# Pennatula
**Pennatula** is a genus of sea pens, colonial octocoral cnidarians that anchor upright in soft marine sediment with a muscular peduncle and bear feathery arrays of feeding polyps. It was named by [Carl Linnaeus](https://www.edgepedia.org/carl-linnaeus) in the tenth edition of *Systema Naturae* (1758), and the name of the order to which it belongs, Pennatulacea, is derived from it[1](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0022747). The common name "sea pen" itself comes from the resemblance of *Pennatula* and related genera to quill pens, produced by their conspicuous, strap-shaped polyp leaves[1](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0022747).
| Key fact | Detail |
|---|---|
| Scientific name | *Pennatula* Linnaeus, 1758; type genus of the family Pennatulidae[2](https://itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=52417) |
| Classification | Animalia; Cnidaria; Anthozoa; Octocorallia; Pennatulacea; Subselliflorae; Pennatulidae[2](https://itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=52417) |
| Synonyms | *Penna* Bohadsch, 1761 and *Phosphorella* Gray, 1870[3](https://www.gbif.org/taxon/84RWV) |
| Named species include | *P. aculeata* Danielssen, 1860; *P. phosphorea* Linnaeus, 1758; *P. rubra* (Ellis, 1761); *P. fimbriata* Herklots, 1858; *P. naresi* Kölliker, 1880[4](https://www.marinespecies.org/aphia.php?id=286637&p=taxdetails) • [5](https://www.marinespecies.org/aphia.php?id=286640&p=taxdetails) • [6](https://www.researchgate.net/publication/284445950_Identificacion_de_las_especies_ibericas_del_genero_Pennatula_L_1758_Octocorallia_Pennatulacea_Campanas_DEMERSALES_ECOMARG_INDEMARES_y_MEDITS) |
| Broader group | Pennatuloidea, the sea pens, currently includes 236 extant species in 16 families and 42 genera[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC12971188/) |
| Depth range of sea pens | Intertidal zone to depths greater than 6100 m[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC12971188/) |
| Conservation relevance | *P. phosphorea* and its habitats are recommended for protection within marine protected areas[8](https://academic.oup.com/icesjms/article/72/2/576/675444?searchresult=1) |
## Position within the sea pens
Sea pens (superfamily Pennatuloidea) are distinguished from other octocorals by a basal peduncle that anchors the colony into the substrate and by specialized polyp types, including oozooids, autozooids, siphonozooids, mesozooids, and acrozooids[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC12971188/). The colony grows from a single large primary polyp, the oozooid, whose distal region forms a rachis carrying secondary polyps: the larger feeding autozooids and the smaller siphonozooids that circulate water[1](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0022747). Some species, such as *Pennatula inflata*, also have mesozooids, polyps intermediate in form[1](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0022747).
Within the classical two-suborder system established by Kükenthal in 1915, *Pennatula* is placed in Subselliflorae[2](https://itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=52417) • [7](https://pmc.ncbi.nlm.nih.gov/articles/PMC12971188/). The genus sits in the family Pennatulidae[2](https://itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=52417).
## Species and identification
Species of *Pennatula* are recognized mainly by external morphology, but the variability of some characters makes identification difficult. A key to the four [Iberian Peninsula](https://www.edgepedia.org/iberian-peninsula) species distinguishes *P. aculeata* Danielssen, 1860, *P. grandis* Ehrenberg, 1834, *P. phosphorea* Linnaeus, 1758, and *P. rubra* (Ellis, 1761), and notes that molecular study would be needed to clear possible cryptic taxa[6](https://www.researchgate.net/publication/284445950_Identificacion_de_las_especies_ibericas_del_genero_Pennatula_L_1758_Octocorallia_Pennatulacea_Campanas_DEMERSALES_ECOMARG_INDEMARES_y_MEDITS). Variability is particularly evident in the development of polyps on the dorsal side of the rachis[6](https://www.researchgate.net/publication/284445950_Identificacion_de_las_especies_ibericas_del_genero_Pennatula_L_1758_Octocorallia_Pennatulacea_Campanas_DEMERSALES_ECOMARG_INDEMARES_y_MEDITS).
**Bathymetric segregation.** In the northern Iberian Peninsula, the three commonly recorded species show partial depth separation: *P. phosphorea* is most typical of the continental shelf and reaches the shallowest levels, *P. aculeata* is more abundant in the upper bathyal zone down to about 800 m, and *P. grandis* inhabits the deep bathyal, although *P. aculeata* and *P. phosphorea* have wider bathymetric ranges across the [Bay of Biscay](https://www.edgepedia.org/bay-of-biscay) as a whole[6](https://www.researchgate.net/publication/284445950_Identificacion_de_las_especies_ibericas_del_genero_Pennatula_L_1758_Octocorallia_Pennatulacea_Campanas_DEMERSALES_ECOMARG_INDEMARES_y_MEDITS).
## Taxonomic instability and molecular phylogeny
The genus as traditionally circumscribed does not hold together well under molecular data. A phylogenetic study of deep-sea sea pens concluded that the morphological criteria used to identify members of *Pennatula* poorly resolve their phylogenetic relationships compared with analysis based on DNA sequence data, and found a high level of incongruence between the traditional morphology-based classification and molecular phylogeny[9](https://www.vliz.be/imisdocs/publications/ocrd/251249.pdf).
