Endomyzostoma scotia Summers, Al-Hakim & Rouse, 2014, n. sp.

Endomyzostoma scotia n. sp. Summers & Rouse

Fig. 2 A–E

Endomyzostoma cysticolum — Grygier (2000); Lanterbecq et al. (2006) Endomyzostoma sp. MZ-2009— Bleidorn et al. (2009)

Holotype: SIO-BIC A3865 (S6842) hologenophore (1 spm: 95% ethanol). Elephant Island, Antarctica (Stn. 2–83)(61°20.3263'S, 55°37.4961'W), 143– 162 m. Collected via the R/V Nathaniel B. Palmer using a Blake trawl on 23 October 2011 by Nerida Wilson, GWR, MMS, and science team. Genbank (COI—KM491738).

Host. Promachocrinus kerguelensis Carpenter (Antedonidae, Comatulida, Crinoidea). Clade A from Wilson et al. (2007). SIO-BIC E4910 (S6807). Genbank (COI—KM491767).

Paratypes: SIO-BIC A3870 syngenophore (S6847) (1 spm: 95% ethanol). Elephant Island, Antarctica (Stn. 2–83)(61°20.3263'S, 55°37.4961'W), 143– 162 m. Genbank (COI—KM491739). Collected via the R/V Nathaniel B. Palmer using a Blake trawl on 23 October 2011 by Nerida Wilson, GWR, MMS, and science team. Host: Promachocrinus kerguelensis clade A, SIO-BIC E4909 (S6812); Genbank (COI—KM491768). SIO-BIC A3841 (S6205) syngenophore (1 spm: 95% ethanol). Bransfield Strait, Antarctica (St. 2–89)(63° 20.5962'S, 59° 54.6094'W), 198– 213 m. Genbank (COI—KM491740). Collected via the R/V Nathaniel B. Palmer using a Blake trawl on 25 October 2011 by Nerida Wilson, GWR, MMS, and science team. Host: Promachocrinus kerguelensis clade A, SIO-BIC E4882 (S6332); Genbank (COI—KM491769). SIO-BIC A3849 (S6403) syngenophore (1 spm: 95% ethanol). Bransfield Strait, Antarctica (St. 1–87)(62° 45.1707'S, 57° 19.3005'W), 272– 292 m. Genbank (COI—KM491741). Collected via the R/V Nathaniel B. Palmer using a Blake trawl on 24 October 2011 by Nerida Wilson, GWR, MMS, and science team. Host: Promachocrinus kerguelensis clade A, SIO-BIC E4889 (S6489); Genbank (COI—KM491770). SIO-BIC A3875 (S6853) syngenophore (1 spm: 95% ethanol). Elephant Island, Antarctica (Stn. 2–83)(61°20.3263'S, 55°37.4961'W), 143– 162 m. Genbank (COI—KM491742). Collected via the R/V Nathaniel B. Palmer using a Blake trawl on 23 October 2011 by Nerida Wilson, GWR, MMS, and science team. Host: Promachocrinus kerguelensis clade A, SIO-BIC E4869 (S6816); Genbank (COI—KM491771).

Etymology. Named for its distribution throughout the Scotia Arc.

Diagnosis and description. Solitary, located in cysts along ambulacral grooves of host, near mouth or on arms (Fig. 2 A–B). Holotype body folded along anterior-posterior axis, dorsal side inward (Fig. 2 C–E). Length ~ 9 mm, width ~ 6 mm following fixation. Mouth and cloaca terminal. Five pairs of reduced parapodia with small chaetae, approximately midway between midline and body margin (Fig. 2 C–E). Live color cream, faded in preservative.

Remarks. Endomyzostoma includes seven gall-forming taxa that reside in stalked crinoids— E. cryptopodium (Wheeler, 1896), E. clarki (McClendon, 1906), E. belli (Wheeler, 1896), E. eremita (Wheeler, 1896), E. deformator (Graff, 1884a), E. pentacrini (Graff, 1884a), and E. robustum (Hara & Okada, 1921) [transferred to Endomyzostoma here]—and seven (possibly eight) other cyst-forming taxa on feather star crinoids. Most cyst forms have been recorded from multiple hosts, these records likely representing different species. Endomyzostoma inflator (Graff, 1883) was described from Adelometra angustiradia (Carpenter) from southwest West Papua (Indonesia) and later recorded from Neocomatella pulchella (Pourtalès) from the Barbados in Graff (1884a). Endomyzostoma tenuispinum (Graff, 1884a) was described from four host species— Glyptometra inequalis (Carpenter), Glyptometra angusticalyx (Carpenter), Charitometra basicurva (Carpenter), and Charitometra incisa (Carpenter) —from three sites in the Pacific. Endomyzostoma murrayi (Graff, 1883) was described from Horaeometra duplex (Carpenter) from St. Vincent and the Grenadines (Caribbean) and subsequently recorded in the Pacific on Adelometra angustiradia by Graff (1884a). Endomyzostoma beardi (Graff, 1887) [here transferred to Endomyzostoma] was recorded from the Arafura Sea (Australia) on Monachometra flexilis (Carpenter). Another possible member of Endomyzostoma is Myzostoma willemoesii Graff, 1884a, which was described from the Kermedec Islands and southwest of Fiji on Charitometra basicurva (Carpenter) and Glyptometra inaequalis (Carpenter). The specimens were described from a cyst, but possessed 20 long cirri and lateral organs, the latter feature is absent in all other members of Endomyzostoma. This specimen was folded along an axis so that anterior and posterior ends meet, while Endomyzostoma are otherwise folded at 90° to this, along the anterior-posterior axis such that the lateral margins meet. Myzostoma willemoesii may therefore be a juvenile stage of a free-living Myzostoma and we leave it in that genus pending further collection and study.

Endomyzostoma cysticolum (Graff, 1883) was described from Cape Frio, Brazil, associated with Comactinia meridionalis (Agassiz). A variety and a sub-species of E. cysticolum have also been named, both of which we raise to species rank. Endomyzostoma cysticolum cystihymenoides (McClendon, 1907) (now E. cystihymenoides) was described from Florometra asperrima (AH Clark) in Arctic waters. Endomyzostoma cysticolum orientale (McClendon, 1906) (now E. orientale) was recorded from Calometra discoidea (Carpenter) in Japan. Endomyzostoma cysticolum has also been reported from many different crinoids species from the Caribbean Sea, Red Sea, Japanese and Indonesian waters, and from Antarctica (Grygier 2000). Many of these records are likely unrecognized Endomyzostoma species. Sequences available online for E. cysticolum (GenBank DQ238194, DQ238165, DQ238130) published in Lanterbecq et al. (2006) and the mitochondrial genome for Endomyzostoma sp. MZ-2009 (GenBank FJ975144) published in Bleidorn et al. (2009) are from specimens of Endomyzostoma scotia n. sp.

Among Endomyzostoma associated with feather stars, E. tenuispinum and E. beardi are distinguished by the presence of cirri (14 and 20 respectively). All other forms lack cirri, and are separated based on host, locality, and in some cases, size. Endomyzostoma scotia n. sp. is the first species of Endomyzostoma described from Antarctica, as well as in association with Promachocrinus.