Prionospio Malmgren, 1867

Radashevsky, Vasily I., 2015, Spionidae (Annelida) from Lizard Island, Great Barrier Reef, Australia: the genera Aonides, Dipolydora, Polydorella, Prionospio, Pseudopolydora, Rhynchospio, and Tripolydora, Zootaxa 4019 (1), pp. 635-694 : 648-649

Prionospio Malmgren, 1867 sensu lato

Prionospio Malmgren, 1867: 201 ; Blake & Kudenov 1978: 211 –212; Maciolek 1985: 329, 332; Wilson 1990: 245 –246.

Type-species. Prionospio steenstrupi Malmgren, 1867 , by monotypy.

Remarks. Prionospio Malmgren, 1867 and closely related spionids constitute the most diverse and complicated group within the Spionidae . The group currently comprises more than one hundred species occurring worldwide from the intertidal to deep sea. Historically treated together and referred to as a generic Prionospio complex, for a long time the genus was not explicitly defined and no single character or group of characters was suggested to support its monophyly. Systematic treatments of the complex were overviewed by Foster (1971), Blake & Kudenov (1978), Maciolek (1985), Wilson (1990), Blake (1996), and Sigvaldadóttir (1998). Different generic breakdowns of the complex were suggested by various authors based on different suits of external morphological characteristics of adults and ideas about their weight for taxonomy. All those groupings were considered artificial, convenient for identification purposes rather than reflecting phylogenetic relationships.

Sigvaldadóttir et al. (1997) and Sigvaldadóttir (1998) provided the first attempts to elucidate phylogenetic relationships within the Prionospio complex with explicit cladistic methodology. The analyses resulted in essentially different hypotheses and, as it was concluded by Sigvaldadóttir (1998: 185) herself, were based on “a too small number of characters to obtain reliable estimates”. Preliminary phylogenies of spioniform polychaetes shown by Blake & Arnofsky (1999: fig. 13C) suggested Prionospio complex as a monophyletic group comprising Prionospio , Paraprionospio Caullery, 1914 , and Streblospio Webster, 1879 but no single character was noted for its support.

The generic analysis by Sigvaldadóttir (1998) suggested monophyly of the group containing Prionospio Malmgren, 1867 sensu stricto, Minuspio Foster, 1971 , Aquilaspio Foster, 1971 , and Apoprionospio Foster, 1969 . More than 80 valid species of these taxa were referred to Prionospio Malmgren, 1867 sensu lato which further generic division based on branchial form was suggested to be avoided. Ultimately, Sigvaldadóttir (1998: 185) concluded that future study of Prionospio “should endeavor to identifying natural groups rather than disputing Linnean ranking of taxa”. Being in agreement with this conclusion, I suggest that in the absence of phylogenetic analyses of broader suits of diverse characters, it is useful to revise various groups of the Prionospio complex based at least on their superficial similarities, not necessarily following subgeneric categories established by Foster (1971) and subsequently modified by Maciolek (1985). Description of additional characters including internal anatomy and reproductive characteristics, and taxonomic revisions of certain groups of species with keys to their identification would clarify the diversity and composition of the complex in total. Good examples of those revisions are by Hylleberg & Nateewathana (1991) of the Prionospio with both pinnate and apinnate branchiae on chaetigers 2–5 from the Andaman Sea, Dagli & Çinar (2011) of the Prionospio with only apinnate branchiae, and Delgado-Blas (2014, 2015) of the Prionospio with five pairs of branchiae, and Prionospio with both pinnate and apinnate branchiae on chaetigers 2–5 from the Grand Caribbean Region.

The two characters in support of Prionospio sensu lato in the analysis by Sigvaldadóttir (1998), the neuropodial lamellae of segment 2 pointed ventrally, and neuropodial hooks starting at segments 14–19, appear rather ambiguous. Nevertheless, this grouping is used in the present study, the subgenera are dispensed, and corresponding species from around the Lizard Island Group are referred to Prionospio sensu lato.

Foster (1971) clarified the terms “dorsal crest” and “dorsal fold” with regard to structures between notopodial postchaetal lamellae on the dorsal side of segments, and Maciolek (1985) clarified the terms used to describe branchial appearance (pinnate vs. apinnate) and shape of the pinnae (pinnules; digitiform vs. plate-like) on their surface. These terms are used in the present study.

Sigvaldadóttir & Mackie (1993) highlighted the importance of investigating size-related variability of Prionospio worms, and this importance is stressed again in the present study. Many crucial taxonomic characters, such as dentition of hooks, arrangement of hooks, sabre chaetae and branchiae, and the presence of pinnae on branchiae, are shown to modify during individual ontogenesis. Correct identification of certain stages is therefore problematic or even impossible without knowledge of the entire transformation series.

