Archinotodelphyidae Lang, 1949

Kim, Il-Hoi & Boxshall, Geoff A., 2020, A revision of the family Archinotodelphyidae Lang, 1949 (Copepoda: Cyclopoida Oithonida), with the recognition of 15 new species, Zootaxa 4801 (1), pp. 1-56 : 3-5

Family Archinotodelphyidae Lang, 1949

Diagnosis of family Archinotodelphyidae

Body cyclopiform in both sexes: prosome comprising cephalosome and 4 free pedigerous somites. Dorsal cephalosomic shield typically distinctly wider than first pedigerous somite; posterolateral corners of shield sometimes produced over tergite of first pedigerous somite. Urosome 5-segmented; with genital and first abdominal somites fused to form genital double-somite in female; plus 3 free abdominal somites. Genital apparatus variable in female: paired or single median copulatory pore located on ventral surface of double-somite; paired gonopores located dorsolaterally on double-somite. Urosome 6-segmented in male; comprising fifth pedigerous, genital and 4 abdominal somites: paired genital apertures located on ventral surface. Caudal rami typically slender, with 6 setae. Paired external egg sacs with multiseriate arrangement of eggs.

Rostrum well developed, anteriorly or postero-ventrally directed. Nauplius eye present. Female antennule 10- to 17-segmented; segmental homologies in 17-segmented antennule: I-II, III-V, VI-IX, X, XI, XII-XIV, XV-XVI, XVII, XVIII, XIX, XX, XXI, XXII, XXIII, XXIV, XXV, XXVI-XXVIII. Male antennule geniculate on both sides; ranging from 12-segmented with geniculation between segments 10 (XIX-XX) and 11 (XXI-XXIII) to 17-segmented with geniculation between segments 15 (XIX-XX) and 16 (XXI-XXIII).

Antenna biramous; with coxa and basis separate; coxal seta lacking; basis bearing inner seta plus 1 or 2 setae on outer margin representing exopod; endopod 3-segmented; segment 1 with 1 seta, segment 2 with 1 inner and 4 distal setae (or reduced), segment 3 with 1 claw and up to 6 setae. Mandible comprising coxa with well-developed gnathobase and biramous distal palp: palp consisting of basis armed with 1 inner seta, 2-segmented endopod and 4-segmented exopod; endopodal segments 1 and 2 with between 1 and 6, and up to 10 setae, respectively; exopodal segments typically armed with 1, 1, 1, and 1/2 setae. Maxillule biramous, comprising 3-segmented protopod bearing 1-segmented exopod and 1 or 2-segmented endopod; precoxa with arthrite bearing between 9 and 11 elements; coxa with endite bearing 1 seta and with 2 setae on outer surface of segment representing epipodite; basis with proximal and distal groups of 2 to 3 and 4 to 5 setae, representing endites: endopod typically 1-segmented and armed with up to 12 setae, rarely indistinctly 2-segmented (as in A. bimerus sp. nov.): exopod armed with 4 setae. Maxilla primitively 6-segmented with precoxa and coxa separate, or 5-segmented with precoxa and coxa fused to form syncoxa; setal groups of 4, 1, 2/3 and 3 setae representing precoxal and coxal endites; basis with claw plus 1 or 2 setae; free endopod 3-segmented; segments 1 to 3 armed with 2, 2, 4 elements, respectively, or with setation reduced. Maxilliped primitively 4-segmented; syncoxa armed with groups of 1, 3/5, and 2/5 setae representing endites; basis with 1 or 2 setae; endopod primitively 2-segmented with each segment bearing up to 4 setae; endopodal segments often fused to form compound segment carrying maximum of 7 setae.

Swimming legs 1 to 4 biramous with 3-segmented rami. Spine and seta formula typically as follows:

coxa basis exopod endopod

leg 1 0-1 1-I I-1; I-1; III,I,4 0-1; 0-1; 1,2,3

leg 2 0-1 1-0 I-1; I-1; III,I,5 0-1; 0-2; 1,2,3

leg 3 0-1 1-0 I-1; I-1; III,I,5 0-1; 0-2; 1,2,3

leg 4 0-1 1-0 I-1; I-1; II,I,5 0-1; 0-2; 1,2,2

Inner coxal seta present in legs 1 to 4, sometimes lost from legs 3 and 4. Outer spine on second exopodal segment lost in legs 2 to 4 in Archinotodelphys nudus sp. nov.

