Microthalestris sarsi, sp. nov.

Microthalestris sarsi sp. nov.

urn:lsid:zoobank.org:act: 23B221A4-6328-4AA6-9563-1344D0C0FBE1

Microthalestris forficula (Claus, 1863) sensu Sars (1905)

Parastenhelia spinosa (Fischer, 1860) forma typica [sensu Lang (1948)]

Although Lang (1934: 24) cursorily disputed the conspecificity of Sars’s Norwegian and Claus’s mediterranean material of M. forficula, he did not elaborate on the issue in later contributions that promoted his all-embracing concept of “ Parastenhelia spinosa ”. Claus’s description is of limited value for morphological comparison but illustrates two characters of significance ruling out conspecificity with the Nordic population, i.e. the segmentation of the female antennule and the proportional lengths of the rami of P1. Females of the type population display 8- segmented antennules whereas the Norwegian specimens have an additional segment. The rami of P1 are distinctly more elongate in the mediterranean material with exp-2 being 3.1 times as long as exp-1 (vs 2.1 in the Norwegian specimens) and about 80% the length of enp-1 (vs about 60%).

Sars (1905) treated Thalestris karmensis and T. forficuloides as synonyms of M. forficula but did not provide any justification. Although Sars and Boeck were contemporaries in the early stages of their careers it is unlikely that the former had the opportunity to examine Boeck’s material of T. karmensis thirty years after his untimely death in 1873. Boeck (1865) did not present any illustrations and the essence of his concise description translates as follows: “The body is elongated, but the cephalothorax is somewhat inflated. The abdomen is short and wide, with rows of spinules around the posterior margin of the two middle somites. The caudal rami are wider than long. The antennules are short, with the second segment being about as long as the following two segments combined. The bases of the maxillipeds are oval and their claws very long. The first pair of swimming legs are elongated, with the endopod bearing a short seta at the end of the proximal quarter of the inner margin. The P1 exopod is shorter than the endopod; the middle segment has spinules along the outer margin, and a longer spine near its distal corner; the claws on exp-3 are very strong and several times longer than the segment. The oval exopod of P5 is longer than the endopodal lobe.” Based on Boeck’s (1865) description no positive statement can be made as to the validity of T. karmensis or its relationship to other parastenheliids. The little information that is given raises grave doubts that it belongs to Microthalestris at all or that it is a member of the Parastenheliidae. The species must be redescribed and pending this it is considered here as species incertae sedis in Microthalestris.

Microthalestris forficuloides is similar to Sars’s material in P1 exopod/endopod length ratio, the position of the inner seta on P1 enp-1, the absence of the inner seta on P4 exp-1, the presence of only one inner seta on P4 exp-3, the maximum number of eight elements on the female P5 exopod, and the slightly swollen proximal part of caudal ramus seta V in the female, however, differs from it in the following suite of characters: (a) antennary exopod has one lateral seta on exp-1 and two lateral setae on exp-2 (vs two and one, respectively), (b) P3 exp-1 lacks the inner seta, (c) P3 exp-3 has three inner setae (vs two), (d) the female exopod is shorter (2.4 vs 2.8 times as long as maximum width), (d) the male exopod is 1-segmented (vs 3-segmented), and (e) the larger body size (♀♀: 730 μm vs 580 μm). On the basis of these morphological discrepancies, the previously suggested conspecificity with M. forficuloides can be ruled out and, consequently, Sars’s (1905) form is here attributed distinct specific rank as M. sarsi sp. nov.

Lang (1948: 586) summarized earlier records attributed to Parastenhelia spinosa and stated that three forms of the species had been reported in the literature, forma typica, forma littoralis (for Microthalestris littoralis), and forma penicillata (for M. littoralis var. penicillata Willey, 1935). Although the diagnosis of his forma typica is clearly based on Sars’s material of M. forficula (and not Claus’s original description of the species), it is clear from the contents of his work that he did not intend to propose it as new (in which case “ M. typica ” would have become an available and the valid name for Sars’s material). Lang (1948: 587) unambiguously revealed that the three forms had no taxonomic meaning by stating that “In Wirklichkeit is es unmöglich, die 3 Formen auseinanderzuhalten, den eine Menge Zwischenformen sind vorhanden, und die Merkmalkombinationen variieren in jeder denkbaren Weise”. Although the forma typica could be construed as a name proposed for an infrasubspecific entity, it remains unavailable since it was not adopted for a species or subspecies before 1985 (ICZN Art. 45.6).

