Laqueusplana bocki, Rodríguez & Grande & Bulnes & Almon & Perez & Noreña, 2017

Rodríguez, Jorge, Grande, Cristina, Bulnes, NataliaVeronica, Almon, Bruno, Perez, Jacinto & Noreña, Carolina, 2017, Systematic revision of the family Pleioplanidae Faubel, 1983 (Polycladida, Acotylea): new genus and combinations, European Journal of Taxonomy 264, pp. 1-30 : 7-12

Laqueusplana bocki gen. et sp. nov.

urn:lsid:zoobank.org:act:0467FB7F-9254-49E8-AE5F-D02BC2CE89B6

Figs 1–3 , 6A

Notoplana atomata O.F. Müller, 1776 in Bock 1913 (partim): 202, table X, fig. 3 (individuals with a spiral-shaped stylet).

Etymology

The name of the species is dedicated to Sixten Bock, famous Swedish invertebrate zoologist (1884– 1946).

Material examined

Holotype

SPAIN: sagittally sectioned, stained with Azan , Jan. 2012 ( MNCN 4.01 / 1118 a 1150, 34 slides).

Paratype

SPAIN: 1 sagittally sectioned specimen, stained with Azan, among mussels at a depth of nearly 6 meters, Dec. 2013, 42º33.7760′ N, 08º59.3090′ W ( MNCN 4.01/ 1151 a 1189, 40 slides).

Type locality

SPAIN: Galicia, Club Náutico de Riveira, among mussels on a pontoon between half to one meter depth, 42º33.7670′ N, 08º59.2860′ W.

Description

Living worms 25 mm long and 7 mm wide. Body shape elongated, of fleshy consistency, broader anteriorly, then stretching to form a slightly pointed posterior end; few smooth marginal undulations ( Fig. 1 A–C). Dorsal surface with pale beige ground colour and evenly distributed dark brown spots, except in pharyngeal and genital regions; body margin transparent and spot-free ( Fig. 1A ). Tentacles absent; instead tentacular eyes present in two rounded clusters. Cerebral eyes form two elongated groups (between 15 and 17 eyes) next to tentacular eyes; marginal or frontal eyes lacking ( Fig. 1A ). Ventral surface pale brown, almost transparent. Bilobated brain with two symmetrical lobes located ventral to eyes. Pharynx occupies middle third of body, with oral pore opening ventrally in its medial region. Male and female genital pores well separated, opening at beginning of last third of body. Ovaries well developed, lying dorsally between intestinal branches. Testes ventral.

MALE REPRODUCTIVE SYSTEM. Male copulatory organ consists of an interpolated prostatic vesicle, a true seminal vesicle and a penis papilla with a long, slender stylet, and is located almost immediately behind pharyngeal cavity ( Fig. 2C ). Testes located ventrally, sometimes observed between intestinal branches. Vasa deferentia run ventrally along both sides of posterior body region, swelling in spermiducal vesicles before entering seminal vesicle proximally. Seminal and prostatic vesicles forward directed ( Fig. 2A ). Seminal vesicle with thick muscular walls, connected to prostatic vesicle by short and narrow ejaculatory duct ( Fig. 2D ). Ejaculatory duct projects proximally into prostatic vesicle, crosses it and opens near distal end. Prostatic vesicle oval-shaped, enlarged and covered with strong muscular layers. Prostatic vesicle internally subdivided into at least eight parallel tubular chambers extending from proximal end, giving characteristic citrus-like appearance ( Figs 2D , 3A ). Extravesicular glands can be found lining proximal end of prostatic vesicle ( Fig. 2A ). Long coiled stylet emerges from distal end of prostatic vesicle, forms characteristic spiral-like loop between prostatic vesicle and pharynx, turns backwards and opens dorso-ventrally into male atrium ( Figs 2 A–D, 3). Small conical-shaped penis papilla housed within ciliated atrium ( Fig. 2B ).

FEMALE REPRODUCTIVE SYSTEM. Female system consists of external and internal vaginas, oviducts, uteri and Lang’s vesicle ( Fig. 2C ). Muscular external vagina, or vagina bulbosa, lined with cuboidal epithelium with fringe-like extensions. Vagina bulbosa narrows distally, then extends dorsally or anteriorly towards male copulatory system before reaching internal vagina. Internal vagina turns posteriorly and runs dorsally to posterior end. Oviducts lead separately into common receptacle at proximal end of internal vagina. Numerous shell and cement glands open in region surrounding both vaginas. After receiving oviducts, vagina continues into enlarged Lang’s vesicle that extends posteriorly, sometimes reaching posterior end of animal ( Fig. 2E ).

