Phyllocheres, Humes, 1996

Bahiana, Bruna, Farias, Amilcar, Neves, Elizabeth & Johnsson, Rodrigo, 2025, The taxonomic status of Phyllocheres Humes, 1996 and Neoasterocheres Canário et al., 2017, and three new Asterocheres Boeck, 1859 species (Siphonostomatoida, Asterocheridae) from Brazil, Zootaxa 5696 (2), pp. 205-232 : 210-213

Regarding Phyllocheres validity

In the redescription of Phyllocheres petalus , type species of the genus, the major striking diagnostic features, such as the armatures of the third exopodal segment of leg 1 as III,I,3, the third endopodal segment of leg 1 as 1,1+I,3, and the third endopodal segment of leg 4 as 1,1+1,2, are not confirmed. Therefore, the unique species of Phyllocheres , based on the setation of legs 1 to 4, fits other genera, such as Asterocheres , and Neoasterocheres , among others.

The redefinition of Asterocheres as proposed by Kim (2010) is built on the antennule segmentation and leg 3 endopod setation as 1-1+I-3 and left many species a s inquirendae. According to Kim (2010), Asterocheres has an aesthetasc on the 18th segment (XXI), and therefore the 9th segment refers to the fusion of the ancestral segments IX–XII.

Setacheres , as proposed by Johnsson et al. (2016), gathered 8 of the species inquirendae previously assigned to Asterocheres , and it is characterized by the third endopodal segment of leg 3 having 1-2-3.

Six other species inquirendae were grouped in Neoasterocheres according to Canário et al. (2017), which shows the antennule of female majorly 19-segmented, with large aesthetasc on the 17th segment and ancestral segments IX–XIII fused.

However, among the other characteristics included in the diagnosis of Phyllocheres, Humes (1996) states that the female antennule is 19-segmented with aesthetasc on segment 17. This condition implies the fusion of ancestral segments IX to XIII, the same apomorphic characteristic used by Canário et al. (2017) when establishing the genus Neoasterocheres to accommodate the species inquirendae excluded from Asterocheres .

With the exclusion of setation characteristics mentioned above from the diagnosis of Phyllocheres , its major diagnostic features are the same as the ones used by Canário et al. (2017) to erect Neoasterocheres . Therefore, following the principle of priority of the International Code of Zoological Nomenclature, Neoasterocheres has to become a junior synonym of Phyllocheres .

Phyllocheres Humes, 1996

Emended diagnosis. Asterocheridae . Body cyclopiform. Prosome 4-segmented in female, 5-segmented in male. Antennule 18- to 20-segmented in female with aesthetasc on segment 17; ancestral segments IX–XIII fused; distal 3 segments frequently fused to become 1 or 2 segments. In males, 17 or 18-segmented with aesthetasc on segment 15 to 17, and ancestral segments IX-XIII are fused. Exopod of antenna 1-segmented; 3-segmented endopod with terminal segment bearing distal claw. Oral cone short or elongated, siphon-like. Mandible consisting of stylet and 1- or 2-segmented palp bearing two distal setae. Maxillule bilobed. Maxilla 2-segmented; distal segment forming curved claw. Maxilliped 5- or 6-segmented, sexually dimorphic, with medial prominence on second segment. Legs 1-4 biramous, with both rami 3-segmented; second segment of endopods with 2,2,2,2. Leg 5 with free segment bearing 2 or 3 setae.

Remarks. The antennule has a well-defined condition regarding the proximal region by exhibiting the fused segment composed of the ancestral segments IX-XIII. the original diagnosis of Neoasterocheres proposed by Canário et al. (2017) defines the maxilliped as 6-segmented, as seen in on N. breviseta Canário et al., 2017 , however, N. humesi Varela, 2012 , N. scutatus Stock, 1966 , N. serrulatus Humes, 1996 , N. dysideae Humes, 1996 , N. enewetakensis Humes, 1997 , N. rotundus Malt, 1991 exhibit a 5-segmented maxilliped. As Phyllocheres also has a 5-segmented maxilliped ( Humes, 1996a), the diagnosis of the maxilliped now acknowledges this variation.

Additionally, Asterocheres spongus Johnsson, 2002 , species treated as inquirendum by Kim (2010) in his redefinition of Asterocheres , also exhibits the ninth antennule segment composed of the fused ancestral segments IX–XIII, with the aesthetasc on the 17th segment, plus a terminal segment and a 5-segmented maxilliped. By presenting this set of features, this species should also be reassigned to the genus Phyllocheres as P. spongus ( Johnsson, 2002) .

Type species by original designation: Phyllocheres petalus Humes, 1996

Other species:

P. breviseta ( Canario, Rocha, Neves & Johnsson 2017) comb. nov.

P. dysideae (Humes 1996) comb. nov.

P. enewetakensis ( Humes 1997) comb. nov.

P. humesi ( Varela 2012) comb. nov.

P. rotundus ( Malt 1991) comb. nov.

P. scutatus (Stock 1966) comb. nov.

P. serrulatus (Humes 1996) comb. nov.

P. spongus ( Johnsson, 2002) comb. nov.

Phyllocheres petalus shares the 19-segmented female antennule with aesthetasc on the 17th segment with seven congeners: P. breviseta ( Canário, Rocha, Neves & Johnsson, 2017) , P. dysideae (Humes, 1996) , P. enewetakensis ( Humes, 1997) , P. humesi ( Varela, 2012) , P. rotundus ( Malt, 1991) , P. scutatus (Stock, 1966) , and P. serrulatus (Humes, 1996) .

Phyllocheres petalus can be differentiated from P. breviseta , P. humesi , and P. rotundus by exhibiting three setae on the antennal exopod, while those species exhibit only two setae ( Malt 1991; Varela 2012; Canário et al. 2017). The mandibular palp on P. petalus , is 2-segmented, differing from P. scutatus , which is 1-segmented ( Stock 1966a). And ultimately, P. petalus exhibits three equally sized setae on the free segment of leg 5, differing from P. dysideae , P. spongus , and P. enewetakensi , which show three unequally-sized setae, and also from P. serrulatus , which shows only two equally sized setae ( Humes 1996a; 1996b; Humes 1997; Johnsson 2002; Canário et al. 2017).

Phyllocheres petalus exhibits produced epimera on both posterolateral margins of the cephalosome, reaching beyond the anterior margin of the genital somite in both sexes, creating a half-moon-shaped cephalosome as an exclusive feature for the species.