Original description. Sars (1905): 123–124, Plate LXXVI.

Additional description. Lang (1936b): 23–25; Figs 50–52 (as Parastenhelia forficula).

Type material. The female specimen illustrated by Sars (1905: Plate LXXVI) is here designated as the holotype of M. sarsi sp. nov. (ICZN Arts 16.4 and 72.5.6). The species can be differentiated by the characters listed in the diagnosis below and those mentioned and illustrated in Sars (1905) (ICZN Art. 13.1).

Type locality. Sars (1905) recorded material from several places on the south and west coasts of Norway, and in the Trondhjem Fjord. Since he did not specify which specimens the illustrations were based on, the type locality encompasses all of their respective places of origin (ICZN Art. 73.2.3).

Differential diagnosis. Microthalestris. Body length 580 μm in ♀, considerably smaller in ♂. Antenna with 2-segmented exopod bearing two setae on exp-1 and one lateral and three apical elements on exp-2. P1 exopod about two-thirds length of endopod; exp-2 elongate, about 2.1 times as long as exp-1, and about 60% length of enp-1; insertion point of inner seta of enp-1 at 25% of inner margin length; exp-3 with two unipinnate spines and two geniculate setae; enp-2 with one minute seta, one geniculate seta and one geniculate claw. Armature pattern of ♀ P2–P4:

P3 endopod ♂ 3-segmented, with apophysis on enp-3, armature pattern [1.1.02 + apo]. P 5 ♀ with elongate exopod (about 2.8 times as long as maximum width), inner margin and proximal half of outer margin straight, with eight elements, proximal outer one long, outer apical one short; endopodal lobe with five elements, innermost one well developed. P 5 ♂ exopod 3-segmented, with six elements (outer element of exp-1 absent or extremely reduced); endopodal lobe with two elements. Armature of P 6 ♂ unconfirmed. Caudal ramus seta V with slightly swollen proximal part.

Etymology. The specific epithet is named after Georg Ossian Sars (20 April 1837 – 9 April 1927), eminent Norwegian copepodologist, who provided the first illustrated account of the species under the name Microthalestris forficula (Claus, 1863).

Notes. Microthalestris sarsi sp. nov. can readily be distinguished from other congeners that exhibit a 3-segmented exopod in the male by the absence (or possibly extreme reduction) of the outer seta on exp-1. Confirmation of this character in Lang’s (1936b) male of Parastenhelia forficula from the Øresund corroborates its conspecificity with M. sarsi sp. nov. Sars (1905) himself listed the records from the British Isles (Scott 1894b, 1897; Scott & Scott 1894 – all as T. forficuloides; Scott 1900 – as T. forficulus), the Bohuslän coast in Sweden (P.T. Cleve, unpubl. data), between Kolguev and Novaya Zemlya (Scott & Scott 1901 – as T. forficulus), Bear Island (Bjørnøya) and Hope Island, Svalbard (Scott & Scott 1901 – as T. forficulus), Franz Josef Land (Scott 1899 – as T. forficula), and the Arctic islands north of Grinnell Land, Canada (subsequently published by Sars 1909) as valid but considered the conspecificity of Scott’s (1894a – as T. forficula) record from the Gulf of Guinea questionable. It is now clear that at least the illustrated records of T. forficuloides (Scott 1894b; Scott & Scott 1894) are not conspecific with M. sarsi sp. nov. (see above) and that the Arctic records by Scott (1899), Scott & Scott (1901) and Sars (1909) may in reality refer to M. polaris sp. nov. (see below).