Lytocarpia phyteuma ( Stechow, 1919b )

Calder, Dale R. & Faucci, Anuschka, 2021, Shallow water hydroids (Cnidaria, Hydrozoa) from the 2002 NOWRAMP cruise to the Northwestern Hawaiian Islands, Zootaxa 5085 (1), pp. 1-73 : 51-52

Lytocarpia phyteuma ( Stechow, 1919b)

Fig. 14f

Aglaophenia phyteuma Kirchenpauer, 1876: 23 , 33 [nomen nudum].

Thecocarpus phyteuma Stechow, 1919b: 139 , figs C 2, D 2.

Lytocarpia phyteuma .— Coles et al., 2002b: 90, 177.—Carlton & Eldredge, 1009: 36.

Type locality. Tonga ( Stechow 1919b, as Thecocarpus phyteuma ) .

Voucher material. Pearl & Hermes Atoll, 19.ix.2002, one colony, 2.4 cm high, without gonophores, coll. A. Faucci, ROMIZ B5468.—Pearl & Hermes Atoll, 19.ix.2002, two colonies or colony fragments, to 3.5 cm high, one with a developing corbula, coll. A. Faucci, ROMIZ B5483.—Pearl & Hermes Atoll, 19.ix.2002, four colonies or colony fragments, to 4.8 cm high, with corbulae, coll. A. Faucci, ROMIZ B5484.

Remarks. The hydroid examined here from Pearl & Hermes Atoll is essentially indistinguishable from accounts of Lytocarpia phyteuma ( Stechow, 1919b) by Stechow (1919b), Millard & Bouillon (1973), Watson (2000), and Di Camillo et al. (2011). It also resembles the original descriptions of Thecocarpus leopoldi Leloup, 1930a from West Papua, Indonesia, and especially Aglaophenia clavicula Whitelegge, 1899 , from Funafuti, Tuvalu, both now regarded as conspecific with L. phyteuma ( Pennycuik 1959; Vervoort & Vasseur 1977; Watson 2000; Schuchert 2003; Vervoort & Watson 2003; Di Camillo et al. 2011). Watson (2000) and Di Camillo (2011) questioned the identity of hydroids from Moorea assigned to this species by Vervoort & Vasseur (1977) given their longer hydrothecae and downward angle of the lateral nematothecae. In those characters they are also unlike the specimen examined here.

The specific name of this species first appeared, as Aglaophenia (Calathophora) phyteuma , in a work by Kirchenpauer (1876: 23, 33). It is therefore almost universally credited to him in current literature on hydroids. Nomenclaturally, however, Kirchenpauer provided neither a description, nor an illustration, nor an “indication” to accompany the name ( Calder & Brinckmann-Voss 2011), rendering it a nomen nudum (ICZN, 1999, Art. 12.1), indistinguishable from a group of 12 other associated species in his work. The name was first made available by Stechow (1919b), as Thecocarpus phyteuma , in an examination of Kirchenpauer’s material. Both the trophosome and the corbula of the species were described and illustrated in that work by Stechow. In having a hydrotheca at the base of each rib, this species is referable under current hydrozoan classification to Lytocarpia Kirchenpauer, 1872 . Thecocarpus Nutting, 1900 , a name utilized by Stechow and by many others long after, is an objective junior synonym of Lytocarpia in that the type species of both genera is Sertularia myriophyllum Linnaeus, 1758 . Lytocarpus , another name often encountered in older literature, is an unjustified emendation of Lytocarpia introduced by Allman (1883). It was accompanied by a redefinition that created taxonomic confusion by altering the concept of the genus ( Calder 1997).

In not having been made nomenclaturally available until the work of Stechow (1919b), the familiar binomen Aglaophenia phyteuma is threatened by Aglaophenia clavicula Whitelegge, 1899 , a little-known senior subjective synonym. In the interests of nomenclatural stability, Reversal of Precedence provisions under the code (ICZN 1999, Art. 23.9) have been applied here to preserve current usage. Thus, while the senior synonym ( A. clavicula ) has been unused as a valid name in zoology since its original description in a work by Whitelegge (1899) (ICZN 1999, Art. 2.9.1.1), its junior synonym ( Thecocarpus phyteuma Stechow, 1919b ) has been used for a particular taxon, as its presumed valid name, in at least 25 publications by 10 or more authors in the past 50 years, and encompassing a time interval of not less than 10 years (ICZN 1999, Art. 2.9.1.2) (e.g., Millard & Bouillon 1973; Vervoort & Vasseur 1977; Ryland & Gibbons 1991; Bouillon et al. 1995; Watson 2000; Coles et al. 2002b, 2003; Schuchert 2003; Vervoort & Watson 2003; Preker & Lawn 2005; Leclère et al. 2007; Moura et al. 2008, 2012, 2018, 2019; Di Camillo et al. 2008, 2011; Carlton & Eldredge 2009; Reijnen et al. 2011; Calder & Brinckmann-Voss 2011; Gravier-Bonnet & Bourmaud 2012; Maronna et al. 2016; Postaire et al. 2016a, b; Boissin et al. 2018; Mulochau et al. 2020).

