Cephalic Retractor Research Articles

Far away, so close! Integrative taxonomy reveals a new genus and species of land flatworm (Platyhelminthes: Geoplanidae) from southern South America

Abstract Land flatworms usually show low ability to disperse and high endemicity, displaying many singletons in studies on land planarian assemblages. Thus, many species have been described based on specimens sampled in a single locality and/or on a few specimens. Based on phylogenetic analyses of concatenated COI and 18S rRNA genes and morphological analyses, a new genus and species of geoplaninid land planarian is described from central–east Argentina and southern Brazil. Winsoria gen. nov. shows, among its most outstanding features, a ventral cephalic retractor muscle and a subneural muscle layer that extends throughout the anterior region of the body. In addition, characters of the reproductive system and the phylogenetic analyses support the erection of this new genus. According to molecular phylogenies,Winsoria bipatria sp. nov. is closely related to species of Luteostriata, Supramontana and Issoca, taxa that also possess a cephalic retractor muscle. Despite its disjunct distribution, phylogenetic analyses, genetic divergence and morphological features show that the allopatric populations studied herein belong to a single species. We argue that the occurrence of W. bipatria in localities separated by hundreds of kilometres and a geographical barrier should be explained by passive dispersal.

Prey capture and feeding behaviour in an endemic land flatworm from São Tomé Island

ABSTRACTTwo specimens of the endemic land flatworm species Othelosoma impensum Sluys & Neumann, 2017 from the volcanic island São Tomé were observed in the wild in Obo-National Park while they were preying on ants that had descended on a tree trunk after their nuptial flight. A maximum of 41 ants were assembled in a cluster by one of the flatworms, the insects being immobilised by mucus secreted by the worms. A strong cephalic retractor muscle facilitated capture of the mobile prey. Presence or absence of similar cephalic adaptations in other species of Othelosoma and other genera of land flatworms is discussed, as well as the effectiveness of the sticky mucus secreted by the worms during prey capture.

A new Chilean genus and species of land planarian (Platyhelminthes: Tricladida, Geoplaninae) with cephalic retractor muscle and adenodactyl

ABSTRACTA new genus and species of land planarian, Pichidamas piru gen. nov. sp. nov., is described from Pichidamas, province of Osorno in Southern Chile. Pichidamas piru is a sub-cylindrical and slender Geoplaninae characterized by the presence of a creeping sole extending 50% of the body width, a cephalic retractor muscle, five parenchymatic muscle layers, a male atrium with proximal tongue-like fold and distal adenodactyl; and ovovitelline ducts approaching the copulatory apparatus anteroventrally. Details of the organization of the cephalic retractor muscle, the absence of sensory pits, the existence of a parenchymatic muscle layer, located to the inside of the ventral peripheral nervous plexus, and an adenodactyl in the distal portion of the male atrium are unique traits seemingly reflecting an earlier branch of Geoplaninae.http://www.zoobank.org/urn:lsid:zoobank.org:pub:04423258-DB01-4CE3-A474-EF6B563C605C

A new species of the land planarian Issoca sheds light on the polyphyletic status of the genus (Platyhelminthes, Tricladida, Geoplaninae).

A new species of the genus Issoca (Platyhelminthes, Tricladida, Geoplaninae) is described. Issoca assanga sp. n. presents the diagnostic features of the genus, with the exception of the relative position of the subneural parenchymal muscle layer with the cephalic retractor muscle, which are overlapped in the type species of the genus but are intersected in the new species. Rather than a polymorphic character, the relative position of these muscle layers might reflect the polyphyletic status of the genus.

The locomotion system of Mesozoic Coleoidea (Cephalopoda) and its phylogenetic significance