As a result, species formerly placed in *Pennatula* have been realigned among three morphologically similar genera, *Pennatula*, *Ptilella*, and *Alloptilella*, based on molecular and morphological features; the deep-sea species *Pennatula moseleyi* Kölliker, 1880 was transferred to *Alloptilella* as *A. moseleyi* comb. nov.[10](https://link.springer.com/article/10.1007/s12526-022-01260-w). The realignment does not resolve the fact that the numerous named species of *Pennatula* are still in need of revision[10](https://link.springer.com/article/10.1007/s12526-022-01260-w). Older names in the genus have also been reassigned: *Pennatula antennina* Ellis & Solander, 1786 is now accepted as *Funiculina quadrangularis*, and *Pennatula argentea* Ellis & Solander, 1786 as *Pteroeides argenteum*[11](https://www.marinespecies.org/aphia.php?p=taxlist&tName=Pennatula).
## Ecology
Like other sea pens, *Pennatula* species live anchored in soft bottoms. On the northern Spanish shelf, *P. aculeata* and *P. phosphorea* are among the characteristic species of the habitat "pennatulacean communities on circalittoral and upper bathyal soft bottoms", together with *Funiculina quadrangularis*, *Pteroeides spinosum*, and *Veretillum cynomorium*[12](https://scientiamarina.revistas.csic.es/index.php/scientiamarina/article/view/1726).
Sea pens in general are of conservation interest. Several taxa are long-lived, on the order of decades, and many form dense aggregations that modify hydrodynamics and provide shelter and habitat for other organisms, including commercial fish species[13](https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2021.652540/full). *Pennatula phosphorea* and the habitats associated with it are recommended for protection within marine protected areas[8](https://academic.oup.com/icesjms/article/72/2/576/675444?searchresult=1).
Bioluminescence occurs across a variety of pennatulacean taxa and is most likely used for defense, to startle and ward off potential predators[1](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0022747).
## History
Linnaeus established the genus in 1758, the accepted starting point of contemporary binomial nomenclature[1](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0022747). Two earlier or later generic names are treated as synonyms: *Penna* Bohadsch, 1761 and *Phosphorella* Gray, 1870[3](https://www.gbif.org/taxon/84RWV). The 1797 third edition of the *Encyclopaedia Britannica* described *Pennatula*, or sea-pen, as a genus of zoöphyte which, though it swims about freely in the sea, approaches near to the gorgonia, reflecting the old view of such organisms as intermediate between plants and animals[14](https://jimclifford.ca/britannica-articles-1/a/EB.5/192200061/272.html).
## References
1. [Williams GC (2011). The Global Diversity of Sea Pens (Cnidaria: Octocorallia: Pennatulacea). PLoS ONE 6(7): e22747.](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0022747)
2. [ITIS Report: Pennatula Linnaeus, 1758, TSN 52417](https://itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=52417)
3. [GBIF: Pennatula Linnaeus, 1758, Genus Accepted](https://www.gbif.org/taxon/84RWV)
4. [WoRMS: Pennatula fimbriata Herklots, 1858](https://www.marinespecies.org/aphia.php?id=286637&p=taxdetails)
5. [WoRMS: Pennatula naresi Kölliker, 1880](https://www.marinespecies.org/aphia.php?id=286640&p=taxdetails)
6. [Altuna Á (2015). Identificación de las especies ibéricas del género Pennatula L., 1758 (Octocorallia: Pennatulacea)](https://www.researchgate.net/publication/284445950_Identificacion_de_las_especies_ibericas_del_genero_Pennatula_L_1758_Octocorallia_Pennatulacea_Campanas_DEMERSALES_ECOMARG_INDEMARES_y_MEDITS)
7. [Expanding Knowledge of Sea Pen (Octocorallia: Pennatuloidea) Diversity and Distribution Through Integrative Taxonomy: Insights From Hong Kong's Coastal Waters, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC12971188/)
8. [Environmental requirements for three sea pen species: relevance to distribution and conservation, ICES Journal of Marine Science](https://academic.oup.com/icesjms/article/72/2/576/675444?searchresult=1)
9. [Phylogeny and systematics of deep-sea sea pens (Anthozoa: Octocorallia: Pennatulacea), VLIZ](https://www.vliz.be/imisdocs/publications/ocrd/251249.pdf)
10. [Molecular phylogeny and morphological comparison of the deep-sea genus Alloptilella Li, Zhan & Xu, 2021 (Octocorallia, Pennatulacea), Marine Biodiversity](https://link.springer.com/article/10.1007/s12526-022-01260-w)
11. [WoRMS taxon list for Pennatula](https://www.marinespecies.org/aphia.php?p=taxlist&tName=Pennatula)
12. [Sea pen (Pennatulacea) aggregations on the northern Spanish shelf: distribution and faunal assemblages, Scientia Marina](https://scientiamarina.revistas.csic.es/index.php/scientiamarina/article/view/1726)
13. [Discerning the Management-Relevant Ecology and Distribution of Sea Pens (Cnidaria: Pennatulacea) in Norway and Beyond, Frontiers in Marine Science](https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2021.652540/full)
14. [PENNATULA, or SEA-PEN, Encyclopaedia Britannica 3rd ed. (1797)](https://jimclifford.ca/britannica-articles-1/a/EB.5/192200061/272.html)
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*Topic: Encyclopedia › Life and health › Animals › Invertebrates › Other invertebrate lineages › Cnidarians and ctenophores › Anthozoans › Octocorallia › Soft coral genera › Sea pen genera*
*Initially written Sep 17, 2026 · Reviewed: Sep 30, 2026; Oct 21, 2026 · Edited: Oct 11, 2026; Oct 15, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*
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License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license