Thalassas, 27 (2): 49-60 An International Journal of Marine Sciences ANATOMICAL DESCRIPTION AND BIOLOGY OF THE SPLANCHNOTROPHID Splanchnotrophus gracilis HANCOCK & NORMAN, 1863 FOUND PARASITIZING THE DORIDACEAN NUDIBRANCH Trapania tartanella IHERING, 1886 AT THE RÍA DE FERROL (GALICIA, NW IBERIAN PENINSULA) ABAD M.(1), DÍAZ-AGRAS G.(1) & URGORRI V. (1,2) Key words: Splanchnotrophus gracilis, Trapania tartanella, SEM, anatomical description, infection rate, parasitic load, host damage. ABSTRACT the males and with a highly modified anatomy, take up the posterior body cavity of T. tartanella, clutching The genus Splanchnotrophus (Copepoda, the gonad and digestive gland with their long body Poecilostomatoida, Splanchnotrophidae) is a small appendages. Males move freely within the interior group of endoparasites infesting certain shell-less of the body of the host, although they preferably marine opisthobranchs. The present study is focused position themselves near the female and along the on the type species Splanchnotrophus gracilis reproductive system of the nudibranch. Generally, Hancock & Norman, 1863 and its relationship with its at least a single female of S. gracilis appears per host, the doridacean nudibranch Trapania tartanella nudibranch specimen. In the case of males, they Ihering, 1886. This nudibranch presents large appear in a number varying from 1 to 4. populations at the Ría de Ferrol, frequently found on the porifera Desmacidon fructicosum with a large The collection of specimens was carried out by part of specimens parasitized. The parasite female means of autonomous diving. In the present work a is exteriorly visible due to the presence of ovigerous description of the species Splanchnotrophus gracilis sacs. In most of the nudibranchs the parasite can be using Scanning Electronic Microscopy (SEM) and directly observed through the almost transparent light microscopy is presented. New data on the integument of the host. The females, much larger than biology of this species is given. High infection rates (94%) and parasitic loads (up to 43 parasites per (1) Estación de Bioloxía Mariña da Graña, Universidade de host) were found. No clear damage has been found Santiago de Compostela, Rúa da Ribeira, 1 (A Graña), 15590, in the infected viscera of T. tartanella or during the Ferrol. [email protected], [email protected]. reproductive process, as normal copulations and spawns were observed in lab conditions. However, (2) Departamento de Zooloxía e A. Física, Universidade de Santiago de Compostela, Campus Sur, 15782, Santiago de data suggest that a higher mortality exists in those Compostela. [email protected] specimens presenting a higher parasite load. 49 ABAD M., DÍAZ-AGRAS G. & URGORRI V. Figure 1: Figure 1: Ría de Ferrol map,Ría showing de Ferrol map, the showing sampling the sampling area area(black (black circle). circle). INTRODUCTION al., 2010), in the family Splanchnotrophidae, which now comprises five genera: Splanchnotrophus, The family Splanchnotrophidae (Copepoda, Lomanoticola (splitted from the latter), Ismaila, Poecilostomatoidea) is a poorly known group of highly Arthurius and Ceratosomicola. Shortly after Haumayr modified endoparasites on marine opisthobranchs. & Schrödl (2003) introduced the Scanning Electronic 23 species belonging to five genera are currently Microscopy (SEM) as a new and suitable tool to study known: Splanchnotrophus Hancock & Norman, 1863, tiny structures in great detail, giving new light on Lomanoticola Scott & Scott, 1895, Ismaila Bergh, the study of these parasites. Very recently, Salmen et 1867, Ceratosomicola Huys, 2001, and Arthurius al. (2008a, b) used this technique successfully when Huys, 2001 (Salmen, 2010). they described new species belonging to the genera Ceratosomicola and Arthurius. Historically, little attention has been paid to this parasitic group. The first works date back to Like other poecilostomatoids, splanchnotrophids the 19th century (Hancock & Norman 1863; Bergh have a sickle-shaped mandible. There are also 1868, 1898; Hetch 1893, 1895) and they are brief some common characteristics shared by all species descriptions with sketchy habitus drawings. In the belonging to the family Splanchnotrophidae: 3- 20th century some works (Delamare-Deboutteville, segmented antenna, 2- segmented maxilla, second 1950; Belcik, 1981) were focused on this group, but and third biramous thoracopods and one pair of they followed some confused data of the precedent caudal rami (Huys, 2001). authors and they paid little attention on cephalic appendages (except: Laubier, 1964) and their tiny Splanchnotrophids show a remarkable sexual structures. Schrödl (1997, 2002) published solid dimorphism concerning body size and shape (Huys, new data on splanchnotrophid