Plakina finispinata, Lage & Muricy & Ruiz & Pérez, 2018

Lage, Anaíra, Muricy, Guilherme, Ruiz, César & Pérez, Thierry, 2018, New sciaphilic plakinids (Porifera, Homoscleromorpha) from the Central-Western Pacific, Zootaxa 4466 (1), pp. 8-38 : 13-16

Plakina finispinata sp. nov.

( FIgS. 4–5 , TAbLE 2)

Definition. Plakina WITH dIOdS, TRIOdS, cALTHROPS, AbUNdANT TRILOPHOSE cALTHROPS, RARE MONO- ANd dILOPHOSE TRIOdS, ANd RARE MONO-, dI-, ANd TETRALOPHOSE cALTHROPS. LOPHOSE SPIcULES HAVE SIMPLE RAMIfIcATION PATTERN (1M, TS) ANd ALL AcTINES USUALLy HAVE TERMINAL SPINES.

Type Material. HOLOTyPE: MNRJ 18470 (120112 -MQ2GR-TP31), cOLLEcTEd IN NUkU HIVA ISLANd, MARqUESAS ISLANdS , FRENcH POLyNESIA (8°56.231'S, 140°07.240’W), IN A LARgE UNdERWATER cAVE bELONgINg TO A SySTEM Of fOUR cAVES (" LES qUATRE gROTTES") , THE ENTRANcE bEINg AT 19 M dEPTH. JANUARy 12, 2012, cOLL. THIERRy PÉREZ. PARATyPE: MNRJ 21832, SAME dATA Of HOLOTyPE.

Material examined for comparison. Plakina trilopha ScHULZE, 1880 : UFRJPOR 4335, MARSEILLE, FRANcE (MURIcy et al. 1998).

Description. ENcRUSTINg SPONgE, 13 MM WIdE by 1–3 MM THIck ( FIg. 4A–B ). BORdERS ROUNdEd, SLIgHTLy ELEVATEd fROM THE SUbSTRATE, bEARINg A TRANSLUcENT MARgINAL cANAL. COLOUR WHITE in vivo, bEcOMINg LIgHT bROWN AfTER fIXATION ( FIg. 4A–B ). SURfAcE SMOOTH, dENSELy PUNcTUATEd by SMALL INHALANT OPENINgS. OScULES 1–2 MM IN dIAMETER, SLIgHTLy TUbULAR, ASSOcIATEd TO THE MARgINAL cANAL. CONSISTENcy RELATIVELy fIRM, cARTILAgINOUS.

Anatomy. THE SkELETON IS A dENSE, dISORgANIZEd RETIcULATION Of dIOdS, TRIOdS ANd SIMPLE cALTHROPS, WITH LOPHOSE cALTHROPS cONcENTRATEd AT THE bASE, AT THE SURfAcE ANd AROUNd cANALS ( FIg. 4C ). THE EcTOSOME IS dIffERENTIATEd fROM THE cHOANOSOME by A THIN dENSE LAyER Of LOPHOSE SPIcULES WITH THE LOPHOSE AcTINES MOSTLy POINTINg OUTWARdS ( FIg. 4C ). AqUIfEROUS SySTEM SyLLEIbId-LIkE, WITH VERTIcAL INHALANT ANd EXHALANT cANALS, SMALL EcTOSOMAL LAcUNAE 40–50 µM WIdE ANd LARgE bASAL cAVITIES 100–130 µM HIgH LEAdINg TO THE MARgINAL cANAL AT THE SPONgE bORdER. CHOANOcyTE cHAMbERS ROUNdEd TO IRREgULAR, EURyPyLOUS, 29–50 µM IN dIAMETER ( FIg. 4D ).

Spicules ( TAbLE 2). DIOdS AbUNdANT, STRAIgHT OR cURVEd, SMOOTH, AcERATE, WITH A cENTRAL IRREgULARITy VARyINg fROM VERy SLIgHTLy TO MARkEdLy S-bENT OR cENTROTyLOTE-LIkE ( FIg. 5A ): FULL SIZE: 56–83–104 / 2.7–4.0–7.6 µM. SOME dIOdS HAVE ONE AcTINE REdUcEd.

TRIOdS AbUNdANT, IRREgULAR, Y- ANd T-SHAPEd, SMOOTH, AcERATE ( FIg. 5B ). AcTINES: 17–31–38 / 2.7–3.7–6.8 µM.

