix pattern was not determined for very young plerocercoids. The most conspicuous feature of older plerocercoids was the sucker on the apex of the scolex. The bothridia were concave, and each bore an apical region subdivided into three shallow suckers and three conspicuous loculi. Densely packed blade-like microtriches intermingled with filiform microtriches were visible on all surfaces of the scolex except the surface directly adjacent to the opening of the apical sucker of the scolex, which was entirely devoid of microtriches, and the proximal surfaces of the bothridia, which had only blade-like microtriches. The apical sucker was absent from the scolex adult specimens. The only remnant of this structure was a small knob on the apex of the scolex. The bothridia were concave and bore, from anterior to posterior, three conspicuous apical suckers arranged in a horizontal row adjacent to one another, two pairs of single-pronged hooks, and three conspicuous loculi. Densely packed blade-like microtriches were present on all proximal surfaces of the scolex. Microtriches were not present on the distal surfaces of the apical suckers of the bothridia, on the hooks, or on the distal surfaces of the loculi of the bothridia. The latter regions were covered with very small, round structures. The differences in the microthrix components of the various surfaces of the scolex between the plerocercoid and the adult suggest that complex surface changes occur during this phase of ontogeny. Comparison of the development of this species with that of other onchobothriids suggests that, in general, the number of loculi to be expected in the plerocercoid of an onchobothriid is one plus the number of posthook loculi in the adult.

Morphological investigations into Floriceps minacanthus (Trypanorhyncha: Lacistorhynchidae) with analysis of the systematic utility of scolex microtriches

Specimens of Floriceps minacanthus Campbell & Beveridge, 1987 are reported from Carcharhinus melanopterus (Quoy & Gaimard, 1824) taken in the waters surrounding the island of Kirimati in the Republic of Kiribati in the Central Pacific Ocean. This represents a new host and a new locality record. The description of this species is expanded to include the presence of an ovary which is bilobed in cross section and a hermaphroditic duct. The surface features were examined by scanning electron microscopy. With the exception of the lateral margins of the bothridia and the apical region of the scolex, the scolex was found to be covered with palmate microtriches interspersed with filiform microtriches. The palmate microtriches varied in number of digitiform extensions depending on location. Elongate, bifid microtriches were present in the transition zone between the proximal and distal surfaces along the lateral margins of the bothridia. The apical region of the scolex was covered with filiform microtriches. The surface of the anterior margin of the strobila was covered with broad, flattened scale-like structures. The pattern of microthrix distribution was repeated for each of the bothridia of an individual, and this pattern was intraspecifically invariable. Comparison of our results with those from the seven other trypanorhynch species examined by previous authors with SEM indicates that there is much interspecific variability in both the morphology of microtriches present as well as their location on the scolex. This, coupled with the lack of intraspecific variability, confirms that these structures are systematically informative.