A morphological comparison of shell-muscle contacts in coleoid cephalopods mainly from the Early Jurassic (Toarcian) Posidonia Shales of Holzmaden (Germany), the Middle Jurassic (Callovian) Oxford Clay of Christian Malford (UK), Late Jurassic (Kimmeridgian-Tithonian) plattenkalks of Solnhofen (Germany), and the Late Cretaceous (Cenomanian) of Hâdjoula and Hâkel (Lebanon) provides new and meaningful insights into their locomotion systems. The study shows that both pro-ostracum- and gladius-bearing coleoids are typified by a marginal mantle attachment and by distinctly separated fins, which usually insert (indirectly via the shell sac and basal fin cartilages) to posterior shell parts. While absent in gladius-bearing forms, mantle-locking cartilages might have existed already in pro-ostracum-bearing belemnoids. Similar to ectocochleate ancestors, funnel- and cephalic retractors are generally attached to the internal (ventral) shell surface. A comparison of Mesozoic and Recent gladius-bearing coleoids shows that the locomotion system (most significantly the dorsal mantle configuration, and the presence of nuchal- and funnel-locking cartilages) is fundamentally different. This does not support the concept of ‘fossil teuthids’, but suggests, owing to similarities with Recent Vampyroteuthis, placement of Mesozoic gladius-bearing coleoids within the Octobrachia (Octopoda + Vampyromorpha). Classification of Mesozoic gladius-bearing coleoids as octobrachians implies that: (1) unambiguous teuthids are still unknown in the fossil record and (2) the similarity between Recent and some fossil gladiuses represents a matter of homoplasy.

The soft-tissue attachment scars in Late Jurassic ammonites from Central Russia

Soft-tissue attachment scars of two genera and four species of Late Jurassic craspeditid ammonites from the Russian Platform are described. A previously suggested relationship between lateral attachment scars and ammonoid hyponome is confirmed, however, a new interpretation is proposed for dorsal attachment scars: they could have been areas not only for attachment of the dorsal (nuchal) retractors, but also of the cephalic retractors. The new type of the soft-tissue attachment—anterior lateral sinuses, located between the lateral attachment scars and the aperture of the ammonite body chamber is described. Enclosed elliptical or subtriangular areas in apertural parts of the anterior lateral sinuses were found for the first time. Their presence and location suggest that this structure could have been used for attaching the funnel-locking apparatus, similar to those of coleoids. A transformation of shape and position of lateral attachment scars through the evolution of the Late Jurassic craspeditid lineage s...

A new species of Supramontana Carbayo & Leal-Zanchet (Platyhelminthes, Continenticola, Geoplanidae) from the Interior Atlantic Forest.

Supramontana argentina sp. nov. (Platyhelminthes, Continenticola, Geoplanidae) from north-eastern Argentina is herein described. The new species differs from Supramontana irritata Carbayo & Leal-Zanchet, 2003 from Brazil, the only species of this genus so far described, by external and internal morphological characters. Supramontana argentina sp. nov. is characterized by having a colour pattern with a yellowish median band, thin para-median black stripes, and two dark grey lateral bands on the dorsal surface. The most outstanding features of the internal morphology are a ventral cephalic retractor muscle almost circular in cross section, prostatic vesicle extrabulbar, tubular and very long, and penis papilla conical and blunt with a sinuous ejaculatory duct.

Soft‐tissue imprints in fossil and Recent cephalopod septa and septum formation

Several soft-tissue imprints and attachment sites have been discovered on the inside of the shell wall and on the apertural side of the septum of various fossil and Recent ectocochleate cephalopods. In addition to the scars of the cephalic retractors, steinkerns of the body chambers of bactritoids and some ammonoids from the Moroccan and the German Emsian (Early Devonian) display various kinds of striations; some of these striations are restricted to the mural part of the septum, some start at the suture and terminate at the anterior limit of the annular elevation. Several of these features were also discovered in specimens of Mesozoic and Recent nautilids. These structures are here interpreted as imprints of muscle fibre bundles of the posterior and especially the septal mantle, blood vessels as well as the septal furrow. Most of these structures were not found in ammonoids younger than Middle Devonian. We suggest that newly formed, not yet mineralized (or only slightly), septa were more tightly stayed between the more numerous lobes and saddles in more strongly folded septa of more derived ammonoids and that the higher tension in these septa did not permit soft-parts to leave imprints on the organic preseptum. It is conceivable that this permitted more derived ammonoids to replace the chamber liquid faster by gas and consequently, new chambers could be used earlier than in other ectocochleate cephalopods, perhaps this process began even prior to mineralization. This would have allowed faster growth rates in derived ammonoids.

Redescrição de duas espécies de Notogynaphallia Ogren & Kawakatsu (Platyhelminthes, Tricladida, Geoplaninae) e confirmação da heterogeneidade do gênero

Notogynaphallia caissara (E.M. Froehlich, 1955) and N. fita (Froehlich, 1959) are redescribed. Both species are included in the so-called group 2 of E.M. FROEHLICH & LEAL-ZANCHET (2003), in Notogynaphallia, and are provided with a cephalic retractor muscle derived from the ventral longitudinal subepidermic muscle layer. A muscle retractor does not exist in the type-species of the genus. This is strong evidence of the morphological heterogeneity within the genus, as E.M. FROEHLICH & LEAL-ZANCHET (2003) previously proposed mainly based on characters of the reproductive organs.

