Itaipusa

Reygel, Patrick C., Willems, Wim R. & Artois, Tom J., 2011, Koinocystididae and Gnathorhynchidae (Platyhelminthes: Rhabdocoela: Kalyptorhynchia) from the Galapagos, with the description of three new species, Zootaxa 3096, pp. 27-40 : 35-36

Discussion on Itaipusa

Both new species of Itaipusa , I. biglandula and I. renei possess all diagnostic characters of the taxon Itaipusa as given by Karling (1980): muscular copulatory bulb with an irregular (spiny) cirrus or (spiny) papilla, often combined with strong hooks; filiform prostate ducts; seminal receptacle (i.e. female duct) opening distally in a caudallylocated bursa; testes at about half body length; strong proboscis juncture sphincter of the Itaipusa - type and a pharynx without a closed mouth sphincter.

As to the bursal organs in koinocystidids, Karling (1980) distinguishes between a (primary) bursa, which is mostly surrounded by strong circular muscles, and a resorptive vesicle, which is not muscular, and which is proximally connected to the muscular primary bursa. Additionally, he recognises a “receptacle bursa” which is a swollen, sperm-containing duct between the (stalk of the) primary bursa and the distal sphincter of the seminal receptacle. This terminology is mainly based on conjectures regarding the evolutionary trends in the origin of these structures (for details: see Karling 1980: p. 264−265). However, to allow comparison with other kalyptorhynchs we prefer here a more traditional terminology in which the distal, sperm-resorbing part is called a bursa (the “resorptive vesicle” of Karling 1980) and the muscular duct that connects it to the common genital atrium a bursal stalk. This bursal stalk can be swollen and contain sperm (the “primary bursa” of Karling 1980). The “receptacle bursa” of Karling (1980), occurring in a number of species (e.g. I. ruffinjonesi Karling, 1978 ), on the other hand is typical of koinocystidids and is not found in any other kalyptorhynch taxon.

Whereas the epidermis of I. biglandula is syncytial, the epidermis of I. renei is cellular. Whether the epidermis is cellular or not is an important taxonomical marker in kalyptorhynch systematics. Karling (1980) considers the cellular epidermis, consisting of “distinctly delimited cells”, to be a putative symplesiomorphy not only of species of Koinocystididae , but of rhabdocoels in general. However, he does not elaborate on the distribution of this character state in members of the family. In many cases, species descriptions in literature do not mention the nature of the epidermis, but it is clear that both a cellular and a syncytial epidermis occur within the taxon Koinocystididae , and even species of the same genus may differ as to this character. Apparently, all species of Utelga Marcus, 1949 have a cellular epidermis ( Ax 1959), whereas all species of Koinocystis Meixner, 1924 have a syncytial one ( Meixner 1924; Karling 1954). For the latter genus, this conclusion is mainly based on the statement by Meixner (1925: p. 261) that all species of kalyptorhynchs posses a syncytial epidermis. Within the genus Itaipusa , the epidermis can be syncytial or cellular, depending upon the species considered. Our study shows that the epidermis of I. divae is indeed syncytial, as was already mentioned by Marcus (1949), who described the epidermal cell borders as “generally indistinct” ( Marcus 1949: p.28: os limites inter-celulares, geralmente indistintos). Brunet (1972) also mentions a syncytial epidermis for I. similis ( Brunet, 1972) . I. biglandula , therefore, is the third species for which it is sure that the epidermis is syncytial. Apart from in I. renei , a cellular epidermis is also found in I. acerosa ( Brunet, 1972) Karling, 1980 (see Brunet, 1972), I. scotica ( Karling, 1954) Karling, 1978 (see Karling 1954), I. sophiae ( Graff, 1905) Karling, 1978 (see Ax 1959) and I. variodentata (see Karling et al. 1972; confirmed in this study). Data are lacking for all other species of Itaipusa . From the above it is clear that at the moment it is not easy to assess which situation is plesiomorphic within Koinocystididae . Only a thorough phylogenetic analysis can elucidate this question.

At present 13 species of Itaipusa have been described. Five species ( I. bispina Karling, 1980 , I. curvicirra Karling, 1980 , I. evelinae ( Marcus, 1954) Karling, 1980 , I. riegeri Karling, 1978 and I. ruffinjonesi ) have a male copulatory organ combining a cirrus armed with small spines and some larger hooks ( Karling 1980). This combination is also found in I. renei , although the spines in this species are considerably smaller and the hooks are not pointed as in the above-mentioned species. A tubiform penis papilla, as in I. evelinae (see Marcus 1954; Karling 1980) or an accessory cirrus as in I. riegeri and I. variodentata are missing in I. renei . In I. bispina the hooks are located in side pockets of the male atrium ( Karling 1980), whereas they are situated in the male atrium proper in I. renei and the other four species ( Marcus 1954; Karling et al. 1972; Karling 1978, 1980). Another striking feature in this species group is the detailed structure of the female system and the bursa. In I. evelinae and I. ruffinjonesi , a so-called receptacle bursa (the most distal part of the female duct, which is swollen and highly muscular and is separated from the proximal part of the female duct by a strong sphincter; see above) is present ( Marcus 1954; Karling 1978, 1980). In all other species of the group, including I. renei such a receptacle bursa is missing. In I. curvicirra , I. renei , I. riegeri and I. variodentata , the bursa is non-muscular and connected to the genital atrium by a muscular bursal stalk. In I. bispina also the bursa proper is muscular ( Karling et al. 1972; Karling 1978, 1980).

The presence of an unarmed penis papilla as in I. biglandula is unique within the taxon Itaipusa . I. scotica ; I. sophiae and I. evelinae have a penis papilla, but in these species it is provided with spines, and therefore armed. This situation is referred to as a permanently-everted cirrus ( Karling 1980). Even within the Koinocystididae an unarmed penis papilla is very uncommon, and only found in four species: Neoutelga inermis Karling, 1980 , Sekerana stolzi ( Sekera, 1912) Strand, 1914 ; Tenerrhynchus magnus Brunet, 1972 and Parautelga biloi Karling, 1964 (see Karling 1980). However, these four species differ in many characters from the species of Itaipusa (see Meixner 1925; Karling 1964, 1980; Brunet 1972), whereas the new species from Galapagos shows all diagnostic features of this taxon. Hence we decide to keep the new species within Itaipusa . Another unique feature of I. biglandula is the presence of the two globular complexes of glands, surrounding the opening of the female duct into the common genital atrium.