Polydorella dawydoffi Radashevsky, 1996

Williams, Jason, 2004, Reproduction and morphology of Polydorella (Polychaeta: Spionidae), including the description of a new species from the Philippines, Journal of Natural History 38 (11), pp. 1339-1358 : 1348-1352

Polydorella dawydoffi Radashevsky, 1996

( figures 6 , 7 )

Polydorella dawydoffi Radashevky, 1996: 684–693 , figures 2 , 3 .

Material examined. Polydorella dawydoffi : 10 paratypes from Thailand, Gulf of Thailand, Thom Island of Anthoi Archipelago , 7 m, 2 February 1986, from Xestospongia testudinaria (Lamarck, 1815) ( USNM 148722 ; one prepared for SEM) ; 60z specimens from Philippines, Puerto Galera, Small La Laguna Beach , y 3 m, 30 June 2000, from Chalinula sp. , ( USNM 1008713 ) ; 50z specimens from same locality and sponge as above, 1 July 2000, ( AMNH 4348 ) ; 18 specimens from same locality and date as above, from Niphates sp. ( USNM 1008714 ) ; 60z specimens from Philippines, Puerto Galera, Agus Beach , y 3 m, 1 July 2000, from Niphates sp. ( AMNH 4349 ) ; 30 specimens from same locality and sponge as above, 25 July 2000 ( USNM 1008715 : 24 specimens; USNM 1008716 : six specimens, on three SEM stubs) ; seven specimens from Philippines, Puerto Galera, Big La Laguna Beach , y 3 m, 24 July 2000, from Petrosia sp. ( USNM 1008717 ) ; 37 specimens from Red Sea: Egypt, Hurghada , 0.1 m, November 2001, from Xestospongia sp. ( USNM 1008718 : 32 specimens; USNM 1008719 : five specimens, on two SEM stubs), coll. Pliascheva.

Description

Single individuals with 14–15 segments; approximately 1.5 mm in length and 0.4 mm in width at segment 5. Prostomium bifid; caruncle short, reaching anterior margin or middle of segment 2; occipital tentacle absent; two round, white eyes observable in life only. Palps extend posteriorly for 8–12 segments. Pigmentation variable, present on dorsal and ventral sides of anterior and posterior segments or absent ( figure 6A, B ).

Segment 1 without notopodial lobes or notosetae; neuropodial lobe present without neurosetae ( figure 6A ). Unilimbate capillary notosetae of segments 2–4, 6 and subsequent segments in two rows. Unilimbate capillary neurosetae of segments 2–4, 6 and 7 arranged in two rows; up to six bidentate hooded hooks begin on segment 8, not accompanied by capillaries; hooks with approximately right angle between main fang and shaft, narrow angle between main fang and apical tooth, with constriction on shaft ( figure 6F ).

Segment 5 slightly modified, about the same size as segments 4 and 6, with posteroventral fascicle of unilimbate capillary neurosetae in two rows; with anterodorsal fascicle of unilimbate notosetae. Two types of major spines of segment 5 in approximately horizontal curved row; ventral row of up to four to six spines with distally enlarged ends, with small digitiform bosses on sides and main shaft, approaching apical edge with eight to nine rounded or pointed teeth, posterior end of spines with capillary extension ( figures 6E , 7A–D ) and dorsal row of up to three to four acicular spines with an apical shelf ( figures 6E , 7B ).

Single pair of branchiae present on segment 7 ( figure 6A, B ). Dorsal ciliary bands from segment 2 continuing to terminal segments.

Posterior segments with large cells (y 20–30 m m); pygidium cylindrical, slightly tapering to distal end ( figure 6A, B ).

Asexual reproduction

The sequence of stolon body formation closely follows that described by Radashevsky (1996), although the growth zone position may vary between segments 10 and 11. Eighteen specimens examined from the Philippines and the Red Sea exhibited a growth zone that appeared to follow segment 10 (these individuals possessed a recently formed growth zone corresponding to stolon 1). Radashevsky (1996) noted that the growth zone may be incorrectly interpreted to form after segment 10 during secondary stolon formation. Yet even during formation of stolon 1 specimens exhibited a growth zone following segment 10. Thus, it appears that the growth zone can form following segment 10, soon after which the anlage of segment 11 is formed. Individuals later in development (with stolon 1 possessing new thoracic segments and newly formed palps) possess a fully developed segment 11 and often a developing segment 12. Records of specimens possessing a growth zone following segment 11 may represent individuals later in development rather than initial position of the growth zone. SEM examination confirmed that 10 segments simultaneously arise in developing stolons ( figure 6C ); early in this stage the setae of the developing segments are not visible externally and develop later in segment formation.