Key to Prionospio from around Lizard Island Group1 1. Prostomium with two long pointed fronto-lateral horns. Median eyes small. Neuropodial postchaetal lamellae of chaetiger 1 with lower part elongated and directed ventrally. Branchiae smooth on chaetigers 2–4, pinnate on chaetiger 5. Hooded hooks in notopodia from chaetigers 12–30, in neuropodia from chaetigers 10–15. Ventral inferior chaetae capillaries throughout body; sabre chaetae absent. Dorsal crests absent.................................... P. cerastae n. sp. – Prostomium anteriorly rounded, without horns. Neuropodial postchaetal lamellae of chaetiger 1 small, not elongated ventrally. Sabre chaetae present in neuropodia (absent in P. anneae n. sp.)........................................ 2 2. (1) Three to four pairs of branchiae from chaetiger 2, at least one pair pinnate..................................... 3 – Up to 8 pairs of branchiae from chaetiger 2, all apinnate........................................... P. cf. tatura 3. (2) Three to four pairs of branchiae, all pinnate.............................................................. 4 – Four pairs of pinnate and apinnate branchiae............................................................. 5 4. (3) Three pairs of pinnate branchiae on chaetigers 2–4 2. Caruncle to end of chaetiger 1. Median eyes small. Chaetiger 1 without notochaetae. Dorsal crests absent. Hooks in notopodia from chaetigers 25–38, in neuropodia from chaetigers 16–21. Sabre chaetae from chaetiger 10............................................................ P. aucklandica – Four pairs of pinnate branchiae on chaetigers 2–5. Caruncle to end of chaetiger 3. Median eyes large. Chaetiger 1 with notochaetae. Dorsal crests present from chaetiger 6 at least on ten succeeding chaetigers. Sabre chaetae after chaetiger 10..................................................................................... P. cf. tetelensis 5. (3) Branchiae with pinnae on chaetigers 2 and 5, apinnate on chaetigers 3 and 4............ Prionospio steenstrupi group-7 – Pinnate and apinnate branchiae arranged otherwise........................................................ 6 6. (5) Sabre chaetae in neuropodia from chaetiger 11. Median eyes small. Branchiae apinnate on chaetigers 2–4, with many pinnae on chaetiger 5. Caruncle to end of chaetiger 1. Dorsal crest on chaetiger 7. Hooks in neuropodia from chaetigers 19– 20 P. cf. tridentata

– Sabre chaetae in neuropodia from chaetiger 10. Median eyes large. Branchiae with few pinnae on chaetigers 2–4 3, apinnate on chaetiger 5. Caruncle to end of chaetiger 4. Prominent semicircular dorsal crest on chaetiger 7; low crests from chaetiger 8 to chaetigers 16–31. Hooks in neuropodia from chaetigers 10–14........................ P. cf. paucipinnulata 7. (5) Sabre chaetae absent in neuropodia. Hooks in neuropodia from chaetigers 8–9. Moderate dorsal crest present on chaetiger 6................................................................................... P. anneae n. sp. – Sabre chaetae in neuropodia from chaetiger 10. Hooks in neuropodia after chaetiger 9. Dorsal crest absent on chaetiger 68 8. (7) Caruncle to end of chaetiger 1. Median eyes large. Dorsal crest on chaetiger 7, no on succeeding chaetigers. Hooks in neuropodia from chaetigers 11–12............................................................... P. lylei n. sp. – Caruncle extending beyond chaetiger 1. Median eyes small or large. Dorsal crests from chaetiger 7 on a series of succeeding chaetigers..................................................................................... 9 9. (8) Median eyes small. Caruncle to end of chaetiger 4. Low dorsal crests from chaetiger 7 on a series of succeeding chaetigers. Hooks in neuropodia from chaetigers 12–14................................................... P. cooki n. sp. – Median eyes very large. Caruncle to end of chaetiger 2 or 3. Moderate dorsal crest on chaetiger 7 and low crests from chaetiger 8 on a series of succeeding chaetigers. Hooks in neuropodia from chaetigers 11–18......................... 10 10. (9) Eyes red in living and fixed specimens. Caruncle to end of chaetiger 2. Dorsal crests on chaetigers 7–24........ P. kulin – Eyes red in living but black in formalin-fixed specimens. Caruncle to end of chaetiger 3. Dorsal crests on chaetigers 7–30..................................................................................... P. multicristata