Lytocarpia phyteuma is currently taken to be a species of the tropical Indo-west Pacific and central Pacific. Its reported range extends from waters off east Africa ( Postaire et al. 2016b; Boissin et al. 2018; Mulochau et al. 2020) to Moorea, French Polynesia ( Postaire et al. 2016b). Records of it from the Mediterranean Sea (Garcia-Corrales et al. 1978, as Thecocarpus phyteuma ; Boero & Bouillon 1993, as T. phyteuma ) were based on Aglaophenia kirchenpaueri ( Heller, 1868) ( Vervoort & Watson 2003) .

Yet, recent molecular phylogenetic studies reveal that L. phyteuma is polyphyletic ( Maronna et al. 2016; Postaire et al. 2016b; Moura et al. 2019), comprising at least six putative species, with three lineages in each of two sister clades ( Moura et al. 2018). One of these is a tropical Pacific clade, with one lineage from New Caledonia and two from Moorea. The other is a predominantly Indian Ocean clade, although a population from the Bonin Islands, Japan, exists in one of its three lineages. There is also agreement in such studies that L. phyteuma is separated phylogenetically from Sertularia myriophyllum , type species of Lytocarpia , while being proximate to several species of Aglaophenia Lamouroux, 1812 , including its type species, Sertularia pluma Linnaeus, 1758 ( Postaire et al. 2016b; Moura et al. 2018). While this has potential implications for nomenclature, current classification is maintained for now in utilizing the binomen L. phyteuma for the species.

The genus Lytocarpia has likewise been shown to be polyphyletic, with multiple lineages occurring at relatively distant phylogenetic positions ( Postaire et al. 2016b; Moura et al. 2018). Based on current evidence from genetic studies, Lytocarpia is closest to Aglaophenia , Macrorhynchia Kirchenpauer, 1872 , and Taxella Allman, 1874b ( Moura et al. 2018). The need for an assessment of taxonomically sound morphological characters in the Aglaopheniidae Marktanner-Turneretscher, 1890 , and a generic revision of the family, is therefore obvious.

Reported Distribution. Hawaiian archipelago. Oahu: Waikiki, Atlantis wreck, 20–30 m ( Coles et al. 2002b).

Elsewhere. Tropical Indo-west Pacific ( Leloup 1930a, b, as Thecocarpus leopoldi ; Pennycuik 1959, as T. phyteuma ; Millard & Bouillon 1973, as T. phyteuma ; Watson 2000; Schuchert 2003; Leclère et al. 2007; Moura et al. 2008, 2012, 2018, 2019; Di Camillo et al. 2008, 2011; Gravier-Bonnet & Bourmaud 2012; Maronna et al. 2016; Postaire et al. 2016b; Boissin et al. 2018; Mulochau et al. 2020); central Pacific ( Whitelegge 1899, as Aglaophenia clavicula ; Stechow 1919b, as T. phyteuma ;? Vervoort & Vasseur 1977, as T. phyteuma ; Ryland & Gibbons 1991; Vervoort & Watson 2003; Coles et al. 2003; Postaire et al. 2016b; Moura et al. 2018).

Figures

FIGURE 14. Aglaopheniidae. a, Aglaophenia postdentata Billard, 1913, part of a cladium with two hydrothecae, Gardner Pinnacles, ROMIZ B5462. Scale equals 0.1 mm. b, Aglaophenia suensonii Jäderholm, 1896, part of a cladium with three hydrothecae, Laysan Island, ROMIZ B5463. Scale equals 0.1 mm. c, Aglaophenia suensonii Jäderholm, 1896, corbula, Laysan Island, ROMIZ B5463. Scale equals 0.2 mm. d, Aglaophenia whiteleggei Bale, 1888, part of a cladium with two hydrothecae, Pearl & HermesAtoll, ROMIZ B5464. Scale equals 0.1 mm. e, Lytocarpia flexuosa (Lamouroux, 1816), part of a cladium with three hydrothecae, Pearl & Hermes Atoll, ROMIZ B5479. Scale equals 0.1 mm. f, Lytocarpia phyteuma (Stechow, 1919b), part of a cladium with two hydrothecae, Pearl & Hermes Atoll, ROMIZ B5468. Scale equals 0.1 mm. g, Macrorhynchia philippina Kirchenpauer, 1872, part of a cladium with two hydrothecae, Midway Atoll, ROMIZ B5470. Scale equals 0.1 mm. h, Macrorhynchia phoenicea (Busk, 1852), part of a cladium with three hydrothecae, Gardner Pinnacles, ROMIZ B5475. Scale equals 0.1 mm. i, Macrorhynchia phoenicea (Busk, 1852), one phylactocarp, without gonothecae, Gardner Pinnacles, ROMIZ B5475. Scale equals 0.2 mm.