CALTHROPS AbUNdANT, IRREgULAR, SMOOTH, WITH AcERATE OR bIfURcATEd ENdS ( FIg. 5C ). AcTINES: 17–27–35 / 2.0–3.3– 5.4 µM.

MONOLOPHOSE TRIOdS ( FIg. 5D ) RARE, IRREgULAR, NON-LOPHOSE AcTINES WITH AcERATE TIPS OR WITH TERMINAL SPINES. LOPHOSE AcTINES RAMIfy ONcE IN MEdIAL TO dISTAL POSITION IN 2–5 cyLINdRIcAL, AcERATE OR TERMINALLy SPINEd RAyS. FULL SIZE: 35–50– 60 µM.

DILOPHOSE TRIOdS UNcOMMON, WITH TWO dIffERENT SHAPES ( FIg. 5E, F ). IN THE MOST cOMMON TyPE, NON-LOPHOSE AcTINES ARE cONIcAL, WITH AcERATE TIPS OR WITH 2–3 SMALL TERMINAL SPINES. LOPHOSE AcTINES RAMIfy ONcE IN MEdIAL

POSITION IN 3–5 RAyS WITH 2–3 SHORT TERMINAL SPINES ( FIg. 5E ). MORE RARELy, THE LOPHOSE AcTINES HAVE ONE MEdIAL POINT Of RAMIfIcATION ANd USUALLy ALSO A dISTAL RAMIfIcATION IN 2–3 VERy SHORT RAyS WITH 3–5 LARgE TERMINAL SPINES ( FIg. 5F ). BOTH TyPES HAVE THE SAME SIZE RANgE. FULL SPIcULE SIZE: 17–24–35 µM.

Measurements are min–med-max length or length / width in micrometres. Numbers of measurements in parentheses.

MONOLOPHOSE cALTHROPS VERy RARE, IRREgULAR IN SHAPE. NON-LOPHOSE AcTINES SMOOTH, WITH TERMINALLy SPINEd, AcERATE OR bLUNT ENdS. LOPHOSE AcTINES RAMIfy ONcE MEdIALLy IN 2–4 cONIcAL RAyS WITH TERMINALLy SPINEd, AcERATE OR bLUNT EXTREMITIES ( FIg. 5G ). FULL SIZE: 40–45–50 µM.

DILOPHOSE cALTHROPS VERy RARE, IRREgULAR IN SHAPE, SIMILAR TO dILOPHOSE TRIOdS. NON-LOPHOSE AcTINES STRAIgHT, AcERATE OR TERMINALLy SPINEd. LOPHOSE AcTINES RAMIfy ONcE IN MEdIAL TO dISTAL POSITION IN 3–5 RAyS WITH AcERATE TIPS OR, MORE OfTEN, WITH 2–5 TERMINAL SPINES ( FIg. 5H ). FULL SIZE: 29–35–45 µM.

TRILOPHOSE cALTHROPS AbUNdANT, VERy UNIfORM IN SHAPE. ALL AcTINES TyPIcALLy HAVE 2–4 TERMINAL SPINES. LOPHOSE AcTINES RAMIfIEd MEdIALLy IN 2–4 RAyS THAT bEAR 2–5 TERMINAL SPINES (RAMIfIcATION PATTERN 1M, TS; FIg. 5I ). FULL SIZE: 10–16.3–25 µM.

TETRALOPHOSE cALTHROPS VERy RARE, IRREgULAR IN SHAPE, WITH AcTINES RAMIfyINg MEdIALLy IN 2–5 cONIcAL OR cyLINdRIcAL, TERMINALLy SPINEd RAyS. TERMINAL SPINES VARy fROM ALMOST IMPERcEPTIbLE TO RELATIVELy LARgE ANd cONSPIcUOUS ( FIg. 5J ). FULL SIZE: 15–19–21 µM.

Reproduction. EMbRyOS 100–240 µM IN dIAMETER ARE INcUbATEd MAINLy NEAR THE bASE Of THE SPONgE, jUST AbOVE THE bASAL cAVITIES ( FIg. 4C ).

