Derogenes spp.

Bouguerche, Chahinez, Huston, Daniel C., Karlsbakk, Egil, Ahmed, Mohammed & Holovachov, Oleksandr, 2024, Untangling the Derogenes varicus species complex in Scandinavian waters and the Arctic: description of Derogenes abba n. sp. (Trematoda, Derogenidae) from Hippoglossoides platessoides and new host records for D. varicus (Müller, 1784) sensu stricto, Parasite (Paris, France) 31 (26), pp. 1-25 : 19-20

Mediterranean Derogenes spp.

The German parasitologist Prof. Arthur Looss (1861–1923) was among one of the most prolific parasitologists and taxonomists and was known for his “ enthusiasm and energy as a researcher that have probably seldom been surpassed, especially a painstaking attention to detail that is unfortunately rare ” [ 33]. After his death, his collection was divided between numerous institutions: Smithsonian National Museum of Natural History in Washington ( USA), the Natural History Museum in Berlin and the Natural History Museum in Leipzig ( Germany), Gothenburg Museum of Natural History and the Swedish Museum of Natural History ( Sweden) (see Kuzmina and Holovachov [ 31]). A part of Looss’ s collection including his archives was sold to the Swedish Museum of Natural History (Naturhistoriska riksmuseet) in Stockholm by his widow, Elise Looss in 1924 [ 31] and includes slides of which some are actually type material and vials containing trematodes preserved in ethanol, along with several publication-ready drawings and original line drawings.

One of the intriguing derogenids that we encountered in this collection, is “ D. limula ” which we described above as Derogenes sp. , ex P. tentacularis , collected from off Trieste, Italy, Central Mediterranean. Curiously, we also found line drawings by A. Looss (see Figs. 3A and 3B ) labeled as “ Derogenes limula ”, which suggests that he intended to describe Derogenes from P. tentacularis as a new species, with the name “ D. limula ”. We found one specimen (SMNH 208361) for which the measurements are presented in Table 6 . The eggs of this “ D. limula ” that we described above as Derogenes sp. are over 40 µm and the species is thus consistent with the “large eggs group”. We compared the measurements of the sole specimen of Derogenes ex P. tentacularis to those of congeneric species from the Mediterranean ( Table 6 ). The single specimen of Derogenes sp. (or “ D. limula ” as initially referred to by A. Looss on the illustrations) ex P. tentacularis differs from D. minor , D. robustus , D. affine , and D. latus by its larger eggs. It resembles D. ruber in egg size (61 × 39 in Derogenes sp. vs. 62 × 39 in D. ruber ) and in having lobed, tear-shaped vitelline masses. However, Derogenes sp. ex P. tentacularis differ from D. ruber by being smaller in all body measurements including the body (855 × 253 vs. 7869 × 1847). We note though that body size is not a sufficient differentiating character and can vary with the age of the worm and the suitability of the host.

The presence of Derogenes sp. in P. tentacularis is not unusual as there are previous records of Derogenidae in blenniid fishes. For instance, Mediterranean blenniid host species of the related halipegine derogenid genus Magnibursatus Naidenova, 1969 [ 29, 51]. The peacock blenny Salaria pavo is reported as host for M. skrjabini (Vlasenko, 1931) [ 2, 29] and for M. blennii (Paggi & Orecchia, 1975) [ 29], whereas the tompot blenny P. gattorugine , the rusty blenny P. sanguinolentus , the ‘futarra’ Paralipophrys trigloides and Parablennius sp. are also hosts for M. blennii [ 29, 51]. Although we have only two specimens, the presence of an external seminal vesicle (vs. internal in Magnibursatus [ 20]), a uterus extending posterior to vitelline masses (vs. almost entirely anterior to vitellarium in Magnibursatus [ 20]), having lobed vitelline masses (vs. entire in Magnibursatus [ 20]) and especially the eggs lacking filaments (vs. present at each end in Magnibursatus [ 20]) indicate that the derogenid collected by A. Looss agrees with Derogenes rather than Magnibursatus .

Lebour [ 34] described some D. varicus adults with a similar “spiny” appearance and stated “ ... curious fact noticed is that all these larval D. varicus are beset with small spines, whereas it is a characteristic of the adult that although it has sometimes a wrinkling of the skin, it is unarmed and usually smooth. It is possible that these wrinkles may be the remains of the spines fused together. The spines are especially distinct in the younger specimens.” Interestingly, some of her specimens also contained eggs (i.e., progenetic). She also showed this spination in her figures [ 34]. Hence, this “ D. limula ” that we described as Derogenes sp. , is arguably an immature D. ruber . We could not find any published records for Derogenes in Blenniidae in the Mediterranean, but D. varicus was recorded from the butterfly blenny Blennius ocellaris in the Atlantic [ 47]. Besides the localities being distant (Trieste, Mediterranean for “ D. limula ” from P. tentacularis vs. Plymouth, Atlantic for D. varicus of Nicoll [ 47]), “ D. limula ” from P. tentacularis can be readily distinguished from D. varicu s by having lobed vitelline masses. Hence, “ D. limula ” of A. Looss is clearly not D. varicus . Herein, we described it as Derogenes sp. pending further examination based on more specimens.

Figures

Figure 3. “Derogenes limula” ex Parablennius tentacularis. Unpublished line drawing by A. Looss.