Redescription of two land planarian species of Notogynaphallia Ogren & Kawakatsu (Platyhelminthes, Tricladida, Geoplaninae) and confirmation of the heterogeneity of the genus

Notogynaphallia caissara (E.M. Froehlich, 1955) and N. fita (Froehlich, 1959) are redescribed. Both species are included in the so-called group 2 of E.M. Froehlich & Leal-Zanchet (2003), in Notogynaphallia, and are provided with a cephalic retractor muscle derived from the ventral longitudinal subepidermic muscle layer. A muscle retractor does not exist in the type-species of the genus. This is strong evidence of the morphological heterogeneity within the genus, as E.M. Froehlich & Leal-Zanchet (2003) previously proposed mainly based on characters of the reproductive organs.

Muscle development in Antalis entalis (Mollusca, Scaphopoda) and its significance for scaphopod relationships.

We applied fluorescence staining of F-actin, confocal laser scanning microscopy, as well as bright-field light microscopy, SEM, and TEM to examine myogenesis in larval and early juvenile stages of the tusk-shell, Antalis entalis. Myogenesis follows a strict bilaterally symmetrical pattern without special larval muscle systems. The paired cephalic and foot retractors appear synchronously in the early trochophore-like larva. In late larvae, both retractors form additional fibers that project into the anterior region, thus enabling retraction of the larval prototroch. These fibers, together with the prototroch, disappear during metamorphosis. The anlagen of the putative foot musculature, mantle retractors, and buccal musculature are formed in late larval stages. The cephalic captacula and their musculature are of postmetamorphic origin. Development of the foot musculature is dramatically pronounced after metamorphosis and results in a dense muscular grid consisting of outer ring, intermediate diagonal, and inner longitudinal fibers. This is in accordance with the proposed function of the foot as a burrowing organ based on muscle-antagonistic activity. The existence of a distinct pair of cephalic retractors, which is also found in basal gastropods and cephalopods, as well as new data on scaphopod shell morphogenesis and recent cladistic analyses, indicate that the Scaphopoda may be more closely related to the Gastropoda and Cephalopoda than to the Bivalvia.

A new genus and species of monostiliferous hoplonemertean (Nemertea: Enopla: Monostilifera) from Japan

A new genus and species of monostiliferous hoplonemertean, Diopsonemertes acanthocephala gen. et sp. nov., is described from Otsuchi Bay, Japan. Significant anatomical features of the new form include a body wall longitudinal musculature anteriorly divided into inner and outer layers by connective tissue, no pre-cerebral septum, the presence of a thin coat of diagonal muscle fibres between the body wall longitudinal and circular muscle layers in the foregut body region, cephalic retractor muscles derived only from the inner portion of the divided longitudinal muscles and a rhynchocoel more than half the body length.

Metamorphic Changes in the Velar Musculature, Head and Shell of some Prosobranch Veligers

The velum of Lacuna vincta (Montagu) and Nassarius incrassatus (Ström) is retracted into the shell by 2 dorsal and 2 ventral groups of muscles, bilaterally arranged, which are components of the larval retractor muscle. Each dorsal group passes forward from its area of origin on the shell to the dorsal part of the head where some fibres insert and adjacent ones enter the velar fold. The velum is bilobed in Lacuna and the muscles radiate through the dorsal half of the lobe to insert on the anterior and posterior surfaces and ciliated edge, whereas Nassarius has 4 long velar lobes, 2 dorsal and 2 ventral, and the muscles form a median bundle from which fibres radiate to similar insertions. Each ventral group of muscles passes through the nerve ring lateral to the developing radular sac in Lacuna and to the developing proboscis in Nassarius, and muscles accompanying them insert on the sac and proboscis wall. Anterior to the ring some muscles insert on the lips and the buccal wall posterior to the oral sphincter and alongside attachments of muscles from the foot. The majority pass to the mentum, a median protuberance of the lower lip with non-vibratile cilia, where right and left ventral cephalic retractors and muscles from the foot converge. The pedal muscles attach here and from this area muscles radiate to multiple insertions on the head and ventral half of the velum. This arrangement of the ventral muscles allows the increased angle of mobility required by the ventral areas of the velum in swimming and feeding and the intimate contact between velum and foot.