Sertularia dichotoma, (Linnaeus, 1758)

Humara-Gil, Karla J. & Cruz-Gómez, Christopher, 2018, New records of benthic hydroids (Cnidaria: Hydrozoa) from the coast of Oaxaca, Mexico, Zootaxa 4455 (3), pp. 454-470 : 461

Obelia dichotoma (Linnaeus, 1758)

FIg. 5

Sertularia dichotoma LINNAEuS, 1758: 812.

Clytia longicyatha .—FRASER, 1938A: 32.

Obelia tenuis FRASER, 1938A: 38, pL. 9, fIG. 42.

Obelia commissuralis.—FRASER, 1938A: 36.—FRASER, 1948: 213.

Obelia dichotoma .—FRASER, 1938A: 36.—FRASER, 1948: 213.— MILLARd, 1975: 227, fIG. 75F‒H, J (SyN.).—CALdER, 1991: 72, fIG. 38 (SyN.).—KELmO & AttRILL, 2003: 138, fIG. 6G‒I (SyN.).—OkOLOdkOV et al., 2007: 40.—CALdER, 2012: 50, fIG. 51 (SyN.).— CuNhA et al., 2017: 118.

Obelia hyalina.—FRASER, 1938A: 37.—FRASER, 1938c: 133.—FRASER, 1948: 215.

Obelia plicata.—FRASER, 1938A: 38.—FRASER, 1938b: 109.—FRASER, 1948: 215.

Obelia biserialis FRASER, 1948: 213, pL. 24, fIG. 6.

Obelia gracilis .—FRASER, 1948: 215.

Obelia griffini.—FRASER, 1948: 215.

Type locality. COAST Of SOUThWEST ENgLANd (CORNELIUS 1975).

Material examined. NINE cOLONIES: UMAR-HYDR-007, fIVE cOLONIES ON Rhizophora mangle ( CORRALERO BAY, OAXAcA, 16°13’04’’N 98°11’11’’W, 1 m, 11 JUNE 2015, cOLL. C. CRUZ-GómEZ); UMAR-HYDR-008, fOUR cOLONIES (MAZUNTE, OAXAcA, 15°39’46’’N 96°33’55’’W, ~ 20 m, 15 SEPTEmbER 2015, cOLL. F. RUIZ-EScObAR).

Description. COLONIES EREcT, 0.7–1.1 cm hIgh, SYmPOdIAL; ARISINg fROm A cREEPINg hYdRORhIZA. HYdROcAULUS mONOSIPhONIc, UNbRANchEd, ZIgZAg; dIVIdEd INTO INTERNOdES AT REgULAR INTERVALS. INTERNOdES SLIghTLY cURVEd, WITh TWO OR ThREE ANNULATIONS bASALLY; EAch ONE SUPPORTINg A hYdROThEcAL PEdIcEL ORIgINATINg fROm AN APOPhYSIS. PERISARc UNIfORm, ThIcK; TRANSLUcENT (CORRALERO BAY SPEcImENS) OR bROWNISh (MAZUNTE SPEcImENS). APOPhYSES ShORT, ALTERNATE. PEdIcELS fROm 450 µm TO 1 mm LONg; WITh AbOUT EIghT ANNULATIONS PROXImALLY ANd SIX dISTALLY. HYdROThEcAE cAmPANULATE, UP TO 200 µm LONg, 275 µm WIdE AT mARgIN; TAPERINg AT bASE. HYdROThEcAL mARgIN NOT cOmPLETELY SmOOTh bUT WITh 12 SOfTLY cURVEd, ALmOST INdISTINgUIShAbLE LObES; SOmETImES ENTIRE. HYdRANThS WITh AbOUT 25 TENTAcLES, 180–200 µm LONg. GONOThEcAE cONE-ShAPEd, WITh SmOOTh WALLS; ELONgATEd, 500 µm LONg fROm bASE TO APERTURE, 300 µm WIdE (mAXImUm WIdTh); WITh A ShORT NEcK ANd dISTAL APERTURE; ARISINg fROm ANNULATEd PEdIcELS.

Remarks. ThE mORPhOLOgY Of cOLONIES fROm OAXAcA cOINcIdES WITh dEScRIPTIONS Of Obelia dichotoma fROm SOUTh AfRIcA bY MILLARd (1975); fROm BERmUdA bY CALdER (1991); ANd fROm BRAZIL bY KELmO & ATTRILL (2003). ALThOUgh ThIS SPEcIES hAS bEEN REcORdEd IN OThER STATES ALONg ThE PAcIfIc cOAST Of MEXIcO, SUch REcORdS NEEd VERIfIcATION bEcAUSE Of ThE gREAT dISTANcE bETWEEN MEXIcO ANd ThE TYPE LOcALITY, ENgLANd. MOREOVER, SIgNIfIcANT dIffERENcES EXIST IN ENVIRONmENTAL cONdITIONS bETWEEN ThE TWO REgIONS, PARTIcULARLY IN WATER TEmPERATURES. Obelia dichotoma IS cONSIdEREd A cRYPTOgENIc SPEcIES bY SOmE AUThORS (OKOLOdKOV et al. 2007) bEcAUSE Of ITS mULTIPLE REcORdS AROUNd ThE WORLd.

FURThERmORE, O. dichotoma IS AmONg ThE mOST mORPhOLOgIcALLY VARIAbLE hYdROIdS (CORNELIUS 1990). ThOSE VARIATIONS ARE REfLEcTEd IN ThE mULTIPLE NEW SPEcIES dEScRIPTIONS, NOW cATALOgUEd AS ITS SYNONYmS. MOLEcULARLY, CUNhA et al. (2017) fOUNd OUT ThAT Obelia dichotoma IS NOT mONOPhYLETIc ANd mIghT cORRESPONd TO A cOmPLEX Of cRYPTIc SPEcIES.

Distribution. Obelia dichotoma WAS REPORTEd bY FRASER (1938A, b, 1948) fROm ThE MEXIcAN PAcIfIc AS dIffERENT SPEcIES, NOWAdAYS cONSIdEREd AS ITS SYNONYmS. AS fOR OAXAcA, IT WAS REPORTEd IN TANgOLUNdA bAY (FRASER 1938A, AS Obelia dichotoma ANd Obelia commissuralis) ANd ChAcAhUA bAY (FRASER 1948). ThIS SPEcIES IS bELIEVEd TO bE cIRcUmgLObAL IN dISTRIbUTION (CALdER 1991; KELmO & ATTRILL 2003; CALdER 2012).

Figures

FIGURE 5. Obelia dichotoma (LINNAEuS, 1758). A, cOLONy; B, GONOthEcA; C, hydRANth; D, hydROthEcA. ScALE bARS: 100 µm (C, D), 250 µm (B), 1 mm (A).