parasitism in Chilean 2001; Haumayr & Schrödl, 2003): females are opisthobranchs from the genus Ismaila. But it was not much bigger than males, with a highly modified until the review of the family done by Huys (2001) body and having 3-6 pairs of lateral processes with when the “taxonomic myopia” surrounding this group three possible functions (Salmen et al., 2008a): the was solved, thanks to the detailed light microscopy first consists in wrapping the inner host organs, descriptions and drawings. Huys gathers all those the second in holding the ovotestis branches (white endoparasites on marine opisthobranchs, except for strings of newly formed eggs shining through the thoseFigure belonging 2: A. T.to tartanellathe genus parasitizedBriarella (Salmen by a S. et gracilis tissuefemale. can B .be T. easily tartanella observed) parasitized and finally, by a theS. third gracilis female and several males. C, D. Desmacidon fructicosum. ap: lateral appendages; es: 50 egg sacs. ParFem: parasite female; ParMal: parasite male. Figure 1: Ría de Ferrol map, showing the sampling area (black circle). ANatOMICAL DESCRIPTION AND BIOLOGY OF THE SPLANCHNOTROPHID Splanchnotrophus gracilis HANCOCK & NORMAN, 1863 FOUND PARASITIZING THE DORIDACEAN NUDIBRANCH Trapania tartanella IHERING, 1886 at THE RÍA DE FERROL (GALICIA, NW IBERIAN PENINSULA) Figure 2: A. T. tartanella parasitized by a S. gracilisFigure 2: female. B. T. tartanella parasitized by a S. A. T. tartanella parasitized by a S. gracilis female. B. T. tartanella parasitized by a S. gracilis female and several males. C, D. Desmacidon gracilis femalefructicosum and several. ap: lateral males. appendages; C, D .es: Desmacidon egg sacs. ParFem: fructicosum parasite female;. ap:ParMal: lateral parasite appendages; male. es: egg sacs. ParFem: parasite female; ParMal: parasite male. consists in extending the body surface in order Ismaila (Schrödl, 1997, 2002; Haumayr & Schrödl, to facilitate the breathing as the gas exchange 2003) the members of the Splanchnotrophidae do not is improved. Males are dwarf, with the typical cause a visible damage on their host, except those ciclopoid body shape and do not show any lateral related with the space competition with the inner process. But this sexual dimorphism is not seen structures of the host. concerning the cephalic appendages, which have the same or nearly the same structure in both sexes The genus Splanchnotrophus was established by (Huys, 2001; Haumayr & Schrödl, 2003; Salmen et Hancock & Norman in 1863. Until the review of the al., 2008a, b). family by Huys (2001), Lomanoticola was believed to belong to Splanchnotrophus, but this author gives it The females are situated inside their hosts with genus category, so the old Splanchnotrophus genus is the lateral processes embracing the inner organs divided in Splanchnotrophus s.s and Lomanoticola. (usually gonads or kidney) and the males are normally Splanchnotrophus currently possesses 4 species situated close to the females or lying freely in the distributed in the Mediterranean Sea and in the body cavity of the host (Huys, 2001; Salmen 2005). European Atlantic: S.gracilis, S. angulatus, S. willemi Except for some of the species belonging to the genus and S. dellachiajei. 51 ABAD M., DÍAZ-AGRAS G. & URGORRI V. Figure 3: S.Figure gracilis female. 3: S. A. gracilis Habitus (light female. microscopy). A. Habitus B. Egg sac (light(light microscopy). microscopy). C. Cephalic B. Eggappendages sac (SEM).(light D.microscopy). Second thoracopod C (SEM).. E. Third thoracopod (SEM). F. Abdomen, bearing caudal rami, genital openings and anal slit (SEM). aa:Cephalic antenna; an:appendages antennule; ao: anal(SEM). opening; D ap:. Second lateral appendages; thoracopod cr: caudal (SEM). rami; ed: E endopodit;. Third thoracopod es: egg sacs; ex: (SEM).exopodit; go: F. genital Abdomen, bearing caudal rami,opening; genital la: labium; openings lr: labrum; andma: maxilla; anal slitmd: mandible.(SEM). 52 aa: antenna; an: antennule; ao: anal opening; ap: lateral appendages; cr: caudal rami; ed: endopodit; es: egg sacs; ex: exopodit; go: genital opening; la: labium; lr: labrum; ma: maxilla; md: mandible. ANatOMICAL DESCRIPTION AND BIOLOGY OF THE SPLANCHNOTROPHID Splanchnotrophus gracilis HANCOCK & NORMAN, 1863 FOUND PARASITIZING THE DORIDACEAN NUDIBRANCH Trapania tartanella IHERING, 1886 at THE RÍA DE FERROL (GALICIA, NW IBERIAN PENINSULA) The present work shows the results obtained Dissections during a research project carried out by the Estación de BIoloxía Mariña da Graña (EBMG) focused on the Those T. tartanella that were kept alive were species Splanchnotrophus gracilis. High infection vivisected after one hour in a 7% MgCl2 solution with rates were discovered for the doridacean host Trapania the aim of