Ecology. Plakina finispinata sp. nov. IS A ScIAPHILIc SPEcIES dWELLINg IN dARk cAVES. SEVERAL SPEcIMENS WERE fOUNd AT 20 M dEPTH ON THE WALL Of THE bAck Of THE cAVE WHERE THE cOMMUNITy IS dOMINATEd by ENcRUSTINg SPONgES. THERE, THE SPONgE fAUNA IS MOSTLy UNkNOWN (PÉREZ et al. 2016). NO SIgN Of EPIbIOSIS OR PREdATION WERE ObSERVEd ON THE NEW SPEcIES.

Distribution. NUkU HIVA, MARqUESAS ISLANdS ( FRENcH POLyNESIA; FIgS. 1 , 3 ).

Etymology. THE NAME finispinata REfERS TO THE cONSISTENT PRESENcE Of TERMINAL SPINES IN MOST LOPHOSE SPIcULES, ANd ESPEcIALLy IN ALL AcTINES Of THE TRILOPHOSE cALTHROPS, WHIcH ARE THE dOMINANT LOPHOSE SPIcULES IN THIS SPEcIES (fROM LATIN finis = ENd, EXTREMITy, ANd spinae = SPINES).

Taxonomic remarks. AMONg THE 34 SPEcIES Of Plakina cURRENTLy AccEPTEd, P. finispinata sp. nov. IS MOST SIMILAR TO P. trilopha ANd P. anisoactina ( ScHULZE 1880; MURIcy et al. 1998; LAgE et al. 2018). THE NEW SPEcIES SHARES WITH P. trilopha THE ENcRUSTINg SHAPE, SMOOTH SURfAcE, WHITE cOLOUR, ANd PRESENcE Of TRILOPHOSE cALTHROPS. HOWEVER, P. trilopha HAVE NEITHER A MARgINAL cANAL NOR MONO- ANd dILOPHOSE TRIOdS, ANd ITS TRILOPHOSE cALTHROPS RAMIfy MEdIO-dISTALLy IN RAyS THAT MAy bEAR TERMINAL SPINES bUT ARE USUALLy AcERATE ( ScHULZE 1880; MURIcy et al. 1998), WHEREAS IN P. finispinata sp. nov. ALL AcTINES Of LOPHOSE SPIcULES ARE VERy OfTEN TERMINALLy SPINEd ANd ONLy EXcEPTIONALLy AcERATE. Plakina anisoactina SHARES WITH Plakina finispinata sp. nov. THE PRESENcE Of A MARgINAL cANAL, Of MONO- ANd dILOPHOSE TRIOdS, ANd Of MONO-, dI- ANd TRILOPHOSE cALTHROPS. IN P. anisoactina HOWEVER THE SPIcULES ARE TyPIcALLy ANISOAcTINAL (WITH bOTH AcERATE ANd TERMINALLy SPINEd EXTREMITIES IN THE SAME SPIcULE), TRILOPHOSE cALTHROPS ARE RARE ANd MONO- ANd dILOPHOSE TRIOdS ARE cOMMON, cONTRARILy TO THE NEW SPEcIES. Plakina finispinata sp. nov. dIffERS fROM ALL OTHER SPEcIES Of Plakina by ITS LOPHOSE cALTHROPS bEINg PREdOMINANTLy TRILOPHOSE ANd WITH ALL AcTINES TERMINALLy SPINEd.

Figures

FIGURE 1. Location of collection sites. A, Pacific Ocean showing New Caledonia and Marquesas Islands. B, Marquesas Islands showing Nuku Hiva and Hatutu Island (red circles). C, New Caledonia showing Bourail and Hienghène (red circles)

FIGURE 3. Distribution of Homoscleromorpha species in the Pacific Ocean. Records identified only to genus level (as sp., cf., or aff.) and from Antarctica were not included. See Table 4 for locality names and references

FIGURE 4. Plakina finispinata sp. nov. A, holotype MNRJ 18470 in vivo. B, specimens after fixation: h, holotype (MNRJ 18470); p, paratype (MNRJ 21832). C, Transverse section through the whole body showing the ectosome, embryos, and the system of basal cavities. D, Semithin section after desilification showing the basal cavity, canals, and eurypylous choanocyte chambers. Key: bc, basal cavities; ca, canals; cc, choanocyte chambers; ect, ectosome; em, embryos.

FIGURE 5. Plakina finispinata sp. nov. Spicules (SEM): A, diods. B, triods. C, calthrops. D, monolophose triod. E–F, dilophose triods. G, monolophose calthrops. H, dilophose calthrops. I, trilophose calthrops. J, tetralophose calthrops.