Oerstediidae Chernyshev 1993

Dataset
Higher classification of the Monostilifera (Nemertea: Hoplonemertea): Rank
FAMILY

Classification

kingdom
Animalia: phylum
Nemertea: class
Enopla: order
Monostilifera: family
Oerstediidae

description

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description

Oerstediina having a two-layered rhynchocoel wall; the cephalic vessels protrude into the rhynchocoel as they pass through cerebral ring; the mid-dorsal vessel does not penetrate the rhynchocoel to form a vascular plug. Clade definition Eumonostiliferans that are more closely related to Oerstedia dorsalis (Abildgaard, 1806) than to Plectonemertes sinensis Gibson, 1990 a. See the clade definition for Plectonemertidae for the potential problem stemming from the absence of molecular sequence data for Plectonemertes sinensis. Remarks Thollesson & Norenburg (2003) were the first to recognize the clade Oerstediidae, as treated herein, which in their molecular phylogeny included Antarctonemertes varvarae Chernyshev, 1999; Nemertellina yamaokai Kajihara et al., 2000; Oerstedia polyorbis Iwata, 1954 [two specimens, erroneously identified as Oerstedia venusta Iwata, 1954 and Oerstedia zebra (Chernyshev, 1993), respectively; see Akhmatova et al. (2012) for the corrected identifications]; ‘ Tetrastemma ’ elegans (Girard, 1852); and ‘ Tetrastemma ’ wilsoni Coe, 1943. Thollesson & Norenburg (2003) referred to this clade as Tetrastemmatidae, probably because it included two species of ‘ Tetrastemma ’; furthermore, Gibson (1982 a) had placed Nemertellina Friedrich, 1935 b in Tetrastemmatidae, and Bürger (1895) had once placed Oerstedia Quatrefages, 1846 in Tetrastemmatidae. In a subsequent study by Strand & Sundberg (2005 a), however, Tetrastemma flavidum Ehrenberg, 1828 (type species of Tetrastemmatidae) and Oerstedia dorsalis (Abildgaard, 1806) (type species of Oerstediidae) appeared in different clades, representing the Amphiporina and Oerstediina, respectively, as treated herein. The name Tetrastemmatidae should thus be used to denote a subclade in the Amphiporina, given the species identification of T. flavidum (see Nomenclatural notes below). Listed in Table 3 are species that have been confirmed to constitute Oerstediidae by means of molecular phylogenetics. Among the 24 species listed, none is known to possess a mid-dorsal vessel that penetrates to form a single vascular plug, and 18 are known to lack a single vascular plug on the mid-dorsal vessel (see also Table 4; Fig. 2 A – I); the vascular-system anatomy is unknown for the remaining six species. Instead of a vascular plug from the mid-dorsal vessel, these 18 species tend to have cephalic vessels protruding into the rhynchocoel lumen as they pass through the cerebral ring (Fig. 2 F – G; Kajihara et al. 2000: fig, 19; Kajihara et al. 2011: fig. 24), although the protrusions can be subtle in smaller specimens (Fig. 2 H, I). In larger species and specimens, the vascular epithelium in these protruding portions may be thickened (Fig. 2 A) and specialized (Fig. 2 D), so that these could be referred to as ‘ vascular plugs’ (perhaps a different terminology for the ‘ plugs’ in Oerstediina may prevent confusion: Gibson [pers comm.] suggests ‘ monovascular plug’ and ‘ bivascular plugs’ respectively, which I now propose). The ‘ vascular plug’ (or, vascular protrusion into the rhynchocoel) in hoplonemerteans presumably functions to facilitate material transfer between the blood vascular system and the rhynchocoel (Crandall 1993 a). Therefore, small-bodied species may actually lack a vascular plug because diffusion could compensate for its function. * Lacks a single vascular plug from the mid-dorsal vessel (see Table 4; Fig. 2). † Judging from the shape of the head, Antarctonemertes unilineata (Joubin, 1910) of Taboada et al. (2018) is different from Tetrastemma unilineatum Joubin, 1910 of Gibson & Tait (1984); furthermore, the latter has been reported i) to lack an accessory lateral nerve and ii) to possess a single vascular plug from the mid-dorsal vessel (see Table 6), each of which suggests a non- Antarctonemertes identity. ‡ “ Prosorhochmus nelsoni ” of Andrade et al. (2012) represents a different species, most likely as the result of mislabelling or a sample mix-up. Among specimens collected in Coquimbo (Chile) on 2 February 2009 by Per Sundberg were NemPhyl 27 (DNA 105586 at Museum of Comparative Zoology, Harvard; COI accession number HQ 848606) and the three specimens NemBar 0842 – 0844 (COI accession numbers KU 840164 – KU 840166; identical sequences); NemPhyl 27 was used in Andrade et al. (2012). BLAST searches with KU 840164 – KU 840166 (NemBar 0842 – 0844) indicate a 100 % match with EF 157586 [P. nelsoni identified by Maslakova & Norenburg (2008 a)] and close similarity to other congeners [P. belizeanus (EF 157591), P. claparedii (MH 106532), and P. americanus (HQ 848595)]. However, HQ 848606 (NemPhyl 27) differs from KU 840164 – KU 840166 and EF 157586 by 15.8 % in uncorrected p - distance. Prosorhochmus nelsoni of Maslakova et al. (2005) (Table 6) has been reported to possess a vascular plug.

Name

Homonyms: Oerstediidae Chernyshev 1993