Female fifth leg comprising 1-segmented protopod with outer basal seta, and 1-segmented exopod bearing 4 or 6 setal elements. Male fifth leg typically as in female; rarely sexually dimorphic, with 6 setal elements on exopodal segment in male but only 4 in female (as in A. antarcticus sp. nov.). Leg 6 represented by 1 to 3 setae on genital operculum of female; by 3 setae in male.

Type-genus: Archinotodelphys Lang, 1949 .

Remarks. Currently five species of archinotodelphyids placed in two genera are recognized as valid ( Boxshall & Halsey, 2004), but here we provide descriptions of 14 new species. We also recognize Archinotodelphys polynesiensis Monniot, 1986 as a species complex (as discussed below). The availability of a much wider range of taxa within the family revealed numerous apparent series of changes in setal patterns (see Table 2). For example, the first endopodal segment of the mandible carries 6 setae in five species, 5 in one species, 4 in 13 species and 1 seta in a single species. Similarly, the number of setae on the endopod of the maxillule varies from 12 in two species, 11 in two species, 10 in seven species, 9 in one species, 8 in seven species and 5 in a single species. [The possession of 12 setae in Pararchinotodelphys phallusiae ( Hansen, 1923) and in A. polynesiensis is in need of confirmation.] The key diagnostic character that Lang (1949) used to distinguish between his two genera was the number of segments on the endopod of the maxilliped: Archinotodelphys has a 2-segmented endopod whereas in Pararchinotodelphys it is unsegmented. Twelve of the species documented in this paper have a 2-segmented endopod, while the other eight lack any articulation separating proximal and distal endopodal segments. There is considerable variation in the setation of various limbs but most of these character transformations are gradual and we detect no major dichotomy that is common to these different transformation series or that is congruent with the change in segmentation of the endopod of the maxilliped.

The other diagnostic character used by Lang (1949) to support the recognition of Pararchinotodelphys as a new genus was “abdomen in female four-segmented”. Hansen’s figure of female P. phallusiae ( Hansen, 1923: pl. I, Fig. 1a) clearly shows the urosome as comprising a short fifth pedigerous somite, a large genital double-somite and three free abdominal somites. Lang (1949) presumably included the genital double-somite in his count of “abdominal segments”. Lang’s figure ( Lang, 1949: Fig. 13) of Archinotodelphys typicus Lang, 1949 was labelled “Abdomen” but the relative lengths of the five somites (i.e. the first somite is the shortest and is likely to be the fifth pedigerous somite, the second is the longest and likely to be the genital double-somite, and the remaining three somites are free abdominal somites) suggest that this illustration depicts the entire urosome. On this basis we believe that Lang was mistaken in his interpretation. Indeed, Huys & Boxshall (1991) examined material of A. typicus obtained from, and identified by, Claude Monniot and figured a genital double-somite in this species ( Huys & Boxshall, 1991: Fig. 2.8.31D-F). It appears that the female urosome is 5-segmented in all archinotodelphyids.

We found no evidence to support the maintenance of Pararchinotodelphys as a valid genus distinct from Archinotodelphys : recognizing two genera leaves one paraphyletic. We currently recognize only a single genus within this family, the type genus Archinotodelphys . As a consequence of treating Pararchinotodelphys as a junior subjective synonym of Archinotodelphys , two new combinations are created, A. phallusiae ( Hansen, 1923) comb. nov. and A. gurneyi ( Illg, 1955) comb. nov.

The descriptions of some of the existing nominal species appear to contain inaccuracies: for example, the presence of only 1 outer seta representing the exopod of the antenna in A. gurneyi comb. nov. and A. phallusiae comb. nov., rather than 2 as present in all other species suggests that the second (often very small) seta has been overlooked or broken off during dissection in these species, Similarly, the setation of the second endopodal segment of the antenna is given as 2 + 0 and 2 + 1 in these two species, respectively, and we consider it probable that some setae have been missed. Doubtful setal counts such as these have been avoided in our comparisons and in the key to species provided here. Monniot’s (1968) description of the maxilliped of A. profundus as 6-segmented is based on misinterpretation of transverse folds associated with the margins of the endites on the syncoxa, as segmental articulations.