Wellstenhelia euterpe Karanovic & Kim 2014, sp. nov.

Wellstenhelia euterpe sp. nov.

(Figs. 30–33)

Type locality. South Korea, South Sea, Gwangyang Bay, sampling station 2, muddy sediments, 34.881861°N 127.635083°E (Fig. 1).

Specimens examined. Female holotype dissected on one slide (collection number NIBRIV0000232689), female paratype mounted on SEM stub (collection number NIBRIV0000232690), type locality, 39 July 2012, leg. K. Kim.

Etymology. The species is named after Euterpe (Ancient Greek: Eύτέρπη), one of nine Muses from Greek mythology, who was a patron of lyric poetry and song. The species name is a noun in apposition (in the nominative case).

Description. Female (based on holotype and one paratype). Body length 460 µm and 373 µm respectively. Integument thick and surface smooth, without minute pits. Body segmentation, colour, nauplius eye, and hyaline fringes as in Wellstenhelia calliope sp. nov. Most somite ornamentation also similar to Wellstenhelia calliope, and presumed homologous pore and sensilla numbered with same Arabic numerals (see Figs. 30A, B, 31A, B, C, D, E, 32A) to allow easier comparison. Habitus (Figs. 30A, B, 33A) more robust, with prosome/urosome length ratio 1.3, body length/width ratio about three, cephalothorax twice as wide as genital double-somite.

Rostrum (Fig. 30A, C) similar in shape and ornamentation to Wellstenhelia calliope but dorsal pore no. 2 position much more anterior (arrowed in Fig. 30C) and rostrum larger in comparison to cephalothorax.

Cephalothorax (Figs. 30A, B, 31A, B, 33B) about 0.85 times as long as wide; comprising 28% of total body length. Surface of cephalothoracic shield with 34 paired or unpaired sensilla and pores, most of which probably homologous to those in Wellstenhelia calliope (indicated with Arabic numerals in illustrations), but 12 pores and sensilla missing (nos. 4, 6, 7, 10, 14, 16, 19, 21, 33, 34, 35, 37, 39); absolute and relative positions of some pores and sensilla differ and posterior dorsal sensilla no. 40 paired; six unique pores and sensilla indicated with geometric shapes in Fig. 31A, B.

Pleuron of second pedigerous somite (Figs. 31C, 33C) ornamented as in Wellstenhelia calliope, except lateral pair of sensilla no. 48 and anterior pair of pores no. 43 missing.

Pleuron of third pedigerous somite (Figs. 31D, 33C) ornamented as in Wellstenhelia calliope, except anterior pair of pores no. 51 more widely spaced.

Pleuron of fourth pedigerous somite (Figs. 31E, 33C) ornamented as in Wellstenhelia calliope, except anterior lateral pair of pores no. 57 missing.

First urosomite (Fig. 30A, B) as in Wellstenhelia calliope, except pores nos. 63 & 67 missing.

Genital double-somite (Figs. 30A, B, 32A, 33D) as in Wellstenhelia calliope, except much more slender, with dorsal pair of sensilla no. 69 more widely spaced, anterior pore no. 68 missing, and shorter ventral row of spinules (arrowed in Fig. 32A).

Last three urosomites (Figs. 30A, B, 32A) as in Wellstenhelia calliope, except for shorter ventral row of spinules (arrowed in Fig. 32A) and more closely spaced sensilla pair no. 77 on first of them, as well as somewhat stronger spinules in anal sinus.

Caudal rami (Figs. 30A, B, 32A, B, 33E) short and stout, much shorter than in Wellstenhelia calliope (arrowed in Figs. 30A, B, 32A, B), about as long as anal somite, cylindrical, 1.7 times as long as wide (ventral view), parallel, with space between them about one ramus width; most ornamentation and all armature as in Wellstenhelia calliope, except both ventral pores (nos. 82, 83) missing.

Antennula (Figs. 31F, 33F) ornamentation and armature as in Wellstenhelia calliope, except first segment with more spinules in distal row and sixth segment proportionately shorter (arrowed in Fig. 31F).

Antenna (Fig. 30D, E), labrum, and paragnaths as in Wellstenhelia calliope.

Mandibula (Fig. 30F) as in Wellstenhelia calliope, except with larger spinules on basis (arrowed in Fig. 30F) and additional row of spinules on coxa (arrowed in Fig. 30F).

Maxillula, maxilla (Fig. 30G), and maxilliped (Fig. 30H) as in Wellstenhelia calliope, except maxilliped with row of long and slender spinules on coxa (arrowed in Fig. 30H).

Swimming legs (Fig. 32C, D, E, F, G) segmentation, most ornamentation, most armature, and proportions of various armature elements as in Wellstenhelia calliope, except all legs without anterior pore on first endopodal segment, first leg without inner spinules on coxa (arrowed in Fig. 32C), second leg with proximal row of spinules on coxa slightly longer (arrowed in Fig. 32E) and with additional inner seta on third endopodal segment (arrowed in Fig. 32F), and fourth leg with distal inner seta on third endopodal segment less spiniform (arrowed in Fig. 32G).

Fifth leg (Figs. 30B, 31G, 32A, 33D) segmentation, general shape, and most armature and ornamentation as in Wellstenhelia calliope, except innermost endopodal seta missing (arrowed in Figs. 30B, 31G, 32A), two additional rows of anterior spinules of basis (arrowed in Fig. 31G), and endopodal lobe without spiniform process at base on exopod (arrowed in Fig. 31G). Length ratio of endopodal setae, starting from inner side, 1: 1.2: 0.85. Length ratio of exopodal setae, starting from inner side, 1: 0.5: 0.3: 0.85: 0.8: 0.5.

Sixth leg as in Wellstenhelia calliope.

Male. Unknown.

Variability. Only two females were studied and no variable morphological feature was observed.

Morphological affinities. Wellstenhelia euterpe sp. nov. differs from all congeners by the armature of the female fifth leg endopod, which bears only three setae (Fig. 31G). The complete reduction of the innermost element is considered here a clear autapomorphy. Other unique features of this species include two inner setae on the third endopodal segment of the second swimming leg (Fig. 32F) and slender distal inner seta on the third endopodal segment of the fourth swimming leg (Fig. 32G), but these are plesiomorphic character states in a larger group of stenheliins. Compared to other congeners, Wellstenhelia euterpe has the smallest body, shortest caudal rami (Fig. 32A, B), shortest sixth antennular segment (Fig. 31F), and smoothest and thickest cuticulum. It also has a unique position of the dorsal rostral pore (Fig. 30C), which is much more anterior than in other congeners, but the state of this character is unknown in Wellstenhelia bocqueti (Soyer, 1971) comb. nov., Wellstenhelia hanstromi (Lang, 1948) comb. nov., and Wellstenhelia melpomene sp. nov. (see Lang 1948; Soyer 1971; Kornev & Chertoprud 2008). Other unique features include position and/or presence of several pores and sensilla on somites (Figs. 30A, B, 31A, B, C, D, E), size of spinules on the mandibula (Fig. 30F) and maxilliped (Fig. 30H), and presence of two rows of large spinules on the basal part of the female fifth leg baseoendopod (Fig. 31G). Quite clearly this species has no close relatives among recent congeners. Unfortunately, the males are still unknown.