Differentional diagnosis

Due to the presence of a prostatic vesicle filled with tubular chambers ( atomata - type), separated gonopores and a vagina bulbosa, the genus Laqueusplana gen. nov. belongs to the family Pleioplanidae . However, the presence of a long stylet with a spiral loop and a of forward directed male copulatory system justifies the erection of a new genus within this family.

Species of the genera Izmira Bulnes, 2010 , Melloplana Faubel, 1983 and Persica Maghsoudlou et al., 2015 share some characteristics of the Pleioplanidae family, mainly the presence of an atomata - type prostatic vesicle. However, these genera can be differentiated from the genus Laqueusplana gen. nov. et by the following: Izmira lacks cerebral eyes and Lang’s vesicle and has a backwards directed male copulatory system and a penis rod; Melloplana is characterized by the presence of an unarmed, muscular penis papilla and Persica presents distinct characteristics such as the presence of nuchal tentacles, a male copulatory organ wrapped in a muscular bulb and an elongated stylet.

Laqueusplana gen. nov. and Pleioplana Faubel, 1983 are morphologically most closely related to each other, which is reflected in a number of shared characteristics. Externally, both have an elongated body with pale ground colour, two clusters of both tentacular and cerebral eyes and lack tentacles. They also possess a ruffled pharynx that occupies the middle third of the body and a copulatory system that begins posterior to the pharynx. Laqueusplana gen. nov., unlike Pleioplana , has the seminal and prostatic vesicles directed forward and a longer, coiled stylet situated between the pharynx and prostatic vesicle.

The female copulatory system of the genus Laqueusplana gen. nov. consists of a well-developed vagina bulbosa and an enlarged Lang’s vesicle, which sometimes reaches the posterior end of the animal. In general, the female system in this genus is larger than those of other Pleioplanidae genera. Pleioplana and Melloplana show a similar female system as Laqueusplana gen. nov., although smaller in size, while Izmira and Persica present a shorter female track and a complete absence of Lang’s vesicle.

Biology

Live specimens have rapid scrolling movements and, when stressed, are able to swim by rotating the body, orienting the ventral body surface towards the water surface, and shaking the body while waving its edges.

Remarks

During the study and analysis of Laqueusplana bocki gen. et sp. nov. and similar species we discovered that in the description of Notoplana atomata of Bock (1913: 202), this author mentioned that some individuals in his material showed a long stylet forming a loop. However, in his reconstruction of Notoplana atomata ( Bock 1913: 201, fig. 39) this author did not draw a stylet with a loop or a prostatic vesicle directed forward, but he photographed a specimen ( Bock 1913: table XX, fig. 3) with these characteristics. This fact means that Bock took note of the outstanding features of the new genus Laqueusplana gen. nov., but probably due to the scarcity of material did not give it any importance and considered the differences as exceptions or artefacts of fixation that did not allow the establishment of new species. Nevertheless, it is clear that of Laqueusplana gen. nov. was present in the study of Bock but it wasn’t described; therefore, we dedicate the new species to this great specialist of Polycladida .

Distribution

Laqueusplana bocki gen. et sp. nov. has only been found along the north-western Atlantic coast of Galicia, Spain. Notably, within the family Pleioplanidae (4 genera and 13 species), Pleioplana atomata (O.F. Müller, 1776) and Laqueusplana bocki gen. et sp. nov. are the only representatives of the family found along European Atlantic coasts. Nonetheless, further research must be done to determine the entire distribution range of the new species.

Figures

Fig. 1. Species of Laqueusplana gen. nov. A. Dorsal view of a fixed specimen of Laqueusplana bocki gen. et sp. nov. B–C. Dorsal views of living specimens of L. bocki gen. et sp. nov. D. Dorsal view of a fixed specimen of L. megala (Marcus, 1952) comb. nov. E. Higher magnification view showing the eye arrangement of L. megala comb. nov.

Fig. 2. Laqueusplana bocki gen. et sp. nov. A–B. Histological sections of the reproductive system (anterior end to the left). C. Sagittal reconstruction of the reproductive system. D–E. Histological sections of the male organ.

Fig. 3. Laqueusplana bocki gen. et sp. nov. A. Transverse histological sections of the male reproductive organ. B. Transverse reconstruction of the male reproductive system.

Fig. 6. Schematic representations comparing the copulatory apparatus. A. Laqueusplana bocki gen. et sp. nov. B. L. megala (Marcus, 1952) comb. nov. C. Melloplana ferruginea (Schmarda, 1859). D. M. japonica (Kato, 1937).