Type material: 1♀ holotype dissected on five slides (NHM1990.421), 2♀ paratypes on four slides (NHM1990.422 – 423), 2♀ paratypes in tubes (NHM1990.1213 – 1214), collected by grab from the North Sea (site S58).
Other material examined: France: 3♀ in tubes (NHM1990.1215 – 1217), 1♀ on two slides (NHM1990.424), collected by grab from the subtidal, off Banyuls.
Description of female holotype
Length: Habitus 375 µm; sum of all somites 455 µm; cephalothorax 55 µm; genital double-somite 130 µm. Habitus fusiform (Fig. 4A). Cephalothorax gradually attenuating anteriorly. Rostrum broadly rounded and partially fused at base with cephalothorax and furnished with two small sensilla subapically. Labrum terminating in two spinous projections (Fig. 4B). Genital double-somite subdivided ventrally by a short transverse chitinous stripe and laterally by a suture. Penultimate somite with broadly rounded pseudoperculum.
Caudal ramus (Fig. 4C, D). Much shorter than broad. Principal setation and general form as in H. pseudosarsi Clément and Moore.
Somitic ornamentation (Fig. 4A, C, D). Body somites, apart from penultimate, sparsely furnished with sensilla and pores. Posterior margin of cephalothorax, first and second free thoracic somites unadorned. Posterior margin of third free thoracic somite and first urosomite finely spinulose. Genital double-somite with complex arrangement of rows of fine spinules and semi-incised subulate hyaline frill. Urosomite 4 with hyaline frill similar to preceding somite and furnished with one row of fine spinules dorsally and two rows ventrally. Penultimate somite with one spinular row and a fully incised subulate hyaline frill, which extends dorsally to pseudoperculum. Anal segment with posterior row of spinules, which become lappet-like dorsally.
Antennule (Fig. 5A). Short and six-segmented. Principal setation and form as in H. pseudosarsi.
Antenna (Fig. 5B). Coxa short. Basis with a short row of fine spinules along outer margin and a set of long setules at inner distal corner. Endopodite twosegmented; segment 1 unadorned, segment 2 furnished with two adjacent setae mid-way along inner margin and seven terminal setae (three spinulose geniculate, one dwarfed plumose). Exopodite threesegmented; basal segment well developed and armed with a short seta, second segment short and furnished with a seta, distal segment over twice as long as basal one and armed with two apical spinulose setae.
Mandible (Fig. 5C). Coxal gnathobase furnished with a spiniform seta and a slender seta at ventral base of unidentate pars incisiva and quadridentate lacinia. Basis with a row of fine spinules on surface, a set of setules on inner margin and three slender setae issuing from distal inner corner. Endopodite onesegmented and furnished with ten setae. Exopodite one-segmented with slender hairs along outer margin and armed with three setae, one of which is dwarfed.
Maxillula (Fig. 5D). Praecoxal arthrite broad and armed along distal edge with three unguiform spines and on surface with three small setae. Coxa very short and armed with a bare seta. Basis with six slender setae along inner margin. Exopodite small, onesegmented and furnished with two plumose setae. Endopodite one-segmented and carrying four setae.
Maxilla (Fig. 5E). Syncoxa broad, with two transverse rows of spinules around outer margin and furnished along its inner margin with two endites and a broad spiniform seta. Proximal endite armed with three broad, spiniform setae. Distal endite with three slender setae. Basis as broad as syncoxa, with a broad, spinulose seta with no base, accompanied by a diminutive seta, along its inner margin. Endopodite threesegmented, segments 1 and 2 armed with a thick and very long geniculate seta and the distal segment represented by a broad base from which one lateral and three distal confluent setae arise.
Maxilliped (Fig. 5F). Syncoxa short, armed with one seta and with a row of fine spinules on posterior face. Basis segment long, slightly tapering anteriorly and with strong spinules on posterior face and slender hairs along outer margin. Endopodite segment short, armed with two spinulose setae and two closely set bare apical setae.
P1–P4 (Fig. 6A–D). Coxa with two rows of spinules along distal edge in P2–P4, one row in P1. Exopod and endopod three-segmented, with setal formula as in H. mandibularis sp. nov.
P5 (Fig. 4E). Exopod slightly broader than long and separated from baseoendopod by a suture on posterior surface only. Anterior surface of baseoendopod with three rows of spinules. Inner expansion of baseoendopod reaching halfway along inner margin of exopod, with slender spinules along inner margin and with two broad spinulose setae distally, the inner seta shorter than outer seta. Outer expansion of baseoendopod with one slender seta. Exopod with several proximal spinule rows and with three spinulose lobes at distal edge, each armed with a thick seta: innermost seta short and much shorter than outer seta of inner expansion of baseoendopod; middle seta twice as long as innermost seta; outer seta thicker and longer than innermost seta. Surface-seta reaching beyond exopod and inserted just within proximal half of surface seta insertion line.
Variability: The following variation in length was observed among paratypes: habitus 375–390 µm; sum of all somites 435–450 µm; cephalothorax 135– 145 µm; genital double-somite 50 µm. Two specimens from Banyuls were slightly smaller with the following length: habitus 325–360 µm; sum of all somites 400– 405 µm; cephalothorax 125 µm; genital double-somite 45 µm.
Male. Unknown.
Etymology: The species name, latisetifera, alludes to the unusually broad nature of the marginal setae of the female P5.
Remarks
This species can be differentiated from other Halectinosoma species by the following characters: the female P5 is armed with characteristic broad spiniform setae; the inner expansion of the baseoendopod with an outer seta issuing from a lobe, which extends beyond the insertion point of the inner seta (the latter being also slightly shorter and not reaching beyond the outer seta); the proximal endite of the syncoxa of the maxilla with only three thick setae and the middle endite is represented by a large, broad seta between the proximal and distal endites; the syncoxa of the maxilliped is furnished with only one seta.
This species is most closely related to H. cooperatum Bodin, Bodiou & Soyer, 1970, as it shares some distinctive features such as the presence of a broad seta with no defined base along the inner margin of the basis of the maxilla, the characteristic setation of the mandibular exopod, the number of setae on the endopodite of the maxillula and an ornamented pseudoperculum. Halectinosoma latisetifera can be easily distinguished from H. cooperatum by the shape of the setae on the female P5.