Feeding

Examination of specimens collected from the Red Sea showed that nearly all individuals contained sand grains within the digestive tract. The sand grains were of considerable size (164.5¡100.3 m m, mean maximal length¡SD; N ~20) compared to the digestive tract and distributed throughout the digestive tract of paratomic chains ( figure 6D ). These sand grains indicate the worms have the ability to ingest large food particles; their mode of feeding (deposit, suspension, or deposit and suspension) remains unknown but it is likely that they exhibit a combination of deposit and suspension feeding as documented in other polydorids (e.g. Dauer et al., 1981; Williams and McDermott, 1997). If the worms remove sand grains and other deposited material on the surface of sponges they could be benefiting sponges by keeping their surfaces free of debris, as documented in other polychaetes associated with sponges ( Martín et al., 1992).

Distribution South China Sea: south-eastern coast of Vietnam, Philippines; Red Sea.

Remarks

SEM examination has allowed more detailed analysis of the fifth segment spine morphology, leading to the observation of the capillary extension at the apical end of the spines and the digitiform bosses (both difficult to observe with light microscopy). The spine morphology of P. dawydoffi specimens from the Philippines differs slightly from those collected in the Red Sea and Vietnam. The Philippine specimens exhibit spines which are more squat on the denticulate edge and possess a thicker capillary extension ( figure 7A, B ); Vietnam and Red Sea specimens exhibit spines which are more elongate along the denticulate edge and have a rounded distal end with a thinner distal capillary ( figure 7C, D ). No other morphological differences were noted between specimens from the three localities and without further morphological or molecular evidence, the distinctions in the spines do not appear to warrant the erection of a new species. The Philippine specimens exhibited slight pigmentation on anterior and posterior segments while those of the Red Sea were heavily pigmented ( figure 6A, B ); Radashevsky (1996) found no pigmentation on specimens collected from Vietnam. One of the paratypes examined was composed of 18 segments and contained an endoparasitic copepod within segments 11–15; additional parasitic copepods were found in specimens from Vietnam ( Radashevsky, 1996). This is the first record of the species from the Red Sea and the Philippines.

Figures

FIG. 6. Polydorella dawydoffi (AMNH 4348) (A), (USNM 1008717) (B, D, F), (USNM 1008716) (C), (USNM 148722) (E) and P. stolonifera (NMV F42898) (G). (A) Dorsal view of specimen from the Philippines; (B) dorsal view of specimen from the Red Sea; extensive black pigmentation is indicated by grey shading; (C) lateral view showing 10 developing segments of stolon 1; (D) dorsal view of posterior end of stock and anterior end of stolon 1 of an individual containing sand grains (shaded structures) within intestine; (E) dorsolateral view of fifth segment spines; (F) hooded hook; (G) lateral view of dorsal (to left) and ventral (to right) major spines of segment 5. Scale: 100 mm (A–D); 25 mm (E); 12.5 mm (F); 5 mm (G).

FIG. 7. Polydorella dawydoffi (USNM 1008716) (A, B), (USNM 148722) (C) and (USNM 1008719) (D). (A) Lateral view of ventral row of fifth segment major spines, Philippine specimen; note separated teeth along edge; (B) oblique view of ventral row of fifth segment major spines, Red Sea specimen; note acicular spine of dorsal row; (C) lateral view of ventral row of fifth segment major spines, Vietnam specimen; (D) oblique view of ventral row of fifth segment major spines, Red Sea specimen; note acicular spine of dorsal row. In all figures arrowheads indicate apical capillary extension of spines. Scale: 2.5 mm (A, C, D); 1 mm (B).

FIG. 2. Polydorella kamakamai new species: paratypes (USNM 1008712), SEM micrographs. (A) Spines of fifth segment, lateral view; (B) magnified view of spines in (A), showing digitiform bosses on ventral row of spines; (C) dorsal view of individual with developing stolon 1; (D) dorsal view of paratomic chain with stock, stolon 2 (St2) and stolon 1 (St1); (E) lateral view of paratomic chain with stock, stolon 2, stolon 1 and developing secondary stolon (2‡St). Scale: 5 mm (A); 1 mm (B); 100 mm (C–E).

FIG. 3. Polydorella kamakamai new species: paratype (USNM 1008711). Paratomic chain with five developing individuals. (A) Dorsal view; (B) ventral view. Segment numbers of stock, stolon 2 and stolon 1 indicated to left of ventral view. P, pygidium. Scale: 250 mm.